86mm,86.5 or 87mm ?

[DreadedFist]

Some (all?) of JUN's engine internals are made by Cosworth and then doubled in price.

[gtrjon]

yea i am going to go with a tomei hg and see how it goes.

[4jo3]

there is no standard size because 87mm is the standard when going aftermarket

piston size ... headgasket size
86...87
86.5...87
87...88
87.5...88

i have seen cometic gaskets hold on the upwards of 50psi. and reliable. if you use a mls gasket you shud use a copper spray or ANY headgasket will leak. Also prep your surfaces. Plane the block and head. All problems from the cometic head gasket that i have seen have been improper installation

[Zacho]

All problems from the cometic head gasket that i have seen have been improper installation

You are talking about improper installation but cometics site says not to use any additional sealer.

If you look deep into the issue, cometic head gaskets require a certain RA finish to seal properly. I think it is 50. I am not saying they are a bad gasket, but due to the complications involved there are many other hassle free options.

[4jo3]

i know about the extra sealant but the problem is without it coolant leaks out the because its a mls. i dunno ... that wat my engine builder does so that is wat i do. i have had no issues yet... knock on wood.

[rbs14]

im running 87mm Mahle pistons and a 87 mm cosworth gasket !!! no problem yet ...

[Dragon Humper]

You really should run the gasket that fits the bore the closest. If you have an 87mm bore, run an 87mm gasket. If you run a gasket that is larger than the bore you run the risk of carbon collecting in the gap and running into det. issues. The carbon can collect enough to the point that it will act as a glow plug and light off the mixture before you want it to. This is especially important for you guys that insist on running a thicker gasket to lower compression (which you should never do.......tsk, tsk).



Jon.

[cobrAA]

what's the oem thickness btw?

[gtrjon]

i am pretty sure its 1.2mm

[Black BNR32]

Turbo BMW guys have headgasket problems due to close bore spacing and the popularity of using a thick MLS gasket to lower compression. They shoot for RA 20 and highly stress proper surface prep. Sealants are personal preference and copper o-rings are becoming popular too.

[jdms13rhd]

On almost every eng I built I run a 87 Metal gasket on a 86.5 bore. Never had any pre det from that. Maybe on a old engine running crap gas, eventually that could be a possibility. I have also always ran with a 1.2 on 91/94 gas without problems with a light deck. Not big ass power on the builds tho so it was justified.

[cobrAA]

Apexi does sell 86mm head gasket. guess apexi will be my best bet.

I just don't justify the need to bore my engine for no reason.

[cobrAA]

and how much should I expect to pay to bore to 87mm ? What else do i need to take into account beside piston and head gasket?

[4jo3]

make sure they use a torque plate... as for a price ... i have some what of a clue but not really sure so i dont wanna say

[jdms13rhd]

and how much should I expect to pay to bore to 87mm ? What else do i need to take into account beside piston and head gasket?

Your right, if the cyl is in excellent shape, there really is no need to over bore. Ive only been in that situation once tho. Take the block to a reputable builder/machinist and get an expert opinion before you go and order up a STD size piston. Remember, a bore doesnt cost much. Around $25 a hole is the regular. Nissan has good cylinders out of the box. All the rb30's I've had I could still see the factory cross hatch from the machining process. Looks can be deceivin tho, so get that expert opinion. Once i looked at a block and figured it was perfect. suSre enough, it was far from it.

I pay $25 a hole or $20 i forget. Should be within that area, maybe give a lil if your building a new relationship with a builder.