A Lesson in Fail - a piston pin circlip escapes

msr · October 07, 2026, 03:29:16 PM

In case you've ever wondered what might happen if a piston pin circlip works its way out, I can tell you it's not pretty. We installed this top end around 3 years ago. It probably has around 300 miles on it as a guess. Not sure if the clip was faulty or if it wasn't completely seated in the piston, but either way ... boom!

m in sc · October 07, 2026, 04:05:52 PM

yeah one of us did that. not sure who but was def an install fail.

It was Deron, tho.

msr · October 07, 2026, 05:26:16 PM

Quote from: m in sc on October 07, 2026, 04:05:52 PMyeah one of us did that. not sure who but was def an install fail.

It was Deron, tho.

It WAS Deron!

RDnuTZ · October 07, 2026, 08:30:03 PM

was that a Chinese cylinder kit? And why wasn't the tang removed from piston skirt? I thought that is basically standard procedure these days.

msr · October 07, 2026, 10:54:22 PM

Quote from: RDnuTZ on October 07, 2026, 08:30:03 PMwas that a Chinese cylinder kit? And why wasn't the tang removed from piston skirt? I thought that is basically standard procedure these days.

Yep, it was. The other cylinder was fine, and I know of at least two other bikes running those kits that have had zero problems, so ... ??? I'm betting we just missed it on assembly. As for the tang, it's smoothed inward to ensure it couldn't catch on the port but complete removal is always an option too.

rodneya · October 08, 2026, 12:20:59 AM

The clips on some cheaper pistons have no spring in them. when you push them in they stay bent and dont spring back against the piston

m in sc · October 08, 2026, 07:33:37 AM

the clips on mine are atill hanging in there. as farcasxthecceterctab, you can radius them back, the result is the sane

1976RD400C · October 08, 2026, 08:28:27 AM

They sure like to dig deep when they escape.

m in sc · October 08, 2026, 08:34:13 AM

I've actually seen worse. to the cip point, the prox ones are def better. i would recommend using them and throwing the kit ones out.

RDnuTZ · October 08, 2026, 10:26:32 AM

Quote from: m in sc on October 08, 2026, 07:33:37 AMthe clips on mine are atill hanging in there. as farcasxthecceterctab, you can radius them back, the result is the sane

good to know, radiusing sounds easier and faster. Any negatives to completely removing re: skirt strength, fail rate etc.?

m in sc · October 08, 2026, 10:56:01 AM

zero risk doing it either way. just break the sharp edge w a file if you cut it.

i 1st did the radius thing years ago as a test to see if it would work, have never had an issue.

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A Lesson in Fail - a piston pin circlip escapes