<VV> TRW Piston Problem

Mark Durham 62vair at gmail.com
Sun May 19 19:56:54 EDT 2013


Smitty, you need to measure the skirt to cylinder wall clearance.
Piston to cylinder wall clearance will be much greater as the head of
the piston expands more than the skirts will in operation. Too much
clearance will cause piston skirt slap.
My GM manual says .0011 to .0015 skirt to cylinder wall clearance. Not
much.
You need to mike out those pistons then use a guage set to get the
reading on the diameter of the honed cylinder.
The procedure is in your GM manual, engine overhaul section 6. Do it
yourself or take the piston and cylinder to someone who has the tools
to do it right. I have never used a piece of paper and not sure that
would give satisfactory results because you cannot measure the cylinder
for out of round or taper. My cylinders were worn in the center. Mark
Durham

Sent from my Windows Phone
From: Smitty
Sent: 5/18/2013 10:43
To: virtualvairs at corvair.org
Subject: <VV> TRW Piston Problem
Smitty Says;  I have run into a problem I need some professional advice on.
Keep in mind I am talking about using a used and somewhat worn cylinder.  I
am using a Sunnen hone which should pretty much guarantee a round cylinder
bore and no taper.  I have measured it and this is proven to be correct.  I
have honed the cylinder to take out a little surface rust from inside.  To
check piston clearance I used a new TRW piston and tried to put it in the
cylinder.  It went into a point just below the ring area, but then started
to tighten up.  I honed it some more and now it goes in but with drag on the
piston skirts.  I am sure the piston is cam ground which would account for
the skirt being larger than the body of the piston.  At this point I got a
gently used TRW piston and tried it.  It also has drag on the skirts when I
get past the main body of the piston.  The piston body to cyl clearance is
around .004.  All components I have mentioned are marked standard. (except
of course the Cyl).

I sure as heck don't want to keep honing to get more skirt clearance and
make more body clearance.  What the heck is going on here and what do I do
about it.  I don't feel comfortable with using the pistons with and physical
drag on the skirts.

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