Norton Production Racer

I have a small eligibility problem to do with historic racing. Can anyone please tell me what year the 750cc Norton production racer with the short stroke engine was produced, and if the 850 barrel type with the through bolts was used before 1973 on any commando engine ?

Aco, my understanding is, the 850 type flangeless barrels were developed for the J.P.N. F750 racers, P. Williams has claimed credit for them, so check those threads which show the factory race bikes, the `72 machines are blue, with the spine frame, `73s went monocoque..

Did the space frame come after the monocoque ?

Yes, `74, then `75 Cosworth Challenge, but that fizzled [ & was not a Commando anyhow].

The 1972 JPN racers (blue ones) have through bolt barrels but they are just modified "old style", not the 850 casting.

Aco, it might be worth contacting Norman White for verification of in-use dating of the modified barrels, he`d likely know if it was before Dec `72.

johntickle said:

The 1972 JPN racers (blue ones) have through bolt barrels but they are just modified "old style", not the 850 casting.

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This and similar setups is where the idea for the 850 style cylinders came from ?

Rohan, several of the durability-related items progressively introduced on production 850s stemmed from J.P.N. race development experience..

The short stroke 750 engine was not available until late in the 1973 season, when it was used in the 1973 F750 JPN Monocoque. It was advertised in 1973 in one of the sales brochure as available on special order for installation in the Commando Roadster, although there has been a lot of argument over the years about whether any Commandos with this engine were ever sold to the general public. None of the roughly 120 factory Production Racers (Norvil Racers, Yellow Submarine, or whatever you choose to call them) were offered with the short stroke 750 engine, although some racers (including me) swapped them into their PRs when the engines became available. This engine was standard in the Thruxton Club Racer that was offered in 1974, but very few were sold.

That's one of the reasons that AHRMA outlawed short stroke Commando engines in the Sportsman 750 class back in the '80s, but did allow them in the F750 class. There was a lot of argument about it in AHRMA, but based on the information available, including statements by Brian Slark, they determined that the engines had not actually been available in legitimate production bikes.

FWIW, the short stroke 750 cylinder was just a normal 850 cylinder, with no other special features, although the factory did supply some to their race teams with nitrided bores.

Regarding adding through bolts to the conventional 750 cylinders, I've heard that mentioned, but have never seen one. All the Commando Production Racers I've ever seen, as well as all the ones I've seen in photographs, including the ones the factory raced, had the regular studs and nuts at the base of the cylinder. Some of the aftermarket alloy cylinders used visible through bolts, including the Drew Robertson cylinders I sold back in the '90s, like the one below. You can see the through bolts in this picture.



Ken

Nortons had had through-bolted heads and cylinders on their singles engines since the 1930s.
Its surprising it took so long to get to the twins, even in small measure ?

BSA went through-bolted in the 1930s also - the story was that somewhere the race shop acquired a stroboscopic light, and were "stunned to see the top end at high rpm waving about in the breeze." The Gold Star was mixed up in this story somewhere...

Rohan, you must understand that pre-war, machines were being flogged around Brooklands [Goldstar to be earned] running exotic fuel cocktails &/or blown..
Post-war however, pool petrol was weak as piss, machines designed to run on such dishwater didn`t have to have massive pressures factored in.
Only when pumped out way beyond design parameters [racing on hi-comp using hi-test U.S. gasoline] did things get , ah , sticky..esp if production regs meant Domiracer-prototype specs were not allowed..

Postwar Nortons, apart from sidevalves and twins, all had bolt-through heads.
Manx engines had stronger and deeper spigots, wider flanges, reinforced everythings etc.
This continued to the end.

Maybe the designers had forgotten how to design for strong engines... ?

Rohan, you do realise that as a pukka Grand Prix machine, the Manx was not going to revert/devolve design-wise.. right?..
Road-bikes for everyday use are a completely different kettle of fish, & have to be designed & mass produced for profit, not racing durability...or so it was, back then..

All the ohv single engines were all through-bolted, until the end.
No offence to singles owners, but performance is not what you think of with these.
Where does this come in your Yamaha-think ??

Of course, one of the problems with through-bolted heads is being able to remove the head with the motor still in the frame. This alone could well be the determining factor in why they went the way they did - and why the 850 got through-bolted cylinders, but not heads...

Rohan, which post-war Norton singles were clean-sheet [new] designs? Hmmmmm.
As for Yamaha thinking, after the late `60s G.P. rule changes that restricted numbers of cylinders/gears that could be utilized, Yamaha had a policy of parallel development between sports-road & racing production bikes, something that worked well, albeit less successfully for 4-strokes - cost/complexity-wise- & is now the fundamental basis for world championship racing, sadly enough.

Well, good morning J.A.W. Another day on forum.

I will be watching all night and the next morrow for your many many poignant posts.

Your record trend is quite remarkable.

And remember, don't let us commoners keep you from holding back.

Well, that post stat above was helpful, in the thread subject context...wait..no.. it wasn`t.. So if you wish to be personal, do kindly refer to J.D.`s reiteration of forum protocol, & P.M. me..

J.A.W. said:

Well, that post stat above was helpful, in the thread subject context...wait..no.. it wasn`t.. So if you wish to be personal, do kindly refer to J.D.`s reiteration of forum protocol, & P.M. me..

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Yes sir, you are quite right about that. The real solution is to simply block you from my view which is sound advice for anyone who feel as i do, violated. Consider this done.

No P.M. then? Crikey dick!..... [ Note: colloquial expression of surprise, not personal insult.]