Anyone know rod length to stroke comparisons on other bikes? Like Norton
NickL when you used the Norton
crank in your BSA
, was that short rods, or how did it work?
How did you manage the various different angles, I can imagine the difficulties with cams? Even harder with BSA
than Triumph I would expect (1 cam as opposed to 2).
I admire you pioneers!
On the first conversion i was using a Norton
crank with Norton
rods+ t140 pistons in a 360 deg config. It vibrated badly at higher 5k+ rpm.
I tried a couple of factors 65 and 85%. the Norton
rods are shorter than the 6 inch a65 rods. I really cannot remember flywheel weights.
The second time around was a 68 deg offset with 6 inch special corrillo rods and t140 pistons, using 65 then 55% balance factors, the drive
from the motor out of corners was noticeably greater and with 55% as a factor the rpm was able to be extended to 7000 until retina detachment
or handlebars greater than 6 inch diameter forced gearchanges. 50% factor improved the higher end, it was like that for a while.
When i bought the long type srm barrel i used a 76 deg crank with 79mm B44 pistons this is where i used it most with a 50% factor and tried
lighter and heavier flywheels, heavier was better. That engine was run at 80.5mm bore with a 91mm stroke at one time and was very good,
it would rev easily to over 7.5k but better lap times were achieved with a 6800 rpm gearchange. The old crate would pull a house down.
There's a few japper owners here that went home with their tails between their legs after meetings. Beezers ain't supposed to go that fast,
was a comment i heard a few times. They didn't know the hours that went into it though.
After all the messing about though, i still think it would have been cheaper and easier to have just bought a 900 Weslake motor to start with!
I won't mention gearbox problems......... or cylinder head heating problems.....or valve guide wear etc etc.
We were lucky in as much as we knew Ivan Tighe well, he was a camshaft guru from way back and worked with the Repco team (Brabham)
He would build us up cams and was a keen supporter, sadly he's brown bread now. His son still runs the firm but not so interested.
Happy racing days, i still miss it.
When my brother had the shop here he did several offset conversions on various bikes including a 500 Notron twin which was bloody fast.
A few 76deg t140's with Norton
cranks etc etc. The 180 was a motor i didn't use much as i was not that happy with the feel of it but after
putting some extra weights on the cheeks it was much better, that was how it was when sold. Classic racing up here in Queensland died
a death in around 2002.
Using a Norton Commando
crank mean't that by making up different flywheels you could set the offset, Pete (my brother) had a lathe and
a later a mill and by making backing plates we could turn them up, he was the real mechanical engineer, i was just an apprentice but i made
good tea and chivied him up. He was a toolmaker and worked in the R+D division at Glaciers in the UK. So was a cluey old bugger.
The offset of 68 degs was arrived at based on piston speed at crank angle as well as the couple effect. Believe me, the offset motor was
a lot smoother at higher rpm and the later ones we did were not dynamically balanced either, just a pair of knife edges.