MS 311 Crank Bearing Failure & Repair ???

[Jims55]

Hi. I'm new to the site and hope someone can guide me towards getting my saw running again. As the title says, the crank bearing on the chain side of the saw self destructed and resulted in the saw locking up. Unfortunately, this saw is only a couple of years old and used mainly for cutting 5-6 cords of firewood per year. Upon teardown, I found a broken oil pump, scored piston/cylinder, and what appeared to be contact between the coil and the flywheel. Although scored, the piston cleaned up pretty good with some fine scotchbrite and the cylinder was not scratched too deeply. Anyhow, I ordered new crank bearings and seals, new oil pump, and new rings for good measure. Upon reassembly, I ran into a couple of problems. Spark was good, compression was around 100 PSI on my cheapo gauge, and fuel was being drawn into the cylinder, but the saw wouldn't start. I did set the coil gap with the Stihl gauge. The main issue I ran into was the fit of the new bearings and possible clearance issues on the new oil pump. I'm measuring .006" interference between the bearing faces and the inside face of the bearing saddle. They were tight going in, but I was able to tap them into place without too much of a problem. Also, (and this may be related to the bearing interference), my oil pump drive is getting pinched between the cover washer and the oil pump body when I tighten up the clutch. So, either the oil pump body is too wide, or the step on the crankshaft is sitting below the top of the pump drive. I do have a couple of questions:

1. Is there a specification on the bearing clearance and is .006" too tight?
2. What's the best way to seat the bearings on the crankshaft?
3. Can any RTV be used to seal the crankcase or is something special required?
4. Are there baseline settings for carburetor adjustments in terms of number of turns from fully closed?
5. Other than a visual spark, is there anyway to check coil performance?
6. What's the best plug to use on this saw?
7. Anything else I should look at?

Thanks! I know it's a lengthy post, but I wanted to provide as much detail as possible to paint an adequate picture.
Jim

 

[Tobystihl]

Hi. I'm new to the site and hope someone can guide me towards getting my saw running again. As the title says, the crank bearing on the chain side of the saw self destructed and resulted in the saw locking up. Unfortunately, this saw is only a couple of years old and used mainly for cutting 5-6 cords of firewood per year. Upon teardown, I found a broken oil pump, scored piston/cylinder, and what appeared to be contact between the coil and the flywheel. Although scored, the piston cleaned up pretty good with some fine scotchbrite and the cylinder was not scratched too deeply. Anyhow, I ordered new crank bearings and seals, new oil pump, and new rings for good measure. Upon reassembly, I ran into a couple of problems. Spark was good, compression was around 100 PSI on my cheapo gauge, and fuel was being drawn into the cylinder, but the saw wouldn't start. I did set the coil gap with the Stihl gauge. The main issue I ran into was the fit of the new bearings and possible clearance issues on the new oil pump. I'm measuring .006" interference between the bearing faces and the inside face of the bearing saddle. They were tight going in, but I was able to tap them into place without too much of a problem. Also, (and this may be related to the bearing interference), my oil pump drive is getting pinched between the cover washer and the oil pump body when I tighten up the clutch. So, either the oil pump body is too wide, or the step on the crankshaft is sitting below the top of the pump drive. I do have a couple of questions:

1. Is there a specification on the bearing clearance and is .006" too tight?
2. What's the best way to seat the bearings on the crankshaft?
3. Can any RTV be used to seal the crankcase or is something special required?
4. Are there baseline settings for carburetor adjustments in terms of number of turns from fully closed?
5. Other than a visual spark, is there anyway to check coil performance?
6. What's the best plug to use on this saw?
7. Anything else I should look at?

Thanks! I know it's a lengthy post, but I wanted to provide as much detail as possible to paint an adequate picture.
Jim

Hi, do you mean Stihl ms361? If so, the pto ( clutch) side bearing needs to be fitted in the crankcase with the oil pump already attached, the oil pump acts as the bearing stop.

 

[HarleyT]

No,
the ms311 is similar to the ms271 in setup.

 

[HarleyT]

Here is the bottom of a ms271.

 

[Tobystihl]

Here is the bottom of a ms271.
View attachment 719410

Oh I see, it's a clamshell, not familiar with the model sadly to comment!

 

[HarleyT]

Oh I see, it's a clamshell, not familiar with the model sadly to comment!

Yeah, it is a different animal....

 

[a. palmer jr.]

I have one apart right now and just waiting for warmer weather to start slapping it together. To seat the bearings heat them with a light bulb and chill the crank in your freezer, after awhile they will generally slip together. If not just tap them in place using a pipe and a hammer. The sealer that Stihl uses is Dirko red heat resistant. I will probably use Motoseal on mine though..Visual spark is usually good enough, usually one turn from lightly seated on H & L carb screws on most Stihl saws. Only other thing is to check the other bearing also and take your time and carefully assemble the saw...Good Luck

 

[Jims55]

I have one apart right now and just waiting for warmer weather to start slapping it together. To seat the bearings heat them with a light bulb and chill the crank in your freezer, after awhile they will generally slip together. If not just tap them in place using a pipe and a hammer. The sealer that Stihl uses is Dirko red heat resistant. I will probably use Motoseal on mine though..Visual spark is usually good enough, usually one turn from lightly seated on H & L carb screws on most Stihl saws. Only other thing is to check the other bearing also and take your time and carefully assemble the saw...Good Luck

Thanks for the tips. First thing I'm going to try is to see if I can seat the bearings any further onto the crank.

 

[Okie294life]

Since this is a clamshell design you will Pull the head and like everyone’s saying here put the crank in the freezer for several hours before putting the bearings back over the ends of the crank. I would also recommend touching it up with some fine grit sand paper and putting some penetrating oil on there before sliding the bearings on. You shouldn’t have to beat on them or you’re doing something wrong. You can destroy a good high dollar set of crank bearings if you whack them in the wrong spot. Run up a small bead of yamabond or permatex motoseal on the bottom plate to seal. May want to look at another set of rings also.

 

[a. palmer jr.]

Motoseal works like contact cement...you put it on both sides to be joined, let set for a couple of minutes then stick the two surfaces together. If you have to tap the bearing to get it in all the way use a pipe to slip over the crank end and contact only the inner race of the bearing. If you have a wife like I do you'll need to put that crankshaft in a plastic bag before putting it in the freezer..

 

[Jims55]

Motoseal works like contact cement...you put it on both sides to be joined, let set for a couple of minutes then stick the two surfaces together. If you have to tap the bearing to get it in all the way use a pipe to slip over the crank end and contact only the inner race of the bearing. If you have a wife like I do you'll need to put that crankshaft in a plastic bag before putting it in the freezer..

Got the saw running! I couldn't get one bearing properly seated so I pulled it off. It looks like the chamfer on the bearing was a little smaller than the radius on the crank. I enlarged the chamfer with a tapered grinding stone I had laying around, reinstalled the bearing and it seated properly. Reassembled the cylinder with Motoseal, which I'd never heard of before. After letting that set up for 24 hours, the saw fired up on the third pull. Seems like it's running pretty strong - I'll be testing it out on some ash once the weather warms up a little.

 

[jeremyc]

Glad you got it together right! Those series saws are a little tedious to get apart but once you've done It a time or two its pretty simple.
On another note, the initial bearing failure may have been caused by too much chain tension. Too much tension will stress the bearing.

 

[Jims55]

Glad you got it together right! Those series saws are a little tedious to get apart but once you've done It a time or two its pretty simple.
On another note, the initial bearing failure may have been caused by too much chain tension. Too much tension will stress the bearing.

I set cold chain tension so that I'm able to pull the chain away from the bar to almost see the tip of a drive link. I've read somewhere on this site that the FAG bearings in these saws are prone to failure. They have a plastic retainer ring in them that can disintegrate - pretty sure that's what happened to mine as the retainer was missing when I pulled the saw apart and loose ball bearings were laying in the bottom of the crankcase.

 

[a. palmer jr.]

The loose ball bearings is what happened to mine. What kind of bearings did you replace them with and how much did they cost? I'm kinda on a budget on this saw..

 

[Jims55]

The loose ball bearings is what happened to mine. What kind of bearings did you replace them with and how much did they cost? I'm kinda on a budget on this saw..

I bought a Proline bearing & seal kit for $38.95 shipped. Here's the link: https://sawzillaparts.com/proline-c...or-stihl-ms270-ms271-ms280-ms291-ms311-ms391/

Since I had it apart, I also bought Caber rings from Amazon for $13.25 shipped. They're Italian made and nice quality.

The bearing failure also took out my oil pump drive - better make sure yours isn't stripped. Amazon and/or Ebay sells a chinese oil pump kit for $14 bucks.

Good luck!

 

[a. palmer jr.]

I don't know about the oil pump, haven't checked that side yet. It did take out the ignition module though, another high dollar item if you buy from Stihl, it even broke off the mount for the module so I had to buy another case..