500 downdraught head

by worntorn » Mon Apr 16, 2012 2:05 pm

"I would not say that the 650 head came from the Domiracer, since the Domiracer did not appear in public with that head until several months after the Manxman was running with it, it is anybody's guess about the history of the Norton down-draught twin head.beng "

Interesting the comments made about the original Domiracer. Does this mean that the 500 racer had 650 pistons also :?:

The reason I ask is that my 8 fin 500 barrel is over bored & fitted with 600/650 pistons :!:

The cylinder head on the 62' and later 88ss and 650ss were the identical part number and interchangeable.

If your 88 cylinders would have to be .080, or 2mm overbored to accept standard 650 pistons, which means they might be sleeved because if you go that much over on a 88 cylinder then in some spots it is either going to be as thin as newspaper or cut right through to the outside.

John Gregory, who built a very fast model 88 road racer in the 1960s used to turn 600 pistons undersize to fit a model 88 oversize, so he could have nice light domed pistons for the racer., his words.

Ken Hayes was to ride the bike for Gregory at Daytona in 1968 and in qualifying turned in some very fast times around 140 mph or more, again the words of Gregory and Hayes, but they blew the engine before the race and threw it down the track, the bike was finished. It had a custom alloy cylinder and an Atlas head on it and ran a Manx four speed cluster. The crank was welded together into one piece and I remember Gregory saying he used an automotive steel connecting rod in it out of some Buick.

Hayes recently dug up a photo of the bike and said he would get a copy to me, if he does I will add it here.....

Thanks for your infro.
Seems I will have take a close look at the liner to determine if I am in any danger of some engine blow –up.