morecowbell
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@MrSled nailed it. Center piston had upside down rings 
Oops. i blame the assembly beers. Other pistons fine.
Nothing seems to be catastrophic in there. Never pinned it super hard. Obligatory pictures / video of everything now that it's disassembled / partially cleaned. Obviously new rings are in order but open to whether y'all think i need to go get the cylinders honed. I'd put a new piton kit in too I guess if the consensus is it's the right thing to do.
This will really only be a trail-duty sled and it's 25y/o but it is the nicer of the two and I'd like it to last for a good long service life of ski access. It got all new bearings everywhere and a new track etc. Does not need to be a race face machine; it just needs to not explode 25mi up the forest service road, basically.
MAGNETO SIDE
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CENTER
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CLUTCH SIDE
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VIDEOS
Oops. i blame the assembly beers. Other pistons fine. Nothing seems to be catastrophic in there. Never pinned it super hard. Obligatory pictures / video of everything now that it's disassembled / partially cleaned. Obviously new rings are in order but open to whether y'all think i need to go get the cylinders honed. I'd put a new piton kit in too I guess if the consensus is it's the right thing to do.
This will really only be a trail-duty sled and it's 25y/o but it is the nicer of the two and I'd like it to last for a good long service life of ski access. It got all new bearings everywhere and a new track etc. Does not need to be a race face machine; it just needs to not explode 25mi up the forest service road, basically.
MAGNETO SIDE
---
CENTER
---
CLUTCH SIDE
---
VIDEOS
Put the piston rings in correctly and give it another shot 
Hard to tell if the center cylinder surface is damaged or not. I always liked run a ball hone through the cylinders when freshening them up with new rings. If you cant catch your finger nail on any of the surface marks on the cylinder you should be good to go. Red head triples are a very forgiving motor to work on so you should be good.
morecowbell
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Hokay folks. Snowstorm kept my new rings from me for longer than I'd hoped, but they made it.
@sideshowBob @MrSled - Ran a ball hone down the cylinders and they cleaned up really nicely. New rings on the center cylinder where they'd been installed upside down. Other cylinders same rings.
New pilots installed #55. Fuel screws 1 3/4 turns out.
Mixed some oil in the gas tank. Left the oil pump off the engine on this pull so it stayed primed (verified that on reinstall)
Got it started up this morning and gave it a couple good heat cycles. Rode it around the block twice.
Seems to run happy enough. Still some rattling. Overall it's less aggressive rattling and it doesn't vibrate like an earthquake. Videos attached of both with and without the clutch mounted.
Unsure if I should keep chasing the rattle or move on. I think it needs a new set of clutch springs. It's engaging the belt at a pretty high RPM.
Have not compression tested it yet but will tonight.
@sideshowBob @MrSled - Ran a ball hone down the cylinders and they cleaned up really nicely. New rings on the center cylinder where they'd been installed upside down. Other cylinders same rings.
New pilots installed #55. Fuel screws 1 3/4 turns out.
Mixed some oil in the gas tank. Left the oil pump off the engine on this pull so it stayed primed (verified that on reinstall)
Got it started up this morning and gave it a couple good heat cycles. Rode it around the block twice.
Seems to run happy enough. Still some rattling. Overall it's less aggressive rattling and it doesn't vibrate like an earthquake. Videos attached of both with and without the clutch mounted.
Unsure if I should keep chasing the rattle or move on. I think it needs a new set of clutch springs. It's engaging the belt at a pretty high RPM.
Have not compression tested it yet but will tonight.
I am probably not the right guy to give you advice as I will not give up on a project I have started, no matter what, and a lot of times I go well beyond the point of reason to get it right.
Having said that...
I believe that the piston/cylinder clearance has exceeded tolerance on one or more cylinders on that engine.
I would not regularly ride that sled until the issue is sorted out.
An easy way to see if the cylinders are badly worn is to measure the stock rings "end gaps" especially above the height of the exhaust ports...a large out of tolerance end gap would indicate a cylinder that needs replating.
If you haven't installed new pistons that could be your issue as well and most likely .The skirts wear on high mileage engines and can make a lot of noise. SPX offers a decent piston set for these engines at a fair price.
If the cylinder/pistons clearance checks out then you need to focus on the crankshaft,
Having said that...
I believe that the piston/cylinder clearance has exceeded tolerance on one or more cylinders on that engine.
I would not regularly ride that sled until the issue is sorted out.
An easy way to see if the cylinders are badly worn is to measure the stock rings "end gaps" especially above the height of the exhaust ports...a large out of tolerance end gap would indicate a cylinder that needs replating.
If you haven't installed new pistons that could be your issue as well and most likely .The skirts wear on high mileage engines and can make a lot of noise. SPX offers a decent piston set for these engines at a fair price.
If the cylinder/pistons clearance checks out then you need to focus on the crankshaft,
morecowbell
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@sideshowBob we're more similar in that than I care to admit. The pistons were reused, at ~5k mi on the clock it was a bit of a gamble. Replacing those does feel like the next logical step.... That "click" sound is more obvious on camera audio than in person. It almost sounds like valves clicking on a four stroke. Probably piston slap? ... See video in prior post of inspecting the crank. A little lateral play in the rod bearings but none vertically. Nothing else obvious when I had it all the way apart
I'm not in love with pulling it apart a third time and it doesn't need to throw max horsepower.... but I would like it to not explode
I'm not in love with pulling it apart a third time and it doesn't need to throw max horsepower.... but I would like it to not explode
It sure sounds like piston slap to me. Usually piston slap will get a little quieter as the engine warms up...I wouldn't buy new pistons until I checked the cylinders even though the nikasil usually is pretty resistant to wear.
morecowbell
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Some more evidence for review.... Started it up this evening to move it back into the garage. 7F outside - reasonably cold - was left outside overnight and all day in the cold. It did not want anything to do with turning over on its own again regardless of choke lever position and needed a spritz of liquid encouragement. It did not like idling on its own at first and I had to give it some throttle for a while to keep it from stumbling, bogging down and dying.
After warming up, it held idle fine at ~2k RPM. It turned back over pretty easily after being warmed up too. Once warm, adding choke bogged the engine down and killed it. So.... we are back to square one
@sideshowBob not sure if that confirms any of your suspicions but yeah I think the right next move if she's gonna last is at least new pistons and re-plated cylinders isn't a bad idea, haven't done another compression test yet or cleaned the sparkies but it definitely is still not pleased.
After warming up, it held idle fine at ~2k RPM. It turned back over pretty easily after being warmed up too. Once warm, adding choke bogged the engine down and killed it. So.... we are back to square one
@sideshowBob not sure if that confirms any of your suspicions but yeah I think the right next move if she's gonna last is at least new pistons and re-plated cylinders isn't a bad idea, haven't done another compression test yet or cleaned the sparkies but it definitely is still not pleased.
I wouldn't replate the cylinders until I confirmed they are actually worn because as I say they are pretty resistant to wear if undamaged. The piston skirts usually are the culprits in excessive cylinder/piston clearance. If you have a digital vernier caliper you can get a rough idea of clearances by measuring piston skirts and cylinder bore and check the difference in size. These red heads will rattle pretty good when getting to max tolerance or beyond. Poor oil and crappy fuel accelerate piston skirt wear.
You have equal heat accross all 3 cylinders?
almost sounds like its running on 2.
Compression test after the rebuild?
almost sounds like its running on 2.
Compression test after the rebuild?
morecowbell
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@MURDER YAMAHA sorry caught the flu and been down for a few days. Bad news is, compression test cold on that HF gauge (cylinder walls were hit with that ball hone this time, new rings in the center replacing the upside down ones, same rings as first teardown on the outside cylinders):
Clutch side 96psi
Centr 103psi
Mag side 103psi
It really did not want to turn over so I didn't even bother trying to get a warm reading.
I think probably pre-first rebuild the cylinders and pistons probably pretty worn and the rings were just real well seated/worn in alongside 'em and that's what was keeping the compression a bit higher. Pulling them at all broke that seal even with new rings. No good deed goes unpunished
I haven't pulled the top end again yet to measure ring gap but there is definitely a noticeable "rounded edge" at the top of the cylinder walls where the pistons top out. So I'm willing to hazard a guess that ring gap is pretty wide.
@sideshowBob probably the "right" thing to do to give this dinosaur a new life is just bite the bullet and drop in re-plated cylinders and new pistons, send my old ones in for a core charge (found a few places that will do this) and pray that fixes the rattle issue along with fresh compression because a reman crank on top of that would hurt a lot
That said, when I measure the ring gap - who has the OEM specs for acceptable gap handy?
Clutch side 96psi
Centr 103psi
Mag side 103psi
It really did not want to turn over so I didn't even bother trying to get a warm reading.
I think probably pre-first rebuild the cylinders and pistons probably pretty worn and the rings were just real well seated/worn in alongside 'em and that's what was keeping the compression a bit higher. Pulling them at all broke that seal even with new rings. No good deed goes unpunished
I haven't pulled the top end again yet to measure ring gap but there is definitely a noticeable "rounded edge" at the top of the cylinder walls where the pistons top out. So I'm willing to hazard a guess that ring gap is pretty wide.
@sideshowBob probably the "right" thing to do to give this dinosaur a new life is just bite the bullet and drop in re-plated cylinders and new pistons, send my old ones in for a core charge (found a few places that will do this) and pray that fixes the rattle issue along with fresh compression because a reman crank on top of that would hurt a lot
That said, when I measure the ring gap - who has the OEM specs for acceptable gap handy?
Ring End Gaps:
.014" to .022"
.014" to .022"