> Daryl
> I am building a stroker engine. I have oversize valves @ 1.70 IN and 1.35 EXH.
> The valve faces are thicker than stock, so are closer to the piston before
> lift starts. I am running a cam that will give me .387" valve lift.
> The head has been shaved about .020", the block about .010".
> The piston will top at about .012" above the block deck. (custom pistons)
>
> Anyone have enough experience to know whether I will have valve clearance
> issues, or should I just take some molds of the combustion chambers to send
> with my piston order?
Several things popped into my head after thinking about your question for a
few minutes. First, just because the valves are larger and thicker they
shouldn't sit further into the chamber. The seats should be opened up and
machined to fit the valves, unless you have the valves cut down to fit the
existing seats, which defeats the whole idea of the bigger valves.
Secondly, do you need to eyebrow (notch) the block to keep the bigger valve
from catching the top edge of the cylinders? This is usually just on the
intake side, but I'd check both.
Then you can check valve to piston clearance by putting a thin layer of clay
on a piston (at top dead center). Using light springs, install the valves
for the cylinder you're checking and install the head on the block using a
decent used head gasket. Using a dial indicator to tell how far the valve is
open, push it down gently to max lift. If you can't push it down to max lift
without hitting the piston then you've definitely got trouble, but you can
probably get the pistons notched provided the crown is thick enough.
If you can then pull the head and see if there are dents in the clay on the
piston, measure the clay left from the deepest point of the dent to the
piston top. Off the top of my head I'm not sure what the minimum clearance
is, but someone else will probably let us know.
FWIW,
Ron
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