a sad day for the 066...

[68kaiser]

i pulled the muffler to modify the baffle and checked the cylinder while i had it open and noticed part of the top of the *#$&ing piston was missing. its the little lip at the top above the first ring. i noticed the saw didn't have the power it should last time i used it but didn't think to check anything then.

i checked the compression and it has 145 psi. now my question(s), should i run it till it dies or will that put the bottom end at risk? how much longer till the big bore kit?

i have rebuilt small and big block chevy's and have mechanical experience but have never rebuilt a chainsaw. i hate to pay people to do things that a should be able to do. how hard is it to put a piston kit in a saw? any pointers would be great.

 

[Lakeside53]

It's not difficult...

Don't run it. Right now you can probably drop in a new piston after a light hone. Run it and you'll soon need a new cylinder, and the bottom end is definitely at risk from a broken ring. Priced an 066 crank and/or bearing lately?

 

[68kaiser]

what causes this? i don't want to have it happen again. the saw was over revving for a short time. i didn't have a tach and was stupid and ran it anyway, i think it was turning 13500 rpm after i found out i have hated my self for it. i run fresh gas, stihl mix, clean the air filter after each use.,.,.,.,
i take better care of my saws than my ol' lady. this chapps my ass and if its something i did i don't want to do it again.

 

[Lakeside53]

Thermal stress on the piston. The 066 runs real close to the edge... and you were likely runing it way too lean. Just keep it rich enough to limit the RPM to less than the max... and be "in-tune" with how your saw sounds. The 066 is a proven design... but easy to exceed what it was designed for.

 

[68kaiser]

i have checked old threads and come up with a ball hone size of 2.25-2.375" or 59.4 mm and 240-360 grit. is this correct for a 066?

 

[Lakeside53]

Seems about right. Maybe one size smaller. Finer the grit the better. The 066 has a chrome based coating, not nikersil.

 

[68kaiser]

i took the jug off after work and it seems to be in good shape nothing a slight hone job shouldnt take care of. should i replace the gasket that seals the jug to the crank case?
oh and i got some good news out of the deal, i was ordering parts from Bailey's and it terns out they have a distributer warehouse in my home town in Woodland so i can get parts with in a day if in stock.....

 

[Lakeside53]

You need to replace the jug gasket - the correct gasket is a 0.5mm steel gasket that has a raised lip (crushed when torqued down). It's non-reusable. If you have the old paper gasket, carefully scrape it off...

In an 066 I'd have used an oem piston if I had a good jug... but I'm biased (and have seen too many fried pistons in big saws). Tune it to the rich side... i.e. Don't try to extract "peak performance" and you'll probably be o.k.. If your orginal piston pin is in good shape, reuse it. It's taper ground and much better than the aftermarket pins.