Ate a Circlip, Lunched the Motor - Autopsy Time.

[Chris-PA]

The ported PP315 engine I had finally got working well ate a circlip and destructed, and I'd like to figure out what I did wrong so as to avoid it in the future.

There's major damage on the skirt at the intake, but that picture didn't come out. Anyway, there is serious wear all around the clip groove. The other side is showing wear too. I'm not sure why there was force on the clips. It feels like the small end bearing is free and seems to be in decent shape.

At this point I'm thinking that the pin was spinning in the piston. From wear? Was the piston getting too hot and expanded enough to let the pin float?

Any suggestions would be appreciated.

 

[Mad Professor]

OEM parts?

How long before chaos hit?

I think all pins are going to spin/move , as thermal expansion for aluminum (piston) is greater than steel (pin).

What is important is the clip stays in place.

Did it seat well it the groove?

 

[nmurph]

Incorrectly sized clip? Too thin???

 

[Chris-PA]

Well, they were all the OEM PP315 parts. The clip was clearly in the groove as it's very heavily worn all around the groove. If you look at the first picture you can see the metal flanged out on both sides of the groove. Could the clip have been getting hot?

I'm trying to figure out if the flanging/wear in the clip groove was mechanical or if the aluminum was getting soft.

 

[thomas1]

How does the other side look?

 

[hotshot]

Were both of the two clips gap pointing straight up? Did it take
any "unusual" bending or force to put them back in?

I don't see any of the clip body itself across the "removal" gap in the second piston
picture, is that the way it went back together? I understand that it can rotate easily
now that it's worn the pocket out.

 

[Chris-PA]

Well, it shows signs of wear, but not as extreme. I tried putting the remaining clip in the side that broke, and it holds in pretty well. I'm wondering why this piston has that gap in the ridge where the clip groove is - that seems like asking for trouble, and that is where it's worn the most. It's also more worn there on the other side.

It's not making much sense to me. It seems like the clip was being driven back and forth or around in a circle, and that would have to mean the pin was driving it. I can sort of see how that could happen, perhaps with the aid of a sloppy small end bearing. But I'm not at all sure why the pin would be pushing on the clip that hard.

Maybe I didn't get the pin well centered in the piston and it was pressed against the clip - but it would have to move in the piston to wear on the clip, and then it would center itself in time.

 

[Chris-PA]

Were both of the two clips gap pointing straight up? Did it take
any "unusual" bending or force to put them back in?

I don't see any of the clip body itself across the "removal" gap in the second piston
picture, is that the way it went back together? I understand that it can rotate easily
now that it's worn the pocket out.

No, they came out and went in pretty easily. I do not really remember how they were oriented, but they clearly moved anyway. I think I set it so the gap in the clip aligned with the gap in the piston flange, as that part of the clip would have been unsupported. But like I said, I doubt it stayed that way long.

Maybe the clips were "sprung" and weak, and the wear is just from them bouncing in the groove until one broke.

Well, time for bed - this one is going to puzzle me for some time!

 

[zogger]

Just too loose? Rattling back and forth on the pin? Slamming side to side vigorously.

 

[leeha]

I bet the clip didn't have enough tension in the groove
and was allowed to move causing the heavy groove wear
and finally failure.






Lee

 

[Chris-PA]

Didn't quite get to bed yet.....

I'm thinking a loose clip is probably the answer. That wear is probably not from rotating, rather from the clip hammering on the groove. There's a bit of force at 10,000rpm or better, lots of G's even for a clip that light.

Darn. That's a lack of experience on my part - I should have seen that, or rather recognized it wasn't right.

 

[Dieselbreath]

If you are overhauling a car engine, it is recommended you put new cir-clips in. I imagine it is even more critical for a chain saw engine.