Clutch side bearing failure causes

[brandonstc6]

I picked up a Stihl MS261 with a bad ignition coil and missing clutch parts. I then discovered a bad oil pump, a busted seal and a bad pto side bearing. What caused this bearing failure? Half the balls are gone.

On a positive note, the saw does still have good compression.


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[Andyshine77]

Likely abuse of some type, my guess is dull or jumpy chain.

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[brandonstc6]

Likely abuse of some type, my guess is dull or jumpy chain.

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I wonder if the failure has anything to do with the bad oil pump

 

[Andyshine77]

I wonder if the failure has anything to do with the bad oil pump

If the pump failed first the chain could has bound up, and they kept running that saw overheating the clutch and subsequently the bearing and seal. But I would guess the bearing failed first. Either way it was likely abuse.

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[jmssaws]

Likely abuse of some type, my guess is dull or jumpy chain.

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Agreed
Running one to tight will do it also

 

[brandonstc6]

If the pump failed first the chain could has bound up, and they kept running that saw overheating the clutch and subsequently the bearing and seal. But I would guess the bearing failed first. Either way it was likely abuse.

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That makes since, I guess I'm lucky they didn't toast the cylinder too


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[jmssaws]

Bearing will shoot craps then get the seal and if ran long enough it can get the oil pump also.

Is the plastic around the clutch brown and melted?

 

[brandonstc6]

Bearing will shoot craps then get the seal and if ran long enough it can get the oil pump also.

Is the plastic around the clutch brown and melted?

Wouldn't it cause a scored piston and cylinder if run that long? My saw still has 155 psi compression. I may or may not replace the piston rings too.


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[jmssaws]

Wouldn't it cause a scored piston and cylinder if run that long? My saw still has 155 psi compression. I may or may not replace the piston rings too.


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No
It will only score when it gets hot enough to do,just because it's got a airleak doesn't mean it should seize.

Some can be tuned or tune themselves to hide a big airleak.

 

[jmssaws]

A got a question, where's the missing ball bearings?
Ain't but one place they can go unless the cage is gone and it makes it look like some are missing.

 

[brandonstc6]

A got a question, where's the missing ball bearings?
Ain't but one place they can go unless the cage is gone and it makes it look like some are missing.

I didn't see any come out when I removed the pump and seal. It may just be a missing cage. I haven't torn into the saw. I am certainly not throwing any more money at it until I take it apart.


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[brandonstc6]

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[jmssaws]

It just lost its cage.
Bearings are cheap
I put bearing in extremely cheap if you want it fixed.

 

[Andyshine77]

Yes just the cage. Looks like maybe the they ran engine oil as bar lube, that's hard on the pump.

 

[brandonstc6]

Thanks for the information and the offer. I've completely rebuilt 3-4 pro stihl saws before but not anything this new.


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[Wood Doctor]

Heat burns out bearings, but the exact cause of the heat has to be determined. Several possibilities exist when it comes to chainsaws or any other mechanical device: excess force, lack of lubrication, foreign particles, etc.

On the clutch side of a chain saw, I've seen saw operators drive the chain right through the rim sprocket, through the clutch drum, and into the needle bearing. The idea was to keep the chain tight and keep on cutting to get the job done.

 

[brandonstc6]

New bearing is $16 at the dealer and a new gasket set is $16 as well. I am started pulling the saw apart today. Does anyone happen to know what size nut driver I need to remove the carburetor. All of the stihl saws I've ever take apart took a 5/16. It seems to be between 5/16 and 1/4.


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[Leerod83]

New bearing is $16 at the dealer and a new gasket set is $16 as well. I am started pulling the saw apart today. Does anyone happen to know what size nut driver I need to remove the carburetor. All of the stihl saws I've ever take apart took a 5/16. It seems to be between 5/16 and 1/4.


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8mm?

 

[ncfarmboy]

All the Stihls I've worked on was 8mm.
Shep

 

[brandonstc6]

Thanks guys, that was the right size. I got it all apart and the cylinder looks perfect but the piston has a crack in the intake side skirt. I am kind of wary of a oem piston after this one was cracked. Would I be better off with a Meteor, OEM or Hyway (assuming they sell just the piston and rings)?