Another short stroke

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Feb 21, 2012
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Hi guys,

It's been a long time!
I bought this factory short stroke crank, that came with a letter authorizing its use.
A real piece of history.
But what pistons could I use with it in order to build a road racing bike? The ones I got are trashed. And the conrods seem a bit on the heavy side. Would you reuse these?

Regards

[url=https://postimg.cc/RqTQ8DrR]Another short stroke Another short stroke Another short stroke Another short stroke Another short stroke Another short stroke Another short stroke[/URL]
 
The short stroke Manx Norton 500 was faster than the long stroke Manx Norton 500, but my short stroke Triumph 500 was faster than a short stroke Manx Norton 500. However it was a piece of shit. If it was balked in a corner, the clutch need to slipped to get back into the power band, and the bike would go sideways. My Seeley 850 is the easiest motorcycle on the planet to race really well. I can just flick it into corner while braking. then immediately get on the gas and power full bore through the corner, under the other guys and with less lean. With most bikes, the rider cannot gas them until they are almost out of the corner. When I built my bike I believed it would be useless, because I knew how most bikes handled. The 850 motor is radically different in the way it needs to be used.
When my bike self-steers it's way around corners, it feels absolutely wrong. However it is very effective. If I gas it when on a lean, it turns in the direction of lean and stays more upright. I used to be very careful with the throttle when racing. Smooth power delivery is better, when you accelerate really hard when on a lean.
I only ever picked-up on this stuff, because I rode a Short Stroke 500cc Manx Norton and I know what they do when you gas them when on a lean. It is the reason they were much faster than most other bikes. The weight distribution is important- needs to be well forward, or you can lose the front.
Of course I might be an idiot and not know what I am talking about.
 
I worry about racing again, because if I was to get into a corner miles to hot and accelerate hard to get around, the speed would be horrendous. If a tyre lost grip or I twitched, the whole thing might become very spectacular. I now have 6 speeds close ratio instead of 4 close with a high first. So it would be on from the word go. It is probably lucky my wife has banned me.
 
I bought this factory short stroke crank, that came with a letter authorizing its use.
I'd be interested in seeing that letter!

WHO "authorized" the use of the subject crank, in WHAT machine/application? (Not to mention why the user would need authorization).

I have to assume something is lost in translation...
 
My Short Stroke (Maney crank) uses JSM rods and pistons. Jim has a suitable longer rod for his pistons in short strokes. They will differ in length to your factory rods, which are designed for the Omega pistons, and of course the original Omega pistons were intended for use with a fully hemispherical combustion chambered cylinder head.

I have an Australian made Fullauto head, so JSM longer short stroke rods and lightweight pistons work fine, assuming your barrels are around standard deck height. (I have 0.020" skimmed off mine)

The only parts I have left of my original '75 built race motor are the pistons, similar to yours, but with a smaller gudgeon pin hole to fit standard rods. Except one of mine has the head of a rather large vale stuck in the top.

The '75 motor was in effect an 850 version of the 750 short stroke. I raced it from '76 to end '79. Thruxton used similar motors for non 750 restricted UK races, at National level we ran mostly 501 to 1000 class.

(whereabouts are you located? I am near Flers in Orne)
 
My Short Stroke (Maney crank) uses JSM rods and pistons. Jim has a suitable longer rod for his pistons in short strokes. They will differ in length to your factory rods, which are designed for the Omega pistons, and of course the original Omega pistons were intended for use with a fully hemispherical combustion chambered cylinder head.
Hi Steve, please help jog my memory. The Omega pistons have a circular squish band, so the head's squish band is different obviously. Is depth of the combustion chamber different to a standard head, e.g.,RH4 ? Is the RH7 (?) head geometry depicted somewhere?

- Knut
 
Here's the factory 335 gram omega piston compared to the JS 216 gram piston for the fully hemisphered factory short stroke head.
Another short stroke


Be sure to put a radius on the crank output shaft to keep it from cracking (see details in the JS race manual).
Another short stroke



Here's the heavy factory to JS Carrillo rod comparison
Another short stroke
 
Thanks Jim for these inputs.
I'll get in touch with you when I am sure of what's needed.
Unfortunately, I only have a RH4 head on the shelf. And I need sone barrels as well.

Regards
 
Thanks Jim for these inputs.
I'll get in touch with you when I am sure of what's needed.
Unfortunately, I only have a RH4 head on the shelf. And I need sone barrels as well.

Regards
Send your head to Steve Maney for his stage 2 or 3 conversion.

Andy Molnar does fabulous alloy barrels.
 
That is the strangest looking "short stroke" crankshaft I've ever seen. The stock Norton short stroke 750 crankshaft looks just like a standard Commando crankshaft, except the rod journals are ground and finished at a closer distance from the mainshaft centerline. If you saw one on a bench, you would probably think it was just a standard crankshaft, unless you measured the stroke, or had enough experience with the short stroke to notice the slight difference in the journal location. I'd really like to know the history of your crankshaft, who made it, and why. My fading memory tells me I've seen pictures of a similar welded together Commando crankshaft, but I've been unable to find any, so that might just be another senior moment.

Ken
 
In rummaging through my files, I did find this picture, that I had labelled as a "Martin Bernert Crankshaft", and which looks quite similar to the one in this thread, except it has had the welds machined flat. Martin Bernert is (was?) a Spanish Norton enthusiast, and at one time was on this forum.

Another short stroke


Ken
 
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