What did this 576XP ingest?

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... Now I have a lot of work to find and repair the damage. I'm starting part-time at a saw shop so that will be helpful. Or maybe I should just part it out and not stick any more into it?
Depends if you want to keep the saw and use it for "learning on the job". If you're looking to make money, OTH, parting it out would likely work out better. Sure sounds like something wrong with the bottom end, so the case gets split, etc. If the conrod bearing is bad, an OEM crank is expensive and AM has its risks. Hopefully you'll be able to borrow tools from the shop, including the pressure/vacuum test setup & seal press. I'm going through a similar process with a blown ms460; the whole thing had to come apart and the local shop loaned some tools plus will install the crank bearing seals and perform the pressure/vac test. No guaranties for me, though, and the whole thing may end up a bust. Guess it depends on how curious you are. ;)
 
Jim, I think you got it. That piston damage is identical to mine. Now I have a lot of work to find and repair the damage. I'm starting part-time at a saw shop so that will be helpful.
Or maybe I should just part it out and not stick any more into it?

If the cylinder is not damaged, I think it deserves to be repair. A piston and two bearings (one of the crankshaft and one of the piston ), more hand labor should not be that expensive and gets a new chainsaw.
 
You might want to look at your decompression valve. I once had a MS361 that lost one of the decomp detent balls which went into the cylinder and caused similar type damage. Although your damage appears to have a wider groove like a needle bearing, which others have suggested.
 
If the lower crank bearing is bad, that dooms the entire crank assembly. Best move financially is to part it out. Gets you money with no further investment. If it gets fixed with OEM parts, you'll have more in it that it's worth. If it's a learning tool, then you're paying tuition and that may be acceptable.
 
The valve doesn't have much hold on the detent. I'll take it out and have a look.

I inspected the rod bearing closely, turning it with a pin. I saw no damage or marks on the cage either side of the rod. Rollers looked clean and turned smoothly.


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...I inspected the rod bearing closely, turning it with a pin. I saw no damage or marks on the cage either side of the rod. Rollers looked clean and turned smoothly.
That's good news. Keep tearing it down. Hopefully you'll find a broken cage on one of the main bearings and the search for the failure can end. Is the cylinder salvageable?
 
Cylinder is quite clean and has no damage. I found a small piece of debris stuck to the squish area though. No clue to what it might be from, looks like a drill shaving.


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Sounds like you have to dig further. You will probably find a failed crank bearing. If so and that piston, cyl, and crank are still good then its well worth fixing IMHO
 
It does look a whole lot like the 394 I got with no compression... on mine it was in fact the big end rod bearing just like @Chainsaw Jim's saw had.. In my case I couldn't see the missing piece, but I feel slop in the bearing.

Both rings were stuck, but not too badly, I managed to get them freed by heating the piston up well, and filed the ring grooves a little to make them fit again.. I reassembled it and it fired up well (ran it 10 seconds), but it'll be parked until I get a crank for it.. I could hear the bad bearing while it was running.

If your rod bearing looks and feels good, I'd start by prying out the crank seals to look at the main bearings.. it's the best you can do without splitting the case.
 
Oh, and in the last picture of the first post.. it looks to me like the cylinder skirt is broken? Is that an illusion?

Good luck with it
 
Do you see any scrub marks on the casing around the crank? signs that something got dragged around a few times? Might be pretty hard to see around it with things assembled I guess though, it is a full circle crank which doesn't leave much room for inspection
 
Do you see any scrub marks on the casing around the crank? signs that something got dragged around a few times? Might be pretty hard to see around it with things assembled I guess though, it is a full circle crank which doesn't leave much room for inspection
I looked for scrubbing even on the softer plastic of the crank stuffers. Nothing of the sort, everything is smooth and clean. No debris in the bottom of the crankcase either. Whatever it was it went through in a hurry and the only damage it inflicted was on the piston. I'll look at the main bearings later this week.
 
I found the problem. The clutch side bearing melted it's plastic retainer. Some of it melted to the crank stuffer and the rest worked it's way out.

I'm lucky the saw lost it's compression before the rest of the bearing started to migrate.

Everything has a nice coat of oil even to the point of dripping, so it doesn't seem to be starved. I've been reading since that a lot of 575s and 576s had bearing failures. Would new OEM bearings be of a newer spec than these plastic originals? Or would another brand of bearing be better?



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