Interesting wrist pin retention

[SilverXJ]

I was at work today doing some crap on the XJ (repainting withe arms, replacing parts on my lightforce lights, other random bs) and my boss comes in. He has a problem with one of the cylinders on his small plane. The exhaust valve isn't sealing correctly on one cylinder. He brought the piston and cylinder with him to ship(its air cooled so he can remove the cylinders). The piston itself was huge, around 6". Anyhow instead of using snap rings or spiro locks the wrist pin has aluminum inserts at bots ends that actually ride against the cylinder walls.


I searched for an image but I was unable to find one. Instead I found a VW performance parts site that had aluminum buttons that basically exten the wrist pin to the cylinder walls. http://www.jayceevw.com/products Seems like a simple solution for converting a piston with out grooves for snap rings (like the KB944) to a full floating design.

[lafrad]

Yea, thats the REAL way to do floating pins.

With that, you can have a proper amount of play, so the piston to rod interface never is the same line repeatedly.

On Street engines that use that, the buttons are usually Teflon coated aluminum, and it can be setup to run a bias to the front or back of the engine, per cylinder. They get setup to go in with the rings... the ring compressor just holds them in.

[SilverXJ]

What other engines use this method? I don't know why it isn't used more often as this is the first time I have seen it. Seems like a pretty simple idea. Heck, if I had known about this I would have talked to my machinist about making my connecting rod and using this on my KB944s.

One other thing I noticed is that the piston had 4 piston rings and the oil ring was something different. The 4th ring was right above the skirt and below the wrist pin.

[lafrad]

Don't know about the other rings, but something to keep in mind is how low the piston comes into the crankcase. if the pin is exposed, the buttons won't work.

[SilverXJ]

I would think that if your piston is being pulled so far out of the cylinder as to expose the wrist pin that one would be having other problems besides the wrist pin.

[dwg86]

Small aircraft engines use these.

[SilverXJ]

Small aircraft engines use these.

yeah.. I guess you missed the part where I said it was from his small plane.

[dwg86]

Guess I did.

[SilverXJ]

I'll let is go this time since it was monday.