Twin-engined Triumph Drag bike - USA blog

[Tony oily bike]

Found this interesting blog about a period twin-engined Triumph drag bike............  envious? moi!!!   



http://www.jockeyjournal.com/forum/showthread.php?t=87454&showall=1

[Manky Monkey]

Isn't that a beautiful thing. 

[Tony oily bike]

Bike looks luverleeeeee 

Suspect the Triumph gearbox might go bang though with all that oomph, personally I'd do for a Bewley 2 speed or AMC Norton.

[Manky Monkey]

Norton seems to be the box of choice for these double motored bikes. Is that because they have the right gear ratios or because they're super heavy duty? Are those home made carb manifolds?

[Tony oily bike]

The AMC Norton boxes are strong old beasties, and ratios can always be changed. Current price for such a box is around the £180 -£230 mark.

The manifold looks like its probably a normal splayed-head head with a 'rubber' (the reinforced/braided type) coupling to the carb, so they can be made to any length, have a degree of mechanical damping, doesn't conduct heat, and can be easily replaced.

[Manky Monkey]

I've owned a couple of unit construction Triumphs, but never a pre unit one, (seperate engine & gearbox, rather than gearbox integral in the engine casings, for our younger readers). Presumably the box is chain driven from the engine? So changing the sprocket size would change all the gear ratios in one go?

[hunter]

And the cylinder heads off those motors,Would have originally been off the unit motor.9 Stud.

[Tony oily bike]

If you've had unit triumphs, and have taken the primary drive cover off, there's a chain that joins the engine to the clutch/gearbox, exactly the same as a pre-unit.

The photo shows the primary chain from the front engine (sprocket on the end of the crank) going to the second engine, and another primary chain going from the second engine to the clutch. (most modern bikes have this transfer carried out by gears. Harley's still run a primary drive, a belt in many cases)
The final drive sprocket is hidden just behind the clutch, and this takes power from the gearbox output shaft to the rear wheel (as per modern machery)



"So changing the sprocket size would change all the gear ratios in one go?"

Kinda - There be various options:

The engine sprocket can be changed to make all the gears either shorter or taller (so quicker acceleration and less top speed, or, less acceleration and higher top speed).

Changing the rear wheel sprocket, or the gearbox sprocket will have the same effect.


The other option is changing cogs within the gearbox.
Lets say you make first gear first gear shorter (but keep all the others the same), the machine would pull away quicker, but then you'd have a bit of a gap between first or second. The most difficult part of acceleration is from a standstill, so this could have benefits.
You could on the other hand only change top gear to make it taller, so you'd accelerate as normal, but when you hit top, it would initially feel a bit boggy (kinda like going from 2nd to 4th), but once the revs got going, you'd have a higher top speed (assuming wind drag etc aren't the dominant factor).

4 speed Triumph  boxes can be converted to 5 speed, so there can be an advantage there.

For circuit racers, its not un common to fit a close-ratio gearbox, which is great for keeping the engine in the power band / torque curve on circuits. Fine tuning between circuits can be done using a sprocket change.

Land speed record vehicles have a very tall first gear which is why they're pushed up to say 40ph. Helps take the load off the clutch too.

If you follow F1 (yawnnnnnn), the car's ratios will be set for the track they're at, so the car's will just be hitting the rev limiter at max speed before hitting the brakes, how ever with DRS( drag reduction system which makes the rear wing more slippery) the car can go a little bit quicker, as long as the gearing/rev limiter will allow it. It's all a matter of compromise.

[spanners]

i notice its still on magneto ignition with 2 mags  a bet its fun keeping them accurately ,timed,  with points wear an all

[Tony oily bike]

i notice its still on magneto ignition with 2 mags  a bet its fun keeping them accurately ,timed,  with points wear an all

There's always a weee bit of compromise if the cam-ring isn't perfect, but it would be a fair bet that if the bike was used for top-notch racing, they'd check the timing before each run.
If it's the more clubman stuff, guess it would be set up in the workshop, and then "if it ain't broke, don't fix it" !!

Bear in mind, the bike would be wramed up a bit, thrashed for 10 -12 seconds, and then ridden back. Say 6 -12 runs at an event, that's around, what, 15 -20 minutes of use.

Look like they're Lucas K2FC (C for competition) mags running auto advance/retard (as opposed to manually adjusted - now that would be fun to adjust!!)

[spanners]

ther,s a couple of that type magneto up at wonderland they were a pretty common fitment on MOD twin stuff

[Tony oily bike]

ther,s a couple of that type magneto up at wonderland they were a pretty common fitment on MOD twin stuff

K2F or K2FC ??

[spanners]

ther,s a couple of that type magneto up at wonderland they were a pretty common fitment on MOD twin stuff

K2F or K2FC ??

i,ll have to check when i go over  bloody mags are turning up all over the place and i even found some in a box under what used to be dads bed,