cometic head gasket issue

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340twister

340twister

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minneapolis,MN
has any one else ever used these cometic head gaskets,I just had a 340 rebuilt and wanted to keep the com.ratio under 10:1 well after all the machining was done the trw 9.5:1 pistons were installed the sat .045 above the deck so they used .074 cometic's MLS(multi layer steel) and with my luck they leaked all over on the dyno. my ? is can this leak be fixed with a stop leak of somekind. if so what type would be the best suited for this app. ok so its a 70,340 .040 o/s trw forged,w/27lbs oil ring tension.eagle sir rods.all balanced int.and alinhoned,sqr decked.etc. cam is Custom by cam motion hyd.502/510 w/240-246 duration@50 inst.@106 deg. as for the heads there j castings w/205 int. 160 exh. REV valves,comp cam springs,ret.& locks controlled by pro magnum roller rockers @ smith bros.pushrods the head flowed [email protected] int. &[email protected] exh. pretty damb good for iron heads w/only minor intake bowl work... well the head cc.is 66.comp.ratio is 9.85:1 so to make a L.S.S. dyno #s 406 lbs.@5100 430hp @6200. but the heads leak what should i do.W/.040 gaskets comp.would be like 10.6:1 thats not pump gas friendly.
 
you shouldnt put anything on a cometic gasket except for the stuff mopar recomends...I take it you didnt use it?
Also you need a certain micro inch finish for cometic gaskets to seal
 
Mrmopartech said:
Order a gasket kit from SCE.These are copper head gaskets make to your spec,and thicknes,mrmopartech
Click to expand...


Dont you need to O-ring the block for copper gaskets ?
 
Don @ FBO used cometic head gaskets on the engine he built for me he said its normal for them to leak coolant awhile untill they have seen sufficiant heat. And true enough the more times I drove the car the better it got untill it doesn't leak.

But the type of finish on the heads and deck was importent as well
 
im sure the finish was proper the motor was built be lofgren auto specialties in cedar MN has built many many HEMIS & strokers. i guess time to put it in.and just run it with straight water untill i figure it out.
 
Once it gets hot a few times it'll stop leaking. Don says his own car leaks for the first weekend of racing after its been part and then its good my car leaked bad the first few hours and slowly got better each time untill it doesn't leak a drop now
 
71Duster said:
Don @ FBO used cometic head gaskets on the engine he built for me he said its normal for them to leak coolant awhile untill they have seen sufficiant heat. And true enough the more times I drove the car the better it got untill it doesn't leak.

But the type of finish on the heads and deck was importent as well
Click to expand...

Did you re-torque the head bolts after the intial heat cycle? I know you shouldn't have to with MLS, but seems odd they would leak initially, then reseal after time. I've always heard good things about Cometic.
 
If the finish was the right one (very smooth on block and head) they may seep slightly until they are heat cycled a few times. It's very common with them. I would also check to see if the surface finish for copper is the same *** MLS..I dont think they are. $.02
 
With that compression why wouldn't you just use a felpro for a fraction of the cost. Over the past few months I have heard several stories of the cometic gaskets leaking water. The only good thing that I have heard about them is that they will build them to your spec where felpro will not. I would almost bet that half the people using them did not special order them but bought what was on the shelf including myself as I thought I was going to need them right away. I would hate to think I had to put some type of block seal in my engine to seal a leaking head gasket and for someone to tell me to just drive it and it will seal off. What if it's leaking water into the cylinder? Now I am concerned if I should use them or not, but will be running close to 14.1 compression.
 
I use the Mr. Gasket MLS head gskets on my 340 and they leaked/seeped water for race weekend and sealed up fine. It is common for MLS gaskets to seep water for a bit. Adam, SCE now makes a copper head gasket that does not require O rings to seal. I had to go the the MLS because of my 14:1 compression. When I built the motor I ran the "standard" Mr. Gasket high performance head gasket and blew out all 8 cylinders after two races and and you want to talk about a water leak. I have season and a half on the MLS's now and are working flawlessly after the seeping stopped.
 
allright then im takin your word for it the moters goin in tomorrow.ill run w/just water untill i make sure it stops leaking.
 
I have never had a problem with the Cometics. They work great. The Fel Pros will blow after a while. Just spray the Cometics with copper spray, 3 light coats. Take em off and do that. They are reusable!
They are the best gasket out there, period!
 
Mine leaked on me. took the heads back off and sprayed copper spray on them. No leaks at all now.. :thumbup:
 
FYI

During installation use a couple of light coats of Permatex Coppercoat to ensure a good water seal.
If any water seepage should occur allow the engine to heat cycle a few times, most likely it will seal itself once the gaskets form to the head and deck. If it continues to seep add a can of Justice Brothers Radiator Pepper Based Sealer Part # RSL/2 .
 
I don't recommend coating the head gaskets with anything if the manufacturer does not recommend it. My Mr. Gasket MLS gaskets were supposed to be installed dry with no sealers, so that is what I did. I would rather have it seep a little liquid for a while than blow out a cylinder because it was not installed per manufacturers specs.
 
I guess my question would be "How did the piston end up .045 out of the hole in the first place?"

Shouldn't the calcualtions have been done 1st and the correct pistons ordered for the application?

As far as the seeping goes, just run it a few times up to temp and it'll stop, if it doesn't then the block and or head finish is not smooth enough but I doubt that's the issue.
 
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