JPN Monocoque Specs

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lcrken

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I just ran across an article from the magazine "Moto Tech" back in 2008 about the John Player Norton Monocoque and Peter Williams, and realized it had more detailed specifications than I had seen in other articles on the subject. In light of some recent discussions on the forum, I thought the fact that it had a 27° steering head angle, 98 mm trail, and 18" wheels, 3.00" rear and 2.25" front, with a 48/52% front/rear weight distribution to be quite interesting.



Also, it had a nice summary of the engine and transmission development. I had never heard before that the engines (short stroke 750s) in the monocoques had one-piece crankshafts. Also a good explanation of how they finally overcame the transmission breakage problems.



Ken
 

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I was under the impression that the gearbox/primary mods were used on the '72 ( the blue JPN with the Commando frame).
 
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The specs mention an electrical fuel pump. I thought the fuel was pumped to the main i.e. centre fuel tank by swing arm movement? Maybe this is a modification done by Joaquin?
 

lcrken

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lutewizzard said:
The specs mention an electrical fuel pump. I thought the fuel was pumped to the main i.e. centre fuel tank by swing arm movement? Maybe this is a modification done by Joaquin?

I thought so too. Could just be a mistake on the author's part (Alan Cathcart). He's been known to get the details wrong before. Or it could be correct.

Ken
 
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The rake and trail figures are interesting. It is difficult to get an idea what geometry was used by looking at the photo of the forks with the forward axle. I think my trail is about 92mm.with a rake of 27 degrees. The monocoque Norton might be slightly more stable in corners.
 

lcrken

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acotrel said:
The rake and trail figures are interesting. It is difficult to get an idea what geometry was used by looking at the photo of the forks with the forward axle. I think my trail is about 92mm.with a rake of 27 degrees. The monocoque Norton might be slightly more stable in corners.

This is what Alan had to say about the handling.



Ken
 

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lcrken said:
lutewizzard said:
The specs mention an electrical fuel pump. I thought the fuel was pumped to the main i.e. centre fuel tank by swing arm movement? Maybe this is a modification done by Joaquin?

I thought so too. Could just be a mistake on the author's part (Alan Cathcart). He's been known to get the details wrong before. Or it could be correct.

Ken


I rode a 72 JPN and it certainly had those mods, but it was a replica, not an original bike so I guess the mods could have been retro fitted.



Who's Monocoque did Cathcart ride? Was it Mike Braid's? I've ridden that one around the pits at Brands Hatch... nearest I'll come to being works rider :)
 

yves norton seeley

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lcrken said:
I just ran across an article from the magazine "Moto Tech" back in 2008 about the John Player Norton Monocoque and Peter Williams, and realized it had more detailed specifications than I had seen in other articles on the subject. In light of some recent discussions on the forum, I thought the fact that it had a 27° steering head angle, 98 mm trail, and 18" wheels, 3.00" rear and 2.25" front, with a 48/52% front/rear weight distribution to be quite interesting.

JPN Monocoque Specs


Also, it had a nice summary of the engine and transmission development. I had never heard before that the engines (short stroke 750s) in the monocoques had one-piece crankshafts. Also a good explanation of how they finally overcame the transmission breakage problems.

JPN Monocoque Specs


Ken

Very intristing info's
Thanks
Yves
 

lcrken

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pommie john said:
I rode a 72 JPN and it certainly had those mods, but it was a replica, not an original bike so I guess the mods could have been retro fitted.



Who's Monocoque did Cathcart ride? Was it Mike Braid's? I've ridden that one around the pits at Brands Hatch... nearest I'll come to being works rider :)

It was the one owned by Joaquin Folch, the Barcelona collector. He had the original Williams TT winning bike restored from what was left of the chassis (made into a lamp for Peter after the crash) and a spare engine by P&M. There's more detail in the article, and I'll post the rest of it soon.

Ken
 
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lcrken said:
pommie john said:
I rode a 72 JPN and it certainly had those mods, but it was a replica, not an original bike so I guess the mods could have been retro fitted.



Who's Monocoque did Cathcart ride? Was it Mike Braid's? I've ridden that one around the pits at Brands Hatch... nearest I'll come to being works rider :)

It was the one owned by Joaquin Folch, the Barcelona collector. He had the original Williams TT winning bike restored from what was left of the chassis (made into a lamp for Peter after the crash) and a spare engine by P&M. There's more detail in the article, and I'll post the rest of it soon.

Ken


Ah yes.

http://www.norton.norvil.net/gallery/pics201.htm


Mike Braid and Joachim Folch are both in this shot, and Cathcart.
 

lcrken

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This is the rest of the article, except for the page I already posted above.

Page 1



Page 2



Page 3



Page 4



Page 5

Page 6

EDIT! In converting from photobucket to VIP images, I'm limited to 5 attachments per post. The remaining pages will be added to a new post dated 9/1/17.

Ken
 

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BritTwit

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These accounts of the JPN racers are truly fascinating.
The melding of the ancient powerplant to such a radically new chassis design, and getting the whole thing to actually work – it’s just incredible.

Thanks for posting.
 
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I notice the comments about the stability of the JPN Monocoque in corners. My Seeley handles a bit different to that and I hesitate to use it on large circuits with it's tendency to self-steer and tighten it's line. Often when I am on the gas so early coming out of corners I think 'I should really not be doing this'. It has never stepped out, however I feel it has to happen. My wheelbase is 54 inch - 2 inch less than the JPN Monocoque. With my bike, you simply put your head where you want to be and the bike is there. - Probably not everybody's cup of tea ? Perhaps the worry should be that the differences in steering geometry between the two bikes are very minor ?
 

Ron L

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Also, it had a nice summary of the engine and transmission development. I had never heard before that the engines (short stroke 750s) in the monocoques had one-piece crankshafts.

73 mm bore X 89 mm stroke would be standard, not short stroke. Which were used in the monocoques?
 

lcrken

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My apologies. I left out the page that talks more about the engine details. This is actually page 5. The page labeled above as 6 is actually page 7, and the one previously posted as page 5 is actually page 6.

JPN Monocoque Specs


Also, I misread the statement about the short stroke motor. It wasn't used until the space frame bike. The Monocoques, including the one tested, had the normal long stroke motor. Sorry for the confusion.

Ken
 
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Have you got any articles which compare the performance characteristics of the short stroke motor with those of the long stroke motor ? During my lifetime, I have had quite a few 650cc Triumph motors which have had both 80mm and 82mm stroke - my 89mm stroke 850cc Commando motor is far superior. Of course, the comparison might not be fair. The gearbox is probably make or break as far as these bikes are concerned. Most of my hotted-up road bikes did not have close boxes. The close box makes a radical improvement to the Commando's acceleration, when you use it to ride the top of the torque curve. In some respects, I think the long stroke might be better than the short. There might be a problem in getting the overall gearing high enough for big circuits such as the IOM and still getting around tight corners such as Governor's Bridge.
 
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The stuff about the wind-cheating aspects of the Monocoque is interesting. It is amazing the way a bike rolls further when you back off and you need more brakes, after you have fitted a fairing to your normally unfaired bike. When PW raced the 76 BHP Monocoque, weren't his opposition riding 100 BHP TZ750s ? His big win was in the wet and that is understandable, however in other situations he was still up with them - I find that surprising.
 

lcrken

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There might still be some confusion over the use of the short stroke 750 in the JPN race bikes. In previous articles, Cathcart has stated that the short stroke arrived towards the end of the 1973 season, while the factory was still racing the monocoque. For the 1974 season they developed the space frame bike, which appears to have used the short stroke engine. I have to admit that all the monocoque racers that I have seen had the regular long stroke engine, but it is still possible that the short stroke was tried at some point in the monocoque. We'll have to wait for someone with more accurate history than I have to settle that. The one that Alan tested in this article for sure had the long stroke engine.

For what it's worth, I've put a lot of racing miles on both long and short stroke 750 engines in the same bikes, and the short stroke was the "happier" engine. But the difference isn't as much as one might think. The factory claimed only 2 more horsepower for the short stroke compared to the long stroke, both in racing tune. As I recall, the difference Ron Wood was able to produce was a bit more, but still not really a huge improvement. Contrary to what some people claimed back in the day, the short stroke engine didn't really give up good mid-range performance for the higher rev limit. The breadth of the powerband is more determined by the choice of camshaft and valve/port design than by the difference in bore and stroke. You can build a torque monster or a narrow band high horsepower, high rpm engine out of either one. You just can't have both at the same time. For a street bike, there's not much to choose from between the two engines. I did notice in the rigid mount bike (wideline featherbed) that the short stroke seemed to produce less vibration than the long stroke, and that could be a plus. I couldn't tell any difference in vibration in the Commando. Both engines were balanced to the same 62% BF.

Still, I think that a short stroke 750 with the stock big valve head and conservative porting, with a moderate street camshaft, and a reasonable CR, would make a really fun street engine, particularly with a 5-speed gearbox with the street ratio set, not the close ratio racing one. That's what I'm hoping to build for my wideline race bike when I convert it back to the street, if I ever actually catch up enough to start that project.

Ken
 
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My 850 is balanced to 72% BF and when revved between 6000RPM and 7000 RPM vibrates little. However when it is idling, it rocks backwards and forwards. I don't believe short stroke needs to be used solely to stop vibration unless the bottom end lasts longer due to the different stroke.
 
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