CYLINDER HEAD SPECS.


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By DANIEL TINDER - 17 Years Ago
Need some advice:



I recently had a set of unposted "G" heads rebuilt at a local shop (hard seats/stainless valves). While not a race-quality engine shop, they generally do an acceptable job when it come to getting motors rebuilt and back on the road. I have been taking measurements to check their work, but don't really know what level of precision is acceptable for a street motor, or the point of diminishing returns if I decide to spend more $.



Problem #1: Several seats are cut/lapped deeper than the rest. I measured the valves before installation (all to spec.), and now one stem is .040" taller than the shortest. A few are .020" taller. How much latitude do I have before rocker geometry is off enough to affect guide wear? How much can I file off the stem before surface hardness is compromised? Is this enough of a problem to warrant the expense/trouble of replacing/re-cutting the deepest seats?
By DANIEL TINDER - 17 Years Ago
Problem #2:



What is the acceptable "installed spring height" tolerance? Valves with deep seats can be shimmed, but the spring on the shallowest seat is installed .050" short. Is it better to lap the valve in until the installed height is right and accept increased shrouding, or take the trouble to machine the spring seat?
By DANIEL TINDER - 17 Years Ago
Problem # 3:



I CC'd the chambers, and find 2.6 CCs difference between smallest/largest volume (67.4/64.8: milled .005"). Luckily, the smaller ones have enough sharp edges to warrant grinding anyway, but I wonder how close they should be before I quit (for a daily driver)?

A lot of trial & error grinding/measuring will likely be required.
By pegleg - 17 Years Ago
Dan,

       If they installed NEW seats as you said and you've found that much variation I'd be taking them back to the machine shop to correct. There's no reason to accept .050" variation in seat depths. When that's corrected, you can check your chambers again. They may well be closer than they are now.