BP6.9
Full Access Member
hey i have a set of spare heads i wanted to have rebuilt but their warped just a little bit, can i have them saved to fix the problem? or should i chunk them for scrap?
shaved heads?
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rhkcommander
Full Access Member
how warped lol?
The heads can be shaved, i forgot the maximum suggested number though. I wanna say 80 thous. But no promises. There was a thread about it not long ago
The heads can be shaved, i forgot the maximum suggested number though. I wanna say 80 thous. But no promises. There was a thread about it not long ago
BP6.9
Full Access Member
its not really warped that bad i think like 11 thousanths, i was hopin i could save em
icanfixall
Official GMM hand model
Factory specs on heads are 4.801 thick max.
Minimum is 4.795. Thats not very much but. These heads are flat. They do not have a combustion chamber other than the valves being sunken in the heads. So whats the deal with this small amount of material that can be taken off.... I have yet to find any reasons for these specs. We run a hydraulic needle bearing roller lifter so its not like we have a solid lifter. Problem with finding a shop that can mill the heads and the precups at the same time is a tuff one. The precup material is so much harder so the cutting tool must be differant than the norm for cast iron... BTW the precups have a tollerance in the heads too. They must be +or _ .0025 of the head surface. That means they can be recessed or stick out of the heads by 2.5 thousands. A member had his 3.5 out and the head gaskets could not seal it off and coolant leaked up the head studs...
Minimum is 4.795. Thats not very much but. These heads are flat. They do not have a combustion chamber other than the valves being sunken in the heads. So whats the deal with this small amount of material that can be taken off....
I have yet to find any reasons for these specs. We run a hydraulic needle bearing roller lifter so its not like we have a solid lifter. Problem with finding a shop that can mill the heads and the precups at the same time is a tuff one. The precup material is so much harder so the cutting tool must be differant than the norm for cast iron... BTW the precups have a tollerance in the heads too. They must be +or _ .0025 of the head surface. That means they can be recessed or stick out of the heads by 2.5 thousands. A member had his 3.5 out and the head gaskets could not seal it off and coolant leaked up the head studs...PwrSmoke
Full Access Member
Yeah, icanfixall helped take the agony out of my recent head cutting job in which about 0.008" was taken off my heads which were already below the minimum thickness. The critical element is making sure the valve recession (depth of the valve in it's pocket) is within spec.
The machinist that did my heads used a grinder rather than a cutter. He locktited the precups that were loose before doing it. He said you could use a cutting machine if you had the right setup but the grinder made it easier. Otherwise, you must remove the precups and mill them and the head separately.
Anyway, the end result for me... engine runs like a top.
The machinist that did my heads used a grinder rather than a cutter. He locktited the precups that were loose before doing it. He said you could use a cutting machine if you had the right setup but the grinder made it easier. Otherwise, you must remove the precups and mill them and the head separately.
Anyway, the end result for me... engine runs like a top.
Yup, like stated above, the minimum thickness is 4.795. The machine shop I used was able to machine the heads with the precups in rather than out, which is best in my opinon. Like Gary said, if the cups protrude too much, it won't let the gasket seal and may even cut the gasket and cause big problems.
Heath
Heath
sle2115
NRA LIFE MEMBER
Best, I dont agree...easiest, yes, but we did them seperate because we could set the depths all the same and we did have a machine that would cut them in the head, but they can move around and get different protrusions. I know this because I questioned my boss...he'd been a machinist about as long as I had been alive. His solution was to have me surface an old head, the protrusions were all slightly different, but even more important is they were different on the cup itself. The cup would "tip" in the bore and get cut on a slight angle. Not much, but when you are dealing with machining measurements, and it was measureable. The shop had a pre-cup machine that cost a pretty penny (I'm thinking like $3500) and the shop owner was tight with money, the machine would easily fit in a gym bag, but it put the right finish as well as square cutting the cups. Not to mention, we could adjust the depth/protrusion as needed. It takes more time, but was worth it to the guy that owned/operated the machine shop.
Sorry Scott. I wasn't very clear in my post. I should have said, machining the precup in the head is better than taking the cup out and putting it back in without being machined at all (as Gary described a member's heads being done in that manner).
Heath
Heath
BP6.9
Full Access Member
so i can have em shaved? because the guy i was going to take em to has the equipmwnt to do it i just wanted to make sure it was possible before i started sinking money into it
He needs to measure the heads first to make sure they are in spec and to ensure they will remain in spec after he machines them (i.e. he doesn't take too much off). Does he have the specs Gary posted above? If not, provide them to him.
Heath
