86mm bore Head Gasket

[downforce22]

Hey guys,

I am building a 3.1L m20 with 89.6 mm crank and 86mm bore. Last night the engine was getting assembled and we were looking at the headgasket clearance. It is very tight! Perhaps it was the Victor Reinz gasket, but after crushing, there does not look to be much clearance from the piston at TDC.

M54b30 crank
86mm bore
86 mm JE pistons from Top End Perforance (Ca) with stock type piston shaping
135mm H beam rods

I read everywhere that stock headgasket will work but the clearance is very close. I talked to a buddy using the Ross pistons with the same bore and he used the Goetza gasket. His thought were the tapered piston woudl not interfere but my mechanic does not like the victor gasket. Does the Goetze have a larger gasket bore?
Any insight would be greatly appreciated.


Here are two crappy pictures:

[nando]

Regardless of the bore i wouldn't use the VR gasket either way.

Wrong time to ask but why did you choose flat top pistons?

[CarsSuck]

Yeah, stock 885 pistons protrude pretty far into the combustion chamber, those appear to be dished quite a bit. Get some "turbo" pistons by mistake or are you gonna rock an eta head?

[SkiFree]

Stock replacement gaskets (VR and/or Goetze) are rated to 85mm. Once you go with an 86mm bore you need to go MLS.

And to echo what's been said, you must be going turbo, becausethose aren't 885 offset dish style.

[nando]

It depends on the piston. Stock works fine with stock piston shape or chamfers like MM.

[downforce22]

Stock replacement gaskets (VR and/or Goetze) are rated to 85mm. Once you go with an 86mm bore you need to go MLS.

And to echo what's been said, you must be going turbo, becausethose aren't 885 offset dish style.

You are right on the turbo. MM uses stock gaskets aside from enlarged coolant passages from what I have seen. Almost all 3.1 L m20s I have seen use stock head gaskets. From Digger's car to Diegom6's car.

http://www.e30tech.com/forum/showthread.php?t=72630

I'm looking at the MLS gasket, but I would rather have a traditional gasket in case of failure. I would rather have the headgasket pop rather than have a steel gasket hold and crack the head or something.

[digger]

i use the stock gasket with MM rally pistons but it overhangs the bore which is not good for a turbo engine IMO, as it exposes more of the gasket to the heat and pressure of combustion which cant be a good thing. the MM piston is chamfered and thats how it clears but you get some bad pockets by doing this which i doubt the ability to allow properer burning of the mixture that resides there. i would get a MLS

[downforce22]

i use the stock gasket with MM rally pistons but it overhangs the bore which is not good for a turbo engine IMO, as it exposes more of the gasket to the heat and pressure of combustion which cant be a good thing. the MM piston is chamfered and thats how it clears but you get some bad pockets by doing this which i doubt the ability to allow properer burning of the mixture that resides there. i would get a MLS

Thanks Digger,

I spoke to Steve from Top End Performance and he said basically the same thing. Really nice to talk to someone on the phone who was willing to discuss and answer questions and support their product. :thumbsup: I would recommend to anyone else considering custom pistons to talk to Top End Performance. I read about that on the MM 3200 rally engines being chamfered and overhanging into the bore, hence the reason I wasn't worries about using a stock gasket.

Thanks for the input. With that comment, is there a difference between the Cometic MLS vs the Ottoco MLS gaskets?

[EyExR]

I second what you said about Steve at Top End. Very informative and easy to talk to. I also bought some 86mm pistons from him.

I would get the Cometic MLS if I was you. Just be aware that the alignment studs NEED to be on and it will be TIGHT. Just be sure everything is super clean.

I could actually feel a slight difference in power vs. the OEM gasket...

[SkiFree]

I'm not after your displacement in general, just your bore size (though there are many many examples of 3.1's running mls, not limited to the internets). Stock head gaskets accommodate up to 1mm oversize on the bore, meaning the stock bore was 84mm, then it'll accept up to an 85mm bore. Beyond that bore size you'll start running into issues where the head gasket encroaches into open bore space.

Edit: looks like I took a little too long with the response.