6.9 cylinder heads milled .020. Is this acceptable?

[MTKirk]

I know specs say minimum head thickness is to be 4.795, but; what if they have been cut to 4.775 and valves have been recessed to maintain clearance? Has anyone successfully run heads cut this far?

 

[riotwarrior]

Likelyneed run shorter pushrods be my guess

 

[Hydro-idi]

When you recess the valves another .020 (out of spec), too much material has been removed from valves & seats. Valves will cup and seats will crack due to the "lesser" material & increased heat.
Just happened to me & wasn't a happy camper. Recessing valves will eliminate your piston-valve contact but create another problem. There's a reason specs are there in the first place.

 

[icanfixall]

Someone owes you a set of heads. As posted.. Cut the heads too much and another issue is created. If the valves are sunk in the heads you will end up cutting that 20 thous off the stems. If you don't cut back the stems you push the lifter plunger down the same 20 thou and you really don't want that. How did the shop end up cutting that much off the heads? If they did it on their own not knowing the end result then you bet you bet another set of heads on their dime. Also those heads will cause the intake manifold a hard fit because the heads are closer to the engine center line. Milling the intake manifold gasket surfaces is not a good way of fixing the shops mistake either.

 

[MTKirk]

Not to worry, my heads haven't been touched yet. I was thinking of using another set of "rebuilt" heads, so I took them to my shop. First thing I measured thickness and got 4.7719" on one & 4.7879" on the other. I confronted the re-builder on this and he said "we do this all the time even 30 thousandths and have had zero issues. I thought bunk, but that at least I'd check it out. Along with hearing from the Oil Burners, I pulled the springs and checked a few other things. To put it simply I WILL NOT BE USING THESE HEADS. I'll just have to rebuild mine. Mine are full 4.800 height with no warping, some minor pitting that should come out with in 5 thousandth's.

 

[dunk]

I have no first hand experience so my thoughts are worth exactly what you paid for them... Could work but that's a pretty hefty cut for these heads from what I've read of others troubles. Measure and see how far off spec they are for thickness. Make sure precups have been cut appropriately as well and aren't protruding past spec (a couple thousandths?). Valves will need shorter or different length pushrods, check geometry and rocker to valve contact area. Seat may or may not be a problem. Lap and measure the contact band width on exhaust valve to seat. Too small and the valve won't lose heat fast enough to the head. May be difficult to seal the intake. I had trouble sealing the intake on a 460 I had to cut the heads. Had vacuum leaks in the valley. Ended up going to the thickest non-metal intake gasket I could find and very light RTV around each port. Sealed fine with that, but that's not getting 10+ psi shoved down it. May need to alter the angle slightly on the intake side of heads or the intake itself if it's a problem.

Either way if you didn't OK the work in attempt to fix severe warpage or other damage I'd be seeking the shop to replace the heads with heads that measure in spec. Curious how this turns out.