Crankshaft replace?

[Gold Coast Shipping]

Somehow (!?) one of our saws (Stihl 241) was run without the needle bearings on the clutch side of the crankshaft. Now there is significant play between the clutch drum and the crankshaft stub with the bearings properly in place.

I expect the wear was to both the crankshaft stub and the clutch drum - Putting a new clutch drum on reduces the amount of play significantly, but doesn't eliminate it.

Do I have to replace the crankshaft? Expensive, I'd probably just retire the saw...

Or can I still safely use the saw with a new clutch drum? What else is going to wear if we do this?

Thanks

 

[Vintage Engine Repairs]

Hi mate,

The correct solution is a dial indicator to test runout. There shouldn’t be any play between the bearing / clutch drum / crank. If you run the saw with slop, you’ll prematurely wear the sprocket, chain and drum. You’ll struggle to get even tension on the chain too. It will tighten and then loosen continuously.

Warm regards,
Tom

 

[Gold Coast Shipping]

Thanks Tom, I appreciate the info. That makes sense. We've gotten a lot of miles in on this saw, so I guess it's time to retire it.

Cheers

Tony

 

[Vintage Engine Repairs]

No worries, if you really want rid of it, stick it in the for sale section - someone will snap it right up for a rebuild project.

 

[Mad Professor]

Got a picture of the crank end?

Have you measured the bearing surface on the crank with a micrometer, at several points?

 

[Gold Coast Shipping]

Hi Professor - No, I'm in the middle of a move and my micrometers are packed up. I think it's pretty clear what's happened though - What else could have been damaged running it without those bearings?

 

[Deleted member 117362]

This is just my thought, without that bearing, crank would be spinning inside that clutch without being under load. For saw to cut, clutch would center that drum by applying even 3 shoe clutch pressure. Doubt a lot of crank wear occurred under load.

 

[dmb2613]

new bearing and drum, then run it like you stole it

 

[Mad Professor]

Hi Professor - No, I'm in the middle of a move and my micrometers are packed up. I think it's pretty clear what's happened though - What else could have been damaged running it without those bearings?

I have 036 that came with the smaller wimpy bearing. it grenaded and I knew it right away. A good Stihl dealer gave me the bearing/clutch upgrade free. It might have been warranty then?

Your crank is main concern. Rest of parts are cheap and easy fix.

 

[Mad Professor]

new bearing and drum, then run it like you stole it

Yup all I needed when my 036 grenaded the clutch bearing. Need to check crank though.

 

[dmb2613]

the saw is not worth a new crank, run it

 

[SteveSr]

Hi Professor - No, I'm in the middle of a move and my micrometers are packed up. I think it's pretty clear what's happened though - What else could have been damaged running it without those bearings?

The odds are that the saw was run with a dry bearing and an overtightened chain. The resulting heat buildup melted the plastic bearing carrier and all of the little rollers fell or worked their way out. There was also a supposed issue where some Stihl crankshafts missed the final hardening / heat treatment process and ended up being too soft.

 

[MacAttack]

I agree with DMB2613, what have you got to lose by running it with a new drum and bearing? I bet that crank is a whole lot tougher material than the drum, it probably didn't damage the crank much.

 

[Gold Coast Shipping]

I agree with DMB2613, what have you got to lose by running it with a new drum and bearing? I bet that crank is a whole lot tougher material than the drum, it probably didn't damage the crank much.

Thanks for all the replies folks.

I put a drum from another 241 on this saw, and there's still a fair bit of slop. Definitely less slop, but clearly still an issue.

I guess it could be worth trying, but those drums aren't cheap.

 

[lone wolf]

Thanks for all the replies folks.

I put a drum from another 241 on this saw, and there's still a fair bit of slop. Definitely less slop, but clearly still an issue.

I guess it could be worth trying, but those drums aren't cheap.

Compared to the other saw how much slop?

 

[Gold Coast Shipping]

Compared to the other saw how much slop?

The undamaged saw has zero slop, nice and tight.

The damaged saw with the undamaged drum is clearly still wobbly, but much less so than it is with the damaged drum..

It's all relative until I'm able to measure something, sorry folks.

 

[Mad Professor]

Measure the crank ends on both saws. Several places and 90 degrees to each other.

Is there visible damage to the crank end?

 

[Mad Professor]

One more thought. The clutch is going to grab the drum whenever you have the chain driven. The drum can't wobble then.

When the saw is idling there won't be much stress on the bearing/crank/drum. Might want a gob of thick grease on the bearing.

I had an early 036 grenade a clutch bearing. It was still cutting but was not right. The clutch upgrade has been in it for ~20 years now and no problems at all.

 

[MacAttack]

I have saws with a "wobbly" fitting drum that I've been running for years. I wouldn't worry unless there was a significant amount of radial play (feels like you can lift the drum right off the crank).

 

[Henry E]

Try the chain break. My MS261 has the same problem. If you put on the chain break it causes the clutch to pinch the shaft and snub out the saw.