cometic head gasket oil leak ?

[fekbmax]

i have heard and seen cometic's leak water before but im wondering if anyone ever experienced an oil leak situation ?
i have a leak and its frustrating. 100% sure its not valve covers or intake manifold. i was sure before but went ahead and took it all apart and re done the intake and valve cover gaskets.
bone dry at the china walls, at the intake to head surfaces, all around valve cover gaskets is bone dry, no oil to be found anywhere.
now where the heads meet the block along the lower edge i keep having oil appear there and eventually get a slight trail running down the outside of the block. no issues with water leaking at all.
could it be the head and deck surfaces are not prepped and smooth enough for the cometic's and some oil is getting by on the way to the heads ?
im plane frustrated and about to rip it all apart and go back to the tried and true 1020's and see if that solves the issue.. so be it if i loose a tiny bit of compression.
im wide open to any suggestions. is it possible a few heat cycles will seal it ? so far the engine has only ran for about one minute .   

[jayb]

There is the oil hole going up through the deck of the block, transfering oil to the heads.  I suppose it is possible that it is leaking there, and not water anywhere, but I've never seen that with Cometics.  I have seen water leaks with Cometics, and now I give them a good coat of Copper Coat before installation, and that seems to have solved that problem.  Cometics are reuseable, so if you take it apart try cleaning up the gasket and spraying it with Copper Coat, two coats on each side.  Also look at the block and head around that oil passage to see if there are any nicks or scratches that could be contributing to the problem.  Good luck solving the problem Keith!

[CaptCobrajet]

I've seen this happen.  If the deck or the head is not smooth enough, the oil can make it's way along the grooves in the flycut, between the cylinders, and leak externally.  It can also put oil in the water the same way.  The oil pressure will send oil to places the water will not.  Just for grins, look in the radiator for oil.  That would confirm 100%.  I'd bet your leak is from the deck feed if the surface(s) is/are not smooth.

[fekbmax]

Thanks guys, i really believe that's whats happining. Hell it even looks like a small bit of oil is pushing up around one of the lower center head studs. I believe  the block wasn't surfaced properly for the cometic's . All i can do at this point is use some kinda sealer or just go with tried and true 1020's . I'm just over 13.5/1 with the .032 cometic's so i believe the 1020's would hold up for a little while.

[Falcon67]

As noted, block and head deck surface is key for Cometic seal. On the recent 351C I made sure to tell the shop that I was using Cometic and to surface appropriately.  Shiny more or less LOL.  They sealed up dry, no issues, no leaks.  Takes 20th century equipment to do that, not sure you can get there with a old Storm Vulcan, maybe with the right head and cutters.

[fekbmax]

Got it all taken apart last night. By the time i got the gasket off it was hard to tell but i really believe that's the issue. Kuntz did the heads and they seem to be almost a mirror finish so I'm sure they are OK. Block looks good and all but def not a mirror finish. Right now I'm not  up for putting it all back and tearing it apart again 6 times till sunday so I'm just gonna toss some 1020's or 5790G's on with a good coat of copper coat and call it done. I'm tired of wearing the dam bolts out taking stuff apart over and over again. I just wanna go do some testing..

[scott foxwell]

Unless the surfaces are fresh machined, I automatically use Coppercoat on Cometics. But I will also say that Cometics are not always the best choice especially on stock type rebuilds. They're expensive for one thing and in 99% of cases a stock type composite gasket will be more than adequate and seal "rebuilt" surfaces a lot better. JMO

[Falcon67]

I used them specifically because 1) race engine not street 2) aluminum heads on cast iron block 3 ) thin and still seal for keeping as much compression in the motor as possible.  Anything street/strip kind of stuff especially iron heads on iron block would get Felpro Blue performance items, with a regular rebuild finish on the deck surfaces.  The surfaces still have to be tongue lickin' clean for any gasket.  And I mean clean, like clean and wear gloves during gasket/head install.

[scott foxwell]

Flatness is more of an issue than surface finish with Cometics. I've used composite gaskets on blower engines. It's all in the prep.

[Falcon67]

Flat for sure but it's more than that -  at least with under .040 cometic and aluminum heads/ iron blocks that have been run through a normal perp by a shop that doesn't know better or the racer didn't tell the shop what gasket.  Standard finish like you get from an old Storm-Vulcan block machine set for conventional gasket surface will leak after it runs a bit because the aluminum walks it across the divots in the finish.  Pretty much any MLS gasket will act like that.  Devil is in the details. 

"A surface finish of 50 RA (roughness average) or finer, is recommended for a proper gasket seal. Anything rougher may conflict with the gasket design."

"Fel-Pro® surface-finish recommends a finish of 60 to 100 Ra (roughness average) for cast iron cylinder heads and blocks, and 50 to 60 Ra for aluminum. Fel-Pro uses proprietary head gasket coatings and facing materials designed to fill in minor surface imperfections and allow for improved sealing on imperfect surfaces found in the repair environment. OEM MLS gaskets work well on new, flat, clean castings, since they require a very smooth surface finish, usually 20-30 Ra or less. Fel-Pro’s PermaTorque® MLS head gaskets use a specialized coating that accommodates finishes as rough as 60 Ra. Surface flatness is equally important to surface finish, so always check components to ensure they are not warped or distorted. To maintain constant contact between the head gasket and mating surfaces, all deck surfaces must start out flat and remain flat after being torqued to specification. A good rule for flatness is that surface flatness, measured in thousandths of an inch, should never exceed the number of cylinders on each bank across the length of the block."