Hi. I have a set of heads. They came with my 1970 Plymouth GTX. I want to put them on the current engine that is in the car because I want to take the numbers matching heads and eventually attach them back to the original engine that is sitting in my garage. The person who gave me the heads told me they were milled, and they were milled too much for the engine in the car currently.

Is there a way I can find out how much they were milled? Also, can I use thicker head gaskets to make up the difference? Hope, this does not sound like a dumb question.

How does the former owner know they were milled too much? Do the intake bolts holes no longer line up? Do the heads knock and ping? The heads could be cc'd by a good machine shop to determine the chamber volumes and estimate the amount they've been milled. There are various thicknesses of head gaskets.Stock steel shim head gaskets are around .020"; blue fel pro perma torques around .039" compressed. Sounds like you have a 2nd set of heads - the 'original' 906 heads - get them cc'd along with the others and compare them to the 2nd set. You might also mike the surface of the heads between the deck and the bottom row of bolt holes between the two sets to get an idea on the about they have been milled.

Check the casting numbers on both set of heads, all four heads, and post them on here That way we can see if they are all open or closed chamber heads and what the original CC where on them
You can also measure the thickness of the outer head bolt bosses to see if they have been cut or not also
CC each head is the best way to know exactly the size of the combustion chambers, don't be surprised to see form 1.0 to 5.0 CC variance on your stock heads, even on 426 Hemi heads
I have new set of 440 source aluminum heads in my shop now that vary 5.0 cc between all eight chambers
I have another set of them that had been CNC ported and cut down from stock thickness to get 72.0 CC for each head, the intake manifold had to be cut a bunch on each side to get the manifold to fit correctly, now those heads are being switch from a 440 block to a new 400 stroker motor, I'm having .050 cut off both sides of the new Eddy Super Victor low deck intake manifold now hoping that is enough

Karl there are no dumb questions & that for sure sounds like something that I would want to know if I was in the same situation. iirc the outer boss where the short head bolts is 1" thick on an unmilled head but others will clarify. As said do some measureing/cc ing & holler back with what you find out.

Post the head part numbers, I have figures for both closed and open chamber heads, both at headbolt boss thickness, and the flat target next to the sparkplug to get you in the ballpark. Will dig out tommorow.

The outer row of head bolt bosses are nominally 1.00” thick.

Using a caliper or a mic, measure several and average the results.

How much smaller that dimension is than 1.00” will get you really close to knowing how much has been milled off.

However, having them cc’d will be a more accurate way of determining if they’ve actually been milled “too much” for you to use.

Here you go

915 closed chamber, .710-.730 to flat target area next to sparkplug. Lower row of headbolt bosses.955-1.010, this is average of 6 pair of 915 big and small valve heads.

906 open chamber, .729-.735 to flat target next to sparkplug, lower headbolt boss all were 1.00, with my chinese calipers only 4 heads with 1970ish date codes.

Now the real important measurement

Valve tip to outer unmachined valve spring seat area, 2.095-2.135. Stock low mile untouched heads measure 2.110 pretty co sistant. If you want your rocker arm geometry correct, with stock parts this is critical. Measurements are taken from a miller c3648 go no go tool that is mentioned in the service manual.

I have learned after 40 years if I walk in a machine shop to pick up my heads and they say, hey are you going to be running adjustable rocker arms on these? My heads are done wrong, may be ruined but will for sure need more work and $$$$ to fix. Give them a valve stem height that you need as they are not smart enough to measure it before they start.

I might add, you cannot just cut the valve stems anymore to fix this. I called a bunch of valve companies last week and most do not allow more than .010 of a cut, Manley gen2 valves can be cut clear past the keeper grooves, SI allows about .050, but have heard they are not very good valves.

Good morning! I pulled the 906 heads off the shelf that I had in the garage. These are the numbers I found stamped on: 28161 and 21412. These were both stamped on the heads by the machine shop supposedly. Does anyone have any idea what these #'s mean? And I have no way to measure the thickness of the heads.

I would be worried, usually a job number or invoice number, would think both should have same# may not be the same set of heads, in other words each machined different. To measure, borrow or buy a cheap set of calipers, 10 bucks at harbor freight or ebay.

Those are not the numbers we're looking for on top of the heads between the rocker shaft pedestals is a number cast into the head....

Yes there are. No dumb questions is a little like everyone gets a trophy.

That said, the OP's questions are not dumb.

what he said ...