MS251 Meltdown

[Paul Fithian]

Our SIL's MS 251 siezed up when running. Brake was stuck and the clutch was locked.

It appears this one had a clutch drum needle bearing failure, allowed the drum to shift position, and melt a bunch of plastic nearby:


I was able to dig most of the junk out and clean it up, all looks good to reassemble


Saw fired right up and ran perfect, plug shows a good burn pattern also.

New OEM parts ordered. Any other advice before re-assembly?

 

[huskihl]

The damage is likely from extended periods of warm-up time on high idle with the brake applied

 

[bogieboy]

The damage is likely from extended periods of warm-up time on high idle with the brake applied

As a certified stihl tech.... this....right.....HERE......brake band and clutch bell blueing is the dead giveaway... if theres enough heat to turn the steel of the brake band blue, it got over 650°F... that doesnt happen unless the clutch is engaging, and trying to spin the clutch bell....

 

[Oldbuzzard]

The damage is likely from extended periods of warm-up time on high idle with the brake applied

Exactly. I see this routinely from a volunteer group that trains people to use chainsaws. I’m getting them to switch to 261s.

 

[huskihl]

Exactly. I see this routinely from a volunteer group that trains people to use chainsaws. I’m getting them to switch to 261s.

If they do it on a 251 it melts some plastic. If they do that same thing to a 261, the heat transfer through the magnesium will take out the seal as well as burning some plastic.
They need taught not to leave it on high idle

 

[Paul Fithian]

Thanks fellas!

Could this type of overheating happen if running and the bearing starts to degrade gradually, without the long term high idle with the brake on?

 

[sawmikaze]

I was gonna say..

Switching to a 261 doesn't eliminate the problem.

 

[huskihl]

Thanks fellas!

Could this type of overheating happen if running and the bearing starts to degrade gradually, without the long term high idle with the brake on?

Something smoked the bearing. But the bearing going bad didn’t cause all the black melted plastic. Even clutch slippage doesn’t melt plastic like that without the brake being on

 

[Paul Fithian]

Parts showed up yesterday and put it all back together. Found that the brake cover was contacting the clutch drum, caused by some melted scar tissue that had to be removed:



All back together with no interference, runs perfect



I advised owner not to let it idle or rev with the brake on

 

[Gearshifter]

Parts showed up yesterday and put it all back together. Found that the brake cover was contacting the clutch drum, caused by some melted scar tissue that had to be removed:
View attachment 417051
View attachment 417052

All back together with no interference, runs perfect
View attachment 417053


I advised owner not to let it idle or rev with the brake on

Love this site, post a picture and people know exactly what has happened and why .
The owner of the saw will probably tell u he hasn't done as people have stated in the posts above , but the evidence is clear

 

[Paul Fithian]

Love this site, post a picture and people know exactly what has happened and why .
The owner of the saw will probably tell u he hasn't done as people have stated in the posts above , but the evidence is clear

He already did!