Gudgeon (wrist) pin pads

[MRA]

Hi folks

I have a piston in a full-size engine which has chewed up one of its circlip grooves. Luckily I got it out before the clip escaped and scored the barrel. I think the end load occurred as the pin part-seized in the small end, and cracks were developing in it (pictured - crack highlighted red) - I was lucky not to blow it up in a big way. I'll need to check the rod is not twisted. You'll also see the photo of why the bottom end was telling me it wanted to come apart

I know pre-war motorbikes used end pads (alu / brass) to retain the pin, and it struck me I could do this at one end to reclaim the piston, which is rather hard to find. It seems IC modellers also do something similar. I wonder if anyone on here has any tips on materials (nylon / PTFE?), where to get them, fits, radii etc based on their IC modelling experience? I have a big truck piston I could cut up for some alloy which might be suitable.

Thanks
Mark

 

[Mechanicboy]

Better to replace piston/wristpin and clip.

 

[MRA]

Well, yes, but the piston itself is hard to obtain. So yes, clips and pins will need to be replaced - and my question is about materials and techniques IC modellers use for end pads, or buttons as they were sometimes called.

 

[Mechanicboy]

Well, yes, but the piston itself is hard to obtain. So yes, clips and pins will need to be replaced - and my question is about materials and techniques IC modellers use for end pads, or buttons as they were sometimes called.

Bronze or Teflon for pads with radiused ends. The pads is light pressed into wrist pin.

 

[cwelkie]

Aluminium is used as well - re-purposed (solid, dome head aviation) rivets for example.

 

[xpylonracer]

Hi Mark, the end pads you refer to were not used to retain the pin in the piston, there only use was to prevent the hardened pin end rubbing on the cylinder and scoring a groove.

Marcus

 

[MRA]

Well, I've gone hi-tech and ordered a stick of Teflon. It reckons it's OK to 200 deg C, and although a bit crap in bending, it's OK in compression. So let's see - I'll maybe drill a hole in it down to the pin end so I can keep an eye on how thin it's getting; head and barrel on this engine is a 10 minute job.

cheers
Mark