[Rocky Rotella]

Based on parts manual information, Pontiac's "thin" No. 9792995 head gasket measures .028 to .033-inch thick. However, many non-Pontiac-printed sources show its compressed thickness at .022-inch thick.

Has anyone actually verified the compressed thickness of this gasket?

[unruhjonny]

I know there are normally a couple of these on eBay;
I normally am watching them because I would love to buy a reasonably priced OE quality "thin" head gasket set.

Maybe an eBay seller can measure their gasket(s) to give you measurements.

[steve25]

The gaskets Motion performance of LI New York use to supply with there hop up kit went down to .022" but I forget who made them

[unruhjonny]

oh!?

I would be very interested in such a gasket!

Just none of the copper cometic - requiring a re-torque stuff please.

[dataway]

Squish sure would be easier to tweak if we had a selection of thicknesses ... also not a fan of the cometic copper, or their prices. Used their copper stuff for some vintage race bikes for a year ... did not work out well for me, although their other stuff was good ... just stupid expensive.

Come to think of it, why is the OEM thickness so hard to replicate? I notice that number crosses over to a Fel-Pro gasket that is .041-.048 ... so not even close.

[unruhjonny]

Originally Posted by dataway

Come to think of it, why is the OEM thickness so hard to replicate? I notice that number crosses over to a Fel-Pro gasket that is .041-.048 ... so not even close.

my understand has been that the replacement gaskets are made a smidge thicker because the presumption is that the deck and head surfaces are going to be milled - so adding gasket thickness compensates for this...

unless you're trying to do a pure stock type build - then you're options are very few.

I did buy a whole bunch of vintage multi-layer metal headgaskets a long time ago;
I cannot recall if any are OE, but my suspicion is that they are all aftermarket...

[Firebob]

Seems like I used a pair old Victor-Reinz OE MLS gaskets a few years ago. I seem to remember they compressed to .026. Doesn't help much though because I don't recall what the part number was.

[unruhjonny]

I just went and looked;
I don't have a ton, but I thought I had more than one set of composite steel gaskets...
iirc that was what the OE stuff was...

[unruhjonny]

do these orange-ish ones look like the VR ones you used?



I cannot with clarity recall why I was buying spare sets of head gaskets, but it may have been because i was swapping heads and reusing intake gaskets and found buying local was exponentially more expesive than ebay.

[dmac]

Cometic can make MLS head gaskets almost any bore/thickness you want- this should be pretty representative of the price because this one is a made to order item. .012 thick, 4,200 bore, $228, don't know if that is for single or pair, probably single. And a question- If the cylinder bore is 4.185, and round, not like the 350 bores, what is the smallest bore gasket I could use? Is this 4.200 too small?


https://www.cometic.com/i-24769293-p...bore-each.html

[unruhjonny]

that's for a single;
and not that I am suggesting that thier gaskets are anything but top quailty;
The price for a pair ($456) makes NOS gaskets look really attractive.

[tom s]

When using factory NOS gaskets you need to pay attention where the valve relief areas are.389 421s have them in diff location than 400 428 455s.Gaskets you buy from felpro have them made to work with either valve angle.Tom

[grandam1979]

Cometics are 189.00 a set not per gasket just got a set.

[Schurkey]

Originally Posted by dmac

Cometic can make MLS head gaskets almost any bore/thickness you want- this should be pretty representative of the price because this one is a made to order item. .012 thick, 4,200 bore, $228, don't know if that is for single or pair, probably single.

Originally Posted by grandam1979

Cometics are 189.00 a set not per gasket just got a set.

Are the $189 gaskets shelf-stock, or custom?

First Guess: $189 for normally-stocked gaskets, $400+ for custom-made.

[grandam1979]

https://butlerperformance.com/i-2462...d%2Bgaskets%2B

[grandam1979]

https://butlerperformance.com/search.html?q=Cometic+

[dmac]

Originally Posted by unruhjonny

that's for a single;
and not that I am suggesting that thier gaskets are anything but top quailty;
The price for a pair ($456) makes NOS gaskets look really attractive.

Getting the right thickness of a head gasket could be worth $500. The local machinist didn't have experience with pontiac parts. I asked him to zero deck the block. When I picked it up, it was .030 in the hole. He said that a thinner gasket would take care of it and said it saved me some money. My fault possibly for telling him I was on a tight budget. Now. that it is all assembled, rather than disassembling it, decking it, and reassembling it, getting a custom gasket looks better to me. He was basing his 'savings' on the cost of Chevy gaskets, which are available cheap no matter what you need. I knew upfront that he wasn't familiar with pontiac parts. He builds race engines for local racers, but hadn't seen a pontiac in his 20+ years in the same location. Small town an hour to anyone who even knows Pontiacs at all, and two hours, or more the well known Pontiac builders.

[scott70]

I wanted a certain thickness head gasket (.036) and cometic has a good selection and also wanted a 4.20 hole for my 4.185 bore. I ordered them through jegs and if I remember right it was a couple of weeks before I got them so it makes me think the cometic company made them to order. Looking at the butler link..the 4.20 gasket looks like it's recommended for up to a 421 block. The 4.22 gasket is for the 455. Doing prior research I thought the 4.20 was ok for a 4.185 bore?

[Cliff R]

It's good to see folks paying close attention to quench distance these days. It can be a deal breaker with good success and building yourself a "turd" that runs hot, overheats and doesn't make good power on pump gas.

The problem I see is that most of these old blocks need decked and squared up. So I pay more attention to selecting pistons that end up around .015-.018" in the holes at TDC vs worrying about head gasket thickness. Not having to cut a ton of material from the top of the block is a good thing, and Felpro head gaskets are right where we want them for thickness on a zero decked block, problems solved.

As far as the OP's question, I've torn down a couple of these engines that had thin factory head gaskets on them, but never took the time to measure them.......Cliff

[mechanic17]

It's an old thread, but I dug up a set of sealed ones from GM. No date that I could find. I opened one up because I'm going to be using it. It's a sandwich type gasket, two metal shims with whatever the "paper" material is in between. .033" as per the spec noted above. Measured with a vernier. Whether these can compress down to .022", I don't know how to find that out.

So I'm just using an even .030 in my calculations for SCR. I'm about .015" in the hole so I'm happy. Valve to piston clearance won't be an issue with the cams I use, though I will check as always