200T case split

[Al Smith]

Actually it's Toms 020T which has a 200T case .The thing was leaning out so I changed the bearings seal crank shaft from the original cases .

What I found out was the crank had excessive play both lateraly plus up and down on the clutch side .I checked 4 cases .My stock and souped 200 .The original 020 cases plus the replacement case I installed early in the spring .Found problems on two .More later on that .

Of all the Stihls I've done this is the easiest case to split I've found yet .Most Stihls use shrink fit ball bearings on the crank .This one is roller bearings .Peel it down to just the engine and it's six case bolts .A little tap with a rubber hammer and it comes apart easy as pie .

Once the crank is out it's easy to knock the seals out with a blunt screwdriver going above the bearing real gentle like .Heat the bearing pockets up and drive the bearings out .Install in reverse ,install the seals and bolt the whole thing back together .

 

[Al Smith]

Now what the problem was on both this case plus my little super bee .The thing is built with an 8 roller roller bearing with captive hard retainers instead of ball bearings .Ball bearing will take sideways thrust where rollers aren't so good at it .The actual bearing with this hard plastic material seats against two shoulders on the crank and relies on this material to act as a thrust wall .Well it works for a time .The plastic wears out and it gets sloppy

So after high hours usage the crank wobbles to and fro .The seals get rubbed on the rough carbon like material outside the witess marks and heat up and leak .See the pic of the crank shaft ,it's obvious .The seals are most likely viton instead of the usual buna n .Viton is some tough stuff but not as limber as buna n .They can heat up which will swell them.They cool off they shrink .

That plus the fact they are single lip seals instead of the usual double lip seals I think causes lean run conditions .Usually people just keep opening up the jets and continue on with what they are doing until it gets to the point like these two that lean out after 5 minutes or less .

It's only speculation on my part but I believe that in addition to carb problems this little thing here might also be a leading cause of the failure of these saws after some extended usage .It would cost probabley 70-80 bucks to redo the crank case with bearings and seals if you did it yourself .However if a shop did it you'd have half the price of the saw tied up .

 

[cory]

I don't have enough technical knowledge to comment further than: Mighty impressive, Al!

 

[Ax-Man]

Good show Al, I have yet to get into a 200 that far but your kind of comfirming what I have suspected for a long time. In addition to carb problems these saws can have small air leaks that can make them run a little on the irratic side and not be able to dial in the carb where it should be. Those bearings speak volumes.

I blame everthing on air leaks

 

[Al Smith]

Another thing .The seal size is 20 -12-5 .The same size but I think different seal material is used on the flywheel side of an 024 and 026 which I think is buna n double lip .

 

[stemwinder]

This is pure wizardry to me. Thanks for the tutorial Al!

 

[MasterBlaster]

Al's a hella tutorializer!!!