Gordon,
Thanks for the memory jog on the piston pin offset.
I was trying to figure out how to "measure" if there
is an offset to the pins without any machinist tools.
Only thing I can think of is to slide a piston pin
between two pistons. Lay the pistons on a flat surface.
Now remove one piston, rotate it 180 degrees and compare
the two pistons side by side again. Piston pin would
only remain horizontal if the pin hole was not offset.
By offsetting the pin towards the "upstroke side"
it will help reduce piston slap by giving a more
straight "up" travel on the piston. Result is the
piston will change direction in two movements
instead of one, reducing wear and noise.
For a little more "oomph" to the piston down stroke,
you can flip the offset towards to down stroke side.
Tuners trick as gives a little more push against
the rod journal. Yep, increased wear and noise.
Tom Walter
Austin, TX
Gordon Glasgow wrote:
> You may have to take one to a machinist to have this checked out, but the U20
> piston is supposed ot have an offset piston pin. It's only offset by about
>.040"
> so you can't see it by eye. See
> http://www.gordon-glasgow.org/Images/U20_Piston_Sizing.JPG. I believe the
>offset
> should go toward the spark plug side of the engine. Dennis/Tom/Dan, can you
> verify this?
>
> Gordon Glasgow
> Renton, WA
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