066 has funny looking piston

[mtngun]

I had been bucking a 20" doug fir with my 066, running it hard and only stopping for gas and oil. The saw was cutting like a champ, but suddenly it just stopped. The gas tank was nearly empty, so I refilled and lectured myself on the dangers of letting the tank run dry.

When I went to start it, there didn't seem to be any compression, and it wouldn't start. I finished bucking the fir with a 33cc Homelite , and sure missed the awesome 066.

A compression test showed only 60 psi, even after squirting wd-40 into the cylinder. I pulled the muffler and couldn't see anything wrong ????

So today the cylinder comes off. That's odd. I didn't know chainsaw pistons were supposed to have antenna ?

There was also damage on one transfer side.

The exhaust side looks decent, considering.

Both wrist pin circlips were in place. The top ring was broken, but I take that to be a result, not a cause. The cylinder is scored high enough on the transfer side to warrant a new cylinder..... good excuse to spring for the big bore kit.

The "antenna" is 0.040" diameter. I presume it came from the carb side. I am a novice at chainsaws internals, so does anyone recognize the "antenna." ???? I'd sure like to fix the root cause of the problem before I put the saw back together.

This saw was new to me, with only about a dozen tanks through it. The guy I bought it from had done a total rebuild, including the carb. It ran like new until this happened.

 

[maico490]

Piston ring peg possibly?

 

[mtngun]

It does look to be about the same size as a ring pin, however, both ring pins are still in place.

 

[Cameljoe73]

wow thats ugly, I wonder if the guy that built the saw left something in the muffler, that finally fell back in to the cylinder.. did ya look at the plug? looks like electrode sticking out of the piston.

 

[04ultra]

It does look to be about the same size as a ring pin, however, both ring pins are still in place.

Needle bearing......





.

 

[gary A.]

I agree with 04ultra.... part or all of a needle bearing....

 

[timberwolf]

Look at the little end wrist pin bearing, make sure its all intact, then get worried about the big end, but no way to inspect that other than feel, rod should be free to move on the big end bearing and have a little side to side play, but no up and down slack or any roughness.

Can't think of anything carb end that would look like that. Filter was on?

 

[mtngun]

The plug is fine.

The muffler had been off many times for modding, but there was no damage on the exhaust side, and it's hard to imagine anything in the muffler that would be shaped like that. It is too big to be a piece of screen. It is a round rod, not a random shape.

It could be part of a needle bearing, but which bearing would be that small ??? The wrist pin bearing is intact and its needles are much fatter than the mystery piece.

I am not familiar the the bearings in the bottom end. Do any of them use an 0.040" needle ?

The throttle shaft screws are in place, and they are much bigger in diameter, as well. I will probably go through the carb just to be sure, even though the carb had been working fine.

 

[mtngun]

Yes, the air filter was on.

I am not sure what the big end bearing is supposed to feel like, but to my inexperienced way of thinking, it feels "OK." A little side to side, but no obvious up and down play.

 

[blsnelling]

Only way I can see it is that something entered through the intake, went to the crankcase, went up through the transfers and then got pierced into the crown. Is the squish band of the cylinder beat up from it riding around in the top for a while? Either the filter was off, which you've eliminated, or you blew/dropped something in there when cleaning the filter, or the builder left something in there.

 

[ShoerFast]

My $0.02 cents worth....

A ring-keeper, for grins, look again, they should be near flush with the piston land, and have a flat look with a slight camphor.

If it worked out and broke on 'up-stroke' some of the pin could stihl be in the grove, with a jagged look, and part in the dome?

 

[pdqdl]

What he said !

Needle bearing......





.

I went through this recently on our 0666.

Rod/Crankshaft bearing loose, lots of slop. Lost a needle bearing and it mulched the side of the piston.

Neat effect getting it to stick to the top of the piston like that. I'll bet you can't do that again.

 

[woodheater]

That is part of a needle bearing from the rod. I hope its from the top or you may not have enough good parts left to be worth putting that thing back together.

 

[nilzlofgren]

Maybe some part of the decompression valve. That would explain low compression.

 

[mtngun]

This 066 doesn't have a decompression valve.

Anyone know the diameter of the big end needle bearing ? By eyeball, I'd judge the big end needles to be around 1/10" diameter. Anyone know different ?

Shoerfast, you may be onto something. No, my piston pins are not flush, they are recessed about halfway into the groove.

The piston is a Golf.

This evening I'll try to pull one of the piston locating pins and measure it.

Small end rod needle = about 0.096" diameter.

Circlip diameter = 0.039". The "antenna" was 0.040". Suspicious, but both my circlips were present and accounted for.

Wait just a dog gone minute ....... one circlip lacks about 1/4" from making a full circle. This is the circlip on the side that was trashed. One end of the circlip has a smooth, square edge, the other end has a jagged edge -- as if a piece had broken off ????

I've got to get back to work, but I'll post more pics and measurements tonight.

Thanks for the suggestions, everyone. I'm getting an education, the expensive way.

 

[pdqdl]

Look at the wrist pin bearing again.

No one seems to have commented, so I am beginning to doubt myself here.

Doesn't the bearing inside that scored piston look totally burnt up, with tapered/fractured ends ?

 

[mtngun]

Picture of circlips, "antenna", and wrist pin bearing.

To my noobie eyes, the wrist pin bearing looks fine. Supposedly, it was replaced during the rebuild, just before I purchased the saw.

The good circlip has two ears that facilitate installation and removal.

The suspicious circlip is only 3/4 of a circle. It's bent, too, but that's due to me prying it out of the groove with a screwdriver (and yes, it was in the groove).

The "antenna" and the circlip are the same diameter.

Did the suspicious circlip originally have two "ears" like the other circlip ?

I suspect it did. I don't know why it failed, but it did. Perhaps it was not tempered correctly, or perhaps the builder handled it roughly. I suspect the former.

So..... what is the lesson learned here ? Did the builder do something wrong ? Or is Golf simply an unreliable product with known QC issues ?

A big bore kit has been ordered from Bailey's. I believe it is made by Golf. Should I toss the circlips that come with the kit and substitute Stihl circlips ? Is there a right way or a wrong way to install circlips ?

 

[timberwolf]

I have use the tail type cir clips with no trouble, but there have been failures. I have also cut small slots in the piston so I could remove the Stihl circlips and used them esp on saws turning over stock RPM.

I put the tails to the top if I do use them. The greatest G force is upward so placing them at 12 o'clock is the place they take the least abuse.

Anyway, looks like you found the culprit and your only out a jug and piston, thats a lot better than crank bearings. Make sure you clean the case out really well to get any metal scraps out before rebuilding.

 

[PES+]

You should get real Stihl clips as the ear clips are not made to work with the cut out that the Stihls have for the non ear clips.

It is up to you and if you are comfortable with a suppliers guarantee use their clips but it is always wise to use the correct type of part for the application.

Many after market clips are pretty dicey even when used in the correct application.

 

[Trigger-Time]

The piston is a Golf.

You should get real Stihl clips as the ear clips are not made to work with the cut out that the Stihls have for the non ear clips.

It is up to you and if you are comfortable with a suppliers guarantee use their clips but it is always wise to use the correct type of part for the application.

Many after market clips are pretty dicey even when used in the correct application.

Gary