Stihl MS 660 crankshaft snapped!

[edaigle]

Hey Folks!
I thought to tell my story here and try to understand the issue I had with my 660. I bought that saw two years ago from a guy that use it mostly for milling. I use it now for personal use and no problem at all. So last month, while doing firewood, I noticed that the saw while raving it was creating a stronger vibration than usual. The next day, 1/2 hour out, the crankshaft snapped at the clutch!! Never seen something like this… So order all the parts and rebuilt it as all the standard and it runs like new again. I fully verify and disassembled the clutch and check but nothing wrong with it. So my concern is why it snapped? Was it the clutch? if I reuse the same one, would the shaft snap again??
Any advise would be great!

 

[Big_Wood]

this isn't the first time this issue has been mentioned about the 066/660.

 

[nmurph]

this isn't the first time this issue has been mentioned about the 066/660.

Yep.

 

[Big_Wood]

http://www.arboristsite.com/community/threads/testing-a-raisman-platt-crankshaft-in-an-ms660.237350/

 

[edaigle]

http://www.arboristsite.com/community/threads/testing-a-raisman-platt-crankshaft-in-an-ms660.237350/

Wow! ok!! Still what is the problem?? I have 5 Stihls and they are all great!

 

[Big_Wood]

some run forever and some break right away. i'm gonna go with inconsistent metallurgy. could also be that the ones that have broken suffered some abnormal abuse.

 

[Mr.Moose]

Ive had it happen once about 5 yrs ago
Snapped off right at the end of the threads.
I thought i was the only one

 

[Thommo]

looks like it has been cracked for a while and finally let go when a bit of load was put on it. I would say that the chain has either been pinched or over tightened at some stage, which caused the start of the crack

 

[bezza1]

i snapped one of mine not to long ago aswell

 

[firebrick43]

Longer bar and not loosening the chain before storing? The chain will shrink significantly, longer the bar the more it shrinks. Subzero weather to boot make it shrink even more putting high stress right where your saws crank broke. I am not saying this is the cause, just that I have seen it before.

 

[thechainsawguy]

I have heard that limbing a log cutting full out and hitting the chainbrake can cause this or at least major crank problems. I had a couple Dolmar 7900's cranks that broke inside the case and a saw guy EHP mentioned limbing and the brake coming on can be hard on the crank. Just my 2 cents.

Dave.

 

[edaigle]

I have heard that limbing a log cutting full out and hitting the chainbrake can cause this or at least major crank problems. I had a couple Dolmar 7900's cranks that broke inside the case and a saw guy EHP mentioned limbing and the brake coming on can be hard on the crank. Just my 2 cents.

Dave.

Dave that make sense too!! Will be carful on that!! Thanks!

 

[edaigle]

Longer bar and not loosening the chain before storing? The chain will shrink significantly, longer the bar the more it shrinks. Subzero weather to boot make it shrink even more putting high stress right where your saws crank broke. I am not saying this is the cause, just that I have seen it before.

It definitely make a lot of sense as I also live in a subzero weather country!! Thanks!!