Ever seen this happen to a piston?

[fryeguy2]

So, I got an 056 recently and it ran great for a few weeks. So I cleaned it up and put new filters on it, and got a new bar and woodsman pro chain. And then the damn thing decided to sieze up on me. Except I could turn it 3/4 turn forward, and 3/4 turn backward. I pulled it apart to find that half of the piston skirt had broken off. Before cleaning the two small attachment points at the bottom of the piston had some black residue on them, leading me to belive that they had been broken for a while before the top part of the skirt broke off.

Anyways, cleaned out the bottom end really well, and bought a new piston and rings. I was wondering if I need to do any cleaning or honing on the cylinder before putting it back together. It looks clean and is totally smooth to the touch. No grooves or gouges at all. I was also wondering how I should align the piston rings so that they wouldnt catch on the ports or the other openings in the cylinder (for mixing fuel and air I suppose). And do I need to buy a ring compressor, or has anyone installed a piston in this saw without one. Thanks a lot for all the help.

Pics of the piston and cylinder.

 

[SmokinDodge]

Fryeguy was it a Stihl piston or aftermarket? I don't have a theory as to the failure, just curious.

As for the rings, my 064 has small pins located in the ring lands on the piston to locate the ends of the rings to keep them from catching in the ports. Pic attached below.

 

[fryeguy2]

The piston was a stock Stihl Piston. I bought it from an older owner who bought it new. This saw had never been taken apart.

Thanks for the info on the rings, i see the pins that line them up.

 

[Lakeside53]

As for ring alignment... The OEM piston will have an arrow on top pointing to the exhaust. If you have an aftermarket piston it might have an arrow or you'll need to align the ring pins to the inlet side.

 

[drunkenredneck]

You need to at least hone that cylinder and make sure that the chrome isn't peeling. You can install it without a ring compressor, use a hose clamp to do that but it is tons easier with the plastic compressors. Hope that helps you out.

 

[DGG]

I'm not a saw mechanic but it doesn't seem to me that this is a simple metal fatigue issue of the piston. I'm guessing that something else caused a massive stress, breaking the piston in the process. I just can't imagine what the forces were to cause a piston to break like this one.

Just slapping a new piston in may not solve the problem. Were crank and seals okay? Was the saw hotrodded?

Anyone else ever experience such a piston failure?

 

[spacemule]

I would imagine the saw had a lot of wear on it? Also, I would speculate that running one with no air filter allow the piston skirts to wear faster and cause piston slap, eventually breaking the piston. Am I anywhere close?

 

[PES+]

Check the top and bottom edge of the exhaust port for sharpness
I have seen quite a few saws of all brands do this after the piston wears and it is usually a lack of chamfer on the ports
It is not an issue until the piston wears some and begins to rock a bit

 

[Al Smith]

It's nearly impossible to analize a blown piston cause over the internet.If however you look at pic #1 in high resolution ,on the left side,near the ring is a rusty spot on the aluminum,at the point of failure.It would be my wild guess that this is the initial point of failure.


Could be piston slap,a tiny bite of foriegn material the saw ingested,don't really know.

 

[wood rat]

Ether start ?

 

[sperho]

It's nearly impossible to analize a blown piston

The possibilities are endless here... :angel:

 

[rreidnauer]

Wow! whatever the cause, I'd say it was a lucky break, (pun not intended, but fits well) since it didn't tear everything up inside. Despite what happened, consider yourself lucky. It could have gone a lot worse.

 

[pgg]

When removing/replacing the clutch, rope jammed down the sparkplug hole, the piston can break like an eggshell if cranking the clutch bolt the WRONG DIRECTION, that piston may have been stressed in a similar fashion once or twice before..

 

[fryeguy2]

Now that im thinking about it, I recently removed the clutch. I attempted it with an impact wrench before finally getting it off with a torque wrench. That seems a likely way to break the skirt.

This saw ran great when I got it. Nothing ive seen on the saw indicates that it is very worn. The seals and bottom end are in great shape also. Im amazed that there was no worse damage to the saw when the piston broke. I had the throttle pegged and then the saw just stopped dead. I cleaned the bottom end out really well so hopefully there are no small metal shards in there that will cause it to wear out quickly. It really looks like its in great shape.

thanks for all the help.

 

[fryeguy2]

So what would you guys reccomend as far as honing this cylinder. With this particular saw do I need to pretreat it with acid or anything? And what is the best way to hone at home.

Has anyone had any luck taking the jug to a dealer or machine shop to have it honed?

 

[pgg]

Chinese honing kit over the counter at cheap-mart

 

[Lakeside53]

So what would you guys reccomend as far as honing this cylinder. With this particular saw do I need to pretreat it with acid or anything? And what is the best way to hone at home.

Has anyone had any luck taking the jug to a dealer or machine shop to have it honed?

The best hone is 320 grit Silicon Carbide ball hone - you can get them from Baileys. You can get way with a 3 winged brake hone in an 056... but you'll need some care to get a decent cross-hatch.

 

[joesawer]

If the cylinder is as good as you described, I would not mess with honeing.

 

[SawTroll]

You need to at least hone that cylinder and make sure that the chrome isn't peeling. ....

Hopefully it is Nicasil, not chrome - Andy will surely correct me, if I am wrong.....:rockn:

 

[Lakeside53]

Chrome...