Norton Production Racer

Rohan, your point about practicable top-end work while leaving the mill in-situ is interesting. How much thought was given to this when the Norton design team were working up the Commando would be good to know, it does seem that British machines often have these kinds of nuts & bolts issues.
By contrast, H2s also have through-bolt heads/cylinders, but these can be removed quite readily, sans disturbance to the rest of the engine/frame.

Most two strokes have much shorter barrels than normal four strokes. That is why it is possible to remove heads and barrels with the engine in situ. It is also the reason you could not use my Egli/yamaha frame to house a four stroke motor - the spine is too low. A two stroke engined motorcycle is radically different from any four stroke and handles very differently because of the low weight, lack of torque, weight distribution, different geometry. I always had strong doubts about the Yamsel because it seemed to me that seeley built mainly four stroke frames, and the types are not adaptable or interchangeable. Any two stroke is always easier to ride than an old British bike. The trouble is that two strokes have no soul.
It is pretty obvious that the 850 was built so that you can remove the head with the engine in situ. Some racing triumph twin motors were built with the outer four studs modified to through bolts - they were a pain if you had to get the head off.
I've actually seen a short stroke 750 motor out of a production racer. It had shortened 850 style barrels. My eligibility problem has not eventuated yet, but I expect it t o happen The motor must be pre-72. My Seeley frame is of 1966 manufacture, but the motor is obviously only eligible for the next 'period' up. There is only one other thunderbike in that class - a Ducati 900. I can claim that the 850 motor is 750cc,no-one is going to measure it as oversize motors are common and allowed in period 4. However the appearance of the barrels is the problem, the seem to accurately date the motor as manufactured in 1973 +, obvious to anyone who has ever owned a Norton twin. The bloody motor is no different in technology than any previous model Norton twin, and many of those already racing are oversize. This is the sort of bullshit we have to tolerate in Australia.
Perhaps somebody makes 850 aluminium barrels that look like the early type ?

acotrel said:

I've actually seen a short stroke 750 motor out of a production racer. It had shortened 850 style barrels.

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My apologies if I've misunderstood what you're saying here. Just to be clear, the factory short stroke 750 used a standard size 850 barrel, not a shortened one. The engine had longer (steel) rods from the factory and special Omega pistons to get the proper deck height for the shorter stroke. I've seen short stroke 750s put together using stock alloy rods and shortened cylinders, but that's not how they came from Norton. Maybe that's what you're referring to.

I sympathize with your difficulty in getting the short stroke approved for pre-72 manufacture. I went through a similar process with AHRMA in the US trying to convince them that the short stroke 750 was available in production bikes. The year of manufacture wasn't an issue, but they declined to approve it because we couldn't produce any evidence that the factory ever sold Commandos to the general public with short stroke 750 engines. Having the advertising brochure that listed it as an option wasn't enough. They were probably right. AHRMA rules required that for a bike to be considered production there had to be a reasonable number of them made available to the general public. Other than one or two examples (that could have been the bikes Norton used for shows) there just aren't any production Commandos out there with original short stroke engines. I've seen a few street Commandos with short stroke 750 engines that were installed by the owners, and a fair number of race bikes with them, but that's about it.

Ken

acotrel said:

I've actually seen a short stroke 750 motor out of a production racer. It had shortened 850 style barrels. My eligibility problem has not eventuated yet, but I expect it t o happen The motor must be pre-72. Perhaps somebody makes 850 aluminium barrels that look like the early type ?

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Gooday acotrel,

I only know of 1 factory 750 shortstroke actually still racing locally. I do not know if it is Period 4 but I will find out. I have a factory 750 shortstroke (Standard height 850 barrels, RH7 head etc) that I would like to put in a P4. I will let you know how I go.

Cheers

Aco, perhaps you could clarify if the Aussie rules apply to standard production items sold on road-bikes, or allow [genuine or replica] factory built racing prototypes?
Incidentally, 2-stroke heads, rather than the cylinders are simple/compact, since their heads only have the task of combustion, with no incandescent poppet valves & associated gubbins [ports/valve drives & etc] to complicate matters. & 2-strokes actually possess a torque advantage, - inherent to every piston downstroke being a powerstroke -the myth is due to state of tune/engine displacement issues which tend to cram a powerband into a short rev-range, but radical camming has a similar effect on a 4-stroke too.

These things were alledged all 750 short stroke . the real TX750 .







Loose barrels chattering are as likely cause as any of splitting the flange off ,
so HOW does one RETOURQUE the ' improved ' through bolt barrel without removeing the head . ? :?

Anyone removed the head and found the side bolts slack , on the 850 .

and YES , we know its rather difficult to burst the 850 through bolt barrel , but theyve overlooked this ?

Everyone knows the TX750 was 1974, and later....

http://bikepost.ru/blog/moto_news/3263/ ... racer.html

Rohan, are you sure about that? Which year did those TX 750s disgrace themselves in the Castrol 6 hour?
Not that a Norton P.R. would `ve been allowed entry to the C`6hr...

'2-strokes actually possess a torque advantage,'
Have you ever ridden a 250cc two stroke racer into a head wind ? TZ750s are torquey, but nothing like a commando, they are mostly top end motors getting torque was the reason for the reed valves which were not use d on TZ350s - the barrels are interchangeable. TZ250s and 350s work on a different principle , all top end - point and squirt. You couldn't afford to have a TZ750 be like that, it would be too nasty. When you make an H2 pull a sidecar you change the stinger size on the chambers and give it a dose of alcohol. But you wouldn't try to ride it like that in a solo. I accidently made a set of chambers wrongly for a T250 Suzuki, it was really queer to ride . Great out of corners then it seemed to stop revving. When you build a motor you must decide what rev range it w ill work best in. In a two stroke motor that dictates your internal port dimensions and timings, the chamber specification and the intake length. If you have n't got the gearbox to cope wth what you build, your project becomes dead in the water. So always start at the gearbox, and go from there . With your early Kawasakis it is possible to change ratios by using gears from other kawasaki models, but it would be a research and purchasing nightmare to do it these days. Most historic racers simply ride around their problems, and I suspect many dont know when they've actually got a problem. Better to simply buy a factory built production racer such as a TZ250.

Way back in the day Aco, razors-edge tuned 2-strokes did have a very narrow powerband & needed vast gearbox ratio selections [more than 10 in a box]..but still won races.
However, with modern tech, even 55hp G.P. 125 singles [440hp/ltr] were fully race-tractable with the allowable 6-speeds... something you are going for on your 850..
If you check that 500cc roadbike Bimota Vdue on the youtube dyno-run, you will see the numbers.
Cycle World tested one, & got rwhp/tq of 104hp & 57ft/lbs at under 10,000rpm, show me a stocker 500cc 4-stroke roadbike that can match that..

Not sure anyone over 10 stone ever did well one one of the tidlers .

Long Range Norvil tank . Were three capacity options , I believe .

J.A.W. said:

Rohan, are you sure about that? Which year did those TX 750s disgrace themselves in the Castrol 6 hour?
Not that a Norton P.R. would `ve been allowed entry to the C`6hr...

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The TX750 had a slow birth which pretty much coincided with its death!

.....at the end of '75 Norton was bust.....I bought a Rickman chassis and an 850 motor with an ex race shop Short Stroke head and Omega Pistons (machined from blank for the 850 piston pin) with a cam stamped TX, from a Norton Experimental employee who had just been made redundant, and was off to mechanic for Alex George....

....an option would have been the TX750 ready made, but it had became apparent that the TX750 was not really happening, and anyway too tall, heavy and expensive at £1500 to sell to anyone as a club racer, and completely uncompetitive, even at that level.

I never actually saw one in the flesh and certainly in '74 it was just an idea, not a production reality......I know the Andover Norton site says '73/'74, but I recall it being publicised in the UK MCN after I has started racing, which was in '75....and I don't think the pictures were of production bikes...

But whatever they were, whenever they were built, if ever, they were not Norton PR Commando's, different animal.....

A major pity Steve, & sadly indicative of the whole sorry `70s saga for NVT...I did not realize that Norton shared that TX designator with Yamaha, or is it an unofficial abbreviation..

TX750 was the Thruxton Club Racer.
Donchknowanything ? Whereyabeenallyalife ??

Rohan...Whadddarya..
& Shouldn `t it be T.C.R., to match P.R. ?
Or are you & Matt just making this stuff up, like wood screws...?

Are you here 24/7 ??

Go away and google Thruxton Club Racer.
Since you seem to know nothing of Nortons, might learn something....

Have you got one, I`ll take it for a thrash...[I `d rather not ride the wood screw equipped one either, thanks all the same].
No, didn`t think so..
When are you going to have your Commando running, - bring it down to P.I.s for the classic racing in 4/52..even as a roadie, you can cane it around the track in the parade...why not?
If you google TX 750, what do you find, Rohan? L.O.L.

LAB, someone that doesn't own a Norton, and only seems to be here to be rubbishing Nortons, what are they doing on this Forum ???

Rohan said:

LAB, someone that doesn't own a Norton, and only seems to be here to be rubbishing Nortons, what are they doing on this Forum ???

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Yes, it is time for J.A.W. to go.

you going to send him to band camp???

L.A.B. said:

Yes, it is time for J.A.W. to go.

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