MS 200t / Broken Crankshaft Common Problem?

[lync]

Today, when I released the chain brake, and tried to make a cut the engine reved but the chain didn't turn. Shut the saw and took off the side cover. To my surprise the clutch assembly fell out of the drum and to the ground. I could see the tip of the crankshaft where the clutch threads on was still in the center of the clutch assembly. It had broken clean off the crank. Has anyone experienced this before? Any thoughts on what could cause it. I grease the bearing regularly. It doesn't appear to be heat related, no bluish tint around the crank where it broke.

Corey:bang:

 

[THALL10326]

Today, when I released the chain brake, and tried to make a cut the engine reved but the chain didn't turn. Shut the saw and took off the side cover. To my surprise the clutch assembly fell out of the drum and to the ground. I could see the tip of the crankshaft where the clutch threads on was still in the center of the clutch assembly. It had broken clean off the crank. Has anyone experienced this before? Any thoughts on what could cause it. I grease the bearing regularly. It doesn't appear to be heat related, no bluish tint around the crank where it broke.

Corey:bang:

One question. You said you just released the chain brake. Was that saw full throttle and out of the cut when the chain brake was applied? I only ask because I've never heard of a crank breaking on a 200. The only thing I can think of that may have snapped the crank is going from 15,000 rpm's at the crank to zero in a split second due the the break. Just a thought.

 

[clearance]

Never heard of it either, on 020s or ms200s. I don't think the brake could have caused this cause it would slip for a miilisecond before it stopped the drum, I think a flaw of some kind, Stihl would probably be interested in seeing this.

 

[THALL10326]

Never heard of it either, on 020s or ms200s. I don't think the brake could have caused this cause it would slip for a miilisecond before it stopped the drum, I think a flaw of some kind, Stihl would probably be interested in seeing this.

Good point Clearance, I never thought about the slipping. I've never heard of a crank snapping off on a 200, a new one for sure. Seems Stihl would indeed want to see that and replace it as well................

 

[lync]

The brake was on when I started the saw in the tree. Let it idle for a few then released the brake squezzed the throttle and tried to cut a large piece of deadwood. Noticed the chain, not turning. crew sent me another saw, and on lunch opened the side cover , and you know the rest.

 

[THALL10326]

The brake was on when I started the saw in the tree. Let it idle for a few then released the brake squezzed the throttle and tried to cut a large piece of deadwood. Noticed the chain, not turning. crew sent me another saw, and on lunch opened the side cover , and you know the rest.

Well thats a tuff one must say but also a good one for Stihl should give you a new saw or repair that one free of charge. Broken cranks are so rare you hardly ever hear of one snapping off like yours. Get that thing to the shop...

 

[Lakeside53]

I've never seen one on a 200t either... An obvious question: did you or anyone every put the clutch on or off with an air impact driver? Even then you'd expect (worst case) damaged threads not a crack in the crank.

How old is the saw?

 

[THALL10326]

I've never seen one on a 200t either... An obvious question: did you or anyone every put the clutch on or off with an air impact driver? Even then you'd expect (worst case) damaged threads not a crack in the crank.

How old is the saw?

I thought that myself Lake and have seen clutch spiders break but never a crank. He said it snapped right off, thats something........

 

[Lakeside53]

I thought that myself Lake and have seen clutch spiders break but never a crank. He said it snapped right off, thats something........

I had an MS360 that broke the crank right at the flywheel... Glad it happened at starting, not at 14,000... I'll post a picture later: I need to dig it out of my museum of bad and abused parts

 

[RaisedByWolves]

If you can show a real good closeup picture I can tell you if the heat treatment was goofed or if this was a flaw and simply let go.

 

[Lawn Masters]

This is an odd thing to have happen. I'm curious to see pictures of the crank from both pieces to get an idea what it looks like. certainly not something that I'd consider a common occurance. glad ya had another saw to use.

 

[pinus]

Today, when I released the chain brake, and tried to make a cut the engine reved but the chain didn't turn. Shut the saw and took off the side cover. To my surprise the clutch assembly fell out of the drum and to the ground. I could see the tip of the crankshaft where the clutch threads on was still in the center of the clutch assembly. It had broken clean off the crank. Has anyone experienced this before? Any thoughts on what could cause it. I grease the bearing regularly. It doesn't appear to be heat related, no bluish tint around the crank where it broke.

Corey:bang:

Bad rim with a litlebit overtensioned chain.

 

[Lakeside53]

If you can show a real good closeup picture I can tell you if the heat treatment was goofed or if this was a flaw and simply let go.

Try these... small amount of rust is post mortum.

 

[RaisedByWolves]

Too hard, poor quality steel or improperly drawn back (tempering) after heat treat.


The second pic with the big flake off of the side, and the ultra fine grain structure in the first pic is what Im basing this on.


Definatly too hard, Most probably from improper tempering.


That first pic is some weird s??? though. Am I correct there is some shine showing? Like a piece of coal?

 

[Lakeside53]

Too hard, poor quality steel or improperly drawn back (tempering) after heat treat.


The second pic with the big flake off of the side, and the ultra fine grain structure in the first pic is what Im basing this on.


Definatly too hard, Most probably from improper tempering.


That first pic is some weird s??? though. Am I correct there is some shine showing? Like a piece of coal?

No coal... just a over exposure from the flash. This saw had been severely overheated - bearings were crusted with carbon-like material.

 

[t_andersen]

Fatigue fracture

I'm a mechanical engineer. Looks to me like a typical fatigue fracture.

 

[Rotax Robert]

Seen a bent crank from the chain being overtightened probably while the chain was warm and once cool put a slight bend in the crank. With this I could see a fatigue fracture happening.

Rotax

 

[Lakeside53]

Just to be clear, the pictures were from the flywheel side of an MS360 crank.