Head Gasket Recommendation

Kendog 170 · Monday at 5:52 AM

I have my 1968 340 with Eddy 60179 65cc heads.

I bought heads early while collecting parts for my restoration.

Well I had to bore the motor .020 to a 4.060 bore.

I then used the KB Hyper pistons (probably my 1st mistake) and 039 Felpro head gaskets so my compression is low. I can run it all day on 87gas.

Well, I’m getting ready to upgrade my cam and would like to bump my compression up a bit more. I know .020 gaskets don’t exist anymore. What gasket say around .028 will work with a 4.060 bore size? I see the Cometic's are 4.080 bore. Will that be an issue?

I’m my own worst enemy and don’t want to screw up.

Cometic C5622-027 Cometic MLS Head Gaskets | Summit Racing

mbaird · Monday at 7:03 AM

Will depend on your piston to head clearance . Minimum should be .036 piston to head .
And if I remember those early heads are open chamber you might be at more risk of detonation depending on what your squish vs compression ends up at .

Scody21 · Monday at 8:23 AM

.023 thick 3 layer is available from Cometic. Most likely they can do a 4.07 bore. This might be a custom order gasket, which the costs are not much different.

furrystump · Monday at 8:26 AM

You don’t want the gasket hanging into the cylinder, but .010 back each side I wouldn’t think would be an issue. Read up on surface finish if you go MLS. Needs to be smooth, but not crazy smooth. Don’t choose the solid copper gasket because it is the thinnest. I believe it is designed for o rings. Are your pistons at zero deck?

furrystump · Monday at 8:30 AM

What are you running for exhaust manifolds? Headers? Also, be very careful if you run cometics. The center rivet can get pinched between the block and the head. Not good, I had to remove the rivets.

Kendog 170 · Monday at 8:56 AM

Piston info.
KB KB243KTM.020 KB Performance Hyper Piston and Ring Kits | Summit Racing
Head info.
Edelbrock 60179 Edelbrock Performer RPM Cylinder Heads | Summit Racing

Kendog 170 · Monday at 8:58 AM

furrystump said:
What are you running for exhaust manifolds? Headers? Also, be very careful if you run cometics. The center rivet can get pinched between the block and the head. Not good, I had to remove the rivets.

Stock manifolds currently. Would like to add some headers eventually. What do you mean by center rivets? You mean rivets on the gaskets?

Professor Fate · Monday at 9:02 AM

Mr. Gasket 1121G Mr. Gasket Head Gaskets | Summit Racing

Free Shipping - Mr. Gasket Head Gaskets with qualifying orders of $125. Shop Head Gaskets at Summit Racing.

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They come as singles, so remember to order 2.

Kendog 170 · Monday at 9:08 AM

mbaird said:
Will depend on your piston to head clearance . Minimum should be .036 piston to head .
And if I remember those early heads are open chamber you might be at more risk of detonation depending on what your squish vs compression ends up at .

The heads are designed for the above deck 340 pistons.

Kendog 170 · Monday at 9:11 AM

Professor Fate said:
http://[URL]https://www.summitracing.com/parts/mrg-1121g
[/URL]
They come as singles, so remember to order 2.

So you don't think the bore size not matching isn't an issue?

Professor Fate · Monday at 9:29 AM

Kendog 170 said:
So you don't think the bore size not matching isn't an issue?

The stated 4.14 bore will reduce somewhat as the gasket compresses, I've got no actual numbers though.
Even at published dimensions, that leaves just a .040 gap; less than the typical Fel-Pro's 4.18-4.19 bore dimension.

furrystump · Monday at 9:56 AM

Kendog 170 said:
Stock manifolds currently. Would like to add some headers eventually. What do you mean by center rivets? You mean rivets on the gaskets?

Yes the rivets holding the layers of the steel gasket together. Have you run this combo already? If not, the 340 exhaust manifolds may not fit with that head. Where the drivers manifold goes around the steering shaft, the manifold may hit the head. Mine did, not a deal breaker. I bought a header flange and sandwiched the flange between the manifold and the head. That spaces the manifold out enough not to hit. You need longer hardware also. Also there can be fitment issues with a stock alternator that can usually be solved with longer belt. I wouldn’t grind on anything. I got it to work without grinding. That tab right there has a rivet in it.

RustyRatRod · Monday at 10:56 AM

Not bein smart here in the LEAST, but why not call Edelbrock and see what they recommend for their heads?

ch1ll · Monday at 11:41 AM

RustyRatRod said:
Not bein smart here in the LEAST, but why not call Edelbrock and see what they recommend for their heads?

RRR on point there.

I'd also call Cometic about what they recommend for gasket ID for a 4.06 bore.

Is all the do is make head gaskets?
They should know.

RustyRatRod · Monday at 11:43 AM

ch1ll said:
RRR on point there.

I'd also call Cometic about what they recommend for gasket ID for a 4.06 bore.

Is all the do is make head gaskets?
They should know.

They make other gaskets too, but head gaskets is their main gig. Like, you could hire a hooker to cook you some supper, but that ain't what she's best at.

broughj · Monday at 12:25 PM

furrystump said:
Yes the rivets holding the layers of the steel gasket together. Have you run this combo already? If not, the 340 exhaust manifolds may not fit with that head. Where the drivers manifold goes around the steering shaft, the manifold may hit the head. Mine did, not a deal breaker. I bought a header flange and sandwiched the flange between the manifold and the head. That spaces the manifold out enough not to hit. You need longer hardware also. Also there can be fitment issues with a stock alternator that can usually be solved with longer belt. I wouldn’t grind on anything. I got it to work without grinding. That tab right there has a rivet in it.

View attachment 1716531977

Any reason you can't cut the tab and rivet off the gasket. Seems like the dowels in the block would keep everything lined up and the head bolts would lock it all down.

furrystump · Monday at 1:09 PM

No, but I found it easier to use a small 3/8” air power belt sander to sand off the rivet head. Drilling the rivet just spins. The gasket is very hard steel. I used to laugh at those little belt sanders until I was told to cut spot welds with one. One of my favorite tools. Nut stripped? If you can put your finger tip on the bolt. That sander will sand the nut to nothing pretty quick.

Earlie A · Monday at 1:15 PM

broughj said:
Any reason you can't cut the tab and rivet off the gasket. Seems like the dowels in the block would keep everything lined up and the head bolts would lock it all down.

Put one side of the rivet in a vice or vice grips. Other side will drill off quite easily.

furrystump · Monday at 1:18 PM

RustyRatRod said:
Not bein smart here in the LEAST, but why not call Edelbrock and see what they recommend for their heads?

As to the exhaust manifold hitting? They will tell you they never heard of it before.

Kendog 170 · Monday at 1:33 PM

I'm driving the car now. I used a 1/4" header flange for the drivers side head. I will call cometic when I get a chance.

MOPAROFFICIAL · 2026-04-15T15:28:10-0500

At 65 cc's, with a 1008 head gasket, your compression should be decent, unless the cam bleeding off a ton.
We grind the ledge on the head to clear.

Head Gasket Recommendation

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