TT Special Go Even Better? Drive Ratio?

[ttguy]

my first post! anyway thanks guys for any help you can share. Im ripping apart my 1966 tt i got. Going to do a whole engine rebuild and was wondering any suggestion on what i can do to it while im in there. So far i was going to go new pistons but 9to1(what piston company you like) and standard bore and keep jomo cams and do a dynamic balance on the crank. I was also thinking of getting map rods? they are pricey i noticed though? What drive ratio do you suggest? 21 inside sprocket i was thinking. So yeah any suggestions would be greatly appreciated. I want to make it real peppy but reilable and it'd be nice to have some top end to? i want it all i guess but 750 i want to beat a 750

 

[sikatri]

Great project! Looking forward to reading about your progress. Hopefully the crew in the classic section will chime in here as well. Perhaps @Rudie will answer those questions or a couple of others with a bit more experience.

 

[Rudie]

new pistons
standard bore
i want to beat a 750

Until you examine and measure the existing bores, you will not know for certain what piston diameter (standard or oversize for a rebore) the engine requires or even whether a new cylinder block is required - the spigots that extend below the bores into the crankcase are part of the block casting, are prone to cracking.

73 on twins built as 750 are not particularly fast unless things like the timing side main bearing and the cam timing are changed. However, there are 750 block and pistons kits to fit 650's - look up Aerco/Velocette and Morgo - if your bike's engine needs a rebore and/or new block, might not be much price difference to a 750 kit.

If you do fit a 750 kit, a "7 plate" clutch kit likely will be advisable - look up again Aerco/Velocette and Norman Hyde.

map rods? they are pricey

New rods - steel or alloy - will always be better than unknown alloy ones, especially ones that could be nearly sixty years old ...

New rods might be "pricey" but they cost a lot less than an engine rebuild because of a broken old rod ...

suggestions

New oil pump. The latest version with four valves and "oval ports":-


... pumps a little more oil than the Morgo with four valves.

Electrics? Standard TT are "Energy Transfer" AC, no battery, rectifier, regulator, hopeless 6V lights.

Any later (more powerful ) Lucas alternator will fit inside the primary chaincase, inexpensive combined regulator/rectifiers are available, standard 650 parts can be used to add a battery carrier under the seat?