more 066 woes

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1953greg

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HELP!

while the 066 was waiting for the second decomp (i found one screw stripped that holds the top cover on and that might have been letting the cover viberate and break the decomp button, although thats a streach) to arrive i was fiddleing with the rotation of the flywheel and found some rotational roughness. i removed starter cover, muffler, plug, decomp plug, and clutch housing and roughness remained. then i discovered a round metal ball (about the size of a # 6 shot) lying on the block where the muffler would be and after shaking the saw another fell out from somewhere. there is no endplay in the crank. the remaining roughness is when the piston is top dead center like the piston is hitting the top of the jug and then buckling past the "bump". before the second steel ball fell out i was occasionally getting a crank lockup other than the top dead center one. once the second ball fell out the crank rotates fine except tdc. piston looks fine from exhaust port and plug holes but i have not popped the jug.
saw was running fine when i last shut it off.

what the heck is going on? this is another first for me.

any info appreciated thanks in advance 1953greg
 
Well, the only ball bearings in that saw are the crank main bearings. Better repair that before you trash the rest of the saw.

You're lucky you found out the way you did versus having the bearing self-destruct in the middle of a cut. Not a pretty aftermath.

Chris B.
 
how small were the balls that you got out of the saw, cause if they were real small balls they would be from the decompressure which has 3 little balls in it on a 066 that broke the decompressure , and with the hole beinging so big on the inside of the jug they can drop it to the motor, not sure if they are stihl made this way from stihl
 
the balls are precisely .117 inch and they fit nicely into the 3 holes inside the decomp valve for the detent. so thats in all likelyhood where they came from. now there is still a bump when the piston reaches top dead center. reckon one is stuck to the top of the jug and kissing the piston? or is there a bump on a perfectly good engine? the flywheel can be rolled past the bump with fingers. i cant see any marks on the piston.

thanks again 1953greg
 
That's a big negative on the bump ... smooth as silk.

You better play safe and pull that jug apart,with some luck the bore and piston are OK ... only one way to know for sure.

Well worth fixing, 066's aren't cheap and usually perform well.
 
you said you found 2 balls , I would be looking for number 3 and by the sound of it , it most likely is stuck in your combustion chamber so yes take the jug off and look it only takes a few minutes to do
 
chapter 3

after further inspection of the combustion chamber w/ a dental mirror i found 1 of the ball springs stuck to the outer edge of the inside top of the jug. a couple wiggles w/ a magnetic screw driver and it came loose and out w/ the screwdriver. the spring was flattened to .035". i was amazed that there was <.035" clearance in there. that was the bump i was feeling. so that makes the lower half of the decomp valve stem, and at least 1 spring and one ball going into the cylinder without permanent damage. never did find the 3rd ball. i guess maybe it fell out sometime and i didnt notice it or it could have remained in the first valve as the second one didnt come apart. got it all back together (w/ a plugged valve) and checked compression and found 135 cold and 145 somewhat hot (i thought compression was supposed to go down after warm up). anyhow its been a tedious experience that stretched my perseverance, expertise, and patience.

thanks to all the replies that helped me keep digging.

now i think i wil go buy a lottery ticket! 1953greg

i guess one question remains. should i try another new decomp valve? i really struggle starting it w/o the valve although i can if im fresh. i have fixed the stripped screw on the rt side of the top cover that surrounds the valve.
 
Last edited:
I have a decomp on my 066 and I don't use it because I forget it's there. (Unless the temerature is below freezing and I'm cold starting it).
 
1953greg said:
chapter 3

got it all back together (w/ a plugged valve) and checked compression and found 135 cold and 145 somewhat hot (i thought compression was supposed to go down after warm up).
i guess one question remains. should i try another new decomp valve? i really struggle starting it w/o the valve although i can if im fresh. i have fixed the stripped screw on the rt side of the top cover that surrounds the valve.

The rings seal better with heat in them due to thermal expansion.

I would try another decomp valve IMO. Once you get it going and later in the day after lets say re-fueling, I think you would prefer to have a decomp in there to restart because you would be a bit tired after handling that saw thru a tank or so. (but then again you could be the 'incredible hulk' and i just not know it)
 
no hulk here. just 5'6" 185. installed new decomp last evening and everything seems fine. wil put it in a 10' long x 36" cherry bark oak cant (42" bar) this weekend and see what happens. takes bout 10-12 minutes and 1 tank of fuel to rip through. neighbors must love the dual port sound (small subdivison) as i have been told it can be heard 1/2 mile away (i wear ear plugs and muffs) when the wind isnt blowing and they havent complained, to me anyway.

really steep learning curve.

thanks to all 1953greg
 

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