Can't slide cylinder off piston of STIHL MS 362

[Smitty Smithsonite]

Sounds believable, but help me out here. What is it that leads you to thing that?

I'm afraid I'm not going to be much help to the inquiring minds out there as far as providing answers to what was wrong. With this being the first used p/c I've ever laid eyes on, I'm really not sure what I am looking at. To my inexperienced eye, it doesn't look like there is much grievous damage or scoring and the inside of the cylinder feels pretty smooth to me.

That skinny scuff line on the piston reminds me of a "4-corner" seizure, which happens when you don't warm up a 2-stroke, and just pull the cord and go right to cutting a 2' diameter oak. The piston grows quicker than the cylinder, and it seizes on the 4 widest points. A piston isn't perfectly round, and this becomes worse with heat, hence the 4-corner pattern.

I don't see the corresponding scuff to the right of it in the pic, so probably not a 4-corner seizure, but could've got super hot from being slightly lean - either from improper mixture or from an air leak through the crank seals. Usually rings don't break when this happens - they'll stick hard in the piston. It's possible that the previous owner did a half-assed rebuild and never chamfered the ports, which snagged a ring. Piston clearance could've been too tight as well.

 

[T.Bird]

Take a better pic inside the cylinder, this is what we are looking for. Also to see if the plating has been worn/torn/chipping away around the ports as the rings where catching. Run your fingernail over area's like the arrow is pointing at cross ways of the pattern and see if you can catch your nail on it.
It's hard to tell from pics sometimes but we are looking for transfer, gouges and damage to the lining. Also if the rings damaged the chamfers on the ports as well.

Yup! Sure enough. The fingernail test definitely made the damage to the plating pretty aparent.



The ports seem okay though.

 

[pioneerguy600]

Yup! Sure enough. The fingernail test definitely make the damage to the plating pretty aparent.

View attachment 941268

The ports seem okay though.
View attachment 941269

Is that something like the ring keeper pin stuck in the lower transfer port? Or maybe a piece of needle bearing.

 

[Smitty Smithsonite]

The light nicks everywhere around the cylinder tell me it wasn't maintained - constantly dirty, or a holey air filter. The scuff near the exhaust port tells me it was run REAL hard with either a slightly lean mixture or cheap, non-synthetic 2-stroke oil (or both). The rings may have broken from an over rev situation. If the mixture was lean, the thing will SCREAM with no load on it. Previous owner probably kept the throttle pegged as he went about cutting logs. Just a theory. Those port transitions from the cylinder look super rough, but that might just be normal factory work there - I've never looked that close at one (I'm usually always in a hurry).

 

[lostone]

Was there a gasket on this cylinder when you removed it? Your last pic looks like the piston was slapping into the top of the cylinder at the squish band on the intake side. If so you may want to check out that crank and rod.
This would have deformed the piston causing the ring damage and causing them to break. Also a reason not to just do a gasket delete unless a person knows how to measure squish.

 

[lostone]

Can anyone familiar with a 362 cylinder even confirm if this thing is OEM? I'm "GUESSING AT THIS" and that it had a good squish with a gasket and it was deleted causing the issue.

 

[Yukon Stihl]

Is that something like the ring keeper pin stuck in the lower transfer port? Or maybe a piece of needle bearing.

looks big enough to be bearing to my untrained eye

 

[pioneerguy600]

looks big enough to be bearing to my untrained eye

Yes very possible , but I always have a bit of difficulty with camera angles and depth of view/magnification etc. If I had the cylinder in my own hands then its just so easy but pics over the net is and always will be a bit deceptive to my old eyes.

 

[pioneerguy600]

Can anyone familiar with a 362 cylinder even confirm if this thing is OEM? I'm "GUESSING AT THIS" and that it had a good squish with a gasket and it was deleted causing the issue.
View attachment 941461

Check around the base mounting flange, there should be a Stihl logo or a manufacturers name there.

 

[lostone]

When the pic is blown up I believe it is a piece of broken ring.
But like I said before and like you said also, old eyes and trying to tell what it is off a pic in a forum isn't easy to do.

 

[wanab]

Hommie home hot rodder strikes again. Beat the bearings right out of it when it got warm. She ran like a raped ape with .010 squish.

 

[Piotr Pakuła]

I used to give compressed air through the spark plug hole because the corrosion grabbed quite strongly and I did not want to hammer

 

[lostone]

looks big enough to be bearing to my untrained eye

Could be, maybe the bearing let go and allowed the piston to slap the cylinder braking the rings.

 

[Smitty Smithsonite]

Usually piston slap marks up the skirt. Usually doesn't break rings, but anything is possible, especially with modern metals designed to save the company as much money as possible, and still barely make it past the warranty period.

 

[lostone]

Usually piston slap marks up the skirt. Usually doesn't break rings, but anything is possible, especially with modern metals designed to save the company as much money as possible, and still barely make it past the warranty period.

I wasn't meaning normal piston slap on the skirt, my bad. I was referring to the piston hitting into the top of the cylinder as you can see in the pic. I was meaning if a bearing blew up and allowed the crank to go high it could have caused the top of the piston to come into contact with the cylinder which would have deformed the top of the piston and cracked the ring. I just didn't explain very well what I was meaning.

Without the saw in front of me it's hard to tell what actually happened in this case and I'm just throwing out possibilities. Either way I'm guessing this saw needs a top and bottom end worked on.

 

[Smitty Smithsonite]

Yeah, text is always harder to decipher. I get what you meant now!

 

[pioneerguy600]

Was there a gasket on this cylinder when you removed it? Your last pic looks like the piston was slapping into the top of the cylinder at the squish band on the intake side. If so you may want to check out that crank and rod.
This would have deformed the piston causing the ring damage and causing them to break. Also a reason not to just do a gasket delete unless a person knows how to measure squish.
View attachment 941473

Take a good look at the pics on the first page of this thread, where the cylinder was still stuck on the saw. The gasket is clearly there and there is no damage to the top of the piston from striking the top of the cylinder, the ring lands would be squished tight.

 

[lostone]

Take a good look at the pics on the first page of this thread, where the cylinder was still stuck on the saw. The gasket is clearly there and there is no damage to the top of the piston from striking the top of the cylinder, the ring lands would be squished tight.

I see the gasket but I cannot see the intake side of the piston at the top, It shows the top edge on the exhaust port side plus there is clearly marks where the piston has been hitting the top of the cylinder on the intake side. Oh well, I guess I am seeing something that isn't there. Like I said before "It's hard to tell over pics".