Cosmetic 85.5mm bore MLS on stock block

onefast2gdsm · Mar 14, 2011

I can't find a solid answer anywhere. The smallest bore cometic makes headgaskets for is 85.5mm. I have a stock block and want a MLS gasket but don't have the money in my budget for the OEM one. Will this cometic one work? I read the OEM is for stock and .20 over bore.

1990AWD · Mar 14, 2011

If you don't want to spend the money on an MLS, the Mitsu composite has been proven to hold up really good.

What are your goals?

onefast2gdsm · Mar 14, 2011

I already bought the cosmetic from Jnz it was a lot cheaper than OEM. Reason I ask is the receipt says .20 over. I need to know if it will work with stock bore

My goals are about 350 whp and after I get there, then 425.

BigBeans · Mar 14, 2011

It will work with the bore (although it might have a very slight effect on compression), but i'm not sure about the surface of an unmachined block.

MLS gaskets require a surface finish of 50 RA or finer (numerically lower) and i don't know how smooth the stock finish is. MLS gaskets don't fill in the imperfections in the surface, so if it's not smooth enough, it won't seal.

onefast2gdsm · Mar 14, 2011

I talked to the shop that's doing the work on my head and he said as long as the car was never overheated it should be fine. He's making sire the head has a mirror finish though

BigBeans · Mar 14, 2011

onefast2gdsm said:
I talked to the shop that's doing the work on my head and he said as long as the car was never overheated it should be fine. He's making sire the head has a mirror finish though

The surface finish on the head isn't going to help it seal to the block, and overheating would warp the head but have no effect on the block finish.

You need to find out how smooth the OEM block surface is before you can safely run that gasket.

Maybe someone here can provide that info, but if not you need to send a PM to someone like bogusSVO and see if they can shed a little light for you.

onefast2gdsm · Mar 14, 2011

Once I get the block all clean I will be running my hand over it, if it gets caught on anything I will be using the composite gasket. I have the around headstuds as well. Do you recommend using a razor or rolocs or fine sandpaper to clean up the block surface

BigBeans · Mar 14, 2011

A razor or sandpaper will scratch and score the surface. do not use either of those things, use a rag and do it chemically with something like engine degreaser or brake cleaner.

Make aure you get it spotless, and it is recommended to install a Cometic MLS dry, no copper spray.

onefast2gdsm · Mar 14, 2011

Thanks for that info, I was going to use copper to disapate heat but ill stay away from it. I am planning on spraying the hell out of the block with brake clean to make it spotless incase there are leaks. do I have to be careful of the oil and coolant ports on the block and if so should I just use masking tape to cover them

gringo72884 · Mar 14, 2011

Honestly I would return the cometic HG and buy an OEM composite HG or save up and by an OEM MLS. The cometics have been known to fail pretty consistently even with a properly decked block and head. I have personally ran the OEM MLS HG at 28+ psi with no problems. When I used the OEM MLS HG I just used brake cleaner, a razor blade and terry clothes to get the block and head surfaces as clean as possible. Then I did a even coat of copper spray on both surfaces and the seal was perfect with the headstuds properly torqued. The proper torque and sequencing of the headstuds is the #1 most important factor to consider when looking for a perfect head to block seal. Just because you want to use a MLS HG doesn't mean you "have to" have the head and block decked. Just make sure the head hasn't had any warping and that the block is as clean as possible. Goodluck

BigBeans · Mar 14, 2011

gringo72884 said:
Honestly I would return the cometic HG and buy an OEM composite HG or save up and by an OEM MLS. The cometics have been known to fail pretty consistently even with a properly decked block and head. I have personally ran the OEM MLS HG at 28+ psi with no problems. When I used the OEM MLS HG I just used brake cleaner, a razor blade and terry clothes to get the block and head surfaces as clean as possible. Then I did a even coat of copper spray on both surfaces and the seal was perfect with the headstuds properly torqued. The proper torque and sequencing of the headstuds is the #1 most important factor to consider when looking for a perfect head to block seal. Just because you want to use a MLS HG doesn't mean you "have to" have the head and block decked. Just make sure the head hasn't had any warping and that the block is as clean as possible. Goodluck

I agree that an OEM composite would be better in your application OP.

Only thing i disagree with here is using a razor blade, because a small slip could damage the surface.

As for copper spray, some people use it and others don't. Cometic recommends dry installation, so i wouldn't do it with their gaskets.

onefast2gdsm · Mar 14, 2011

Thanks man, my brother has built at least 20 dsms and always used cometic gaskets, he recommended it to me as well. Ill take his word for it and he told me he never had a problem even if the head and block were never sent to the machine shop. If it fails I can get a composite for super cheap. I will be using the arps and torquing them in the correct sequence with three passes, one at 30 ft lbs, then 60, then 90.

If I notice something out of the ordinary I will not use the gasket. The car wont be daily driven and if it fails it fails. I know that's not great logic but I might as well give it a go, and learn from mistakes.

gringo72884 · Mar 14, 2011

Razor blades are fine, just keep a steady hand, take your time and only use it on areas where there is built up old HG material. As for the installation of your cometic HG, I would strongly urge using copper spray to help create a perfect seal. Together with the proper torquing of your headstuds, copper spray will not do anything but help you, trust me. There's no downside to using copper spray as long as your torque you headstuds properly (including heat cycling them btw).

onefast2gdsm · Mar 15, 2011

What do u mean heat cycling

ilco187 · Mar 15, 2011

onefast2gdsm said:
What do u mean heat cycling

Its were you warm the car to normal operating temp and recheck the torque.

BigBeans · Mar 15, 2011

ilco187 said:
Its were you warm the car to normal operating temp and recheck the torque.

After the car has cooled, yes.

I like to run the car several times (letting it fully cool in between) and then retorque the studs

Talipse96 · Mar 15, 2011

Heat cycling has to do with how many times the engine gets up to opperating temperature and then when shut off, cools back to ambient temperature. ARP has a certian number of times the engine should cycle before going back in and re tourqing the head studs.

onefast2gdsm · Mar 15, 2011

Thanks guys. So do you think the 85.5 mm gasket will be fine on stock bore or no? Ill be calling Jnz this morning to talk to paul about it, but I'd like to see others opinions.

gringo72884 · Mar 15, 2011

you will be fine with that bore size

LiquidX · Mar 15, 2011

gringo72884 said:
Razor blades are fine, just keep a steady hand, take your time and only use it on areas where there is built up old HG material.

If there was any resurfacing done then you do not want to use a blade solely for the fact of slipping or accidentally causing a nick in the sealing surface. Then again, if it was resurfaced then there wouldn't be anything on it.

onefast2gdsm said:
Thanks guys. So do you think the 85.5 mm gasket will be fine on stock bore or no? Ill be calling Jnz this morning to talk to paul about it, but I'd like to see others opinions.

85.5 is completely fine to use on the stock bore. The OEM MLS only comes in the 0.02 over size.

onefast2gdsm · Mar 15, 2011

LiQUiDx said:
If there was any resurfacing done then you do not want to use a blade solely for the fact of slipping or accidentally causing a nick in the sealing surface. Then again, if it was resurfaced then there wouldn't be anything on it.

85.5 is completely fine to use on the stock bore. The OEM MLS only comes in the 0.02 over size.

Ok cool. I talked to Justin about it at dms and he said I should be fine without decking the block but he said just to make sure its clean and no imperfections.

And I think I saw your car at dms yesterday.

LiquidX · Mar 15, 2011

onefast2gdsm said:
Ok cool. I talked to Justin about it at dms and he said I should be fine without decking the block but he said just to make sure its clean and no imperfections.

And I think I saw your car at dms yesterday.

Yeah, it's most likely still sitting outside :cry:

My pallet of parts are sitting to the right of the garage door by the fridge.

I'll be heading down there next week or later this week to drop off a couple more parts.

onefast2gdsm · Mar 15, 2011

Yeah I saw a lot of parts where I backed up my Jeep into the garage. I'm hoping everything goes together smoothly I got my buddy mike(turbo4awd) helping me out so its done quick and right . He's also porting everything out for me.

onefast2gdsm · Mar 28, 2011

Just an update- I got the head back today and there's two scratches about an inch in length and one that's about a half inch. They resurfaced the head and that's how I received it. They said it was there when i dropped it off and there's no possible way the head could've gotten gouged. The shop told me it shouldn't effect anything being its not by the combustion chamber...

BigBeans · Mar 28, 2011

onefast2gdsm said:
Just an update- I got the head back today and there's two scratches about an inch in length and one that's about a half inch. They resurfaced the head and that's how I received it. They said it was there when i dropped it off and there's no possible way the head could've gotten gouged. The shop told me it shouldn't effect anything being its not by the combustion chamber...

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