MS271,291,311, and 391 Main Bearing Problems.

[TJ the Chainsaw Mechanic]

Hey guys, so I had a 391 come in that I was almost positive it was seized solid from straight gas. Turns out after checking the gas there was plenty of mix....removed the muffler and the cylinder and rings where barely broke in. Chain was duller than dull so I checked the air filter and it had fine dust, but luckily not much went through. Well a couple days past and I grabbed the saw to work on it and what would you know....sucker pull started and had great compression as if nothing happened! Huh, something wrong with the bottom end. Pulled the cylinder and the walls looked good. Little scoring from the fine dust that past the filter. Bearings all looked perfect...rings were fine. Called JD at stihl and told him what was going on and he said some of these saws had a bearing tolerance issue. We've sold many and this is the 1st. So, two new mains and rings are on order under warranty as this saw is about 3 months old. Just wondering how many of you guys have run across this.

 

[dall]

ive rebuilt 2 311s and i have a 391 waiting for desire and parts all with bearing problems and a reason im not a fan of the newer saws

 

[TJ the Chainsaw Mechanic]

The new parts are supposed to be right. guess we'll find out. haha

 

[Warped5]

TJ, take a look at those bearings. I'll bet you see plastic cages, not metal ones.

I've seen a few of those saws in the last year that were beaten up by tree services. They run them so long and so hot with dull chains that those cages eventually fail. One saw had a crank end that was (nearly) neon blue.

 

[dall]

they are plastic cages and bearings grouped together letting space on one side

 

[TJ the Chainsaw Mechanic]

The originals have the plastic cage. All the balls were in place and the bearings rolled with no problem. According to JD they were made every so slightly to big and when you torque the cylinder down it somehow Oval shapes them causing the issues when hot. He said if I was to accurately measure them I'd find they would be oval shape...to the eye they look fine. Never would have know.

 

[jake wells]

i would replace it with metal cage bearings another case of stihl being cheap and stupid.
plastic cage is a no good no matter the application.