Near 30 years ago I’m was racing go-karts under WKA (world karting association) rules. I was running unlimited 4 stroke class which was a 5 hp flathead on alcohol, max 14.2 cubic inch, any crank, rod, piston, cam and carb but the one stipulation was you MUST use the stock unaltered flywheel weighing a minimum of 5lbs 12oz. I have turned that stock Briggs cast iron flywheel 11,400rpm. We ran outer third bearing supports and girdled blocks to hold them together. We were making near 30hp from a 5hp flathead. We raced a winter indoor track series back in the 90’s and I did not attend the final race due to schedule and I had the points championship locked down. The race I did not attend, a spectator was killed by and exploding flywheel. The engines evolved faster than the rules adjusted. After that disaster billet flywheels quickly became the rule.
WOW, 11,400 rpm with a stock Briggs flywheel! That is crazy that they ever held together for that rpm. I contacted Briggs back in the late 80s regarding my Sleeve valve engine, wondering what was a safe max. rpm to run it at. If my memory is correct, they recommended that I limit it to 7000 rpm on the 3 horse sized steel flywheel (the conversation was off the record, in case I had a problem though). I was doing a little research about restrictor plates for go karts, as my son is making a mini-bike for the grandkids, I built a 2 horse Briggs for it, but didn't want it to be able to rev 5500 rpm, so I made a restrictor with a 5/16" hole in it, we shall see if I guessed right!
Great video sir. I have a Briggs 3.5 classic and wanting to use to make a generator. Epicenter has everything I need to do it. I was just wondering if a 2.5" cast iron pulley that they sell would be a sufficient enough mass to attach where the blade was and run that just to use to burn some old gas before I complete the project.
That might work OK, as long as you have the full circle type flywheel that would come with a blade brake on the lawnmower. The 2.5" pulley may be OK, but I wouldn't go any larger, unless you can find out the rpm rating for the pulley. Many of them are made for electric motors which typically run much slower, perhaps 1800 rpm. I know I have ran a similar sized iron or steel pulley at 3600rpm, but please verify with the producer that this pulley has a high enough rpm rating of 3600 rpm plus. Good luck building the generator, sounds fun.
The trick we did on Kart engines, we put the lightest "Push Mower" style flywheel....(we used the clutch for flywheel) - The guys that ran the standard flywheels were getting their butts handed to them....
Yes, I could see that working in a race, lighter can be better for acceleration. When you want a smoother running engine for say an outboard motor, or an air compressor heavier would be best.
Yes, interesting point, you want a light flywheel for fast acceleration, but a heavier one makes the engine run smoother, and thus doesn't strain the drivetrain parts as much....always a compromise!
how hard is it to swap the crankshafts on these briggs motors? there's a long story here, the tldr is I can have an operational motor if I swap the crankshafts between two blocks (same motor otherwise, flywheel, carburetor etc etc is all the same). I swapped motors between mowers and now have a good motor on a good deck, but the shaft is about 3" too long. I have a bad motor with the correct length shaft, but the motor itself is bad. I'm debating tearing it down and swapping the cranks or just giving the whole lot of it to my neighbor that collects scrap metal.
Not to be a dick, but if you have to ask it’s probably scrap metal. If you’re sure everything else is the same go for it, if you want to tinker/learn, go for it see if they’re the same and do it. You could probably check by model/serial number if they’re interchangeable but you haven’t given that information so Nobody can say one way or the other...
I guess there are 3 options: Cut off the crankshaft to the proper length, but then you will need to file or machine a keyway in the correct location, as well as re-do the center bolt threads (not an easy option). 2 Take the crank out of the other motor, examine it to make sure it is good (the con rod journal is usually the deciding factor), if good, install it in your good engine. This will be a few hours of work, but you probably will end up with a good motor. 3. Scrap both of them, which is the simplest, but not the most useful option. Generally speaking the internal parts will interchange, but you need to use the parts that come with a given crank type. What I mean is, if it has a removable metal gear, you need to use that. If it has a plastic crank gear (I hate those), you need to use that, and the thin steel washer that goes with it. Hope this helps.
Yes, I admit they are somewhat hard to find. Horizontal shaft engines always have them. Some vertical shaft engines like pressure washers and possibly generators and roto-tillers can have the heavy flywheel also. I would recommend the heavy flywheel, since the smoother motion will be better for whatever type of drive train you hook it up to. The more jerky motion of a lighter flywheel will be harder on the parts.
Hmmm, I am afraid I can't say for sure, since I am really only familiar with the old Briggs flathead engines. I don't see why an OHV engine wouldn't work, though in any case I would bring some oars with me just in case the engine conked out!
Old Guy here. Tried that in early 1970's. 2 cylinder Johnson outboard. Rod through block. Junk push mower that ran well. Found lower unit was 3/8 square into crankshaft. Welded 3/8 drive socket to Briggs crank; No other engine changes. Made frame from light angle iron that bolted to lower unit and Briggs verticle shaft flathead engine. Never took cover off to see what flywheel had but lower outboard drive and prop always turning with engine. Worked great Except only go about speed of cheap electric trowling motor. Actually expected that as Briggs 3600 rpm, original 2 stroke maybe 7000 rpm.
Near 30 years ago I’m was racing go-karts under WKA (world karting association) rules. I was running unlimited 4 stroke class which was a 5 hp flathead on alcohol, max 14.2 cubic inch, any crank, rod, piston, cam and carb but the one stipulation was you MUST use the stock unaltered flywheel weighing a minimum of 5lbs 12oz. I have turned that stock Briggs cast iron flywheel 11,400rpm. We ran outer third bearing supports and girdled blocks to hold them together. We were making near 30hp from a 5hp flathead. We raced a winter indoor track series back in the 90’s and I did not attend the final race due to schedule and I had the points championship locked down. The race I did not attend, a spectator was killed by and exploding flywheel. The engines evolved faster than the rules adjusted. After that disaster billet flywheels quickly became the rule.
WOW, 11,400 rpm with a stock Briggs flywheel! That is crazy that they ever held together for that rpm. I contacted Briggs back in the late 80s regarding my Sleeve valve engine, wondering what was a safe max. rpm to run it at. If my memory is correct, they recommended that I limit it to 7000 rpm on the 3 horse sized steel flywheel (the conversation was off the record, in case I had a problem though). I was doing a little research about restrictor plates for go karts, as my son is making a mini-bike for the grandkids, I built a 2 horse Briggs for it, but didn't want it to be able to rev 5500 rpm, so I made a restrictor with a 5/16" hole in it, we shall see if I guessed right!
Fantastic Content. Thank You For Sharing. Have a nice day!❤👍
Thanks, you are welcome.
Great video sir. I have a Briggs 3.5 classic and wanting to use to make a generator. Epicenter has everything I need to do it. I was just wondering if a 2.5" cast iron pulley that they sell would be a sufficient enough mass to attach where the blade was and run that just to use to burn some old gas before I complete the project.
That might work OK, as long as you have the full circle type flywheel that would come with a blade brake on the lawnmower. The 2.5" pulley may be OK, but I wouldn't go any larger, unless you can find out the rpm rating for the pulley. Many of them are made for electric motors which typically run much slower, perhaps 1800 rpm. I know I have ran a similar sized iron or steel pulley at 3600rpm, but please verify with the producer that this pulley has a high enough rpm rating of 3600 rpm plus. Good luck building the generator, sounds fun.
The trick we did on Kart engines, we put the lightest "Push Mower" style flywheel....(we used the clutch for flywheel) - The guys that ran the standard flywheels were getting their butts handed to them....
Yes, I could see that working in a race, lighter can be better for acceleration. When you want a smoother running engine for say an outboard motor, or an air compressor heavier would be best.
It's all about the inertia to get it over the various humps in the inner workings like cam lobes and the compression... :)
A flywheel stores energy. It also takes energy to accelerate it. Depends on the application which flywheel will give desirable results.
Yes, interesting point, you want a light flywheel for fast acceleration, but a heavier one makes the engine run smoother, and thus doesn't strain the drivetrain parts as much....always a compromise!
how hard is it to swap the crankshafts on these briggs motors? there's a long story here, the tldr is I can have an operational motor if I swap the crankshafts between two blocks (same motor otherwise, flywheel, carburetor etc etc is all the same). I swapped motors between mowers and now have a good motor on a good deck, but the shaft is about 3" too long. I have a bad motor with the correct length shaft, but the motor itself is bad. I'm debating tearing it down and swapping the cranks or just giving the whole lot of it to my neighbor that collects scrap metal.
Not to be a dick, but if you have to ask it’s probably scrap metal. If you’re sure everything else is the same go for it, if you want to tinker/learn, go for it see if they’re the same and do it. You could probably check by model/serial number if they’re interchangeable but you haven’t given that information so Nobody can say one way or the other...
I guess there are 3 options: Cut off the crankshaft to the proper length, but then you will need to file or machine a keyway in the correct location, as well as re-do the center bolt threads (not an easy option).
2 Take the crank out of the other motor, examine it to make sure it is good (the con rod journal is usually the deciding factor), if good, install it in your good engine. This will be a few hours of work, but you probably will end up with a good motor.
3. Scrap both of them, which is the simplest, but not the most useful option.
Generally speaking the internal parts will interchange, but you need to use the parts that come with a given crank type. What I mean is, if it has a removable metal gear, you need to use that. If it has a plastic crank gear (I hate those), you need to use that, and the thin steel washer that goes with it.
Hope this helps.
It's amazing how little had changed in 50 years. Until the EPA came along
HaHaHa :) You are right!
if you could find a heavy flywheel
Yes, I admit they are somewhat hard to find. Horizontal shaft engines always have them. Some vertical shaft engines like pressure washers and possibly generators and roto-tillers can have the heavy flywheel also. I would recommend the heavy flywheel, since the smoother motion will be better for whatever type of drive train you hook it up to. The more jerky motion of a lighter flywheel will be harder on the parts.
So you saying it is safe to go with a modern pressure washer ohv engine and it will make a good outboard motor ?
Hmmm, I am afraid I can't say for sure, since I am really only familiar with the old Briggs flathead engines. I don't see why an OHV engine wouldn't work, though in any case I would bring some oars with me just in case the engine conked out!
Old Guy here. Tried that in early 1970's. 2 cylinder Johnson outboard. Rod through block. Junk push mower that ran well. Found lower unit was 3/8 square into crankshaft. Welded 3/8 drive socket to Briggs crank; No other engine changes. Made frame from light angle iron that bolted to lower unit and Briggs verticle shaft flathead engine. Never took cover off to see what flywheel had but lower outboard drive and prop always turning with engine. Worked great Except only go about speed of cheap electric trowling motor. Actually expected that as Briggs 3600 rpm, original 2 stroke maybe 7000 rpm.