New generation Norton head (theoretical)

Here's a new drawing of what the Norton head could be. When Norton went from the 650SS to the 750 they simply increased (& offset) the bore and failed to increase the valve size or move them away from each other to allow for increased diameters. The drawing shows the original valve & port layout in green with the new proposed layout shown in red (and black). The valves have been re-angled, seats have a larger outside diameter so even though the original valve diameters can be used - a tuner can open the IDs of the seats and ports leading up to the seats and install larger valves.



The port floors have been raised for increased flow and velocity with a broader curve leading up to the seat. Three floors are shown. The original in green, the Harley XR750 style floor in red and a compromised FA floor in black (re-shaped to more closely match the intake manifold floor angle & with an improved ex port floor).

The ports are cobra head head shaped so they are wider around the guides and I'm working on cross section drawings.

There is actually more material/clearance between the valve spring pockets and the intake port roof than shown in the drawing because the Norton intake valves and spring pockets are rotated on an angle.

An interesting concept and probably worthy of a one off prototype. If you're going to do that there's no reason to make it look like the Norton head. That design is insanely complex and I can't believe they cast it originally and more so I can't believe Full Auto replicated it!

If you were to do a simpler Norton head would it look more like a Triumph head? Simple to cast and having "external" rocker boxes makes it really easy. Or even go with 8 valves...

https://nycnorton.com/not-rain-sleet-nor-hail/

swooshdave said:

An interesting concept and probably worthy of a one off prototype. If you're going to do that there's no reason to make it look like the Norton head. That design is insanely complex and I can't believe they cast it originally and more so I can't believe Full Auto replicated it!

If you were to do a simpler Norton head would it look more like a Triumph head? Simple to cast and having "external" rocker boxes makes it really easy. Or even go with 8 valves...

https://nycnorton.com/not-rain-sleet-nor-hail/

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Or maybe it would just be a 961 head. That was Kenny Dreer's idea in making it a simpler design with separate rocker mounts and a BSA style rocker cover.

Ken

lcrken said:

Or maybe it would just be a 961 head. That was Kenny Dreer's idea in making it a simpler design with separate rocker mounts and a BSA style rocker cover.

Ken

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I don't like the separate rocker mounts like a Triumph. In theory they could be off by a bit, unlike the Norton, which are fixed. BSA got one thing right.

What puzzles me is reading how manufacturers couldn't cast proper port shapes, not cost effective, but looking at the rest of the head it seems easy. I'm sure its to do with metal cooling, had to leave it thicker there or something.
Jim, The throat diameter in black just past valve seat looks bigger than the green one. The green lines look like the factory stage 1 specs. From my research keeping that smaller, 85% of valve size is a common number, is good for flow. Why so big or was that drawn for bigger valves?

BSA head is certainly easier to work on. Easier to make leak free too. Triumph type separate pieces for the rockers is too fiddly.

edgefinder said:

... Jim, The throat diameter in black just past valve seat looks bigger than the green one. The green lines look like the factory stage 1 specs. From my research keeping that smaller, 85% of valve size is a common number, is good for flow. Why so big or was that drawn for bigger valves?

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The green lines (in the image at the top of this post) are stock. The Black lines (image above) are modified FA port but the entire intake port is moved away from the exhaust port to allow for enlarged ports & valves if the end user wants to install them because the valves are already reangled. The FA modified port isn't really supposed to be or doesn't have to be bigger than the stock port (note that both black lines are moved in relation to the green lines).

The head casting has to look the same to qualify for classic racing. But extra aluminum material should be added between the intake ports and at the outsides near the outer head to cylinder bolts. This would allow the ports to be widened for bigger valves and all out racing. For instance - the Harley XR750 ports have the same side profile shape as the drawing but are VERY wide and flow VERY WELL. See the image of the Harley port at the intake manifold compared to the Norton port below. You should have the choice of starting out with the small round port as with the stock Norton and be able to widen it as far as practical for higher performance.




Such a head shouldn't be a one off but rather the next head offered to the public.

Four valves per cylinder usually gives about a ten per cent increase in power compared with two valves per cylinder. You could use forked rockers ? Also a separate rocker box with centre plugs would be an improvement. I think the location of the pushrod tunnels might be a problem - but perhaps not.

A 4 valve head would require a complete redesign. No way of making one look like stock. It would then not be eligible for classic racing. And the market for 4 valve Norton heads for road use would be very close to zero!

I think the best idea would be a 2 valve head with modified combustion chamber, maybe running hydraulic lifters, and using a new alloy block, and a stronger 270 degree crank, and stronger cases for the crank, perhaps with a centre main bearing. Then a better 5 speed box. And perhaps open it out to 961cc whilst you’re at it. Then put it all in a Spondon designed frame with top notch Brembos and Ohlins...

Fast Eddie said:

A 4 valve head would require a complete redesign. No way of making one look like stock. It would then not be eligible for classic racing. And the market for 4 valve Norton heads for road use would be very close to zero!

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If you are making a cylinder head for historic racing that is different from making one which will make your old Norton go the fastest. It all depends on the rules. For myself, I would much rather race in classes which fully permit development as long as the basic design does not change much. In Australia, historic racing is the only area where the classes encourage development. So it is a nonsense. Everyone looks for ways to cheat. AHRMA rules seem to be well-designed to head off the cheaters, but that must stop a lot of technological improvement.
With historic racing, most of the other idiots cannot ride well, anyway. So why bother getting more horsepower and paying the costs ?

If you were buying a cylinder head for a road bike, would you buy a Fullauto head or an 8 valve head which would make your bike accelerate faster with probably fewer problems, if any ? - Lighter valves are less likely to tangle through over-revving.

I remember reading about an 8 valve head that Norton was experimenting with. This was in Classic Bike and must have been at least 20 - 25 years ago. The artical, if I remember correctly, said that they kept bending pushrods and gave up. A company in Australia was supposed to have acquired the prototype, again that is if I remember correctly.
John in Texas

acotrel said:

If you were buying a cylinder head for a road bike, would you buy a Fullauto head or an 8 valve head which would make your bike accelerate faster with probably fewer problems, if any ? - Lighter valves are less likely to tangle through over-revving.

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Having had more than my fair share of 8 valve modded Triumphs and NRE, of course I’d take the 8 valve head... BUT it ain’t that simple, it would be hideously prohibitively expensive to the point that the market for them would be tiny!

N0rt0nelectr@ said:

I remember reading about an 8 valve head that Norton was experimenting with. This was in Classic Bike and must have been at least 20 - 25 years ago. The artical, if I remember correctly, said that they kept bending pushrods and gave up. A company in Australia was supposed to have acquired the prototype, again that is if I remember correctly.
John in Texas

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I don't remember any reports of bent valves, but it was alleged to have overly stiff valve springs.

Here is a copy of the original 3 page Classic Bike article:

Hosted on Fotki

Hosted on Fotki

Hosted on Fotki

One of our esteemed forum members is building a DOHC 8 valve Commando...

jseng1 said:

When Norton went from the 650SS to the 750 they simply increased (& offset) the bore and failed to increase the valve size or move them away from each other to allow for increased diameters.

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Fact check....
Uhh! The small bolt pattern head Norton p/n S650/136 intake was 1.4"
Only the atlas 750's through 850's got 1.5" intake, which remained unchanged till the end of 850.
All this altered head concept is fine for intellectual bubblegum. I would think most racing sanctioning bodies would not allow them, and the resultant street market, IMO, would be minimal and mainly for bragging rights like a drouin supercharger.
However don't let me stop your fun!!!

BritTwit said:

I don't remember any reports of bent valves, but it was alleged to have overly stiff valve springs.

Here is a copy of the original 3 page Classic Bike article:

Hosted on Fotki

Hosted on Fotki

Hosted on Fotki

Click to expand...

Thank you, this saves me from spending some very non-productive but enjoyable hours looking thru all my back issues of CB.
John in Texas

There are a couple groups that are contemplating the production of a new Norton head to fill the gap left when the FA head ceased to be available. What I'm showing at the top of this post is the easiest way to improve performance with the least amount of effort. The head would start out with the already known FA style (and HD XR750) raised port floor and stock sized valves. Yet have the potential to receive large valves and wider high flow ports (proven by the HD XR 750) with the use of a hand held die grinder and re-cut valve seats (without having to change the valve guides or valve seats). Maybe its just a dream or maybe its more than that. Other people are involved and its up to them to push it through and offer it, or fall short and revert to the original design, or fail to even make it to the finish line.

Fast Eddie said:

Having had more than my fair share of 8 valve modded Triumphs and NRE, of course I’d take the 8 valve head... BUT it ain’t that simple, it would be hideously prohibitively expensive to the point that the market for them would be tiny!

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The market for FA heads is also tiny. I have a problem with historic race classes in that they limit development. 8 valve or 4 valve heads make very little difference, but a small step forward is always worthwhile. Nobody with a Commando engine is suddenly going to find another 10 horsepower unless they use nitro or a blower. The main improvements would be in reliability. When I race I use methanol fuel. However I rode my short stroke 500cc after it had been put back on petrol and there was not much difference. One of my friends raced a unit Bonneville with an 8 valve Rickman head, He said he could not tell the difference from when he used the standard head.
A lot of racers get paranoid. Tyre warmers look great on an historic bike in the pits. If you have not got those, you are definitely going to lose races. For myself - if I could race in BOTT against other bikes with air-cooled motors of less than 1000cc capacity, I would not care what the had done to them - I would still do very well. Guys worry about tyre sizes, suspension changes, date of manufacture - a lot of stuff is utter bullshit.