Found. a true 70 Production Racer

Eyeballing those 2 bikes, they appear to have very little in common.
In a superficial cosmetic sense anyway.
Exhausts excepted, perhaps.

So did the spec change, or is that someones "recreated" version of a Thruxton Club Racer ?

I wasn't aware that Norton made a commando based production racer prior to the post 72 short stroke 750 with the 850 style barrels. I tried to buy a motor a while back, however I would still have eligibility problems because of the appearance. Our period 4 has a 1972 cut-off, my 850 ends up in period 5 with TZ350 and 750 ,Z900, and GSX1100. It is extremely frustrating. If I fitted Maney aluminium barrels and made the motor 1000cc I wouldn't have a problem - 'the system runs on bullshit'

acotrel said:

I wasn't aware that Norton made a commando based production racer prior to the post 72 short stroke 750 with the 850 style barrels.

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Norton introduced the Commando Production Racer in 1969, and it was available in the U.S. in 1970. Cycle World magazine did a test of it in 1969, and Cycle magazine did a test in 1971. The PR was available on special order at least through 1972. I don't know when the last customer PR was delivered. Norton built and raced their own modification of the PR in 1973 in the FIM 750 Production class, but it differed a bit from the true production PR. The PR came in one color only, yellow, and was fitted with the standard long stroke (89 mm) 750 engine with some mods (see my posts above). It did not have the short stroke 750 engine. I repeat, the short stroke 750 engine was not available in the Commando Production Racer. It was fitted to the Thruxton Club Racer that was sold in very limited quantities in 1975 (see pics above). It was advertised as available in the standard Commando in 1974, but I'm not sure if any were actually sold besides the ones the factory built for display at the shows. If so, there certainly weren't many.

I can understand your disappointment that the 1972 cutoff makes the short stroke ineligible in your Period 4 class. We have a similar exclusion here in the AHRMA 750 Sportsman class, which require a pre-1973 production frame and production engine, although it does allow later years if the design is pre-1973. In the case of the short stroke 750, it was declared ineligible primarily because it was not really available in a production bike in any significant numbers, not because of the 1972 cutoff date. There was quite an argument about it back in the late '80s when AHRMA decreed it ineligible for 750 Sportsman. I was involved in the argument, showing the AHRMA officials the factory advertising brochure listing the engine as an option for 1974. We tried to argue that the short stroke was just a slight modification to the pre-73 engine design, but they weren't buying that reasoning. The decision was made in large part based on Brian Slark's statements that there were very few, if any, production bikes delivered to customers with the engine. It was, and still is, legal for AHRMA Formula 750 class. Although I argued against the decision, I think it was fair. The engine really wasn't available in the production Commandos.

Ken

Chris said:

Hi
Acrotel, Rohan is correct about Brands. Clearways especially would have the cases on the ground.
Norman White's proddie bike replica's featured in Classic Racer had the engine raised & moved over in the frame.
Lots of little tweaks done to proddie bikes back in the period. It was a big part of club racing for many years. Sadly not supported much in classic racing now. some people seem to be able to cope with dragging their pipes on the ground. It makes me pass buttons
Remember asking about the plates welded on the front of a proddie T150 frame tubes. Yep worn though. Then again you dont find many standard frame proddie tridents (besides the big bore engines in period) most Tridents had the frame hike. One of our champions of proddie racing had two on his garage wall the 2nd frame jacked the engine higher than the period raised frame due to modern tyres! ie super venoms in race compound. Nothing new under the sun.

Chris

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All true Chris, but when I raced my proddy Commando the first thing to touch down on the right was the reaset footrest!, luckily it folded so it just tracked under your foot...particularly at Charlies at Cadwell.....until the gear lever itself touched and it tried to change down.....!

Rohan said:

acotrel said:

Chris, I think I would increase the ride height before I would offset the motor and gear box to get ground clearance.

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When you've set the ride height to the max, then you start offsetting the motor. ?
Every little advantage...

Wonder if thats within the rules ?

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You guys say these things with the benfit of today's solutions...raising the ride height with a Commando means longer shocks etc...that look suffiently like standard ones for no one to notice....moving engines around sounds more extreme, but was less likely to stand out! until you started measuring....

And to be honest, most of us never thought about it on production bikes....we just dragged them on the floor....OK, I fitted longer shocks to my Rickman, but that was open class....

All the talk about the short stroe was the same too.....I was the only guy I knew who had a short stroke head....

And it came with full hemisphering and altered angles on BIG valves compared to everyone elses.....and cutaway exhaust ports to allow fitting into monocoques or space frames.....

It was also an 850 bottom end with Omega pistons, they were short stroke items, but had smaller piston pin holes to fit standard rods....no one else I knew had those either, so I am sceptical about stories of significant quantities of these being built into unwanted 750ss....

The Short Stroke was a race development for F750, pretty much end of.....as for the TX750...really, who would have bought it for club racing?

At the end of '75 I tried to find where you could get one...you could not...and look at what they used to build it.....Commando frame and 19" rims, fitted with road tyres...it was too tall....too heavy...and far too bloody expensive...it was also the wrong capacity for club racing which ran 501-1000cc races...

...club racers were busy moving over to 70bhp TZ350s, or already running lower and lighter 850 Seeley's and the odd Rickman or one off, I built a Rickman from scratch for less money than Norton talked of for a TX750, and I did it with an 850 motor with lots of TX stamped parts in it.....it would have been faster as well...yes it benefited from the extra cubes and stroke of the 850...I still don't accept the 750ss was pointless, it was designed to be used by world class riders in F750.....but I never, ever saw a 750ss in British racing...outside of a works race bike...in a Commando frame, Seeley, Rickman or anything else....

Can someone please review what's going on with the almost vertical shocks PR's and other fast ones converted to. I mainly want to know how it felt-feels compared to the angled shock versions.

As far as I'm concerned racing bikes which use Norton twin motors are all the same old garbage. Don't get me wrong, I love my Seeley 850, however I know it's limitations. In Australia, because the classes are based primarily on year of manufacture, we have mixed grids of two strokes, twin cylinder four strokes, and superbikes. It is absolute bullshit and dangerous. If I wanted to win, I'd be riding an alcohol fuelled 250cc two stroke. A while ago I made a conscious decision about what I enjoyed riding, and so sold a good TZ350G, and bought a 6 speed TTI box for the Seeley 850. My two stroke project which is an H1 Kawas aki engine fitted with RD350 barrels in an Egli frame is sitting unfinished in my shed. The motor has TZ750 port timings, reed valves and is of 600cc capacity. It would have eligibility problems, but we've always got those.
I would love to race my Norton engined bike against any two valve aircooled four stroke twin of up to 1000cc capacity. I'm now 71 years of age, and I will be long dead and gone before the guys here ever wake up to what racing is really all about. I've reached the stage where I can hardly even finance an entry in one more race without finding myself another job - so I'm looking . However I suspect the whole thing is wasted effort. I will never get to race agains the aircooled Ducatis, Triumphs, BMWs or any other thunderbikes without a heap of bloody two strokes and four cylinder bikes getting in the way. A grid full of large capacity two valve aircooled fourstrokes is never going to happen in Australia. I really don't care what it is, or when it was made , if it fits that formula, I'd love to race against it. However whatever I do, the expense must be justified by good exciting competition on a level playing field. What happens now in Australia is rubbish.
Historic racing in Australia is run by sidecar riders - enough said ?

Same old cracked record.....

hobot said:

Can someone please review what's going on with the almost vertical shocks PR's and other fast ones converted to. I mainly want to know how it felt-feels compared to the angled shock versions.

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Angled rear shocks gives long travel plush feeling suspension.
Race bikes usually need short travel firmly sprung suspension.
Struck me as odd that the racers stuck with the angled rear shocks - but maybe they wanted the connection with the road bikes ?
Maybe the damping and springing is a magnitude stronger than the road bikes.
Maybe they just raced what they had...

Raising the ride height on a Commando racer would involve the front forks first. ?
Likewise they have long travel - whereas a manx is set up with ~ 1 & 1/2" of (very firmly damped and sprung) usuable travel ??
Way to go... ?

Rohan said:

Thanks Ken. Which Bacon book is that - I've seen those pics, and details, but don't recall them all together like that.

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It's from "Norton Twins" from the Osprey Collectors Library series. ISBN 0-85045-423-9. Page 129. He doesn't say much else about it, other than that it was hand built at the Andover facility in limited numbers.

Ken

Thanks Rohan that is what I needed to be reminded of, angled > squat-tier softer, cool just what I want so will drop thots of moving mounts. Front sag height and fork extension travel makes more lean clearance than same rear lift as forks extend on leans so lifts what ever that much higher to lean further before fouling or runing out of tire curvature, which is what I think I run into on the fat modern tires. Alas bi plane air cooled type engines got bypassed last century yet some can almost break the sound barrier now a days. Getting as far over as quick as I can while sticking fast is what thrills me most on cycles > even when I don't have to.

Rohan
'Same old cracked record.....'

It is obvious that you have never raced . I'm beginning to believe it is time to walk away. If I'm going to race again, I will have to work. I don't t hink it is worth it.

hobot said:

Thanks Rohan that is what I needed to be reminded of, angled > squat-tier softer, cool just what I want so will drop thots of moving mounts. Front sag height and fork extension travel makes more lean clearance than same rear lift as forks extend on leans so lifts what ever that much higher to lean further before fouling or runing out of tire curvature, which is what I think I run into on the fat modern tires. Alas bi plane air cooled type engines got bypassed last century yet some can almost break the sound barrier now a days. Getting as far over as quick as I can while sticking fast is what thrills me most on cycles > even when I don't have to.

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Velocette solved these problem years ago, they fitted non –adjustable rear shocks that where given a softer ride on the lowest part of the arch, moving to the top of the arch, the rear shock gave a firmer, harder ride. See;

http://www.ebay.co.uk/itm/VELOCETTE-RS- ... 405wt_1170

Rohan said:

acotrel said:

How does offsetting the engine and gearbox to the left decrease lap times

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Brands Hatch is primarily almost all right hand turns, so having effectively more ground clearance on the right side could allow it to be heeled over further.
Which could perk up the lap times quite a bit. Providing the tires grip, like you say.

Does sound a little extreme, and outside the rules ?

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re; "Does sound a little extreme, and outside the rules ?[/quote]"


Well of course it was, that is why the Norton boys kept their traps shut- hence nobody knew :!:

acotrel said:

I would love to race my Norton engined bike against any two valve aircooled four stroke twin of up to 1000cc capacity. I'm now 71 years of age, and I will be long dead and gone before the guys here ever wake up to what racing is really all about. I've reached the stage where I can hardly even finance an entry in one more race without finding myself another job - so I'm looking . However I suspect the whole thing is wasted effort. I will never get to race agains the aircooled Ducatis, Triumphs, BMWs or any other thunderbikes without a heap of bloody two strokes and four cylinder bikes getting in the way. A grid full of large capacity two valve aircooled fourstrokes is never going to happen in Australia. I really don't care what it is, or when it was made , if it fits that formula, I'd love to race against it. However whatever I do, the expense must be justified by good exciting competition on a level playing field. What happens now in Australia is rubbish.
Historic racing in Australia is run by sidecar riders - enough said ?

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Save your pennies and put your bike into the container that comes over to NZ every february for the NZCMRR main meeting.

"aircooled Ducatis, Triumphs, BMWs or any other thunderbikes" up to 1976 is exactly what you will be up against and Moto Guzzi, Vincent, Rocket 111, and lots of Commandos.

We dont mind Ozzies at all - so long as we beat them ;-)

Ugh our poor ole clunkers do to run out of breathing horsepower, someone should fix that then see what matters most.

Indy car thats hit the wall backwards , shortening the width of the L H S . usually they hit on the right , and knock that in . :wink: :mrgreen:

Matt Spencer said:

Indy car thats hit the wall backwards , shortening the width of the L H S .

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Ha ha ha. Are you sure of that matty ? Doesn't look bent anywhere (although we can't see under the hood).
I recall doing a demon lap at Indy ( on the simulator !!), and assymetrical setup was big part of the trick.
Its getting a good speed on the bankings that gives the big speeds down the straights.

Note the short front left wheel area also, and again nothing looks bent.