Teflon Pin Buttons?

[donforeman]

I have a long abandoned project I started digging at. I did not build the car or the engine. Both had trouble and most got tossed in the trash. So here is this question. The pistons are fairly low use. The Teflon buttons are what is bothering me. They are two pieces, an aluminum spacer with the Teflon part on top. There was some very big mistakes in the engine assembly when I got it so I am questioning everything. Crazy stuff like hardware store all thread for head studs and one piston bore was honed oversize but the piston was left loose. I tossed most of it in the trash can. If this is an OK setup I do not mind using it as is. I have zero experience with this type of pin retainer though. Should I make new one piece buttons for the pins? I see where people make them from one piece Teflon and some make the whole button out of aluminum. Are the buttons supposed to ride against the bore lightly? These look short of that by a bit. The engine is a 1.2L import used for autocross and vintage track days.

[hoodeng]

Make new buttons one piece with a section that light presses [slide fit] into the gudgeon pin. Teflon or aluminium makes no difference. Pin OAL with buttons -.005"-.010" of bore diameter.

The alloy inserts look if they have been rebated to accommodate piston circlips, is this engine running clips as well? is there a history of not being able to trust retainers?

cheers.

[donforeman]

Thank you very much for the information, that helps a lot. No circlips, I was hoping the pistons had the grooves for them and I would just skip this stuff all together. They are Venolia pistons and the car came with two sets of them, one set used for two races and one set new, so I plan on getting them to work if I can.

[Momus]

I'd machine the pistons for round wire circlips.

Easy single set up job for a machinist.

Those buttons look like trouble from the 1970's.

[Sparksalot]

High reliability piston aircraft engines such as Lycoming have used piston pin buttons for a very long time because they don't fail. The lives aboard those aircraft depend on reliable engines.

That said the pieces in your photos look weird compared with what I've seen as reliable. On the other hand I haven't seen it all. If the button fills the volume and has a materiel not harmful to the bore and enduring of the environment it has good chance of success.

[Momus]

High reliability piston aircraft engines such as Lycoming have used piston pin buttons for a very long time because they don't fail. The lives aboard those aircraft depend on reliable engines.

That said the pieces in your photos look weird compared with what I've seen as reliable. On the other hand I haven't seen it all. If the button fills the volume and has a materiel not harmful to the bore and enduring of the environment it has good chance of success.

Lycoming pin button. The button is an interference fit in the pin bore.

The Lycoming piston I have in my hand is fully circular with no relief allowing button overhang.

[donforeman]

Thank You for the information. I think I will try to do a few aluminum buttons as a test. I am not a machinist, so I think its less risk to putz around with making buttons in the garage than to try to set up the pistons for cutting the wire clips. If Venolia was still in business I would try to see if they would machine them for the wire clips and be done, but they are long gone. If the button is designed to press fit to the pin, how are they removed for disassembly? Both sides of the pin would be plugged with a button.

[novafornow]

Every application is different, but I have used plastic buttons as well. Made a good slip fit in the ID of the pin.0.005" - 0.010" under the bore. No problems.

[donforeman]

The header is finished so this is another loose end I need to take care of before assembly. The piston buttons I have were for a Kawasaki motorcycle and then the previous owner made the aluminum shims to space them out. The Kawasaki's bore is much smaller and that's why the Teflon is only wearing on the tip of the radius. It is hokey with the two pieces and undersized button, sort of like the rest of the car and why I had to toss so much of it in the dumpster. I tried making an aluminum button as a test with my limited lathe skills, but the large radius is giving me fits with what I have to work with. The bore is 2.84 and I was trying to match the outer part of button with that. I have a manual lathe and its just not going well. I need 8 identical parts and probably 2 spares and so far the radius has not been going so hot. Can I skip the radius and make a flat spot or angle? It doesn't seem like it would work as well. More risky but I am thinking that just grooving the wrist pin bores may be the alternative. I can buy an expanding arbor to hold the piston in the chuck and a grooving tool for the lathe. Is the depth of the groove set at 1/2 the circlip diameter? I did a search online and you get all sorts of answers from don't do it that way... you need a specialized fixture jig, to "go for it" with no real details on how "it" gets done. I did contact Ross pistons as they offer custom buttons, but since the pistons are Venolia, they wont touch the project. I appreciate all the feed back and advice, it does help making better choices with the project.

[hoodeng]

Just make a plunge tool out of some 1/2" square HSS. It does not need to match the bore radius perfectly.

Cheers.

[donforeman]

Just make a plunge tool out of some 1/2" square HSS. It does not need to match the bore radius perfectly.

Cheers.

Thank you! I have one of those in Carbide. I did not think to use it since it was only 3/8 radius. That will make it a lot easier! Thank you again!