Short stroke conrods??

madass140 · Oct 26, 2014

Did the short stroke engines use different conrods??

lcrken · Oct 26, 2014

Yes. They were a steel conrod, with 6.200" center-center, as opposed to the stock 5.875" rods. The small end was also sized for the larger .750" pin in the short stroke pistons, with a .751" small end bushing, instead of the .9885" in the standard rod.

There are some pictures of them here on the forum, somewhere.

Ken

madass140 · Oct 26, 2014

Thanks for that Ken.

lcrken · Oct 26, 2014

Pictures of the rods here.

short-stroke-750-build-t5490-30.html?hilit=short%20stroke%20rods#p53019

Ken

Hobot · Oct 26, 2014

What flywheels were short strokes issued?

lcrken · Oct 26, 2014

Standard Commando iron flywheels. Cranks halves were same forgings as 850, but machined for the shorter stroke.

Ken

acotrel · Oct 26, 2014

Why would you short stroke a Norton engine when you could simply make a better head for a Triumph engine ? Has it got something to do with AHRMA rules for historic racing classes ? Is the Nourish engine banned ?

lcrken · Oct 27, 2014

acotrel said:
Why would you short stroke a Norton engine when you could simply make a better head for a Triumph engine ? Has it got something to do with AHRMA rules for historic racing classes ? Is the Nourish engine banned ?

Because you can make more horsepower with a short stroke 750 than with a long stroke 750. And the parts were originally available from the factory, and now from aftermarket suppliers, as opposed to building your own "better" head for a Triumph. Building your own head for a Triumph sounds like a lot more work than bolting some new parts into your Commando engine. Nothing to do with AHRMA rules. In fact, AHRMA doesn't allow the short stroke 750 to be used in the Sportsman class, but does allow it in F750.

And finally, if you're a confirmed Norton fan, you'd want to improve your Norton, not replace it with a Triumph or Nourish engine.

Ken

Rohan · Oct 27, 2014

lcrken said:
And finally, if you're a confirmed Norton fan, you'd want to improve your Norton, not replace it with a Triumph or Nourish engine.
Ken

Good answer - nuff said !!

Rohan · Oct 27, 2014

Those steel rods look heavy - were they ?

They didn't have confidence in doing an alloy version of them ??

P.S. Anyone know where these steel rods came from ?

lcrken · Oct 28, 2014

Rohan said:
Those steel rods look heavy - were they ?

The ones I had, which were out of a factory flat track bike, weighed 530 grams total, with 385 g at the big end, and 145 at the small end. That's compared to a standard Commando rod at around 390 g total, with big end at 312 - 326 g, and small end at 75 - 78 g (the spread in weights is just for the rods I've measured).

Not sure who Norton contracted to for these rods. Someone here probably knows.

Ken

Short stroke conrods??

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