Michael,
The stock 1316 head thickness is 2.750" so just measure the overall thickness
with a caliper and you'll know how much was milled. Still don't tell you much.
If a valve job was done, the chambers get larger, and it may have been milled
to just get the CR back to where it was. Do all of the work you want to do on
the head and then measure the chamber volume for the CR calculation. Only then
will you know what to do to put the CR where you want it, or just make sure it
is safe.
Valve-piston clearance is not only a function of lift, but includes duration
and how the cam is timed. It is usually checked during a trial assembly with
some modeling clay on the piston and turning the engine through several
cycles. I doubt you'd have a problem with a street cam, but race cam lift &
duration usually has the exhaust valves needing a relief machined into the
piston. More of a problem for you could be valve spring coil bind with the
high lift rockers depending on what cam lift and springs you've chosen. Buying
a complete cam kit assures matched components, but you still need to check and
set the springs installed heights and check coil spacing at full lift.
John
Fogelsville, PA
--- On Wed, 1/20/10, Michael Rowe <mdrowe@optonline.net> wrote:
From: Michael Rowe <mdrowe@optonline.net>
Subject: [Spridgets] More heads
To: "Spridgets" <spridgets@autox.team.net>
Date: Wednesday, January 20, 2010, 1:32 PM
How deep is the stock combustion chamber on a 12G 1316 head? This one is a
lot shallower than the 12G 295. It may have been milled, but there is no
evidence of any other work on it.
Do I have to worry about high-lift rockers making valves hit a piston?
Michael Rowe
'74 Midget
'60 Sprite kit
Long Island, NY
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