HD XR 750 & Full Auto port conversion

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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
I know somebody who races an XS650 motor in an American flat track frame in road racing. He has pressed the crank apart and turned it to make a 270 degree twin I think the main thing which is wrong with that motor is the inlet ports are too big. Years ago, I raced the Seeley 850 against him at Winton and out-accelerated him easily . But that is only one bike. I was looking at a magazine article about the XS650 yesterday. They have got potential. It is possible to sleeve ports in a cylinder head. If they are too big, you don't get good torque, even though you might rev higher.
 
@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
Interesting your comments about putting an extra 5 degrees of down draught on the inlet ports, but I haven't seen your follow up on inlet ports, but if you have posted it on her, could you please direct me to your post ta.
 
@acotrel
I did not have yet sufficient time to scrutinize the ports, but i can tell you just by looking that the exhaust ports of the xs650 are way too big and the port floor also does not seem to be too outrageous.

@Bernhard
As i do not own an English bike yet (although planning to hot rod a M20 eventually in the future) i depend on having stuff on hand.
As far as i remember on the commando head there is still a good margin that one could go up porting the intake without getting through to the spring seat, thus if one leaves the SSR (short side radius) as fulcrum on could most likely turn the intake port steeper and by reinclining the intake valves outwards towards the liner one would rake in also the benefits of a steeper valve surrounding area.
Both of these steps would make intake flow much more stable and less turbulent around the SSR.
At the last step one would see how much material there is left for going around the SSR in turning the port into D-shape.
Hope my explanations are sufficient.

Kind regards

Christian
 
@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?

Your Gardner example reminded me of another interesting downdraft combination that still looks good to me. This is a pair of Amal Mk2s mounted on the Quantel Cosworth with Amal external float chambers racing at Brands Hatch. I was racing my Norton a few years later at the Daytona AMA meet where Roger Marshall won on the Quantel, and got to check out the bike in some detail. By then it had been converted to fuel injection.

HD XR 750 & Full Auto port conversion


Ken
 
@lcrken
As mentioned previously I'm somewhat ignorant to some of the Brit Bike peculiarities (one of the reasons why I got my LM2 in order to have a big pushrod twin besides the fact that I couldn't afford a beeza single back then and now even less) but i think that is exactly that engine that I saw back then in Santa Cruz at britalia.
I just love the plumbing of the matchbox float!!! If that really works it would open new worlds, rest assured i will ponder the next couple days bout it during graveyard shift!

Thanks a lot for the mighty cool pic!

Christian
 
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