HD XR 750 & Full Auto port conversion

gortnipper

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At the risk of exposing my ignorance, Why didn't norton consider widening the crank cases, placing a 3rd bearing in the center along with a sprocket to drive an overhead cam/cams?...

I believe that's what the yamaha brand norton-clones did.... It would mean the cylinders would move further apart, which would allow for a bigger bore also, and then the crankcase wouldn't be an exercise in geometry with the pushrods...

Was that design even around to be considered by norton?...
@comnoz did the center bearing.

IIRC someone else did too.

 
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I believe that's what the yamaha brand norton-clones did....

Was that design even around to be considered by norton?...
The yamaha brand twin was not a Norton rip off nor a Bonnie rip off but a very (I may say so as an owner of a XS650) clever design pretty much of its own, owning if some of its heritage to hired and the previous company that produced the Hosk 500 SOHC.
The Xs650 got build in large quantities from I think 1967 on initially as the XS1 and had already than a pretty bullet proof reputation also cuz it has basically almost (besides the frigging Ignition advance joke) everything on roller bearings.
But I'm positive that the 3d main bearing also the AJS twin has, although I do not understand why nobody ever got that thing to go as the motor looks very nice to me and the race model should have even 2intake valves.

Kind regards

Christian
 
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The yamaha brand twin was not a Norton rip off nor a Bonnie rip off but a very (I may say so as an owner of a XS650) clever design pretty much of its own, owning if some of its heritage to hired and the previous company that produced the Hosk 500 SOHC.
The Xs650 got build in large quantities from I think 1967 on initially as the XS1 and had already than a pretty bullet proof reputation also cuz it has basically almost (besides the frigging Ignition advance joke) everything on roller bearings.
But I'm positive that the 3d main bearing also the AJS twin has, although I do not understand why nobody ever got that thing to go as the motor looks very nice to me and the race model should have even 2intake valves.

Kind regards

Christian
My point was that adding a center bearing and a center sprocket to drive a cam chain would accomplish a few things. It would space the cylinders further apart which could allow for both a bigger bore/shorter stroke without reducing displacement. The bigger bore would give more area to double the number of valves, and the shorter stroke would yield more managable piston speeds and a higher working RPM range. Of course, it wouldn't be a pushrod engine anymore, but I'm not sure the pushrod part of the norton is what characterizes it's performance as much as the 360 crank does...

I worked on a dirt race car crew, when ever I came up with an idea about how to improve the car, my crew chief always laughed because everything I ever suggested, had already been tried. If the idea produced a positive result, then race teams were playing with that application in one form or another. If it was a bad, dead end idea, my crew chief would say, "That idea has been tried already by many different race teams, and nobody found it to be an advantage of any kind, and "Here's why,....".

So my reason for making my first comment was to hear the "HERE'S WHY" norton didn't try a different configuration like the chain driven overhead cam/cams, given all the possible things I said in the first paragraph... Usually, every design has a trade off. I just wondered if there was a known trade off for what I asked about....


.
 
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My point was that adding a center bearing and a center sprocket to drive a cam chain would accomplish a few things. It would space the cylinders further apart which could allow for both a bigger bore/shorter stroke without reducing displacement. The bigger bore would give more area to double the number of valves, and the shorter stroke would yield more managable piston speeds and a higher working RPM range. Of course, it wouldn't be a pushrod engine anymore, but I'm not sure the pushrod part of the norton is what characterizes it's performance as much as the 360 crank does...

I worked on a dirt race car crew, when ever I came up with an idea about how to improve the car, my crew chief always laughed because everything I ever suggested, had already been tried. If the idea produced a positive result, then race teams were playing with that application in one form or another. If it was a bad, dead end idea, my crew chief would say, "That idea has been tried already by many different race teams, and nobody found it to be an advantage of any kind, and "Here's why,....".

So my reason for making my first comment was to hear the "HERE'S WHY" norton didn't try a different configuration like the chain driven overhead cam/cams, given all the possible things I said in the first paragraph... Usually, every design has a trade off. I just wondered if there was a known trade off for what I asked about....
If you read the forum you will find that Norton did produce a ohc prototype with a chain drive that was more a Atlas, it resides in the NMC museum. They dropped the idea because the chain was so long. . . .. . . .
 
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The 500cc Paton twin has eventually become successful. The number of valves affects the BMEP. 4-valve four cylinder bikes have twice as many, but water-cooled V-twin Ducatis are still successful.
I have only ever lost one race in the pits and now I do not listen. There are many ways of winning a race with a Commando, and they are more fun.
 
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The yamaha brand twin was not a Norton rip off nor a Bonnie rip off but a very (I may say so as an owner of a XS650) clever design pretty much of its own, owning if some of its heritage to hired and the previous company that produced the Hosk 500 SOHC.
The Xs650 got build in large quantities from I think 1967 on initially as the XS1 and had already than a pretty bullet proof reputation also cuz it has basically almost (besides the frigging Ignition advance joke) everything on roller bearings.
But I'm positive that the 3d main bearing also the AJS twin has, although I do not understand why nobody ever got that thing to go as the motor looks very nice to me and the race model should have even 2intake valves.

Kind regards

Christian
The AJS twin suffered with poor oil flow to the left hand side of the crank. It also had sizing holes in the con-rods where they used to break. You put the pin in the hole and if it fell through, you knew the rod was about to break. The last AJS twin which came out in about 1962 was OK - good for making a G45 cheater.
 
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If you read the forum you will find that Norton did produce a ohc prototype with a chain drive that was more a Atlas, it resides in the NMC museum. They dropped the idea because the chain was so long. . . .. . . .
So, you're telling me to use the search function... instead of seeing if one of the professional mechanics would answer my question as to why the idea would be disguarded. That's kind of like your last post on this same page where you told me it's already been discussed sometime back on April 13, 2016. It's as if my posting was irritating you, so you answer twice in a dismissive way for me to go search for myself for the answer. I was hoping for an opinion and maybe some history lesson from someone who's opinion I respect.

.
 
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Sorry if you are annoyed by my answers, but at the moment I do not have access to a computer, so cannot copy and paste the information, I'm using a mobile phone. I did Google up the DOHC Norton and up came up with both those answers- not trying to annoy you, but if I can use a search engine, why can't you?
 
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With a 2-valve air-cooled motor, the down-angled ports on the Manx and the Commando, might be Norton doing as much a can be done. The internal diameter of the inlet port is dictated by the power characteristics which are desired from the motor - combination with the cam and exhaust configuration and also the stroke of the crank. - At a minimum , 5 variables. When they are combined in different ways few distinct patterns emerge which make certain bikes more suitable for certain race circuits.
If you are going t make a 750 Commando perform better than an XR750 on the dirt, you probably have a lot more to consider than just the shape of the inlet ports.
 
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@o0norton0o

My comment was purely on a informing base and not to be understood as a critic.
Im not working on commandos on a regular bases, but i think i remember that there would be still some space inbetween the bore to enlarge the bores about a 2,5mm's towards each other, not considering the crankshaft.
imho the power crucial point lies mostly in straightening the ports upwards and inclining them even further towards vertical and stuffing in the biggest valves by reinclining the guide bores. imho ovalizing the port area like on the XR750 could be adressed at a later point as i'm submit to eye cancer every time i see that already pretty in comparison to eg triumph's (in particular the trident is imho a nightmare) intake port and then that ridiculous manifold elbow subjecting all the design efforts on the intake port to mediocracy.
Im amazed nobody ever mounted some Fcr's / Tmr's or at least some independent float bowl carbs and went straight outta the door without that friggin redundant ellbow.
i explicitly dont mean this as an offense to the commando type engine but these thoughts occure to my mind.

@ acotrel

thanks for the info regarding the AJS.
regarding pattoni:
the patoni500 was designed as a pure race breed race engine therefore in my opinion comparison with road engine designs are not legit, in particular regarding the fact that at least as i assume that most of the brit companies were at that time already severly low on funds or will to go to war in designing a bad ass engine.
Considering that the kawa twin is somewhat similar to the pattoni500 one can wonder why the mount them on their new road bikes.
Concerning your multi variable concern regarding head design i will try later to emphasize on my thoughts/ approach to head porting, but rest assured that i think that the commando intake ports could be still inclined a further approx 5 degrees (see also my thoughts above)which is in terms of turbulence and thus higher flow numbers with smaller flow areas therefore higher velocity of flow.

Regarding the 4 valve commando:

for the interested i think one of those watercooled norton engines was years and years ago in the property of britalia motors in santa cruz and in exposition there.

kind regards

Christian
 
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lcrken

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Im amazed nobody ever mounted some Fcr's / Tmr's or at least some independent float bowl carbs and went straight outta the door without that friggin redundant ellbow.
i explicitly dont mean this as an offense to the commando type engine but these thoughts occure to my mind.
Christian,

I've seen several cases where someone has mounted carbs with a straight manifold in place of the standard curved one. Most recent one I've seen is from Grandpauls monoshock Commando build, with Keihin FCR carbs, but in the past I've also seen it done with Amal GPs with remote float bowls and with Amal Concentrics. This is a picture of Grandpaul's setup.

Grandpaul's Straight In Manifolds.JPG


And this is from one of the factory monocoque racers with Amal Concentrics

Carb detail ex Aldana bike.jpg


And this is one of the earlier factory JPN racers with Amal GPs. They are straight in vertically, but have been splayed apart a bit for frame clearance, so not really straight.


1972 JPN from PW Book 1200.jpg


Ken
 
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@lcrken

Hi ken,
Ah yes I forgot Williams Jr's monocque yup true, shame on me.
Yesssssz that's exactly what I meant bending that awful plumbers pride and joy sewer ellbow straight, and in case feasible going a couple degrees more upright (I know I know that one can go to further lengths (or better heights) with modern valve springs :) ) and mounting a downdraft carb. Sexy would be imho two Gardner's with central matchbox chamber or SU float chambers and grafting a Helmholtz chamber around the intake stacks.

Anyways wonderful discussion I'm really enjoying it!

All the best and kind regards

Christian

Ps: the last picture is with the 2-1 g.p.Blair saxophon right?
 
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My monoshock racer with straight manifolts and guillotine slide carbs.




My Atlas racer with straight manifolds and guillotine slide carbs.
 
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