Topic: Teflon Piston Pin Retainers

[phillip56]

I'm going to start rebuilding my spare 550 engine in the next month or so. I'm want to make some Teflon piston pin retainers. Does anyone know what kind of Teflon is used for these?

[wdhewson]

Hi:  

Machinist's bars (round stock) of pure polytetrafluoroethylene, PTFE, is the correct starting point.  

However, PTFE has a low yield stress which means it is easily permanently deformed, and could thus could be deformed by the acceleration and deceleration forces experienced with piston movement.

Oppositely, spring steel has a very highly yield stress.  Go with good quality spring circlips and forget the PTFE plugs.   Naturally make sure the circlips are perfectly seated and the open section at 12 or 6 o'clock.

What do others think?

Don

[754]

I have seen a few bike barrels that had major furrows, including some around 1/8 inch deep..    

 But I have never seen a barrel hurt by a teflon button..

[wdhewson]

It is true that a loose clip will rattle around and score a cylinder wall to death with all the accompanying other damage to ringes etc.  

So I'll re-empazsize the need to have the clip seated well and positioned correctly. Thus done it won't get loose and go wild.  Don

[Big Jay]

You can also make them out of aluminum. You can even machine a step that allows you to press them into the pins. make the entire assembly .020" smaller than the bore.