Major 066 problems... Piston& Cylinder...

[JimL]

Well I decided to take the muffler off one of my 066's this morning to get rid of the spark screen. Well I looked at the piston and was none too happy.

I think this saw was one that was used for 2 weeks then got ran over by a bobcat.

I bought it as parts and fixed it up with some other parts and so on and made it usable. I have only used it for maybe 10 minutes. I don't think the piston and cylinder looked like this when I got a hold of it.
Scoring on both intake and exhaust sides...

Any Ideas??

I think I am going to invest in a crank case presure test kit soon...



Pics are big so you can see detail...



Piston

Exhaust

Intake

 

[JimL]

Just some info, its had my gas and oil ran through it, so I KNOW its good.
Know it wasn't revving too fast.

Not sure about the lean, the high end screw was out 1 3/4 turn

 

[Fish]

Most carbs normally set at 1 full turn out, having it set richer
means that something was wrong somewhere. 10 minutes is
plenty of time to burn up a saw. But this saw had been run
over by a bobcat? I would look at the intake and impulse
area and make sure there is no tear in the rubber or something
loose.

 

[JimL]

I put a new boot and impulse line on it. Put a different tank body on it. same carb, new fuel line. Only thing it could be is crack in the crank case i guess or a crank seal.

 

[rupedoggy]

Jim that is DIRT. When it got run over some dirt got into the cylinder or crank case. The clue is you said "I don't think it was this bad when I got hold of it". If you had done a complete dissassembly you would know. Notice it is on intake and exhaust side. Notice the long scratches from the little "rocks". A lean seizure will melt aluminum around the rings and so will raw gas. Because the exhaust side is hotter, it will usually damage only the exhaust side of the piston. I see only damage from foreign material. Mike

 

[Fish]

I didn't realize you had posted pictures, I didn't read it too closely
but it does look like dirt scratches

 

[JimL]

I did do a complete tear down cept crank case.

The saw was filthy, i thought i had all the dirt out but must not have.

So. You think it would be alright if i just put it back together and ran it? or... ?

 

[oldmanmcculloch]

DIRT?

<font color = blue>Hello Jim
<font color = blue><I>I would pull the main case apart and inspect the bearing,cage and rod bearing. I can not see the top of piston,but looking at top of cylinder by plug, there appears to be pitting commonly seen when bearing or cage failure occur. Debris from this type failure is common.
LUCK

 

[Fish]

What would the worse case scenario be if you put it back
together and ran it. You already have piston/cylinder damage,
and if the bearings have failed, you already have crank damage.
But with the cylinder off, you should be able to detect whether
the bearings are shot or not. If you go ahead and tear it down[split the crankcase] you will go back with new anyway, and
if a bearing has failed the crank will be damaged. So it is your
call on what to do, but the damage on the intake side would lead me to think it is indeed dirt.

 

[mikek711]

.

 

[mikek711]

Jim,
It definatly looks like dirt came in through the intake.It doesnt look that terrible though.I'm not sure if the bore is chrome lined.If it isnt,hit it with a fine hone,touch up the piston with a scotch bright pad just to clean it up a bit.I saw the micro pits on top of the piston which definatly could be caused by a bearing that has failed.I dont think so in your case though.If it is the bottom end bearing,you would know it.The crank wouldnt turn smooth and you probably would have some slap in it.You would know it already if it was the little end bearing being that removed it from the connecting rod already.On the thought of a cracked crankcase,if it was run hard for even a little bit,I would think that the lean condition that would be caused by the leak would lock the piston up solid.The piston and the cylinder walls would be scored,not just scratched so I think you're probably safe there too.There are still what looks to be hone marks on the cylinder wall so the saw probably doesnt have too much time on it.
Put it back together again and run it.I'll bet you it will be fine.
The shot of the piston below was in my CR500.The right crank case seal went south and the bike started running real bad.I immediatly stopped and called it a day.After tearing it down,I noticed the cracked, scuffed piston.Thats what a lean condition will get you.It could have been worse.
Mike.

 

[stihltech]

bearings

Remember, no play in the crank bearings. If this has a shield on the inside of the bearing by the crank you will have to pull the bearings off the crank to check the cages. DO NOT install shielded bearings, remove the shields if yours come that way.
It would take a serious amount of dirt to do that to a piston this quick. I bet on the bearings also.

 

[JimL]

I got it tore completely down today. Didn't find anything else wrong. All bearings were in good shape eccept for the one at the crank pin that I dropped and proceded to step on

Ordered some gaskets and a new set of rings.

I think I can make this a runner.

 

[mikek711]

Good Deal Jim!
Let us know details when you're done.

 

[JimL]

I might just use this one for cutting firewood, I got 6 others I can use cutting timber. No need to have this one with me.

Hope that might coax some more lift yet out of it.