I believe that the best solution is to machine the piston for "spiroloc"
retainers. Second best would be "true-arc" circlips. This type or pin
retaining is normally what is used by Porsche, Cosworth, etc. Using
"buttons" either of aluminum or teflon is an old American hot rod trick
which was first used I believe when nothing else would keep the pins
retained on AA Fuel Drag Racing engines. The loads were so high using
Nitromethane and Alcohol fuels along with very high supercharger pressures
that the wrist pins were bending and would hammer out any retaining pins
used. I don't think that your Spit will have that problem.
Using buttons runs the risk of slight wear of the cylinder walls by the
buttons but more importantly, there is a risk of debris getting caught in
the pin hole and causing sever cylinder wall damage. In any case, should
you decide that you must use buttons, be sure to drill a good size hole in
them so that no pressure can build up behind them. Pressure would force the
buttons out against the cylinder walls hard enough to cause real damage.
Regards, Greg Solow
-----Original Message-----
From: Jari Tabell <jari.tabell@pp.inet.fi>
To: vintage-race@autox.team.net <vintage-race@autox.team.net>
Date: Wednesday, February 03, 1999 10:50 AM
Subject: Re: Piston pin buttons
>This thread is getting interesting as I am just rebuilding a new engine for
my
>Spitfire and I'm just trying to mate together con rods with floating pins
and
>pistons without circlip groove. I have heard from some local engine
builders that
>they've used aluminum buttons in the pin ends but I'm a bit suspicious when
>thinking them scratcing against cylinder walls... but on the other hand
pistons
>are of the same material as well... Any experiences, anyone?
>
>Jari Tabell, Finland
>http://personal.inet.fi/koti/jtabell/
>
>JWoesvra@aol.com wrote:
>
>>
>> On this subject: What is the best thermoplastic for this application? I
have
>> used what I thought was Teflon with good results. I have also encountered
some
>> white plastic that I thought was Teflon that melted causing obvious
problems.
>> I now test the material with a flame first. I would think that a melting
point
>> of at least 500 degrees would be the minimum needed. Perhaps higher. With
>> combustion temps of up to 1500 degrees, what would the temp be at the
piston
>> pin? Any thoughts?
>>
>> Jack Woehrle
>
>
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