Ever see this issue with Cometic head gaskets??


Senior Member
Hey guys, Took my heads off due to oil leakage between the layers of copper on the gaskets and noticed all of them had this issue. please look at pic, the copper seperated at several locations near every bore. I have champion heads, arp studs, torqued to 75 ft lbs. The gaskets are for the proper bore size and a sprayed a copper coating before installing. I am running E85.. Any suggestions will be appreciated...


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Yes, Ive encountered that issue. I smeared high temp RTV between the layers at the oil hole areas. Been like that since 2016. No leaks since.
Ralph, post a better pic of the torn area.
It looks like the inner part has not been clamped down to the block.
Did you check the fit on the heads and the block?
GM Chuck, Dowel pins are in block. I took the angle pic so you can zoom in and see the broken seam , if I take a pic from top you see nothing due how small the cut is. Also, I have 5 dyno pulls and about 500 miles on this E85 setup, I am surprised how much carbon is on the piston tops and how different they look from one another.


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You're talking about the fire ring separating from the rest of the gasket?
IMHO, it looks like a fail do to detonation unequal fuel distribution.
I have talked to several shops about copperkote and RTV silicone used with Cometic gaskets. Some vendors/ shops remove the rivets and put a light coating of silicone around the water and oil holes between the gasket layers. Some spray a light film of Copperkote on both outer surfaces of the gaskets before installation, some let it dry, some install them wet.
According to my several conversations with both the sales and engineering staff at Cometic:
Copperkote acts as a lubricant and allows the gasket to move and squirm as cylinder pressures rise. Silicone between the layers or between the gasket and head and deck surfaces, causes uneven clamp loading around the combustion chambers. Both issues will lead to failure.
These improper installation issues along with improper machining practices including:
Not installing the MLS gaskets on FRESHLY machined head AND deck surfaces.

Not machining BOTH surfaces with a CBN diamond tooled head an deck MILL to the PROPER RA finish before installation.

Installing Cometic gaskets on an engine PREVIOUSLY RUN with other types of gaskets without remachining. That is because the head and deck surfaces will have been stressed differently with other types of gaskets, and that causes surface irregularities that will impede proper sealing with the MLS gaskets.
My freshly machined/ built engine in the car when I purchased it with less than 15 miles on it, kicked out both headgaskets immediatly! Those installed, were composition gaskets, and the block and heads were milled on a rotary broach, and that's "old timey" equipment!
Even late model "stock" engines using MLS gaskets, call for all head and deck machining to be done with a CBM tooled mill, and installed dry.
Pic of my block previously milled (not BHJ ed) on an "old timey" broach, and after one pass at .001"cut on my CBN milling machine. You can easily see the irregularities of the broach cuts, and also how far off the decks were from correct "blueprint" orientation.
Follow the manufacturers instructions, look at the pic, and draw your own conclusions.....


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Thanks the reply. 15 years ago RPE built me a motor and I used Cometic head gaskets coated with copper. That motor ran for 10 years without issue. This time around I got the same heads but different block by another vendor and I have issues. I have the heads at a shop right now, Leeper is getting my injectors in the mail, and I am going with the RJC gasket kit. I am very curious if any issues are found with the injectors and heads. I will update you guys on it.
According to Cometic, anything less than following their instructions explicitly, is "getting lucky." Or not....
Or just not making enough H.P. to matter.
Guys are making 1000 HP with those gaskets, others are having failures at 350...
If you call Cometic, and send pics, they will tell you what I just did.
I know I'm not smarter than them, so I called and talked to their tech dept before purchasing their product for the first time. I took their advice, and machined as per their instructions, and have never had a failure with their headgaskets. I build blower, turbo, high compression, and Prochargered engines, car, boat and Harley, with no failures. Mebbie I'm just lucky.
But then again, their Buick V-6 rocker gaskets are too hard to seal to the roughness of the head casting and don't fit correctly. The gasket O.D. is too large to fit inside of the rocker cover flange, and the alignment tabs are also too wide. We have discussed that too. I'll see what happens with that...
Well guys, my 15 year old ported GN1 heads need a full rebuild. Head guys stated my guides and seats are shot and so are my Ferrrea valves :(
The heads are do not need to be cut. The valves are labeled GN1600 and GN1900 but I cannot find them online. If they are to pricey I will go with the Manley valves, do you guys know if summit sells the right valves for the champion heads??
The heads need to be skin cut. At least.
Cometics work great, but like all MLS gaskets, they need an absolutely flat surface. They need to be cut only with a CBN diamond tooled head and deck MILL. You can set those machines to remove a half thousandths or less. Take that cut first and see what they both look like.
Brian at Dakota parts Wharehouse sells Ferrea at 877-235-2832 is an expert, and he can fix you up. Tell him that TUFENUF TIMM from Phoenix sent you. They also have other premium parts too. We have been using them since they opened a way long time ago. I hope he's not stuck in a snowbank! They are Rapid City, SD. Good people. Say hi to Brian and Julie for me.
Excellent advice from timinator. Following cometic’s instruction is the best way to ensure success. Beyond that, using a gasket bore that’s larger than your cylinder bore will move the gasket away from the combustion heat in the chamber. Being conservative on timing is another key ingredient to keeping the seal. With E85 you can make lots of power while still being conservative. With E85 you can also push the heads right off the block without ever seeing a hint of knock.
BeataV8, I am done with E85. Range anxiety and looking for a gas station got old quick, not to mention condensation issues. I am going back to alky. Also it is very possible my bloack was not decked for cometics so I bought RJC head gasket kit. Heads are being redone (Worn valves and guides) and Chuck is checking my 120's.
One of my racer friends/customers ran E85 for nearly a year, and discovered after chasing numerous tuning issues that the alky percentage varied quite a bit. I think I remember him saying he saw it from about 60-65% to near 90%. He went to straight methanol and never looked back.
I think a hydrometer could be your new best friend.
Is that the aftermarket feedback system that uses the GM flex fuel sender to tell the ECU what % of alky is in the fuel?
I've heard of it but never saw one. Who makes it? How does it work in our application?