Bearing ware diagonsing

[omant]

Hello, I wonder if anyone can confirm my fears or dispel them over a MS460 I just bought, it was sold as "hardly used" condition...??...

What is the easiest way of diagnosing if the bearings are worn on a saw?

On starting up my new purchase I thought the engine sounded a bit noisy so I took the pull start recoil off and tried turning the flywheel by hand. When I did this it had play when rocking it back and forth, and sounded clonky when I did full rotations. Is this the sound of bad bearings or normal to these saws?

The next question will be: If the bearing are bad whaich one? Obviously the "small end" is worth replacing but the "big end" is an expensive pain. I don't think I can tell which one it is without taking the barrel off? If I did take it off, is there a technique for telling which one needs replacing?

For now the first question is most important.

Cheers from a slightly worried new owner of a MS460 [most money I've ever spent on a saw yet]

 

[Tzed250]

Not a good sign. Mains and/or rod bearings are probably shot. Time for a tear-down.

 

[Al Smith]

In my own sheltered life I've found that more times than not the clutch side bearing wears out faster than the flywheel side.This would seemingly make sense because that is the side doing all the work and eating all the sawdust chewing away at the seal.

Changing crank bearings is not as big of a deal as many think it is.

 

[drunkenredneck]

:bang: Thats a definate main bearing failure your going to have to completely pull the saw down and split the case and replace the bearings. sorry

 

[omant]

eballs

That isn't the best news. It was an ebay saw from here in England. Paid quite a bit for it and now having problems with the seller. This one could be a bit of trouble to sort it, either if I fix it or try to send it back [he is being prickly not like most the ebay sellers I have bought from, probably knew it had a problem :<

Thanks guys nice to know there's some support at hand.

 

[rreidnauer]

[he is being prickly not like most the ebay sellers I have bought from, probably knew it had a problem :<

Dang right he knew it. "Hardly used" was hardly true. If you don't send it back, at least be sure to neg rep him.

 

[bcorradi]

In my own sheltered life I've found that more times than not the clutch side bearing wears out faster than the flywheel side.This would seemingly make sense because that is the side doing all the work and eating all the sawdust chewing away at the seal.

Changing crank bearings is not as big of a deal as many think it is.

On an 044/046 I agree with you. On an 026 however, I've found the flywheel side bearing being bad more often then the clutchside.

 

[Lakeside53]

Hang on....

Clunking when rotating is almost never bearings... that's just piston slap. Rocking the flywheel back and forth at TDC or BDC.. all saws make noise - again, piston skirt movement against the bore.

If you can grab the flywheel and move it side to side, that's bearings... ditto on the clutch side crank. Also, if the engine make growly noises when idling - often rough mains..

Take off the muffler - look at the piston. If it's polished or scored on the exhaust - you likely have slap. If it's worn or erroded on the inlet side (harder to see even though the carb mount), same.


How much slap is to much? a lot... If it just slaps at pull-over, probably o.k., if it slaps a little at idle, o.k. but worn a lot.. if it slaps when you rev it up - real bad.

 

[Lakeside53]

On an 044/046 I agree with you. On an 026 however, I've found the flywheel side bearing being bad more often then the clutchside.

I agree - The stihl clutch-side main bearing on most saws is protected by the oil pump and is in a nice clean and oiley environment (verses the dry and dusty environment of the flywheel side).

The main reason for clutch side failure on bigger saws is the overtightening of long chains when hot.

 

[omant]

Just to try and describe the problem clearly.

When I rotate flywheel by hand there is no play across the saw just in the rotation in what I presume is between the piston and crank the small or big end? [It could be piston slap?]

I am comparing this to my 038av which has been used for under 10 hours and is like new. It has no play or "slapping" or metal to metal noise what so ever.

How long would the bearings at either end of the con rod typically take to get to this level of play? Or what causes piston slap?

 

[Lakeside53]

Piston slap is the noise of the piston skirt hitting the side of the bore - happens when the piston skirt wears. You won't hear it in a 10 hour saw, but you will in a high hour saw or one that has a worn pistion (gas or air filter).

As you rotate the crank the changing of direction of the rod causes the "other side" of the piston skirt to hit the cylinder wall. Wiggling the crank back an forth causes the piston to hit alternate sides of the cylinder in the same manner.


All saws slap the pistons.. but you can't hear it in most. All do it eventually if run long enough, and even when you can hear it, could run for many many hundreds of hours.. bearing knock - maybe a few hours to 10's of hours and the saw is toast....

 

[Al Smith]

I should clarify what I said about clutch side bearings.I tend to agree about the oily environment on Stihls.Having said that ,on many of the saws I wrench on,non Stihls,they don't have the luxury of this protection.

I did however repair an older Stihl that had spun a main by ingestion of dust due to a faulty air filter ,in combination of a worn out seal on the clutch side. It was likely that the bearing going bad over time caused a wobble that ate up the seal.Most saws,by design use a more robust bearing on the clutch side than on the flywheel side.