Big bore head gasket

GregMcN · Post by **GregMcN** » Fri Sep 29, 2017 6:41 am

Hi G

Do bore-tech do different sizes, they only seem to be listing a 66mm gasket for their 65mm kit. The guy in the US that does copper gaskets says he can do any size needed.

Greg

G-Man · Post by **G-Man** » Fri Sep 29, 2017 1:26 pm

You're right. They only do gaskets for their own system. If you have a laser cutter or a piercing saw and a piece of copper sheet - you can have any size you want..... :-)

G

GregMcN wrote:Hi G

Do bore-tech do different sizes, they only seem to be listing a 66mm gasket for their 65mm kit. The guy in the US that does copper gaskets says he can do any size needed.

Greg

GregMcN · Post by **GregMcN** » Tue Oct 03, 2017 3:52 pm

Can anyone identify the pistons. I measure the bore as 63.75mm.

AlanW · Post by **AlanW** » Tue Oct 03, 2017 4:42 pm

Hi Greg,
I am in the process of building a cb77 and the head gasket in the kit I bought off ebay for £35 measures 63mm.
Al.

GregMcN · Post by **GregMcN** » Tue Oct 03, 2017 5:02 pm

Thanks Alan

I also have a standard gasket and as you say it is about 63mm which is for a 60mm bore. So the implication is for a standard type gasket you need it about 3mm bigger than the bore but I assume this allows for the metal bit squashing down. For copper gaskets I have been told you only need to allow about 0.03" which is about 0.75mm but I do not know if this is correct?

Greg

AlanW · Post by **AlanW** » Wed Oct 04, 2017 4:38 am

Greg,
I have been looking at gaskets and this is what I have found, I have 2 new cb72 sets, 1 measures 55.7 the other 57.0. I also measured 2 used cb72 and they are 55,7 and 55.6, there is no way of telling if the used ones are original but it gives food for thought, does the center dia reduce when crushed?
I also have a big bore kit with Hepolite pistons 64mm and new and old gaskets, 1 new copper is 65.5, and 1 new standard one at 63.9, I have 2 of the old standard type 65.0 and 65.8, both used. I also have a used copper one that's home made but good, it measures 65.5 to 65.7.
It's about as clear as mud what's safe to use, sorry I can't be of more help.
Al.

GregMcN · Post by **GregMcN** » Wed Oct 04, 2017 7:52 am

Al

Thanks as you say as clear as mud, let's hope someone else on the forum can provide some guidance.
On another note do your hepolite pistons look like the ones in my photos ... I assume not as I am measuring mine as a bit smaller but have not identified them yet.

Greg