Richard,
One problem with the "rebuilt" heads is there are
times when you can not see what needs to be inspected.
I have seen NEW U20 heads with casting pockets that
were covered by the valve seats. Not all that common,
but when you see something like that on a new head
it was a bit of a shock.
Are the exhaust valve seats "bronze" material, or
more of a "steel gray" material. Original heads had
the bronze seats, that can wear rapidly with unleaded
fuel. Thankfully there are some good non-lead additives
you can add to the gasoline to prevent valve seat wear.
Almost any head that has been rebuilt in the last 10
years will have "stellite" seats that do not have the
wear problem.
Rocker Arms -- two types. One piece and two piece.
If you look closely at the sides of the
rocker arms, they are made from two pieces. The area that
contacts the camshaft is an insert that has been brazed
onto the rocker arm. You want to use two piece rocker arms
for the longest camshaft life.
Other thing to pay attention to is the thickness of the
cylinder head. 4.245" comes to mind (need my coffee).
You'll want the shop to confirm both BOTTOM and TOP of the
heads are flat and parallel to each other. The camshaft
towers should be shimmed up to proper height, to compensate
for machining the head flat.
One "old crusty" machinist in the Bay Area is Don Potter.
He does fantastic work, but still does it the old fashioned
way of taking his time, and doing an excellent job. Last
I talked to him, he was up in Fremont. He is always backed
up, and does not rush things... so make sure you understand
that up front. Expensive, takes his time, but excellent
machinist.
Cheers,
Tom Walter
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