Competition head identification

rgregory · Post by **rgregory** » Sun Oct 23, 2011 11:19 am

Greetings,

I have a strange sand cast G80CS short stroke head, the same pattern as the 1960 head without recess on the top around the spark plug.

However the plug hole is offset slightly and there is more meat around the valve the plug cavity in the chamber.

All my bikes have die cast heads (thin smooth fins etc).

I suspect this is an aftermarket item, casting number is 026057JS.

Any ideas of its origin ?

Cheers,

Rob

Don Madden · Post by **Don Madden** » Sun Oct 23, 2011 6:18 pm

My 60-up CS head is smooth & the plug is slightly offset to clear the valves. I got it as a do-it-yourself 1963, (I guess, as it does not have date code but is plunger pump type). The touring & CS heads seem to be the same other than the comp having a larger 1-3/8 inlet port. Valves are the same. JSL recently offered newly made heads & cylinders but I've not seen them. Cheers, Don.

rgregory · Post by **rgregory** » Sun Oct 23, 2011 10:03 pm

Hi Don,

I have had 1961 and 1965 G80CS bikes, all having die cast heads.

On the top around the spark plug the area they are scolloped so that leaking oil pools up and bakes/smokes as all British bikes are meant to.

This head is flat right out to the fins as I have once seen on a 1960 G80TCS, also in photos of an ABSAF head. Consequently the plug needs a deep counterbore.

The sand cast alloy seems to be a good heat treated high tensile material and has been finished very well. The only way you would know it is sand cast is by the thicker fins or by looking between them.

Cheers,

Rob