You don't see many of these.

http://cgi.ebay.com/1972-NORTON-COMMANDO-SHORT-STROKE-RACE-MOTOR-750-850-?cmd=ViewItem&hash=item1e67a84916&item=130588100886&pt=Motorcycles_Parts_Accessories&vxp=mtr

It is curious that the rocker feed is the '68-'69 metal line.

Why is anything Norton rare?

Dave
69S

A short stroke race motor generally has barrels that are quite obviously shorter and more squat- those look at a glance like stock height barrels. Short stroke barrels look like they are missing fins (they are).
This phrase used in the ad - "it had a supercharger turbo unit with the motor" makes me think perhaps they have no idea what they are talking about... uuuh, is it a supercharger or a turbocharger?
Of course, I could be wrong.

Maybe the supercharger compressed the conrods , makeing the stroke shorter .

I don't mean to disagree with you Doug, but the factory short stroke 750 didn't use a shortened cylinder. It used a standard 850 cylinder. At some point, some of them may have had tuftrided or nitrided bores, but the dimensions were the same. The factory bike had longer rods to make up for the shorter stroke. A lot of the current field of short stroke motors built by people like Steve Maney, used a short stroke (80.4 mm) crank with stock length rods and shortened their alloy cylinders to make up for the shorter stroke. The ultra short strokers (75 mm stroke) built by Steve, and probably Herb Becker, had even shorter cylinders to allow stock length Commando rods. I think those might be what you are thinking of. Most of them also don't use the RH7 head with the non-squish, full hemi, head. Steve used standard heads converted to bigger valves and different valve angles, and I think this is probably what Herb did. You'd know more about that than I. This engine at least has the right big valve head.

The factory short stroke used the same rough crankshaft halves that Commandos started out with, but they were ground to the shorter stroke. The rods were steel, and longer than the alloy Commando rods. The pistons were specials made by Omega, with a bit of dome, and a slightly larger wrist pin diameter. The cylinders were standard iron 850 items. The head was the famous RH7, with 1 5/8" intake valves at a smaller angle from vertical and stock exhaust valves. The standard cam in the short stroke was a 4S. Other than that, the parts were standard Commando.

This engine is interesting, but I wouldn't buy it without knowing more about it. I raced a factory built short stroke for quite a few years, and had two crankshaft failures and one broken rod (the steel ones), so I would want to know what was inside this one. If it has the original crankshaft and rods, and a lot of racing miles, I'd start to worry about it.

On the other hand, original short stroke engines are pretty thin on the ground, so it might have collector value.

Ken

I agree with lcrken, but still wonder what idiot re-designed the RH7 head without squish. On my current road shortstroke engine we therefore used a standart head (with squish), and when I got the engine it had been run but was all coked up and had obviously run very hot. No great miracle with that combustion chamber design. I still have the RH7 head corroding away in a corner. Did they actually use the RH7 head in competition, Icrken?
If anybody needs short-stroke pistons- I have about two dozen pairs, STD and +.020"...... not useable in a standard engine without mods because the gudgeon pin diameter is bigger. Apart from that nice high-comp pistons! And a set of those bloody heavy steel conrods- would not use them if I could help it. Which I could, using standard production ones and shortening the barrel.

Another point: factory shortstrokes. According to Peter Williams they never used them in the works team. The only ones I know of are the TX 750s, of which probably no more than a dozen were built, on sale as a race bike in about 1973, but by then no longer competitive- a 350 Yamaha could ride rings around them, being much lighter.
Joe S.

I don't know squat about factory short strokes, all I know is that all the built short stroke motors I have personally seen in the flesh have shortened cylinders and are obvious at a glance to be short strokes. Well, you learn something new every day.

Presume the English built Race Engines Short Barrel . American built ?? homlogation engines , as mentione ( steel rod etc )

Matt Spencer wrote:Presume the English built Race Engines Short Barrel . American built ?? homlogation engines , as mentione ( steel rod etc )

I don't think there were any "short barrel" engines?

Any ancient period info I saw from olde blighty , refered to a short 850 Barrel . NOW , what ' WE ' want to know , IS
can you loose a half in , or one fin hight ON the Std. 850 Barrel , when fitting your coustom billet short stroke Crankshaft
or the Maney one , and run Std. Rods . S.S. ( short stroke ) redline was 8.000 rpm . Were listed / shown in the last
colour sales brochure , the one with the blue 850 SS , L & R Hi Pipes.
.I.E. a 750 Short Stroke Roadster , street bike .Specifications listed in that year catalougr ? ? .

I belive one (F-750 ) was used by Croxford & whoever , Mick Grant ?? in the endurance races .

Very disapointing they didnt materialise , along with the Triump / BSA 350 dohc , and A 70 L , Cosworth , Rotisary Et Al .

Matt Spencer wrote: S.S. ( short stroke ) redline was 8.000 rpm . Were listed / shown in the last
colour sales brochure , the one with the blue 850 SS , L & R Hi Pipes.
.I.E. a 750 Short Stroke Roadster , street bike .Specifications listed in that year catalougr ? ? .

The only time the short stroke engine appeared in a brochure was 1973 (which certainly wasn't the last brochure) as far as I know, and no "blue high pipe 850 SS" model was made as far as I'm aware?

1973
http://www.classicbike.biz/Norton/Broch ... LineUp.pdf
1974
http://www.classicbike.biz/Norton/Broch ... ochure.pdf

Roit , thats 9 mm on the Stroke , while we're there . So is 4.5 mm or 3/16 in odd of the barrel , on a 850 coustom crank ? ?
Was inscesant magazine conjecture with varying degrees of tech. info at the time .

While we're there , ! . If anyones got Mercedes 190 Cosworth 4 Valve engines on the way to the scrap , please holler .
' We ' would like ' A Few ' cylinders off one , please . . ( Comparable to Britten specs but there INLINE ) .
, at Tristram ave in the Rover 75 ( No , the 1951 one ) around 78 the Trident with works pipes etc came past a few times , and would scoot off promptly when oggled by the driver of the olde black Rover .( pipes under the frame side rails )
One Day , same place , Lo & Behold , a Blue Dual high pipe , R & L , comes past . Hi Rider tank , I think .But as it was beside the door , First Glance was " 850 " on the side panel . However catching British motorcycles in the
2150 cc I.O.E. was not ordinarilly practicable . Observing the intent they probably decided to evade promptly .

So , young Murrys Brocure showed the Blue one , 750 so bewidered at a 850 . But niether of those show a blue SS .

Ron L wrote:You don't see many of these.
It is curious that the rocker feed is the '68-'69 metal line.

That is either an Atlas or 650SS rocker feed, not the later Commando.