HD XR 750 & Full Auto port conversion

Wasn't there a DOHC comando discussion on this forum April 13 2016?

o0norton0o said:

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?...

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@comnoz did the center bearing.

IIRC someone else did too.

o0norton0o said:

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

Was that design even around to be considered by norton?...

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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

Hudriwudri said:

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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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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o0norton0o said:

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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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. . . .. . . .

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.

Hudriwudri said:

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 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.

Bernhard said:

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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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?

Been there - done that :

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.

@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

Hudriwudri said:

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.

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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.



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



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.




Ken

@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?

Hudriwudri said:

Ps: the last picture is with the 2-1 g.p.Blair saxophon right?

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I believe so, Christian. This is the more common dual exhaust system



Ken

lcrken said:

I believe so, Christian. This is the more common dual exhaust system

View attachment 18255

Ken

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Attached are the long straight manifolds on my 750.

My monoshock racer with straight manifolts and guillotine slide carbs.




My Atlas racer with straight manifolds and guillotine slide carbs.

lcrken said:

Al, most of the horsepower figures you see for the XR750 back in the '70s and '80s, either from the factory or quality tuners like Axtell, are from conventional brake dynos, not inertia dynos. The numbers are directly comparable to values for Norton engines run on similar dynos. In particular, Axtell did accurate dyno measurements on both Norton engines and XR750 engines. He did many dyno runs on the Norton engines he built for Ron Wood, and Mert Lawill used the same dyno for a lot of his XR750 engine development. IIRC, the best numbers for the Norton were 76 or 77 hp for the standard 750 and a few more for the 750 short stroke. I was at the shop once when Mert was running his XR750 on the dyno, doing some exhaust system testing, but I don't recall the exact hp numbers. My memory says it was around 95 hp, but my memory isn't what it used to be. Both measurements were power at the rear axle. The bikes were set up with a long chain from the transmission output sprocket to a sprocket mounted on a dummy axle connected to the dyno. This is a picture of Axtell with a Norton Atlas on the dyno back in the '60s.


View attachment 18101


Other XR750 tuners had also managed to get horsepower in the 90 - 95 hp range by the end of the '70s. The best top end number I've seen published is 107 hp for an engine built by Bill Werner and tested on Jerry Branch's dyno in the mid '80s. I think those numbers were taken at the crankshaft, but again, I'm not sure.

One thing to keep in mind when comparing the Commando engine to the XR750 is that racers were running the XR engines up to 9,200 rpm to make their numbers, where the standard stroke Norton stopped making more horsepower somewhere just over 7,000 rpm. That was before the days of the ultra short stroke engines we've seen being built just in the last few years, which have much higher redlines. If we can get the old Norton head to flow well enough, and the valve train to co-operate at those rpms, it should certainly be possible to hit some pretty good numbers. Interesting times to be watching some of the current development efforts.

Ken

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I had a best reading of 85hp at the wheel of my A65 with a Norton crank @7780 or around that. The operator wanted to use another 1000rpm to see when the power graph went over.

Hudriwudri said:

@Chris

True indeed, but nonetheless unfortunately the weslsake/nourish head needs considerable tender love and care to make it flow as it should/could.
I was working on two of those and it left me with a somewhat delusional feeling when I looked at the initial flow measurements.
Also afaik the cam timing events available could be a hint more suitable for a 4 valver.
@acotrel
So based on what Chris already wrote comparing a to my knowledge prewar based work mule to an almost thoroughbred is like comparing apples to pears.

Kind greetings from Italy

Christian

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Can you remember what the 4 valves flowed? I imagine low lifts may be better than a two valve.

jseng1 said:

I already have the port molds, specs and accurate measurements of the HD XR750 ports. I'm more interested in duplicating those ports than running flow bench tests. Ken - I would love to take you up on your offer but I can't make promises now with my present work load. I also have Axtell port molds courtesy of Ken Canaga. I have a similar copy of those Axtell ports in my current cafe racer.

I've already ported a Fullauto head and widened them as shown in the video below. That head was for a 500cc short stroke so I didn't go too wide.



Reangling the valves so they locate accurately on the tappet adjuster screw.


I've already worked out the compromise port shapes in Autocad so they will fit in the stock Norton heads. There are several stages (widths) depending on how much welding is involved and all of that is readily available in my "Narley port" CD. The current project is for my cafe racer and will only go to 34mm width around the guide which is 2mm wider than the FA head and doesn't need welding on the sides of the ports. I intend to perform the same porting and valve re-angling that I've already done with the FA head for the 500cc full race short stroke - except that the exhaust port floor will be closer to the profile of the XR 750. The only hang up is getting someone to (laser) weld the insert near the valve seats.

For a round port to compete with the "cobra head" shape that widens around the guide it would have to be steeper like you see on 4 valve motors. But because of vertical space restrictions limiting the angle the cobra shape offer more flow and you see the same shape in some Nascars.

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BSA A65 castings vary a bit but on my 883 I made the port 43mm wide at the guide using 38mm carbs. I cannot remember if it went through. The XR looks like it's 49mm. Without welding in the pushrod tunnel I cannot get that width. And even so it's making power past 8,000 with the 89mm stroke and my short rods. Long rods would be great but there is not much space in the frame for a taller engine. And being a road bike with so much midrange it doesn't get revved that high. The little 34mm ports are great between 37-38mm wide and 30mm high. And don't go through any wear. A piece of 34mm alloy tube squashed at one end to match the head. On the big valve head because I'm filling an old big port I have the port lower so the top run is better. That's the problem with a round port or having the carb highish. Like the Lightning because if the port aims down then has to go up then down again it hates air going through.

Depending on variances of calibration the comparisons are like this graph. The air is cold here now so I calibrated and tested without running it long. If the std head is 109cfm which is about right, the experimental head is around 180.6cfm through the 34mm PWK. And 192.8 without carb and a radiused entry to the manifold. I'm hoping this will be potent on a 744 big bore, but I have never tried one like this.