Chainsaw Repair

I've had problems with the clutch covers warping on my 42cc Poulans over the years.  They can warp in two ways - first, the rear corner starts to lift away from the chassis, which can mess with the alignment of the chain brake and cause the band to drag. 

Second, the surface of the bar mounting pad starts to curve, which can cause problems with the oiling.  Because the bar is oiled through the upper tensioning boss which goes all the way through, if there is a poor seal on the outside of the bar then oil can leak out there and bypass the bar groove.

I have repaired a couple by sanding/grinding the bar mount pad flat, and trying to re-angle it so the tail of the cover moves back toward the case.  This is hard to get right because the steel inserts for the bar studs are harder in the center, and so it is difficult to remove all the curvature.  Also, you are removing material, so the whole cover is moving towards the case. 

The first picture shows a cover that is not warped (but broken), and you can see the chambers molded in above the bar studs.  There is not a lot of sealing surface there, so if the top edge pulls away it will leak. 

The second shows an old cover I worked on with a belt sander - it is not all that flat, but better than it was.

The third picture shows a stainless steel outer bar plate I added to a cover I ground (gently) with a 4" grinder.  This helped seal it up quite a bit better.  I'm hoping it will help prevent further warping, but only time will tell.  I'll be getting a new cover and will try it on that from the beginning.

I think the 32/35/38cc Macs have it right for a plastic clutch cover, with an outer bar plate and the extra screws at the back edge.  They're a bit of a PITA when changing chains but no real big deal, and they support the back edge properly. 

Of course I'd rather have a metal clutch cover like the PP5020.

That metal cover is the most expensive part of the 5020, it costs $54, the cyl. is $15 less than that.

    John

Ahh, good info.  I'm going to be fabricating outer bar plates for all the plastic clutch covers that don't have them, which is pretty much all my Poulans.  I'm hoping to reduce both mechanical and thermal stress on the cover, and to improve the seal for better oiling.