Racers run with .006" piston-to-wall because they are using forged pistons
(not cast ones) which expand more as they come up to temperature.
Running .004" won't significantly hurt your performance but you might
experience greater leakdown. The cost of .060" over pistons is quite a bit
higher than even .040" over ones.
Gordon Glasgow
Renton, WA
www.gordon-glasgow.org
> -----Original Message-----
> From: owner-datsun-roadsters@autox.team.net
> [mailto:owner-datsun-roadsters@autox.team.net]On Behalf Of
> JOver4X4@aol.com
> Sent: Saturday, June 21, 2003 8:55 PM
> To: datsun-roadsters@autox.team.net
> Subject: piston to wall clearance
>
>
> List,
>
> I have the U20 out of my 68 torn down. It was rebuilt in 1991
> and has not
> been driven much since then. It had been in storage for at least
> 5 years.
> There was a small amount of corrosion present where the top ring
> mated to the
> wall, caused by condensation in the cylinders. By the time I
> honed the cylinders
> to clean the corrosion my cylinder to wall clearance is at .004".
> The manual
> suggests .002" clearance. My question is, should I run at .004"
> or spend
> the money and bore to the next size? I am at .040" now and am
> not excited about
> taking it to .060 unless I really have to. I would like to allow the
> matching # block to be bored one more time at a later date. What
> do you guys think I
> should do? I know racers run with .006 or so wall clearance but
> they are not
> concerned with longevity or burning a little oil.
>
> Thanks,
>
> John Over
> 68 2000
> Aurora, Co
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