115 Mercury Outboard Powerhead Pull and Teardown - Why Does it Knock?
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- Опубликовано: 18 сен 2024
- This Mercury 115 HP, 4 cylinder, 2 stroke engine has developed a very audible knock that seems the worst at idle. The engine runs fine otherwise and has been running like this for a while, except that the noise is increasing.
Diagnostic work has been done to rule out as much as possible, so the time has come to remove the powerhead and disassemble it completely to find the cause of the noise.
00:20 What is the noise?
00:30 What has been done and what is the plan?
02:05 Start Powerhead Removal - Disconnect cables, hoses and electrical
03:55 Remove Lower Cowl
04:10 Remove Shift and Throttle
04:36 Remove External Electrical Power and Grounds
05:55 Remove Powerhead Studs and Hoist Powerhead
09:25 Remove Airbox & Oil Tank & Bleed Hoses
13:25 Remove Intake Manifolds and Reed Blocks
15:30 Remove Flywheel and Stator
16:30 View into Crankcase at Bottom of Pistons
17:00 Remove Hoses and Wires
19:30 Remove Starter / Coils / Ignition Wiring
24:10 Remove Exhaust Cover and Inspect through ports
28:18 Remove Cylinder Top Cover
30:00 Remove Oil Pump
31:40 Remove Lower Main Bearing Seal Housing
33:30 Remove Lower Crankcase Housing
37:35 Remove Crankshaft, Rods, Pistons as Assembly
39:00 Inspect Pistons and Cylinders
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Poor 115, looks like bottom cylinder was getting moist during storage and rust took its toll :( I recognize those rod bearings, little beastly guys. Designed them back in the day for Merc.
Yes, there is evidence of moisture. As I said in the video, I was surprised at finding water droplets in the crankcase and cylinder as we took it apart. The engine had run a month or more ago for testing. We tried running a Power Tune cleanout to clear any carbon. So, the water jackets should have been well drained down and I really didn't see anything as we pulled the covers. I'm still wondering if there may have been a pinhole leak in a gasket.
Now that's a can of worms!
Yes, there is a lot of plumbing & wiring to keep track of.
I've never seen anyone remove the crankshaft from an engine with the rod bolts still attached, thus pulling the pistons from the bores from the bottom.
These 2 strokes are different since there is not a separate cylinder head to remove. The design intends everything to come out the bottom. The manual advises that crank can come out as a unit or in pieces. Cylinders have a taper in the bottom to load pistons without a ring compressor (very carefully...). I wanted to keep the pieces all together so they wouldn't risk getting mixed up until we had a plan.
@@bitsofwisdom460 Wow! Interesting! Thanx for the information. The cylinders taper outwards toward the bottom? I guess that works because 2 strokes usually have lower compression due to heat issues.
I had a 90 HP Yamaha three cylinder outboard from 1996 and it did have a head gasket.
@@Flies2FLL Yes, these Mercurys have a chamfer at the bottom of the cylinder so that the pistons / rings can slide in.
@@bitsofwisdom460 Interesting.
what year is it? Great vid, thanks for sharing
Thanks. It is a 2001 if I recall correctly from the emissions sticker. S/N is OT236xxx
Lots of wear on that old girl , she needs a complete rebuild . Lean #4 Cylinder , Very common with the 4 cyl merc. this engine only has idle circuits on the top 2 carbs. Buy another set of carbs and us the top 2 for the bottom 2 cyls. Remove the accel pump fittings and plug them.
Yes, I have heard that the lower cylinders can have an issue. We have a line on some used parts that may let us have 4 carbs that idle. More to come as this comes together.
What do you mean by "Buy another set of carbs and us the top 2 for the bottom 2 cyls"?
@@troycarrigan4893 These engines have 4 carbs, but idle on only 2 carbs. The bottom two carbs don't have an idle circuit, meaning that when you throttle down to idle, there is no fuel flow to the bottom two cylinders. Even though it is oil injected, the oil is injected into the fuel, so it would seem that if you idle a lot, the lower cylinders might have less lubrication. I think Mercury has some means of feeding oil to those cylinders when they are off, but I haven't tracked it down yet. So, if you had two more "top carbs" and put them in the bottom positions, it would idle on all 4. I'm not sure what complications that would cause, so it's only a thought for the moment.