It's really tough to tell how much has been removed from each surface. Yes,
you can get the cam chain length back with cam tower shims but they will
have a minor effect on valve train geometry. I really doubt if this would be
noticeable in anything other than a race motor, as long as the wiping
pattern of the cam lobes doesn't run off the end of the rocker arm pads.
This is easy to check with some Machinist's Blueing.
The limits on the bottom side are the resulting compression ratio and the
piston-to-valve clearance. You can check the latter by claying the pistons.
You should have at least .120" on the exhaust valve and probably .090" on
the intake.
The compression ratio measurement is best left to a head specialist, unless
you want to go get a graduated burette, a stand and a hunk of plexiglass and
try cc'ing the head yourself. Modifying it, however, is NOT easy to do
accurately and should definitely be left to a specialist.
Gordon
> -----Original Message-----
> From: owner-datsun-roadsters@autox.team.net
> [mailto:owner-datsun-roadsters@autox.team.net]On Behalf Of
> mjsutter@cox.net
> Sent: Friday, June 03, 2005 6:56 PM
> To: datsun-roadsters@autox.team.net
> Subject: Surfacing Limitations
>
>
> U20 Owners,
>
> In your humble opinions, what is the maximum limit for material
> removal from
> both the top and bottom of the U20 head? Using cam tower shims
> can overcome
> the valve train geometry/timing chain length problems associated
> with cutting
> the head, but when does combustion chamber size start becoming an issue?
> Assume stock pistons. Any thoughts?
>
> One other thing, I just did the first oil change on my recently
> purchased 2
> liter. I don't recall there being a long tube attached to the oil
> filter block
> on the 69's that I've owned. I assume this is an anti-drain back
> feature. Is
> this a 67.5/68 part or were my 69's modified?
>
> Thanks,
>
> Mike Sutter
> 1968 SRL 311
> 1966 Sunbeam Tiger
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