New OEM Piston chipping

[Jon1212]

These are pictures of a new OEM piston in my 5105. I picked up the saw as a $50 non runner, and it looked like it had been "straight gassed" within the first few tanks. The cylinder cleaned up easy enough, but the piston was pretty thrashed, so I decided to go with new OEM.

Clutch side front.


Recoil side front.


Recoil side rear.


Clutch side rear.

I have only run 6-7 tanks of 40:1 88 Non Ethanol and Shindaiwa Red Armor.

I have lost almost 40psi compression.



You can clearly see the abrasive effect those little aluminum chips have had on the lower piston surface, and the cylinder shows similar scratching.

Has anyone seen a similar failure?

 

[RedFir Down]

Sorry to hear about your misfortune with this problem child, Jonathan.

I'm thinking out loud here... Do you think it could be that the bore is not consistent from the factory causing these failures?
Try putting a ring in the cylinder and measure your ring end gap every few mm's (pushing it down with the piston). Maybe that will tell more of the story.

 

[Justsaws]

It looks like the edge of the piston skirt is sharp, was it not relieved at all?

 

[EvilRoySlade]

They look to be the cross hatch that is on the sides, never got cleaned up at factory. Crappie way to find that out. Sorry to see this.

 

[Chainsaw Jim]

I'm thinking straight gassing overheated it enough to warp or egg the cylinder.

 

[Jon1212]

It looks like the edge of the piston skirt is sharp, was it not relieved at all?

Nope, not at all.

They look to be the cross hatch that is on the sides, never got cleaned up at factory. Crappie way to find that out. Sorry to see this.

At least I bought the piston before the price increase ($65). They are now $85.

 

[Deleted member 83629]

i have seen some ugly internals but this beats all i ever seen looks like a it very hot quickly and then it was shut down.

 

[Justsaws]

Hopefully some folks who see the insides of these saws often can give you some advice on what it should be. Really hope that is not what the piston edges are supposed to be like.

If you decide to have another go at it I would knock the knife edge off the piston, as long as there is enough to cover the intake and exhaust.

Cannot really tell on the device I am using but the piston in the photos does not look like it is all that bad, certainly not enough to explain the loss of compression. I see what looks to be some minor score marks on the exhaust side of the piston but not sure, certainly some excessive skirt wear and some heat sinking. Was the ring stuck or scored over? I would look over the ring area at the top of the cylinder very carefully for loss of plating. Before sticking another new piston in that cylinder I would use a ring and measure the bore throughout the stroke. No sense in putting a new piston in a wallered out cylinder, twice cleaned up might be getting thin.

 

[Adirondackstihl]

@166

 

[EvilRoySlade]

At least I bought the piston before the price increase ($65). They are now $85.[/QUOTE]


Maybe the price increase reflects the added machine work on new ones to remedy this.

 

[Jon1212]

i have seen some ugly internals but this beats all i ever seen looks like a it very hot quickly and then it was shut down.

What are you talking about?

Did you read my original post?

Nothing got hot while I was running it.

 

[Jon1212]

 

[Adirondackstihl]

Did you read my original post?

No he didn't


Are all the bearings good?

 

[Trx250r180]

Put a ring on the cylinder ,slide it up and down the bore ,see if can see any gap with a light maybe on the edge of the ring anywhere to see if the sleeve is round still .Did you check for air leaks ?

Edit ,it looks like the skirt is hitting down in the case almost by the marks on the piston .

 

[Gypo Logger]

It probably was just a heat score Jon. Lol

 

[Jon1212]

For the fellas that commented on the apparent lack of finishing from the OEM.

Clutch side.


Recoil side.

I'd have to say that this is pretty clear evidence that the edges didn't get finished properly.

 

[Jon1212]

So for clarification, this saw was pushing 197#psi at 4700' elevation. I used it at 6500' for a couple of days clearing dead standing scrub Oak, and cleaning up really big Juniper Cedars. Very dirty cutting on the Juniper, and I noticed at the end of day three that the saw seemed to be a little less quick in the cut. I didn't think too much of it though, as the Juniper tends to dull chains(I touch it up twice a day while cutting).
Well when I got home last Saturday, I took the saw partially down for a decent cleaning. When looking through the exhaust I noticed the lower portion of the piston didn't look "normal" for a new part.
When I put the saw back together I checked compression, and found under 165#..........WTF!?

This lead me to pull the jug, and that's when I noticed all of the chipping on the piston edges.

 

[huskihl]

Maybe a hippie bluehair got in there and mucked things up? None of this explains the loss of compression unless the chips got up top and there's grooves above the ex port


Edit: just saw junk man's post about being out of round. Yeah that might explain it.

 

[NWCoaster]

It almost looks to me like there is excessive clearance in the piston to bore allowing the piston to rock a lot as it is going up and down, resulting in a lot of wear over a small area of the skirt, especially with that kind of compression. Would be worth measuring the bore if possible.

 

[bwalker]

Looks like sloppy skirt to wall clearance to me as well.