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I had Triumph 650 motorcycles since 1965 and raced a Triton from 1969 until the late 1970s. Then I built the Seeley Commando 850. Nortons are much better than Triumphs. But I would never have believed that. I never believed in my Seeley 850 until I actually raced it. It is a really lovely ride. I have never ridden another bike which was so responsive And what is really amazing - it is quick enough to win races.
 
acotrel said:
The crank on the left is a Saint crank. They are cheap because nobody wants them.. The Saint was the unit construction Tiger 110. They were slower than the pre-unit Tiger 110 because of the lighter crank. They were designed for police use. The heavy crank gives better performance in the 650 motor. My mate bought a couple of those light cranks by mistake. So if you've got a one-piece heavy crank to swap, he might be interested.
Have you weighed a billet Nourish crank ? We bought one - it is a monster. The bike it ended up in won many historic championships. We used Puma crankcases.
The mass of the crank affects throttle response, but if you have the heavy crank spinning high and race-change up through a close rato gearbox, they are beautiful. Some guys don't know how to use the gearbox to go faster. All you do is peak the motor out, then back-off very slightly to take the pressure off the gears, then press the lever. You should only drop about 1500 revs at each up-change. Picking that up is never a problem. My problem with the Seeley 850 is to avoid over-revving. I always try to change up just before 7000 RPM, but usually see 7,500 on the counter.
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I love the light crank! I’d happily buy a NOS or light used one, or two, if anyone knows of any going unwanted?

I have a light crank ‘68 T120 as well as a heavy crank 1980 T140E.

Which crank is ‘better’ is a nonsensical argument. They are just different.

Performance of both bikes from A to B is as close to identical as I can detect.

But the T140 gets there with its low end torque, which really compliments the heavy crank. Whereas the T120 thrives on higher revs with its lightweight crank.

The T120 already has a 5 speed box and lighter alloy belt primary, which all helps its revvy nature. On the shelf I’ve got lightweight MAP billet squish pistons, Jim Schmidt long bushless Carrillo rods, 750 barrels and Spitfire race cams. This kit of parts is all chosen for its ability to support the revvy nature that’s supported by that lightweight crank. I know from experience that this will produce a LOT more go and a LOT more smiles (for ME at least).

Its like having two kids with different personalities and being asked which you love the most! Its not like that. I love both my Bonnies BECAUSE OF, not inspire of, their differences.
 
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acotrel said:
The crank on the left is a Saint crank. They are cheap because nobody wants them.. The Saint was the unit construction Tiger 110. They were slower than the pre-unit Tiger 110 because of the lighter crank. They were designed for police use.
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I’m dubious about your special Police crankshaft story. The Saint was just a Police single carburettor 650.

Triumph fitted a lighter crankshaft to 650s for one year in the 1960s, then went back to the heavier crankshaft.
 
Knactually , wassa gunna mention they might be a bit light for the average tosser ,

But if ya wanna get it to WIND UP quicker , the Lower Inertia helps .
With the lighter earlyer rods , and lighter lower 9.5 pistons . Plus the single row chains less drag, as are Ball races rather than Rollers .
PLUS They are less liable to split the cases , absorbing crank bow, rather than bending the bearing ( total ) and case, too .

Or course , you wont mind the lower lifespan thus reduced time between overhauls , IF YOUR QUICKER .

The LIGHT Crank is actually just a earlyer ( 66 / 67 ? ) one . Rather than type specific . Bar THRUXTON where its STD.

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On the dirt it means its crankier , and just liveable . Or you might say the throttle demands your attention more .
If you have exacting instantaeneous ambitions & abilities , you can ' back it into a corner ' and catch it to
get on the gas ( NOT Fully ! ) Pre Apex. But youll be on it . And right intoit outofit .
Probably unsuitable for people overly intrested in beer , as the reactions are slowed .

Tho a highly skilled rider with the heavier flywheel might get it drifting into & through the corner smoother ,
it wont have quite the same instataeneous connection to your wrist . Assumeing your running MONOBLOCKS .

Used Concentrics likely itll just splutter and bang & maybe toss you off ! :(:p

Tho a set of magneseum concentrics might be worth looking at ! :eek:
 
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These were designed for Cafe Racers with L O N G by-passes . WFO with youkky stacks the RAM AIR in the Ventuie presurises the float bowl through the vent Holes .
Sinking the Float. Somewhat .

And We all Known WHAT THAT MEANS .

It Goes Lean .
and hot.
and not enough cooling fuel.
and the rings pick up.
not to mention the skirts.
or the crowns
the next thing you know
Youve got holes in them .

THEREFORE , anywhere you can Hold It on the stop in top, and count past TEN , you need to do something about it. Like That. Looks like theyre available again,
If youre encumbered by Concentrics . ( Anuver Fing , is do A Flow test . Time fuel outta the pipes - or outta the bottom of the carbs , with the drain plugs .

Unfit for use


Ere now. wots this then .
 
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