Senior, I love the vast welth of tractor knowledge you have, and share with us. I would hand you tools all day long and just learn learn from ya. Keep up the great videos!
I think the mouse was knocking. They can get quite upset when you start up their house. When the fresh acorns tumbled out, I was waiting for a cute face to peek out!!
Like I said I really love everything you and your son post.. It is so educational and entertaining and I'm your age or a little older. With that I have been thinking real hard about the engine problem and want to add my ponderings. I think the genesis of the problem was overheating. You have more than the number 3 piston that shows scuffing, the radiator has seen better days, the oil pump is suspect with low oil pressure, carbon buildup, hotter spark plugs, a higher octane gas. Consider this scenario for discussion, at first the piston rings allowed oil to the top of the piston for whatever reason (too thin an oil ,etc.), causing the plugs to foul, the fix would be to go to a hotter plug, hotter plugs means hotter combustion chamber temperature now you incur an octane knock, so go to 91 octane gas, 91 octane burns slower than 87 so now you have the upper cylinder wall hotter than normal. The top of the piston cannot shed the heat and scuffs, and the skirt is undamaged. I think with the radiator, water pump, oil pump overhaul and the piston replacement parts the old girl will be as good as new. Then you can use a lower octane gas like they used when the "M" was made and a colder plug. Keep up the great work, you two make my RUclips evenings so rewarding.
Interesting story with the old GMC pickup engine knock. Hope you get this back together and running without any further issues. Love both of your guy's videos.
I’d be interested in the condition of the oil pump. If you said it had low oil pressure when the engine was warm maybe it has an issue. Very interesting project!
Your son makes great content videos and now you're doing the same, fantastic. . . you two make a great team! By the way that I beam workbench is brilliant, I so want one.
No clue about the issue, but my guess is that after this “holistic” approach to the rebuilt, the knock will have “come out in the wash”. Get her back together and I’ll be shocked if she’s still knocking. Great upload series!
I've been enjoying this series, Senior. My M had an equally large mouse condo under the radiator also. As far as the knock, I'm guessing the piston. I don't think the nosepiece would have cuased a knock, I would have guessed a rubbing sound instead. If you're still unsure, maybe hold off on as many bolt-on accessories as possible at assembly and just run as bare an engine as you can to see if it is good to go.
Oh,my. You have a considerable engine knock that is not immediately obvious. A few observations here. Running 91 octane fuel on a farm tractor. What is your actual compression ratio ? Those things were low compression from the factory. Were high compression pistons added later ? My own experience has been with a previously overheated engine. They are never really right afterwards. Take those studs off the block and measure absolutely everything. Flatness,square to crankshaft line,etc. Anything you can think of. Spend the money to buy a decent endoscope. They are cheap to obtain nowadays. Check every single cooling passage,particularly around No.3. A buildup of crud can make huge difference. Boil out the block with caustic soda in extreme cases. Old time cooling system acid cleanup product in the engine block and head maybe ? Measure everything just like you been doing. Ignition. Rebuild meticulously and check the spark afterwards. High tension cable replacement is mandatory here. Oil pump,hydraulic pump,anything contributory. As mentioned elsewhere,too bad you did not stethoscope before disassembly. Too late now. Piston slap in No.3 enough to create the sound ? Maybe. Cannot think of anything else. The comments elsewhere are professional people equally stumped. You'll find it with that patient approach you are taking. I would be tempted to suggest a return to actual farm gas,once actual compression is known. Meaning fill one cylinder with oil after reassembly and pipette the volume. Degree wheel on reassembly so TDC and camshaft are precise. All the best. It has been fun to watch,your son's approach to the Minneapolis Moline tells me the apple did not fall very far from the tree there Dad. The two of you have the right to be proud of each other. Your son has raised you quite well. Cheers.
@@tomheringer2047 Why thank you. There are some very experienced people,all trying to help. No smartass types,just decent knowledgeable adults. Happy to help,just like me. Cheers.
I like seniors approach: working in the outdoors, that's how you know a true oldschooler. I think since Senior mentioned the excessive wear on the camshaft bearings. That explains your oil pressure loss. Engines with lower camshaft(s) tend to have oil pressure loss when the bearings wear out. They are very hard to get out and usually a special rack is needed for that. What concerns the knock ain't got no clue maybe a combination of all the problems you mentioned.
I am living my dream thru Senior! I have always wanted to restore an IH tractor but don't have a shop, the time or the money. It is fantastic to follow along with this work and learn a few things in the process.
Great work. You are so neat and thorough. I know the basics of engine principles but my experience is mostly limited to mowers and trimmers. You inspire me to up my game to a higher level!
That cover could even be from another tractor probably not but possible sure. I've really enjoyed watching sir, thanks for your time! I really think that nose cone is your knock, I couldn't even really hear it in the video..... BUT that isn't going to be as good as standing there with it in person hearing it.
Make sure to check the cooling system passages for old flashing and packed sand globs that have come loose and moving around. Been in a lot of old engines and the older it is the more likely all the remains of the casting process did not come out on the shake out table. Dry sleeve engines are worse than wet sleeve and some of the tight corners are a night mare to get clean sometimes. I think every ford flat head we saw had a issue to some extent
I had a 1984 Dodge pickup with a 225 slant six and 3 speed trans. After it was 2 years old it would start knocking so bad you would think it was going to explode. After much trouble shooting I decided to change the distributor cap. The replacement had a vent valve on it, afterwards no more knock. Chrysler back then had a reputation of hard starting, I guess they came to the conclusion the distributor was getting moisture buildup and causing problem.
A car I used to have got an engine knock and it turned out to be the carbon buildup on the piston tops. It got thick enough that it would hit the head at TDC. Perhaps this could be your problem too?
It's possible that you're running a bit rich in the carb. Some engines don't like the high octane, others don't like the low octane. Try different octane levels. Run some seafoam in your gas from time to time too. Does it run hot or higher than normal? The burning and scuff marks, indicates that #3 got too hot at some time. All that carbon buildup on top of the piston's indicates it's a fuel issue. The carbon could be pushing the piston itself slightly causing the scuffing. What do the plugs look like? The valves for the #3, what condition were they? Seriously doubt that the head or block is warped, if it were, you'd know, oil and or coolant leaks and you'd see it in the exhaust. Interesting to see what the machine shop discovers. Cheers :)
My folks had a horrible knock in their Ford 1971 Wagon 120 miles South of home towing a trailer. The town only had a Chevy dealer and they talked to Ford (warranty) and they agreed to let the Chevy dealer repair it. Tore it down, found nothing, put it back together, no knock and never did it again. Kind of an expensive way to fix it but no parts needed! I ran down that night with my Bronco and brought them and the Boat home. Quite an epic run with my mom in back in a bean bag!
Hi S.S.. Scoring. As a guess either the cylinder is slightly pinched at the top or the piston slightly tilted. Given the marks I'd vote for the cylinder - but that in turn suggests some form of coolant problem. The machine shop should be readily able to determine the real cause and I would not make any decisions based on my input! I look forward to the real analysis. Keep 'em coming, you present them very well. BobUK.
Great series. Please update the findings and when you start rebuild please include part numbers for gasket sets and where you got them as well as other parts. My cousin is giving me a 1950 M that has not run in about 20 years. I am not sure if motor is stuck or not I have not had time to look it over that close but I may be going down this same road in the near future. Thanks again.
I bet ya that when you get the parts back from the machinists and you put it back together, that knock will probably disappear. Looks like you're doing everything you can. Great videos Mr. Squatch Sr.!
Very good video I enjoy watching some one else do the tear down. I would check the intake exhaust manifold real close that's a lean condition piston failure and the hot spots on 3 cylinder I would say has run hot and dry check the oil pump out any grooves and they won't flow the right amount of oil that's my 2 cents keep up the good work
The ‚no knock at all‘ thing reminds me of an story from my grandfather being a watchmaker. One day a pendulum clock was brought in for repair because it quits running randomely. My grandfather gave it a close inspection but couldnt find anything wrong with it. He uses every trick in the book but the darn thing keeps on quittin. In desperate he advises the trainee to polish the brass plate at the pendulum - and miraculously the thing runs flawlessly. Afterwards every repair that went well without anyone has a clue why was called a ‚pendulum repair‘.
My first concern is the scoring on #3. If the engine swallowed a little water at some point in it's life, the rod could be bent a little as discussed, causing a side load on the piston. The bearing play on #1 journal of the cam makes me wonder if the gear train is clattering as the cam flexes especially when warm and low oil pressure. Last, and this would be my best guess - when the oil pressure is low you lose the cushion of oil on the bearing surface of the crank. This could be the noise heard. I have seen engines have a pronounced "death rattle" during cold start until the oil pressure comes up, then they are fine. When your M warms up and the oil pressure drops, the clearance, even with good bearings, is going to increase. Perhaps this is the knock. Great video Senior. Keep us posted.
Love everything you fellows post. In my model A Ford if there is any end play in the cam shaft you will get knocking. Just a thought. Best of luck in your repair.
My guess on the knock: It was all of the mentioned possibilities, but on a rotation. The scuffed piston, then the nose cone piece, then that pump you mentioned, and probably even the mouse too.
Hello! Thanks for a wounderful channel! My first car was a volvo pv-1961 with a b18 engine and fourspeed gearbox It had a horrible knocking sound and everybody was convinced it was mainbearings or a faulty piston I had the entire motor in pieces 3 times measuring everything and could not find anything wrong The fourth time as a coincidence i found that the camshaft had an axial play in it because of the coggwheel of the cam was worn The cam was moving back and forth in sync with the rotationspeed and was producing a knock sounding like a bearing or a broke piston/pistonring This is just a speculation from me and jou probably alredy looked it up.. Anyhow:many greetings from peter i sweden and good luck with the engine!
Hey Sr, just wanted to say you and your son are great, you two ought to be teaching this stuff! I have a little story and it might be an answer for the knock. I saw the amount of carbon on those pistons and what was in the head. Back in the early 80’s I purchased my wife an AMC Concord with the straight six in it. I was working in my dads shop when she rolls in with this AMC knocking like it was about to throw a rod. Well my dad walks over and gives it a listen and has that look on his face (he’s an old mechanic that cut his teeth on diesels). Well he looks over at the other mechanic in the shop and asks “Jessie ya think it’s carbon” and Jessie says “yup”. Well we had a product called Carbon Blaster that was sold by Justice Brothers. So we dump a can of this stuff in followed by an equal amount of water and voila, knock gone. I mean to tell you this AMC sounded like it was done for but it turned out it was carbon either caught in the intake or on the piston. My wife drove the wheels off that car and we never had another knock. I will say this, that piston gives me pause. It could very well be a rod problem. It’s funny though with the amount of scuffing on the top of the piston that the skirts not showing anything.
I'd say it could be your carburetor or valve adjustment. I'm not just saying that because it's the only things not on this video. My 7.3 idi knocked bad until I put new injectors in it and the 396 big block knocked with poor timing. Could be some type of fuel issue. Great video. Keep that old girl running.
While the engine is out, try turning the mainsheet input to the transmission by hand in case you can feel or hear anything there. It would be a swine to do all this to the engine, and then discover the knock was related to the transmission input.
Great video, could be a clue with the low oil pressure when running, did you manage to check the oil pump specs? I am sure you would have said if there was anything untoward
Good job Sr. The pitting on the exhaust valve could be from moisture it draws after it's been used for a while. I've saw that on an 8n that I had rebuilt a couple times.
Makes me wonder if the oil pressure issue is contributing to the knock. There's no evidence of dry bearings but perhaps a lack of proper pressure won't fill the tiny void between the bearings and crank, causing it to knock a bit. My dad had a 1973 GMC 3/4 ton 2wd with 454. It had no power. Dealer dyno tested and said it was losing 50hp somewhere. He did valves and no change. He gave up and sold the truck.
Hummm I knew an I H that the oil pump went bad. Knock like all get out. But then # 3 could of had some what of a knock. I'm guessing between you and your son will figure it out. Great video as all ways.
My money is on the piston. If it were me, I would mike the skirts and the bores and see what kind of clearance they have. If you saw wear on the thrust sides of a piston, that would be a dead giveaway but on the pin sides is a bit unusual and not likely to be noisy (IME). Still, a piston can change dimensionally when it's damaged, so maybe the skirt clearance has changed. It doesn't sound conclusively like a piston type knock to me but over the years I have learned that every style of engine has specific ways of "talking." Piston noise in an aluminum block vs a cast iron block, for example. Anyway, I'm enjoying this walk thru the insides of an M engine!
Jim Allen Agree Jim. The pistons aren’t slotted or belted to control expansion, so maybe they’re cam ground. Localized overheating could scuff them, in my experience. In the old days we would knurl them to resize them. Worked well and they held oil well too.
Nice job, Senior. Listening to you reminds me of hanging in the shed as a young lad with the "old guys" that seemed to have the ability to fix anything. That's how I learned everything I know about restoration of just about anything. From Porsches to Piper Cherokees....I love a mechanical challenge! Now...I'm the old guy at 59. Do you think your knock was simply carbon buildup? Something to consider...I've chased that in the past. The scuffing on the piston looks like something from it's distant past. Keep up the fun!!!! Chuck in Coon Valley, WI.
I had a 2.5 liter engine in an 82 Olds Omega (Pontiac 4cyl) that ran hot and scored a piston. Everything was fine except for the scored piston and cylinder wall damage. It knocked. I think that is your noise.
Many years ago, I had a little two bay gas station. A Ford Falcon stopped in for gas, and that car had the worst knock you ever heard. I asked the guy about it, and he said it had just suddenly started making the noise a few days before. We put it up on the lift and found that the oil pan was bashed in and the crank was hitting it. Easy fix.
I went back to episode one to listen to the noise again. It is really more of a tickling noise rather than a knock, which leads me to believe that the noise was the debris rattling against the flywheel.
I am still surmising that cylinder #3 is the culprit, coupled with that oil pump.I am not a betting man, however, all of those specs you have taken have been very good. That engine is not "Beat". As I was observing, there is just one other thought I had. The age of the tractor relative to the cam shafts. There were 3 different ones that you mentioned. When the engine was overhauled before are you sure that the right Cam was installed? Just a thought. Loving this video. A lot of detective work has been done. The comments reflect a lot of direction of that oil pump and #3 cylinder. Fascinated by this video. :-)
Pretty sure the source of the knock was that piston scuff. I’ve seen this on Diesel engines. That hot spot on #3 liner makes me concerned you may not have proper heat transfer to parent bore/coolant transfer of heat. Nice work!!!!
From someone on the internet, not me: Look at parts numbers and you will see the same cam number shown for M through 450 as 48196 DBX. That is cam with key and left hand thread nut to retain cam gear. Nut was needed when replacing cams in M up into 450. If you look at old parts books before revisions they show cam 48196 DX for M through SMTA. That's a cam with key.
in the past we put a new crate motor in and it knock , turn out to be the crank pully, also had one that knock . all the tork converter botes got loss and all but one came out , truck had 3000 mi. jeep.
I kind of agree with that oil pump as do you. What has made me wary is the story of that GMC pickup. Maybe the obvious is staring us all in the face? I am still thinking that #3 cylinder is part of the devil here also. Something to think about is the fuel they were using. Farmall engines are not high compression engines, however, they were using high octane fuel. I know that this is going to sound way out there, but, after the overhaul should they be using lower octane fuel? Thanks
@@ronaldkearn3322 I agree high octane fuel burns slower because of its anti-knock properties and actually requires a high compression to burn correctly. The low compression in this engine along with the use of high test might even act like it has late timing as the flame front travels slower. This may have caused the soft seize on cylinder #3 and contribute to the carbon build up in the combustion chambers.
Lets see what the machine shop says. Use regular gas clean up and check the transmission, new oil pump. That would eliminate 90% of the possibilities. Great content Senior.
I just overhauled a 5.7 Chevy vortec that had a scuffed piston on cyl 8 and it did have a noticeable knock. Was able to hone the cyl to get the scuffs out of it and replaced the piston and all was ok after that
I would check the oil pump for end play wear for the low oil pressure when warm. I think that scored piston is the culprit . Because it was putting extra pressure on the piston in both directions. As for those engines being low compression. How much has been milled off of the block and the head???? Because that would raise it. As for gasoline octane i use 87 with ethanol and have no problem with it. And my engine has been decked. 020 and. 020 off the head . I do have a pretronics ignition system. No detention. Sr i really like all the what if ?????? Thank you and Jr for your videos. 🙂
I don't recall seeing anything on the inspection of the lifters or the lifter bores in the block? It appears there is a pretty fair bit of scuffing on some of the other pistons. It looks like that engine has been run hot, or at least for some reason the pistons have been hot. I don't know if it has been run lean at some point and swelled the pistons from heat? Did you do a compression test prior to tear down? Any gear tooth damage? They can cause a knock. I don't think in the video where you pulled it in the shop I could really even hear the knock, what did it sound like, could you tell at all where it was coming from? I was suspicious that your cam retainer was loose or damaged and it was tapping the front cover but you said it was in spec so likely not that. That hot spot pattern on that #3 liner sure makes it look like it was not in proper contact with the block to transfer the heat away. I would mic that bore and counter real good as well as that liner and see if I couldn't find something up. Hard to measure but I wonder if the counterbore and block bore might not be concentric to each other.
Makes me wonder if the Gas octane is`nt the culprit being in the 30s they probably ran at 70-80 octane todays running 90 plus being wheat fuels / alcohal fuels /Shell might be to hot or running on a really hot day like 80-90 degrees and at 90 fuel it might start to make the jug fluid the skirts start flexing letting the top roll on the rod revolution ??
That starter housing was pushing forward on the flywheel causing it to knock under certain conditions. I had a new 68 Dodge Dart that had a similar problem.
We had a MM445 that had a knock only when cold, once it was up to temp the knock went away. Long story short, blow out a head gasket and when we dropped the oil pan we found out that one of the mains was not torqued to spec. After back together no more knock.
This is NOT my area of expertise at all, but is it possible that the "DX" vs "DB" camshaft number is that the "X" means it can be "DA" or "DB" or "DC" etc? In other words, the "X" is a stand in for a revision number? Perhaps "DA" was the RH thread, and "DB" is the left? *shrug*
I’m curious to see if a rod is bent, it wouldn’t take much ........ I really like your thoroughness. With all journals “less than perfect” may be an oiling issue..........
Looking at the bearings and other items you dismantled, it not an oil pressure issue. Id be keen to measure the pistons and cylinders. No3 piston been hot
What about the counter bore for that liner in the block. Was it in spec? That liner showing the heating with that piston is very suspect. Also the cam bearings is suspect for that knock. Starter nose being pressed into the grease and leaving the mark where it was doesn't seem to me would be the source of the knock. If it was the source, there would be witness marks in that housing of the grease build up. There would be marks on the flywheel, clutch..etc. There will be someone comment that the starter nose just was forced in that location when it was shut off the last time. There would still be witness marks elsewhere if that was true. Only question i would have on the starter, in your ownership time have you ever replaced the starter.
Comment from the peanut gallery here... poking around, seeing a few other people's comments about the use of high-octane gas in the tractor versus regular octane gas, got me wondering how these poor old horses have been faring since the demise of leaded gas in the late 80's. I had a car then that wanted leaded gas, and after a few years of not getting it (even though some gasoline makers, Shell for instance, came up with lead substitution additives that they claimed were being put into their regular unleaded gas... still, my car damaged 2 exhaust valves, which I replaced and carried onward until the car's body was beyond saving. Always intended to tear the engine down prior to disposing of it, to see how things were doing on the so-called gasoline after lead had been removed, never got the time (or made the time) to do it, as I got into a career that I was away more than home. Anyways, I don't think lack of lead is causing any problems with the Squatch's Super M, but just wondered if anyone out there has had any bad experiences post-leaded fuel. note: I know you can still get aviation fuel which is rated 100 octane but has fairly high lead content. You might think you'd be doing yourself a favor and giving your car a treat, but if it's a fairly stock automobile, the lead in the AvGas won't go over too well from the car's perspective... lead deposits in places, and sensors and the catalytic convertor will suffer damages, and may then need to be replaced. A small amount of it wouldn't hurt, but prolonged use of it will cost you, more than just the price of the expensive AvGas. Just don't do it.
So good to find someone who knows what he's talking about. I'd suggest the knocking was a result of low oil pressure, and possibly? a high engine temperature. If?? that piston slightly seized, it might? cause the rod to knock, despite being in spec. I've a Lister D in my shed (see videos) it has a rod knock, why, because I've changed the oil, run it and got it warm. Does it matter.....not at all.
Sr. that motor only has ideally 5.6:1 compression. In my opinion 91 octane is not going to give you a complete burn. I believe that's part of your carbon build up problem! To oversimplify it " The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high-performance gasoline engines that require higher compression ratios." At 5.6 : 1, 91 octane is overkill. That motor should run very well on 87- 89 octane. However if you have equipment that needs the higher octane and you only want to buy one fuel you can make it burn better in the "M" by putting a higher temperature thermostat in the "M". A 190 deg F should work and give you a more complete burn! You may need to work on the carburetor jetting too. As to the knock, it could be a carbon knock? I have seen that in older engines. I hope this helps. Great videos Sr. please keep them coming and thank you!
HI In my opinion 91 octane is a waste in these low compression engines. Again in my experience low compressions engines run better on the cheap gas. When these engines were designed to run on leaded cheap gas the designer knew the owner farmers would not spend extra on premium fuel. Of course the timing must be as designed Thanks for the look into the engine
SR another awesome video sir. How was your oil pressure? Your cam bearing clearance gives you your oil pressure and low oil would be a result of the can #1 wear. I doubt you have any issue with valve train. You took a lot of measurements but I did not see you measure for a collapsed piston, especially on piston number with all the scuffing. The speed of the knock sounded like it is on the crank piston side. Also using premium fuel can cause you issue also. The octane changes the timing and the detonation is to far advanced which will cause a knock also. When this was engineered fuel was not as good as today's fuel, surprising as everything was better back in the day.
It's possible that it's a per-ignition knock. You could of been running rich, which would account for the carbon buildup. The carbon acts like a glow plug. Igniting the fuel to early.
OK Squatch's - I need help. Where do you get tractor (and implement) magnetos rebuit? On the knock, it must be related to the bad piston... The piston tops and the chambers show excess fuel carbon build up (rich). Some of that carbon may have gotten hot enough to glow and caused low speed detonation knock... And that could have been what ate that piston ... I'd take some sanding rolls in the die grinder and clean up all the sharp edges in the chamber. Seems like a sharp ridge around at least one valve seat. They can get hot too. Smooth is what's called for. I'd for sure be into the carb and looking at the fuel level and jets. Anyone with a SMOG snifffer you can borrow? Easy way to see what the mixture is doing once it's back together :)
I have to say, the only thing making any sense to me, is that the rod for the #3 piston has to be bent. It only takes a smidge out of tolerance to do as much damage as it did.
What was the piston to cylinder clearance on that scuffed piston? Any possibility that when it got hot, it expanded enough to try to stick to the sides of the liner at the top of the stroke? Especially if the liner was say a thou or two narrow at that dark spot? I'd think that if it tried to stick that could cause some form of knock. It would also account for the scuffing on both sides of the piston. How fast was the knock? In my limited experience cam shafts usually run at half the crank RPM. So if it was any kind of cam or valve knock the knock frequency would be a lot less than the basic engine RPM.
Great story on the old pickup. Automotive mysteries like that are great for coffee shop conversation. Thanks for keeping us in the loop Senior!
Senior, I love the vast welth of tractor knowledge you have, and share with us. I would hand you tools all day long and just learn learn from ya. Keep up the great videos!
I think the mouse was knocking. They can get quite upset when you start up their house.
When the fresh acorns tumbled out, I was waiting for a cute face to peek out!!
Like I said I really love everything you and your son post.. It is so educational and entertaining and I'm your age or a little older. With that I have been thinking real hard about the engine problem and want to add my ponderings. I think the genesis of the problem was overheating. You have more than the number 3 piston that shows scuffing, the radiator has seen better days, the oil pump is suspect with low oil pressure, carbon buildup, hotter spark plugs, a higher octane gas. Consider this scenario for discussion, at first the piston rings allowed oil to the top of the piston for whatever reason (too thin an oil ,etc.), causing the plugs to foul, the fix would be to go to a hotter plug, hotter plugs means hotter combustion chamber temperature now you incur an octane knock, so go to 91 octane gas, 91 octane burns slower than 87 so now you have the upper cylinder wall hotter than normal. The top of the piston cannot shed the heat and scuffs, and the skirt is undamaged. I think with the radiator, water pump, oil pump overhaul and the piston replacement parts the old girl will be as good as new. Then you can use a lower octane gas like they used when the "M" was made and a colder plug. Keep up the great work, you two make my RUclips evenings so rewarding.
Interesting story with the old GMC pickup engine knock. Hope you get this back together and running without any further issues. Love both of your guy's videos.
You made my day when you told the story about the pickup, thank god there are still people that refer to them as pickups and not trucks!!
Never thought about that much, but i heard plenty call semis or trucks, tractors -that seems odd to me.
Nice job, Senior! You and Squatch are very talented with machinery! And with posting interesting and informative videos. Thank you! 🚜👍
I’d be interested in the condition of the oil pump. If you said it had low oil pressure when the engine was warm maybe it has an issue. Very interesting project!
Looking at a Farmall S M engine for the first time, it looks like an over-engineered engine. That is nice!
Senior, I’m sure glad you changed your mind on making videos!!! I’ve really enjoyed the super m. I own an H, but it’s all great information!!
Your son makes great content videos and now you're doing the same, fantastic. . . you two make a great team! By the way that I beam workbench is brilliant, I so want one.
No clue about the issue, but my guess is that after this “holistic” approach to the rebuilt, the knock will have “come out in the wash”. Get her back together and I’ll be shocked if she’s still knocking.
Great upload series!
I've been enjoying this series, Senior. My M had an equally large mouse condo under the radiator also.
As far as the knock, I'm guessing the piston. I don't think the nosepiece would have cuased a knock, I would have guessed a rubbing sound instead. If you're still unsure, maybe hold off on as many bolt-on accessories as possible at assembly and just run as bare an engine as you can to see if it is good to go.
Enjoying the knock CSI, thanks again Squatch Snr :)
Oh,my. You have a considerable engine knock that is not immediately obvious. A few observations here.
Running 91 octane fuel on a farm tractor. What is your actual compression ratio ? Those things were low compression from the factory. Were high compression pistons added later ?
My own experience has been with a previously overheated engine. They are never really right afterwards. Take those studs off the block and measure absolutely everything. Flatness,square to crankshaft line,etc. Anything you can think of.
Spend the money to buy a decent endoscope. They are cheap to obtain nowadays. Check every single cooling passage,particularly around No.3.
A buildup of crud can make huge difference. Boil out the block with caustic soda in extreme cases. Old time cooling system acid cleanup product in the engine block and head maybe ?
Measure everything just like you been doing.
Ignition. Rebuild meticulously and check the spark afterwards. High tension cable replacement is mandatory here.
Oil pump,hydraulic pump,anything contributory.
As mentioned elsewhere,too bad you did not stethoscope before disassembly. Too late now.
Piston slap in No.3 enough to create the sound ? Maybe.
Cannot think of anything else. The comments elsewhere are professional people equally stumped.
You'll find it with that patient approach you are taking.
I would be tempted to suggest a return to actual farm gas,once actual compression is known. Meaning fill one cylinder with oil after reassembly and pipette the volume. Degree wheel on reassembly so TDC and camshaft are precise.
All the best. It has been fun to watch,your son's approach to the Minneapolis Moline tells me the apple did not fall very far from the tree there Dad. The two of you have the right to be proud of each other. Your son has raised you quite well. Cheers.
All great information Paul. I never considered the blocked coolant passage adjacent to No. 3 cylinder liner.
@@tomheringer2047 Why thank you. There are some very experienced people,all trying to help. No smartass types,just decent knowledgeable adults. Happy to help,just like me. Cheers.
I like seniors approach: working in the outdoors, that's how you know a true oldschooler. I think since Senior mentioned the excessive wear on the camshaft bearings. That explains your oil pressure loss. Engines with lower camshaft(s) tend to have oil pressure loss when the bearings wear out. They are very hard to get out and usually a special rack is needed for that. What concerns the knock ain't got no clue maybe a combination of all the problems you mentioned.
I am living my dream thru Senior! I have always wanted to restore an IH tractor but don't have a shop, the time or the money. It is fantastic to follow along with this work and learn a few things in the process.
Great work. You are so neat and thorough. I know the basics of engine principles but my experience is mostly limited to mowers and trimmers. You inspire me to up my game to a higher level!
That cover could even be from another tractor probably not but possible sure.
I've really enjoyed watching sir, thanks for your time!
I really think that nose cone is your knock, I couldn't even really hear it in the video..... BUT that isn't going to be as good as standing there with it in person hearing it.
Make sure to check the cooling system passages for old flashing and packed sand globs that have come loose and moving around. Been in a lot of old engines and the older it is the more likely all the remains of the casting process did not come out on the shake out table. Dry sleeve engines are worse than wet sleeve and some of the tight corners are a night mare to get clean sometimes. I think every ford flat head we saw had a issue to some extent
I had a 1984 Dodge pickup with a 225 slant six and 3 speed trans. After it was 2 years old it would start knocking so bad you would think it was going to explode. After much trouble shooting I decided to change the distributor cap. The replacement had a vent valve on it, afterwards no more knock. Chrysler back then had a reputation of hard starting, I guess they came to the conclusion the distributor was getting moisture buildup and causing problem.
A car I used to have got an engine knock and it turned out to be the carbon buildup on the piston tops. It got thick enough that it would hit the head at TDC. Perhaps this could be your problem too?
Nice work, Sr.! I like those little stands for the cylinder head. Giving me ideas now!
Definitely an overheat on that 3 liner. Combine that with the damage to 3 piston and I'll lay money you've got your knock.
Thanks again sr. For the very educational videos about the m
Thoroughly enjoyed your work and video!
It's possible that you're running a bit rich in the carb. Some engines don't like the high octane, others don't like the low octane. Try different octane levels. Run some seafoam in your gas from time to time too. Does it run hot or higher than normal? The burning and scuff marks, indicates that #3 got too hot at some time. All that carbon buildup on top of the piston's indicates it's a fuel issue. The carbon could be pushing the piston itself slightly causing the scuffing. What do the plugs look like? The valves for the #3, what condition were they? Seriously doubt that the head or block is warped, if it were, you'd know, oil and or coolant leaks and you'd see it in the exhaust. Interesting to see what the machine shop discovers. Cheers :)
My folks had a horrible knock in their Ford 1971 Wagon 120 miles South of home towing a trailer. The town only had a Chevy dealer and they talked to Ford (warranty) and they agreed to let the Chevy dealer repair it. Tore it down, found nothing, put it back together, no knock and never did it again. Kind of an expensive way to fix it but no parts needed! I ran down that night with my Bronco and brought them and the Boat home. Quite an epic run with my mom in back in a bean bag!
Hi S.S.. Scoring. As a guess either the cylinder is slightly pinched at the top or the piston slightly tilted. Given the marks I'd vote for the cylinder - but that in turn suggests some form of coolant problem. The machine shop should be readily able to determine the real cause and I would not make any decisions based on my input! I look forward to the real analysis. Keep 'em coming, you present them very well. BobUK.
Great series.
Please update the findings and when you start rebuild please include part numbers for gasket sets and where you got them as well as other parts. My cousin is giving me a 1950 M that has not run in about 20 years. I am not sure if motor is stuck or not I have not had time to look it over that close but I may be going down this same road in the near future.
Thanks again.
This is Mississippi man Your knock is that golden piston
I bet ya that when you get the parts back from the machinists and you put it back together, that knock will probably disappear. Looks like you're doing everything you can. Great videos Mr. Squatch Sr.!
d2 cat part for sale in valley springs sd.I seen them listed in craigslist, not too far from you. Great videos and love the moline build.
Very good video I enjoy watching some one else do the tear down. I would check the intake exhaust manifold real close that's a lean condition piston failure and the hot spots on 3 cylinder I would say has run hot and dry check the oil pump out any grooves and they won't flow the right amount of oil that's my 2 cents keep up the good work
Great series of videos! Thank you!
Great job on this video. I hope you find the answer you need.
Could the loose cam bearing be your low oil pressure problem
The ‚no knock at all‘ thing reminds me of an story from my grandfather being a watchmaker.
One day a pendulum clock was brought in for repair because it quits running randomely. My grandfather gave it a close inspection but couldnt find anything wrong with it. He uses every trick in the book but the darn thing keeps on quittin.
In desperate he advises the trainee to polish the brass plate at the pendulum - and miraculously the thing runs flawlessly. Afterwards every repair that went well without anyone has a clue why was called a ‚pendulum repair‘.
My first concern is the scoring on #3. If the engine swallowed a little water at some point in it's life, the rod could be bent a little as discussed, causing a side load on the piston. The bearing play on #1 journal of the cam makes me wonder if the gear train is clattering as the cam flexes especially when warm and low oil pressure. Last, and this would be my best guess - when the oil pressure is low you lose the cushion of oil on the bearing surface of the crank. This could be the noise heard. I have seen engines have a pronounced "death rattle" during cold start until the oil pressure comes up, then they are fine. When your M warms up and the oil pressure drops, the clearance, even with good bearings, is going to increase. Perhaps this is the knock.
Great video Senior. Keep us posted.
Love everything you fellows post. In my model A Ford if there is any end play in the cam shaft you will get knocking. Just a thought. Best of luck in your repair.
My guess on the knock: It was all of the mentioned possibilities, but on a rotation. The scuffed piston, then the nose cone piece, then that pump you mentioned, and probably even the mouse too.
Hello!
Thanks for a wounderful channel!
My first car was a volvo pv-1961 with a b18 engine and fourspeed gearbox
It had a horrible knocking sound and everybody was convinced it was mainbearings or a faulty piston
I had the entire motor in pieces 3 times measuring everything and could not find anything wrong
The fourth time as a coincidence i found that the camshaft had an axial play in it because of the coggwheel of the cam was worn
The cam was moving back and forth in sync with the rotationspeed and was producing a knock sounding like a bearing or a broke piston/pistonring
This is just a speculation from me and jou probably alredy looked it up..
Anyhow:many greetings from peter i sweden and good luck with the engine!
Hey Sr, just wanted to say you and your son are great, you two ought to be teaching this stuff! I have a little story and it might be an answer for the knock. I saw the amount of carbon on those pistons and what was in the head. Back in the early 80’s I purchased my wife an AMC Concord with the straight six in it. I was working in my dads shop when she rolls in with this AMC knocking like it was about to throw a rod. Well my dad walks over and gives it a listen and has that look on his face (he’s an old mechanic that cut his teeth on diesels). Well he looks over at the other mechanic in the shop and asks “Jessie ya think it’s carbon” and Jessie says “yup”. Well we had a product called Carbon Blaster that was sold by Justice Brothers. So we dump a can of this stuff in followed by an equal amount of water and voila, knock gone. I mean to tell you this AMC sounded like it was done for but it turned out it was carbon either caught in the intake or on the piston. My wife drove the wheels off that car and we never had another knock. I will say this, that piston gives me pause. It could very well be a rod problem. It’s funny though with the amount of scuffing on the top of the piston that the skirts not showing anything.
I'd say it could be your carburetor or valve adjustment. I'm not just saying that because it's the only things not on this video. My 7.3 idi knocked bad until I put new injectors in it and the 396 big block knocked with poor timing. Could be some type of fuel issue. Great video. Keep that old girl running.
When you minchened the fuel pump rod. It reminded me I had and engine with a weak fuel pump spring was causing a knocking sound.
While the engine is out, try turning the mainsheet input to the transmission by hand in case you can feel or hear anything there. It would be a swine to do all this to the engine, and then discover the knock was related to the transmission input.
Ain't spell check a bitch?
check the waterpump for bearing knock, the noise sometime travels and looks like a compleet engine rebuild when its just a waterpump. had it happen 2x
Great video, could be a clue with the low oil pressure when running, did you manage to check the oil pump specs? I am sure you would have said if there was anything untoward
Nothing like the smell of PB Blaster in the morning. LOL
Good job Sr. The pitting on the exhaust valve could be from moisture it draws after it's been used for a while. I've saw that on an 8n that I had rebuilt a couple times.
Makes me wonder if the oil pressure issue is contributing to the knock. There's no evidence of dry bearings but perhaps a lack of proper pressure won't fill the tiny void between the bearings and crank, causing it to knock a bit. My dad had a 1973 GMC 3/4 ton 2wd with 454. It had no power. Dealer dyno tested and said it was losing 50hp somewhere. He did valves and no change. He gave up and sold the truck.
Hummm I knew an I H that the oil pump went bad. Knock like all get out. But then # 3 could of had some what of a knock. I'm guessing between you and your son will figure it out. Great video as all ways.
My money is on the piston. If it were me, I would mike the skirts and the bores and see what kind of clearance they have. If you saw wear on the thrust sides of a piston, that would be a dead giveaway but on the pin sides is a bit unusual and not likely to be noisy (IME). Still, a piston can change dimensionally when it's damaged, so maybe the skirt clearance has changed. It doesn't sound conclusively like a piston type knock to me but over the years I have learned that every style of engine has specific ways of "talking." Piston noise in an aluminum block vs a cast iron block, for example. Anyway, I'm enjoying this walk thru the insides of an M engine!
Jim Allen Agree Jim. The pistons aren’t slotted or belted to control expansion, so maybe they’re cam ground. Localized overheating could scuff them, in my experience. In the old days we would knurl them to resize them. Worked well and they held oil well too.
Nice job, Senior. Listening to you reminds me of hanging in the shed as a young lad with the "old guys" that seemed to have the ability to fix anything. That's how I learned everything I know about restoration of just about anything. From Porsches to Piper Cherokees....I love a mechanical challenge! Now...I'm the old guy at 59. Do you think your knock was simply carbon buildup? Something to consider...I've chased that in the past. The scuffing on the piston looks like something from it's distant past. Keep up the fun!!!! Chuck in Coon Valley, WI.
I had a 2.5 liter engine in an 82 Olds Omega (Pontiac 4cyl) that ran hot and scored a piston. Everything was fine except for the scored piston and cylinder wall damage. It knocked. I think that is your noise.
Many years ago, I had a little two bay gas station. A Ford Falcon stopped in for gas, and that car had the worst knock you ever heard. I asked the guy about it, and he said it had just suddenly started making the noise a few days before. We put it up on the lift and found that the oil pan was bashed in and the crank was hitting it. Easy fix.
I went back to episode one to listen to the noise again. It is really more of a tickling noise rather than a knock, which leads me to believe that the noise was the debris rattling against the flywheel.
Awesome stuff!!!
my guess at this point is the scuffed piston. Don't think the cam really.
When you opened the oil pan in that truck, you let the noisy Gremlin out. Poor guy was trapped in there.
I am still surmising that cylinder #3 is the culprit, coupled with that oil pump.I am not a betting man, however, all of those specs you have taken have been very good. That engine is not "Beat". As I was observing, there is just one other thought I had. The age of the tractor relative to the cam shafts. There were 3 different ones that you mentioned. When the engine was overhauled before are you sure that the right Cam was installed? Just a thought. Loving this video. A lot of detective work has been done. The comments reflect a lot of direction of that oil pump and #3 cylinder. Fascinated by this video. :-)
Pretty sure the source of the knock was that piston scuff. I’ve seen this on Diesel engines. That hot spot on #3 liner makes me concerned you may not have proper heat transfer to parent bore/coolant transfer of heat. Nice work!!!!
From someone on the internet, not me: Look at parts numbers and you will see the same cam number shown for M through 450 as 48196 DBX. That is cam with key and left hand thread nut to retain cam gear. Nut was needed when replacing cams in M up into 450. If you look at old parts books before revisions they show cam 48196 DX for M through SMTA. That's a cam with key.
in the past we put a new crate motor in and it knock , turn out to be the crank pully, also had one that knock . all the tork converter botes got loss and all but one came out , truck had 3000 mi. jeep.
We had one, oil pump was the cause the knock.
I kind of agree with that oil pump as do you. What has made me wary is the story of that GMC pickup. Maybe the obvious is staring us all in the face? I am still thinking that #3 cylinder is part of the devil here also. Something to think about is the fuel they were using. Farmall engines are not high compression engines, however, they were using high octane fuel. I know that this is going to sound way out there, but, after the overhaul should they be using lower octane fuel? Thanks
@@ronaldkearn3322 I agree high octane fuel burns slower because of its anti-knock properties and actually requires a high compression to burn correctly. The low compression in this engine along with the use of high test might even act like it has late timing as the flame front travels slower. This may have caused the soft seize on cylinder #3 and contribute to the carbon build up in the combustion chambers.
Spot on Matthew! 99.9% of the average joes out there have absolutely no clue what you are talking about, but you are 100% correct.
@@ronaldkearn3322 Thats a great point. Know a few motorcycles I had. When we lost leaded gas. Man they sounded like a pea thresher.
a very plausible scenario.....most likely the explanation that ties it all together 👍
i cant wait to see how good a of a job they do on that radiator
Lets see what the machine shop says. Use regular gas clean up and check the transmission, new oil pump. That would eliminate 90% of the possibilities. Great content Senior.
I just overhauled a 5.7 Chevy vortec that had a scuffed piston on cyl 8 and it did have a noticeable knock. Was able to hone the cyl to get the scuffs out of it and replaced the piston and all was ok after that
Pre-ignition caused by manifold air leak on the #3 leg?/ crack? bad gasket seal?
I would check the oil pump for end play wear for the low oil pressure when warm. I think that scored piston is the culprit . Because it was putting extra pressure on the piston in both directions. As for those engines being low compression. How much has been milled off of the block and the head???? Because that would raise it. As for gasoline octane i use 87 with ethanol and have no problem with it. And my engine has been decked. 020 and. 020 off the head . I do have a pretronics ignition system. No detention.
Sr i really like all the what if ?????? Thank you and Jr for your videos. 🙂
I don't recall seeing anything on the inspection of the lifters or the lifter bores in the block? It appears there is a pretty fair bit of scuffing on some of the other pistons. It looks like that engine has been run hot, or at least for some reason the pistons have been hot. I don't know if it has been run lean at some point and swelled the pistons from heat? Did you do a compression test prior to tear down? Any gear tooth damage? They can cause a knock. I don't think in the video where you pulled it in the shop I could really even hear the knock, what did it sound like, could you tell at all where it was coming from? I was suspicious that your cam retainer was loose or damaged and it was tapping the front cover but you said it was in spec so likely not that. That hot spot pattern on that #3 liner sure makes it look like it was not in proper contact with the block to transfer the heat away. I would mic that bore and counter real good as well as that liner and see if I couldn't find something up. Hard to measure but I wonder if the counterbore and block bore might not be concentric to each other.
Makes me wonder if the Gas octane is`nt the culprit being in the 30s they probably ran at 70-80 octane todays running 90 plus being wheat fuels / alcohal fuels /Shell might be to hot or running on a really hot day like 80-90 degrees and at 90 fuel it might start to make the jug fluid the skirts start flexing letting the top roll on the rod revolution ??
That starter housing was pushing forward on the flywheel causing it to knock under certain conditions. I had a new 68 Dodge Dart that had a similar problem.
Over heating with a very rich mixture (that scored top area of the piston suggests this). You could be dealing with a carbon knock.
cool, awesome video series.... cant wait
Sir I did have one of those ghost before. It sounded just like a rod knock but it turned out to be a worn key way on the harmonic balancer.
We had a MM445 that had a knock only when cold, once it was up to temp the knock went away. Long story short, blow out a head gasket and when we dropped the oil pan we found out that one of the mains was not torqued to spec. After back together no more knock.
This is NOT my area of expertise at all, but is it possible that the "DX" vs "DB" camshaft number is that the "X" means it can be "DA" or "DB" or "DC" etc? In other words, the "X" is a stand in for a revision number? Perhaps "DA" was the RH thread, and "DB" is the left? *shrug*
I’m curious to see if a rod is bent, it wouldn’t take much ........ I really like your thoroughness. With all journals “less than perfect” may be an oiling issue..........
Looking at the bearings and other items you dismantled, it not an oil pressure issue. Id be keen to measure the pistons and cylinders. No3 piston been hot
What about the counter bore for that liner in the block. Was it in spec? That liner showing the heating with that piston is very suspect. Also the cam bearings is suspect for that knock. Starter nose being pressed into the grease and leaving the mark where it was doesn't seem to me would be the source of the knock. If it was the source, there would be witness marks in that housing of the grease build up. There would be marks on the flywheel, clutch..etc. There will be someone comment that the starter nose just was forced in that location when it was shut off the last time. There would still be witness marks elsewhere if that was true. Only question i would have on the starter, in your ownership time have you ever replaced the starter.
Comment from the peanut gallery here... poking around, seeing a few other people's comments about the use of high-octane gas in the tractor versus regular octane gas, got me wondering how these poor old horses have been faring since the demise of leaded gas in the late 80's. I had a car then that wanted leaded gas, and after a few years of not getting it (even though some gasoline makers, Shell for instance, came up with lead substitution additives that they claimed were being put into their regular unleaded gas... still, my car damaged 2 exhaust valves, which I replaced and carried onward until the car's body was beyond saving. Always intended to tear the engine down prior to disposing of it, to see how things were doing on the so-called gasoline after lead had been removed, never got the time (or made the time) to do it, as I got into a career that I was away more than home. Anyways, I don't think lack of lead is causing any problems with the Squatch's Super M, but just wondered if anyone out there has had any bad experiences post-leaded fuel. note: I know you can still get aviation fuel which is rated 100 octane but has fairly high lead content. You might think you'd be doing yourself a favor and giving your car a treat, but if it's a fairly stock automobile, the lead in the AvGas won't go over too well from the car's perspective... lead deposits in places, and sensors and the catalytic convertor will suffer damages, and may then need to be replaced. A small amount of it wouldn't hurt, but prolonged use of it will cost you, more than just the price of the expensive AvGas. Just don't do it.
So good to find someone who knows what he's talking about. I'd suggest the knocking was a result of low oil pressure, and possibly? a high engine temperature. If?? that piston slightly seized, it might? cause the rod to knock, despite being in spec. I've a Lister D in my shed (see videos) it has a rod knock, why, because I've changed the oil, run it and got it warm. Does it matter.....not at all.
Sr. that motor only has ideally 5.6:1 compression. In my opinion 91 octane is not going to give you a complete burn. I believe that's part of your carbon build up problem! To oversimplify it " The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high-performance gasoline engines that require higher compression ratios." At 5.6 : 1, 91 octane is overkill. That motor should run very well on 87- 89 octane. However if you have equipment that needs the higher octane and you only want to buy one fuel you can make it burn better in the "M" by putting a higher temperature thermostat in the "M". A 190 deg F should work and give you a more complete burn! You may need to work on the carburetor jetting too. As to the knock, it could be a carbon knock? I have seen that in older engines. I hope this helps.
Great videos Sr. please keep them coming and thank you!
HI
In my opinion 91 octane is a waste in these low compression engines. Again in my experience low compressions engines run better on the cheap gas.
When these engines were designed to run on leaded cheap gas the designer knew the owner farmers would not spend extra on premium fuel.
Of course the timing must be as designed
Thanks for the look into the engine
He may be using 91 octane to avoid the associated problems with ethanol in fuel.
@@ron827 Yes, we can get 91 non oxy in MN. That is what I was thinking as well.
SR another awesome video sir. How was your oil pressure? Your cam bearing clearance gives you your oil pressure and low oil would be a result of the can #1 wear. I doubt you have any issue with valve train. You took a lot of measurements but I did not see you measure for a collapsed piston, especially on piston number with all the scuffing. The speed of the knock sounded like it is on the crank piston side. Also using premium fuel can cause you issue also. The octane changes the timing and the detonation is to far advanced which will cause a knock also. When this was engineered fuel was not as good as today's fuel, surprising as everything was better back in the day.
i don't have any ideas about your knock issue, but I was admiring your steel I beam outside bench. Did you anchor the legs in concrete?
its pretty neat ay, be something i wouldnt want to back into thats for sure lol
I have no idea and maybe it just wanted to actlike a diesel a little. Thanks, Senior. Hi to Jr for a change!
It's possible that it's a per-ignition knock. You could of been running rich, which would account for the carbon buildup. The carbon acts like a glow plug. Igniting the fuel to early.
Piston tops and combustion chambers ,look like the engine is not up to tempeture check your thermostat.
Why run 91 octane? I can't imagine the compression is high enough to warrant it. It may even be to blame for the carbon due to incomplete combustion.
OK Squatch's - I need help. Where do you get tractor (and implement) magnetos rebuit?
On the knock, it must be related to the bad piston... The piston tops and the chambers show excess fuel carbon build up (rich). Some of that carbon may have gotten hot enough to glow and caused low speed detonation knock... And that could have been what ate that piston ... I'd take some sanding rolls in the die grinder and clean up all the sharp edges in the chamber. Seems like a sharp ridge around at least one valve seat. They can get hot too. Smooth is what's called for.
I'd for sure be into the carb and looking at the fuel level and jets. Anyone with a SMOG snifffer you can borrow? Easy way to see what the mixture is doing once it's back together :)
I have to say, the only thing making any sense to me, is that the rod for the #3 piston has to be bent. It only takes a smidge out of tolerance to do as much damage as it did.
A few little things you found, but altogether they can make for large problems
Have you specked out the mag or distributor ? I have seen them cause a knock. 🤔
What was the piston to cylinder clearance on that scuffed piston? Any possibility that when it got hot, it expanded enough to try to stick to the sides of the liner at the top of the stroke? Especially if the liner was say a thou or two narrow at that dark spot? I'd think that if it tried to stick that could cause some form of knock. It would also account for the scuffing on both sides of the piston.
How fast was the knock? In my limited experience cam shafts usually run at half the crank RPM. So if it was any kind of cam or valve knock the knock frequency would be a lot less than the basic engine RPM.
Excellent
One way that I can tell the engine has been rebuilt is it had the high compression pop up pistons not the original flat topped pistons
Could it be the muffler bearings gone bad?
I'm going to suggest verifying TDC on your timing marks. Sounds like a gremlin somewhere.