[DeTomaso] Valve job
JDeRyke at aol.com
JDeRyke at aol.com
Sat Jan 26 16:48:02 EST 2008
I've ground a thousand valve seats and you're correct in that this will cause
problems (two or maybe three different). First, all sharp edges in a
combustion chamber are a potential source of pre-ignition and second, the edge
interrupts exhaust flow out, costing power. A typical "3-angle" valve grind starts
with the seat- often ground at 44 degrees to give a tiny interefence fit with
the 45 degree-cut valve, then a 75 degree stone inside the port to blend the
bottom of the seat and finally a 15 degee 'topping' stone to blend the upper
insert and narrow the actual seat to spec's. Sounds like someone skipped the last
step (and maybe the first one, too). Iif true, you need to find another shop
that knows how to do performance grinds for any further work. A third potential
problem might be that thicker seats can be positioned so high in a head that
valve lash range can be affected. Its possible to run out of adjustment on
some 'conversion' valve trains if things get too far out so I hope the heads are
studded. Its also not practical to touch this up with the heads on the engine
because of the clean-up needed for all the grinding swarf generated, so I hope
you haven't mounted them yet. And since there's several kinds of valve seat
possible, and some are almost diamond-hard, the shop needs to have the correct
stones for whats there now. Good luck & keep us posted- J DeRyke
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