os piston pin problem

[impi62]

Hi Guys

Perhaps someone can shed some light on this problem. I an continuously having to replace the piston in my OS 91HZ because the pin in the piston ring groove that's locates the ring in the groove, disintegrates and disappears. The ring is then free to rotate around the groove and the engine looses compression and power. This is the third piston and ring and second liner that I have installed. none of the her pistons has seen more than 10 liters of fuel before this happens. I have run the engine rich for 3 or 4 tanks then gradually leaned it out for good power. It has always been still slightly on the rich side and has neve been over 200 degs. Power is really good until this happens then a noticeable drop on power and compression. Stripping the engine reveals a missing ring locator and the ring gap anywhere except where its supposed to be. No other visible damage. I'm starting to loose my sense of himour with this. Anyone have any suggestions or know what it causing this?

[Jafa]

That's a very rare problem

Notch in the liner lined up with the pimple on the top of the crankcase?

Conrod around the right way (effects thrust offset)?
Bottom end bush has bevel which faces toward the front of the engine

[impi62]

Thanks for the reply. Yup everything is as you say. I'm baffled

[ncampion]

I had the same problem with my engine. It lost compression and when I opened her up I could see the wear where the two ends meet on the ring. On further inspection the pin locator was worn away. I've bought a new OS HZ-R Speed 3D engine now but at some stage I'll have to recondition the old one. I sure hope this doesn't happen again on the new engine! I feel your pain bro.

[Oli 69]

This happened to me three times! And once a YS91SR.

Around me and nobody ever had that!

While it may be rare, but I've seen several times.