Cometic head gasket no decking Opinions

[bob123131]

Ok so before anyone tells me to stop being cheap and get it decked forget it this is going to be like an over night project, its my daily driver. I need new piston rings in one cylinder so im pulling the head replacing the piston and rings. Looked with fiberoptic lens thing and walls appear to still be fine. I have cometic head gasket and arp's. So basically i have a few questions would it be worth it to get the head decked and not the block or would that make things worse? Also what can i use without worring about damaging the block further to clean it. I dont believe its ever over heated bad. It has 92k miles and i have had it since 70k. This is going to happen no matter what anyone says and yes i realize i will ###### end up blowing it anyway so please any help that would decrease my chances would be greatly appreciated. I understand about copper sprays and all the pros and cons related to them extra just curious about prep work i can do? O yea and also is it ok to use wiesco piston rings with oem pistons?

 

[Splitpi]

Ok so before anyone tells me to stop being cheap and get it decked forget it this is going to be like an over night project, its my daily driver.

It sounds like you already have your mind made up. I would not go with an MLS head gasket if I'm not going to take the effort and make it an MLS grade surface to mount the gasket too. A 4 ply Mitsu OEM gasket would do the trick in most applications.

Do your best to ensure the entire block is flat and has no torque in it.

 

[spooled_u_1st]

You should at least check the head and block with a straight edge to see if there is anything is warped.

Also I use carb and chock cleaner to clean the gasket surfaces.

 

[96gstdsm]

Yeah I think it is very unlikely that it will seal correctly. I had a machined and decked block but with stock head not resurfaced(was supposed to be) and I had a Cometic head gasket. It was fine while breaking in engine but as soon as I revved it up a little bit, byebye headgasket. You really have to surface both surfaces for a good seal and not be worried about it going. If you don't want to resurface it, go with a mitsu composite head gasket. Don't be cheap and have to do it again right away.

 

[blcknspo0ln]

Why do you need a cometic in the first place? Unless you're mod profile is from 2002 and you're running a 42R, a cometic headgasket is unecessary. I won't preach about how well the OEM headgasket works, but to answer your question, I would not put a cometic on an uncut head/block. Even my cut head/block leaked when I had a cometic on there. If you're adamant about using a cometic, clean up the head and block surface with a razor blade as an extra preventative measure. Another overlooked procedure is to torque the head studs down in the correct sequence and in torque steps.

 

[bob123131]

Well yes i realize using the cometic is dumb problem is i have had sitting around for a year. Secondly yes i know how to torgue in sequence. Lastly i was going to go with a fel pro or other non multi layer steel, but i have heard they cant put up with the abuse. Maybe i will think about an oem, but still does anyone know of any other good techniques to clean up the block if i dont change my mind.

 

[96gstdsm]

Well yes i realize using the cometic is dumb problem is i have had sitting around for a year. Secondly yes i know how to torgue in sequence. Lastly i was going to go with a fel pro or other non multi layer steel, but i have heard they cant put up with the abuse. Maybe i will think about an oem, but still does anyone know of any other good techniques to clean up the block if i dont change my mind.

I have seen the composite oem head gasket stand up to 28 psi on a 50 trim turbo no problem. Seem pretty set on going with the Cometic so why even bother asking what people think? Everyone has stated that it is a bad idea and it will most likely cause you to tear the head off shortly and do another head gasket job.
The head and block have to be a mirror finish for a successful seal. Just cleaning it a little bit will not work.

 

[bob123131]

Im not an idiot as i said from the begining i know the slim chancs of this working and the reason i have been set on it is because i have one already. All i asked was if i decide to go with it does anyone know any good tips for getting the block super clean maybe using some kind of light air brush or something. Also many people run mls head gaskets without machining the surfaces and they end up find. I realize this is rare and i too would advise against it. But also getting my head decked and then checking my block for straightness and cleaning the hell out of it. Then using the arp lube and correctly torqueing them, might actually work. I'm Just looking for cleaning advice to give myself the best chances if i do decide to go this route. With my 38 percent leakdown in cylinder two i was alreayd pushing 288whp and i had a bad diaphram in my bov. I'm slightly nervous of pushing 330 to 350 whp with an oem on a daily basis at 20+psi.

 

[bob123131]

Nothing useful came of this thread you can just delete it mods.

 

[spooled_u_1st]

Use a lapping block and some 1000 grit.

 

[bob123131]

I have been under the understanding that all mls gaskets need this super flat smooth surface. I guess i dont know if thats true though? Would i have better chances with an oem mls gasket than a cometic?

 

[spooled_u_1st]

A mitsu MLS and a cometic MLS are basically made out of the same thing. You would be best off using a mitsu composite gasket.

 

[Splitpi]

I have been under the understanding that all mls gaskets need this super flat smooth surface. I guess i dont know if thats true though? Would i have better chances with an oem mls gasket than a cometic?

MLS is a rating, so changing manufacturer won't change the design specs to meet the rating. MLS is 50 RA or better (Roughness Average). Though most manufacturers prefer 30 RA or so as ideal. In other words, the average height of the bumbs (or peaks) on a surface as measured in micrometers (about as high as 50 dust particles stacked on a pin head). As said, ensure it is as flat as possible (no torque) and then wet sand to a shine with 1000 grit sand paper. Best of luck.

 

[squeak104]

I must be really lucky with my Cometic HG. I put it on when I rebuilt the motor. The head had been decked 7000 miles prior and the block hadn't been decked (162,000 miles old). My friend and I just cleaned the block and head real good and put it on with the ARPs. No copper sprays or anything. I've got 15,000 miles on the motor and no problems even after an overheating at 120 miles.

 

[96gstdsm]

I must be really lucky with my Cometic HG. I put it on when I rebuilt the motor. The head had been decked 7000 miles prior and the block hadn't been decked (162,000 miles old). My friend and I just cleaned the block and head real good and put it on with the ARPs. No copper sprays or anything. I've got 15,000 miles on the motor and no problems even after an overheating at 120 miles.

WOW that is good. Mine lasted like 200 miles haha. Sucked but oh well. I had the block decked too, but the head I guess was warped a little bit as I did not rebuild the head just the block at that time. After I had the head built and all was good, but went with a composite mitsu gasket this time to be extra safe. Those hold up real nice even with higher boost.

 

[mach4g63t]

I swapped heads after sending a piece of spark plug through an exhaust vavle on my old head. I got another head laying around and swapped it on. I cleaned the top of the block pretty well with 1000 grit sand paper so that it was smooth all the way around, but you could still see super fine imprints of the old gasket. I did the same for the base of the head, but did not get either of them decked. When I put the Cometic Gasket on it, I got low compression results from the start (120's). Is this because neither were decked and Cometic require such strict decking to seal properly?

Also, my car overheated this past weekend when my water pump belt came off and I didnt realize until it had already gotten really hot-- 250+. Well, it was still running fine and I thought I got lucky and skimmed by some disaster. Well, as I approached my 300 mile mark, I realized that I needed to retorque my new ARP headstuds as directed. So, I loosened them 1/4 a turn (if that) and did it all in sequence. Then I retorqued them all to 90ft/lbs (up from 80ft/lbs). After doing a compression test I have HORRID results. Something like 110-65-80-75 or something. My car stutters/detonates in the top end, runs pretty hot 210ish when driving, and stutters on the low end.

Did I ruin this gasket by not decking my head/block and retorquing it? Also, if I were to use a standard OEM Mitsubishi Head Gasket in it's place this weekend, would decking still be such a major issue if I took even more time to clean the surfaces, ie completely clean like a mirror?

 

[Splitpi]

I swapped heads after sending a piece of spark plug through an exhaust vavle on my old head. I got another head laying around and swapped it on. I cleaned the top of the block pretty well with 1000 grit sand paper so that it was smooth all the way around, but you could still see super fine imprints of the old gasket. I did the same for the base of the head, but did not get either of them decked. When I put the Cometic Gasket on it, I got low compression results from the start (120's). Is this because neither were decked and Cometic require such strict decking to seal properly?

Also, my car overheated this past weekend when my water pump belt came off and I didnt realize until it had already gotten really hot-- 250+. Well, it was still running fine and I thought I got lucky and skimmed by some disaster. Well, as I approached my 300 mile mark, I realized that I needed to retorque my new ARP headstuds as directed. So, I loosened them 1/4 a turn (if that) and did it all in sequence. Then I retorqued them all to 90ft/lbs (up from 80ft/lbs). After doing a compression test I have HORRID results. Something like 110-65-80-75 or something. My car stutters/detonates in the top end, runs pretty hot 210ish when driving, and stutters on the low end.

Did I ruin this gasket by not decking my head/block and retorquing it? Also, if I were to use a standard OEM Mitsubishi Head Gasket in it's place this weekend, would decking still be such a major issue if I took even more time to clean the surfaces, ie completely clean like a mirror?

Its not just about the smoothness, its the smoothness across the entire block and head faces. Hand sanding will not create a uniform smoothness. You need a very large sanding board (that is flat) and sand it evenly. This is difficult to do. While the surface must be smooth, it must be smooth and even in relation to the entire face (if that makes sense).

I "think" you lost compression because when you loosened your studs uniformly the gasket moved or unsealed and didn't reseal when you re compressed them. In my opinion I would just get a composite HG and ditch the MLS unless you wanted to spend the money and have the head and block machined to MLS standards. Which may not be a bad idea if you have the time and money considering your head/block may have warped from the overheating (possible, not necessarly happened though). Find a long straight edge and lay it across the block and head faces. The straight edge should rest evenly wit no dips. If it does then you have some warps or uneven spots.

 

[mach4g63t]

Where can I get a TRUE straight edge to find out? This is my DD, so I'm not really to interested in getting both ends machined flat right now. Was wondering, if no warpage occured, if I could slap on a composite gasket (my friend has one in his gasket kit for his new engine build that he doesn't need) and have it hold up fine/better than the cometic? I'm down 90 bucks for that ####er and am not going to put another one on without machine BOTH surfaces at a machine shop. Unfortunately, I don't have the time for that right now.

Also, to clear my confusion, a composite gasket is the same as a stock gasket, correct? It's not the paper gasket, but it's more of a metallic and thick?