Chainsaw Brake Drag/Rub

[Laurence Leveen]

I have a used Craftsman 358351702 chainsaw. I opened up the clutch assembly and can see what looks like dark discoloration on the drum and clutch, plus some melted plastic on the chassis ("~12-1 o'clock" as viewed from the saw's right side) and on the chainsaw brake.




I removed the excess melted plastic with a blade. The brake drags on the drum, however; it does not retract concentrically/evenly all the way around the drum.


When the brake is off, it "sits" on small plastic "seats" molded into the chassis. These were deformed by melting -- see where the tool is pointing -- and my shaving didn't help, I fear.



I can make the band take proper, concentric shape by pushing on on it gently where the tool is pointing and the drum will rotate freely, but it seems that the loss of brake seat material is a real problem here. There are not seats all-the-way-around the band to allow me to shave them all down equally. Before I try grinding of chassis material around the band, I thought I'd ask for advice here. Think "building up" the seats is an option? Could I bond in a seat where the tool is pointing -- that sweet spot for making the brake concentric? I honestly do not think the brake band is bent/deformed. I don't know exactly how the plastic got melted. I have not operated the saw, though it was used recently, and I noticed the chain movement under idle when it was started up. I could not vouch for it being started up properly (brake position, etc.) -- I simply do not recall how it was done.

Also, I'd like to solve the underlying problem for the chain moving while the motor idles. I tried some minor adjustment of the idle screw (not the L and H carb screws), but did not get a solid result before opening things up and revealing the clutch-area issues.

Is the clutch destroyed, or could that just be burned oil coating it and the drum? It appears to be fully retracted at rest, and as I mentioned above, the drum can rotate freely if the brake band is held in a concentric position. The drum's teeth looked OK. Very minor wear, that I imagine is from normal use/contact with the chain. If the discoloration is due to the clutch slipping, could that heat have changed the springs' temper such that the clutch shoes move out at lower-than-normal RPM?

Other constructive thoughts and advice are appreciated. Thanks.

 

[Derf]

That's a very detailed and Long post. Hopefully someone more knowledgeable takes the time to read all of that.

 

[RIDE-RED 350r]

The clutch should be fine.

Obviously things got pretty hot with the clutch to cause the melted plastic. I would think this should only be possible if someone were to mistakenly leave the chainbrake applied and letting it fast idle too long or excessive clutch slippage due to heavy handed operation in wood too big for that saw.

I'm not sure what the best way to address the issue would be but I would likely try to build the melted brake band seat back up with JB Stick Weld or some other similar type of epoxy that is thicker and has a putty-like consistency which would make it easier to form initially.

 

[T.Roller]

I'd say the clutch spring is shot after it got that hot which is causing your chain to turn at idle, that is if it's tuned correctly. As for what caused that amount of heat I'd agree with the above post that the chain brake was engaged at fast idle or could also be your saw is idling high and with your brake engaged was causing alot of friction causing the heat that melted your plastics. Repair it? I dunno I wouldn't put too much into it without replacing it.

 

[T.Roller]

Is the crank itself discolored down the shaft

 

[Laurence Leveen]

I had ordered a new clutch and drum before I saw your question about the spindle. Kinda looks like it was affected too -- see the colors on the spindle end. Why do you ask, T. Roller?

Aside, I can't quite figure out what the small silver part is/does (see red arrow in pix). I mean, I get that it's part of the oil pump, but it doesn't seem to move or be driven by the clutch/drum unlike other saws (with a worm gear). Maybe the visible part is just to allow manual movement of the pump to get part lined up if it is replaced. Thoughts?



I agree that the overheating was either the cause of revving the stuck saw or revving with the brake on. Both totally rookie moves that THIS rookie didn't do. I like learning "the easy way".

I am indeed hoping that the overheating caused the spring to weaken such that the clutch shoes are contacting the drum under lower-than-normal revs (and allowing driving the chain forward under idle). For grins, I set the idle (not the L or H screws) almost low enough for the idle screw and spring to fall out and indeed the chain still moved. I'll see what the new clutch does, if anything. If it still drives the chain forward, I will likely try adjusting the L-idle although it seems doubtful to me that is contributing. I know there is a danger of making killing the engine with too lean a mix (as not enough lube would reach the cyclinder/piston), and too rich is no good either. I'd need a spline tool for that, anyway.

BTW, I did build up the seat for the brake strap and the (old) drum spun without contacting it.

In for a few bucks already, but hey, I'd rather not use a saw that can't have the chain be stationary when idling.