My 1986 C10 with a 350 appears to have at least one warped head. With a carpenter's level and some feeler gauges, I could measure a .006" warpage (right where the gasket blew, between cyl 4 & 6). The motor is a Target 350 installed about 10,000 miles ago in place of a 305.
I believe it warped because the 305 carb was never rejetted for the 350, so it ran lean. It always ran hot because of this, but never overheated. It came with composition head gaskets.
Anyway, to the point: Is there a general limit on how much a head can warp before it should be junked? I didn't see any cracks (yet). I know the proper thing to do would have them pressure checked and magnafluxed, but I just can't afford to do that. I have the opportunity to rebuild these heads (resurface, cut valve seats, new seals) if I do it here at the university all for free.
Or am I just wasting my time with gambling with these Mexican heads?
Lead Mechanical Engineer
Art Morrison Ent. Inc.