Head gasket bore to piston size?

[Liam 589]

Can I use a 87mm bore gasket with 87mm bore pistons or will this cause issues?

I have HKS 87mm pistons that I was going to use the HKS 1.2mm (87.5mm bore) gasket with but the gasket has now been discontinued. Am looking at getting the apexi 1.5mm gasket that has an 87mm bore as opposed to the 87.5mm that the HKS bore is.

 

[campbellju]

I can't comment on the apexi but the HKS gasket is a little too big from personal and others experience. Most people go for cosworth gaskets nowadays. The 87mm cossie gasket at 87mm should be one.

 

[PobodY]

What the idea that the HKS gasket would squash slightly to fit the bore size correctly... but it doesn't because it's MLS?

 

[Liam 589]

I managed to get in touch with apexi who advised me that there gasket is 88mm bore diameter designed for use with a 87mm pistons. The site I bought the gasket from advertised it as 87mm gasket not stating that 87mm is the piston bore for it to be used with and not the actual bore diameter of the gasket. My concern of using an 87mm bore gasket with 87mm bore engine is the possibility that the gasket could very slightly over hang in the combustion chamber causing a hot spot and consequently resulting in det. I may be totally wrong but just wanted to make double sure so I don't end up melting pistons.

 

[campbellju]

The same is also true for too large a gasket as it leaves 2 exposed corners on the head and block as hot spots.

The engine I'm currently re-building failed at the HG/Block using an HKS gasket and pistons. It's a known issue from a few of us on here.

Remember, the gaskets aren't rubber, when compressed they don't squish out everywhere.

Cosworth have a range of thickness and bores for the SR20, you can buy exactly what you need. The only disadvantage is the holes for the dowels need dremeling out slightly to fit the gtir block. I picked up mine for £115 on Ebay.

 

[The Doc]

87mm cosworth gasket will be fine with 87mm bore as long as it is ground correctly in the dowl area to fit the gtir 54c block.

 

[fubar andy]

Blast from the past...

Is there any issues using a 87mm Cosworth head gasket with 86.5mm bore?

 

[The Doc]

No

 

[fubar andy]

8)

 

[Empty Pockets]

But is that not the exact same principle as why people say not to use the hks gasket, can't understand why using a piston that is .5mm smaller than the gasket bore is a no no with hks, & not Cosworth, the sizes are the same ?

 

[Empty Pockets]

Also, i understand the theory of sharp edges, exposed edges being hot spots, prone to det, but logically thinking, i can't understand why this is a problem on Pulsars and not other cars, say the evo, norris etc have no problems using 87mm gasket with 86mm pistons etc, so why is it a problem on ours, and only with a certain brand of gasket, as the dimensions will be the same between brands, and both motors would leave an exposed edge around the bore ?

 

[Empty Pockets]

Thinking about it more, was the problem with the hks gaskets more to do with people not realising they were actually 87.5mm, and using 86mm pistons with them or something, as anything with up to a 1mm difference doesn't seem to be a problem on other motors, and it's not like we run anywhere near as much power, or boost generally ?

 

[red reading]

..........

 

[Empty Pockets]

Doh, totally overlooked the block material difference, but assumed there was some sort of factory lining, and not just bare ally.... That's clears up why the evo boys have no problems with oversize gaskets then...... lol

 

[red reading]

Block material and design is another reason why fitting liners is such a pig.....but there are ways that it can be done.