[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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