Greg, nothing like yours, they have dykes rings and grooves around them and look to be lower compression.
Al.
Big bore head gasket
Identity of pistons?Anyone had an ideas on the identity of the pistons?
Greg Have you had the pistons off the rods and checked the underside for manufacturer's markings?
The wire circlips suggest to me that they aren't Honda clips, they look to me a lot like the ones that used to be supplied with my Asso pistons when I was buying those but I only ever heard of them being made in either 64mm or 64.25mm sizes. Asso pistons would normally have a four digit ref. number cast into the inside of the skirt. Greg,
Have a look at ebay number 122740606034, this is a cb72 fitted with a Hepolite big bore kit that originally consisted of pistons, rings, pins, liners and gaskets. Looks like there are no barrels and liners with it. As DJM says on the underside of the pistons there will be AE cast in, I think that means Allied Engineering, aka Hepolite. Note the amount that has been machined out of the top case so that the liner spigot will go into it. This is the same conversion that I have on a set of barrels that I have on the shelf ( may get to use them one day). A mate of mine converted a cb72 for racing back in 1968 using said barrels and had oil leaks from the fins, we never found if it was bad machining, what we suspected was it was caused by was using cb72 barrels and there not being enough meat to machine out, you could see the liner between the fins in a couple of places or that the liner to barrel bore was not correct clearance. Long time ago and the memory is fuzzy. Al. Big Bore KitsYes, I raced a 347cc CB77 years ago and was involved in quite few conversions. I think there was slightly more material in the CB77 cylinders than in the CB72 casting.
When putting the big liners into the 247cc block they almost always broke through at the base of the finning so the liner was visible from the outside, hardly conducive to good even cooling or oil tightness. By contrast the CB77 cylinders were usually OK although I did have an isolated case where the CB77 cylinder broke though too. In the end we cured the problem with the CB72 blocks by using slightly thinner sleeves but I can't remember the dimensions we used. If contemplating a big bore conversion today I would always suggest starting with a CB77 block, the later die cast ones have a bigger 'air tunnel' between the cylinders so may offer better cooling than the common sand castings. I went round this at the start of this year when building my motor for the season. I got these people to make me one with a 66 mm bore http://www.ebay.co.uk/itm/HONDA-SUPERHA ... 25b5cdfbb8 for my race bike which has 64mm Asso pistons. I did see Hap Jones composite gaskets for sale on eBay too recently.
My barrel is a 250 barrel which has been resleeved, no breaking through of fins. I have a spare 305 barrel which has just been bored to take a 64 mm piston - the liners are terribly thin.
copper gasketHi Charles
I have also gone down this route. They (Lani) would make to any size and I was very impressed with the service though I have not fitted yet. What I was not sure about was the need to use any kind of sealant with copper gaskets? People seem to use silicone sealants with water cooled engines but I am unsure about air cooled? You can buy a copper spray sealant that claims to deal with any small imperfections but unsure if necessary.
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