I’m looking at head gaskets for my 64 3.8L engine. I called Cometic, and for an 87mm bore, they have two types; the CFM (composite perforated galvanized steel core, with sealing rings around the bore) in either .043" or .059" thickness, and the MLS (multi-layer steel) in incremental thickness from .030" to .140". Their tech support said the MLS gaskets are embossed around the water jackets to provide a better seal than the CFM-type gaskets.
One of the usual suppliers sells composite head gaskets, but they are short on specifications. They say it’s .059" thick, but compresses to .055". “We sell a million of them, so just buy it, you won’t be sorry.” Not really confidence-building.
Another of the suppliers sells a composite, but not a Cometic. It’s .059" thick.
I’ve done the CR measurements and calc, and thinner is better for me. The .015" tin gasket puts me at 9:1, so the composite will drop my CR just a tad. I definitely want a composite, I’m just canvassing all my astute and knowledgeable friends at Jag-Lovers: Did you use a Cometic CFM or MLS, or a 3rd-party composite?
I used the MLS one because my head and block have been shaved and I needed one thicker than stock. It has worked great for a decade. if the thin original tin one is good for your car, why not use it? If the MLS one could seal then that should too. Just use that permatex copper spray a gasket on both sides to ensure it seals well around the coolant ports. I wouldn’t want to sacrifice compression if I didn’t have to. Note, prior to finding out the need for the thicker gasket, my car went back together 8 years prior with the thin tin one and nary a leak with the permatex spray on it. What’s your car # BTW? Mine is 880342
Car # is 881596. Engine is correct but not original. Now replacing the head from yet another car.
I’ve had the car 30+ years, but it always pinged. I installed a Pertronix dizzy, and it still pinged. Long story, but now I’m replacing the head. I don’t mind backing slightly away from 9:1 as long as I can use full throttle!
I can get a Cometic MLS at .030", or a Cometic CFM at .043", or a “Cometic-like” composite at .059". Prices vary. Maybe I’m splitting hairs, and I should just go with “cheapest”, because I doubt I could notice the performance difference.
I can say that the sealing rings on the MLS gasket I got were superb. Someone (can’t recall who) recently posted photos of the Cometic composite gasket and they weren’t thrilled at all with the quality. I’d say use the MLS if you want to spend the extra money on added assurance, or just use the standard old Payen or whatever they’re selling as stock nowadays.
I used the .059 on shaved head and block and ended up with compression at 155…runs fine…higher would be nice however not worth the trouble at this point
Dave your pinging probably doesn’t have much to do with the c.r. of your engine. If you are using premium fuel 9:1 compression shouldn’t be the cause. I suspect you are getting too much advance in your distributor at mid range - say 2400 to 3700 or so, where pinging commonly occurs. It would be nice to get that checked out and corrected if necessary. I believe you can find services on line for people with old distributor machines and parts that can correct your problems. It may also be that your needle is too lean, as a lean condition will cause pinging. I feel a UM needle (stock needle), particularly if you are burning a fuel with ethanol, is too lean. You might try a UE needle or my favorite, a UP which is fatter mid range where you need it. These are available from Burlen’s in England with a week more or less wait for shipping, or Joe Curto in the US https://burlen.co.uk/
Thanks everyone. I’ve decided to purchase the MLS Cometic gasket, in size .030" (for 87mm bore), which is what Cometic tech support recommended. I will ask them about re-torqueing the head, too.
Once I get the car running, I’ll definitely pursue the needles and dizzy advance. For now, I’ll make sure my valve timing is spot-on when I install and tension the new timing chains.
One last thing: I ordered a machinist straight-edge 2’ in length, and once I have the deck of the block totally clean, I’ll use the straight-edge to confirm (as much as possible) that the block deck and flat and true. Then, I can get back to re-assembly.
One suggestion, since your head is off, seal up the through holes for the down studs in front. Oil gets flung all over inside the timing gear area. When it lands on the exposed stud hole it collects and gradually seeps down the stud threads. you can sort of seal this after the fact by gluing the stud in place. However with this MLS gasket, it will seep down the hole and work it’s way out between the layers of the gasket. But if you cap off the holes (the way Coventry should have and didn’t) then you’ll save yourself a lot of headache later.
Amen. I’d clean it thoroughly to remove all oil residue and mix up a batch of JB Weld and fill the holes from the top with the studs in place. Put a light coating of grease on the head of the stud and threads going in the head to keep the JB weld from sticking to the stud, ou may need to remove it in the future.
I tried Loctite, I tried Permatex, I tried The Right Stuff on the threads. Maybe I was just unlucky but the only thing that completely stopped the seepage was plugging the holes from above.
That’ll probably help with a solid gasket. With the stacked one, it seeped between the layers. There was no way to get enough goop onto the threads to completely seal it. Capping off the holes prevents it from being a problem.
When I want to seal a stud, I put a LOT of Loctite both in the hole, and on the stud. Never had a problem. BTW - HarborFreight has great thread lockers, for next to no cost - $1/bottle. It’s not sold by mail, so you have to go into the store to get it. I always buy about a dozen reds and a dozen blues. I’ve found it works every bit as well as the name-brand stuff, for a tiny fraction of the cost.