MDchanic

Quick question (I hope):

I read somewhere (I can't recall where) that the factory spec. for head thickness, as measured from the head gasket surface to the lifter pivot surface (which is also the valve cover sealing surface) is 2.200" to 2.220", and, judging by my notes, I actually measured similar thicknesses myself in the past (2.157" and 2.156").

Measuring some heads now, using the same surfaces, I come up with 3.862" for a stock head, and 3.840" and 3.810" for milled heads.

Am I going crazy?
Where did I get the 2.200" spec from?
And how did I measure it?
I can't find any surfaces that are anywhere near that dimension to measure now.

- Eric

coppercutlass

You measure from the head bolt boss to the deck surface of the head. The avg. According to ref. guides here is 2.200 to 2.220. I recently had to measure this on the heads 67cutlassfreak did for me.

MDchanic

Wait a minute.

I need to measure from the head bolt boss by the exhaust manifold side.

I was measuring from the head bolt boss on the intake side.

Thanks!

- Eric

Smitty275

LOL. Don't ya just love it when your own notes throw ya a curve ball.

The 2.220 is print dimension over the short bolt holes on the exhaust side.

MDchanic

Hey, Smitty, here's a real curveball, in part from my notes:

I bought a pair of redone #7 heads a few years ago at a flea market.
They were $75 and clearly had new valves, seats, guides, springs, rockers, bridges, and freeze plugs.

Over the winter (while my wife was out), I dragged them out and did a quick job of cc'ing them on the kitchen counter. I got 60cc for one and 63cc for the other.

This week I pulled one head off the car because I had a leaky exhaust valve (figured I'd pull both, but have only done one so far). I checked and cc'd all of the heads again, outside in the sun on a level bench, using denatured alcohol and a piece of glass as a cover (very flat).

Now I've got 56cc on one head and 61cc on the other (the stock head measured 64cc), measured in different cylinders, and using two different syringes, just to make sure it all matched.

I don't know how I got 60cc when the number was 56cc, but somehow I did.

The 56cc head is about 2.144" at the short head bolt holes, and overall measures out to have been cut 0.040" to 0.050".

So now I've got a problem.
Even figuring a 0.043" Fel-Pro head gasket, I'm still at 10.5:1 with the piston 0.020" in the hole, which I believe is too high.
The stock heads measured out to 10.22:1, and I needed a little bit of Octane Supreme with my 93 octane to keep it happy.

I could drop a buck and a half on a Cometic 0.070" gasket and bring it to 10.19, but that's a lot of money to spend so I can save money.

It all seems strange, because I was certain of my measurements over the winter, and stock heads should cc out to being a bit over their nominal 64cc, and this one (a #5) was right on at 64, so I'm almost wondering whether I somehow did something simple wrong, but I've repeated every measurement, and they're all right (made them all with the same spark plug, too).

Have you got any good suggestions or corrections for me? I'm a bit befuddled by the whole thing right now.
I'm leaning a bit toward accepting 10.5:1 on one side and 9.9:1 on the other right now, but maybe there's a better solution.

- Eric

ps: after some web searching, it looks like some turbo 4-cylinder guys have successfully doubled head gaskets. This wouldn't have occurred to me, but, since I am NOT racing, and NOT running a turbo, I wonder whether a pair of Fel-Pros would survive...

coppercutlass

I got some number #8s here you can have just set up shipping through Fastenal and I can crate em for ya . What are your piston cc's ? Maybe 67 cutlass freak can do a quick valve job for ya on them for a small fee. They would need a valve job since I removed the valves and did not mark them to their corresponsinf chamber. I got some big block 2.0 valves I could have him install. I think shipping was under 50 bucks through Fastenal down to the lower east coast.

MDchanic

I've got two pairs of #8s.

I'd really like to get both of these to work, but if necessary I can just replace the one with a Fel-Pro gasket and get 9.9:1 with a presumed 10.2:1 on the other side (if it matches the one I took off), and be close enough.

Thanks anyway, though.

- Eric

coppercutlass

Yeah I got two pairs two lol. Currently im using them to hold up a shelf with all my paint and body material. What if you polish up the chambers to gain some cc's ?

MDchanic

Yeah - guess I could.

Haven't used the old die grinder in a while anyway.

I wonder how much I'd have to remove to add 4cc to the volume?
Could I get away with just removing the casting texture?

- Eric

Smitty275

How much carbon was in the head when you re-CC'd it? Just taking off the surface texture will net about a CC.
I'm surprised to see you had two heads off the same engine that were a full 3cc off. They are usually right on the money to give or take 1. Then to pull it off and see it that much smaller? Something is not right. I'd pull the other one and CC it too. Maybe the other one also shrunk and by the same amount. Almost putting the mountain before the mole hill on this one. Let us know what you find when you get the other head off and CC them together.

MDchanic

I actually did that: cc'd it in one cylinder once before cleaning it, just to see whether the carbon made much of a difference, then cleaned them all thoroughly and did it again more carefully.

There was what I would say was a normal amount of carbon for a good-running engine in there - maybe ten to twenty thousandths thick.


I've only pulled one head off of my running engine - the head that I knew had a bad exhaust valve.
It has a volume of 64cc.
I would've pulled the other, but my wife had other plans, and then it started to rain...

The other pair of rebuilt heads that I was planning to use are the ones that have been milled to different degrees.
I agree that that's pretty weird, and I didn't even think to check for it initially.

Why they're different, I'll never know - the guy had the heads and a cast iron intake for sale, and was really annoyed that I didn't take the intake. He claimed that it had "just gone a few blocks" (bulls__t) before it had a bottom-end problem and wasn't worth the trouble at that point. Judging by the carbon in the chambers, it'd probably gone a few thousand miles, but not much more - they were darned clean, and there was no surface rust on the outsides, as you would get from having had the car out in the weather for a season.

I put everything aside for a few hours this afternoon, and in between rain showers, I de-carboned the piston crowns and cleaned things up. Tomorrow, I'll probably pull the other head and have a look at it.

I couldn't find any of the stones that I know I have for my die grinder, so tomorrow I'll go out and buy a few, and probably start smoothing the casting texture on the insides of the CCs of the small head. By my estimate, if I make it pretty darned smooth, I should come close to 4cc, and then I MAW smooth a few bits of the intake tracts...

- Eric