066 Question?

[joelamb]

I lost a piece of the piston between the rings on the exhaust side of the piston with no apparent damage to the cylinder and then re-built the saw and now it has started to make a little bit of a funny noise. Now I think I have a bad crank. Has anyone else experienced this problem?

 

[sedanman]

Sounds like ring clipping, The saw must have been over-revving, The rings don't have time to "get seated' on the chamfers on the ports. THey stick out a bit and get 'clipped' bt the port they are passing. The ring usually takes the brunt of this but the piston can suffer too. I think the rcrank bearings "skid" once and now need reoamcement. All this from running the saw too fast.

 

[joelamb]

This saw has a stock cylinder and piston, no modification. After rebuilding the saw it ran normal for a couple of days, then started making a slight noise. I shut it down so it wouldn't waste my new piston. When the piston piece broke out I would think the rings were taking a pounding but not after I replaced the piston and rings. I think it's the crank or crank bearings like you said.

 

[Jacob J.]

If you rebuild any saw after pieces have come off the piston, you always need to replace the main bearings, it's too risky to take the chance otherwise.

 

[joelamb]

One piece broke out, the size of the exhaust port and in between both rings. The main bearings were fine. The rod bearing cage was cracked when I took the piston off. Other than that, clean and no damage.

 

[glens]

I don't have direct experience with chainsaw bottom-ends, but if enough force was present to bust out a chunk of piston, enough force was present to flat-spot and/or crack some bearing components anywhere within the crank/con-rod assembly.

 

[Jacob J.]

If the rod bearing cage was cracked- it is no good. You never assemble a modern saw with a bearing cage that is compromised in any way. There were certain older engines that you could get away with that on, but not anything made after 1972 or so.

 

[joelamb]

When I replaced the piston I also replaced the top end rod bearing. Started and ran the saw. It seemed fine. Then ran the saw for a couple of days, and it started making a funny noise. Kind of a knocking sound, so this is why I think the crank is going bad. It's very hard to tell if the low end rod bearing is bad unless it has a cracked cage or really burnt or wasted bearings. Whats some of your experiences with bad rods or rod bearings?

 

[Grande Dog]

Since it took some time for the the sound to develope. The piston might be hitting the top of the cylinder (carbon build up). Did you put a stock cylinder gasket on it? Or gasket eliminator.

Grande Dog
Master Mechanic
Discount Arborist Equipment and Tree Care Supplies

 

[joelamb]

I used a stock cylinder gasket.

 

[joelamb]

Grande Dog

Does Bailey's sell aftermarket or stock crankshafts for 066's?

 

[cbfarmall]

You're probably going to have to get the crank at Stihl, and it'll be around $250. Maybe you can luck out with a good used one, but used parts are a big crapshoot. I got one off Ebay for $20 for my redeye 066, ready to go. BTW, there are 2 different cranks out there for 066s. Older one has smaller threads on the flywheel nut, don't remember the size.

Before you lay out a ton of money, check to see if the clutch shoes are loose. Being that chainsaws engines are much smaller than auto engines, I don't always recognize a certain knocks and rattles when I hear them. I have more than once, written off a crank as bad, when the problem was elsewhere. I'm stubborn enough, that I found the real problem.

In any case, pull it apart before you start ordering parts. If it's as serious as you're saying, you'll probably see evidence.

Chris B.