Computer scan of Norton Combustion chamber

I'm embarking on an ambitious Norton race head project and I need some help.

The entire combustion chamber will be welded up and lowered approx .120" so the squish band is flush with the head gasket surface (clearance will be restored with thick head and base gaskets). This will effectively raise the ports and allow a steeper downdraught for higher flow (starting with 28m ports and re-shaping for "Narley ports"). The port floor radius near the valve seat will be more gradual. Larger valves will be re-angled as well.

My machinist needs a 3D model of the stock combustion chamber along with the stock valve seat recess (which we can change).

I'm not into Solidworks modeling.

Here is what my machinist has to say about it:

The tough part for me is to make a 3D model of the combustion chamber. I have some options. I can measure a dense grid of points with my CNC machine but creating the SolidWorks model would be a challenge this way. I also have some contacts that can scan with a laser. I will investigate and get back to you.

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If someone has the 3D model already or can help in any way with scanning etc it would be greatly appreciated.

A better way might be to compute the shape from an algorithm which can be used to programme your CNC machine. A bucket or dog-bone shape might be better than hemispherical, however whatever the performance result - a lot will probably depend on luck. The alternative of measuring an existing combustion chamber which you know works, is not really moving forward, but might be more effective. To do it, you will probably end up in the realm of regression analysis.

I wonder if anyone has made a pushrod-operated 4 valve per cylinder head for a Commando ? The Rickman head did not do much for the Triumph 650 engine. I'm under the impression that the normal Commando head was the best production item ever, for a British twin. It is certainly better than any Triumph head from the 60s.

acotrel said:

I wonder if anyone has made a pushrod-operated 4 valve per cylinder head for a Commando ? The Rickman head did not do much for the Triumph 650 engine. I'm under the impression that the normal Commando head was the best production item ever, for a British twin. It is certainly better than any Triumph head from the 60s.

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Of course they have. Do a search on this forum for all sorts of info on them.

Ken

Hi, yes 8 valves had been done , made by Pete Lovell and Les Emery, it had been described in a Classic Bike, they were for sale for a short time , then disapeared..................!

Jim,

That's a lot of welding, it will probably soften the alloy. At least that's what I found doing similar work on Triumph heads.

Have you considered making up skulls that can then be inserted into a head that has been machined to accept them?

This would not risk softening the head, and would create easier, repeatable machining operations as the skulls could be churned out on a CNC and the machining of the head to accept a skull would be a MUCH easier operation.

Skulls are popular in the drag racing world as a way of preventing cracked head, dropped valve seats, etc.

I did it once on an 8 valve Triumph head, the skulls were made from bronze. It seemed a very good way of doing things to me.

Fast Eddie said:

Jim,

That's a lot of welding, it will probably soften the alloy. At least that's what I found doing similar work on Triumph heads.

Have you considered making up skulls that can then be inserted into a head that has been machined to accept them?

This would not risk softening the head, and would create easier, repeatable machining operations as the skulls could be churned out on a CNC and the machining of the head to accept a skull would be a MUCH easier operation.

Skulls are popular in the drag racing world as a way of preventing cracked head, dropped valve seats, etc.

I did it once on an 8 valve Triumph head, the skulls were made from bronze. It seemed a very good way of doing things to me.

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I would rather pour some molten alum into the combustion chamber and machine from there. Let me know more about your skull experience and describe how it is attached and if there are heat transfer problems etc.

Bronze Skulls sound like a lot of machining - the head and both surfaces of the skull.

Welding will soften the metal but you can quench the head in boiling water immediately after welding when its hot and heat treat it in an oven for several hours at about 375 deg F. I've done that for cases and it age hardens. What did the factory do after casting?

The alternative to welding for me is to pour molten alum into the port floors (with conical anchoring plugs) and then re-port/re-angle valves from there.

What did the factory do with them after casting? They threw them into the wheelbarrow with the others of course!

I welded a Triumph head to centre-plug it. A crack developed between a valve guide and the inlet port. Back in those days I did not know anything about solution heat treatment and age-hardening of aluminium alloys.
It is not an insurmountable problem, if you can identify the alloy. There is a system which uses simple chemical spot tests for identification. Then use your national standards to find the appropriate heat treatments.

Fast Eddie
I’m interested in getting bronze skull conversions done on some knackered Weslake cylinder heads I have lying around. I wonder if you could let me know who did the work and what it involved. I knew it has been done before by John Simper but when I mentioned it to Dave Nourish he wasn’t very keen. I then found out that Dave had done a conversion to his own personal race engine. Now he’s retired I don’t have the option of bugging him anymore.
I guess this should go in a new thread if we get into it to save messing up Jim’s topic.

Hi Seeley Weslake

If I see Dave at Donnington I will ask him about skulls.
As an aside, I am sure fast eddie knows. Dave Degans ran a set of 650 cases with an 8 valve top end short stroke Triumph as a 500. I remember reading about him slipstreaming a couple of Rob Norths & getting them into the corner at an airfield circuit. This bike had bronze skull in.

Chris

SeeleyWeslake said:

Fast Eddie
I’m interested in getting bronze skull conversions done on some knackered Weslake cylinder heads I have lying around. I wonder if you could let me know who did the work and what it involved. I knew it has been done before by John Simper but when I mentioned it to Dave Nourish he wasn’t very keen. I then found out that Dave had done a conversion to his own personal race engine. Now he’s retired I don’t have the option of bugging him anymore.
I guess this should go in a new thread if we get into it to save messing up Jim’s topic.

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Yes, Degens 500 8 valve has bronze skulls, and a lot of other trick stuff! It would rev to 11,000. I rode it a few times, it is a fabulous thing. It was faster than my 840cc Triton that had been dyno'd at 74 rwhp!

@ SeeleyWeslake, Nigel Hall Smith at Fluff Racing did my head. He did a great job and is a good bloke for this kind of stuff. You do need to be patient however! PM me if you need his details.

Well the computer scan may be very expensive and maybe not necessary since it is just an offset hemisphere. The hemisphere can be located in relation to the head bolts and machined to the correct depth. Even so its a bit pricey to have it farmed out - $1500 being a rough quote.

Its fine with me if others want to talk about bronze skull installation and Triumphs - I'd like to know how Dave kept the valves in control at 11,000 RPM.

I might be able to help you with a computer model, I would do it in Rhino, that is what I have
I have a great deal of experience making complex surfaces, send me a PM
I have also made complex surfaces from algorithms

jseng1 said:

Well the computer scan may be very expensive and maybe not necessary since it is just an offset hemisphere. The hemisphere can be located in relation to the head bolts and machined to the correct depth. Even so its a bit pricey to have it farmed out - $1500 being a rough quote.

Its fine with me if others want to talk about bronze skull installation and Triumphs - I'd like to know how Dave kept the valves in control at 11,000 RPM.

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Simple, Degens was (is) a huge fan of lightening the valve train. His rockers were carefully minimised, his cams subtly modified, mainly through trial and error, but the main thing was he used valves with 4mm stems.

He later realised that 11,000 rpm was not necessary or helpful so limited it to around 10,000.

Hi Eddie

Bad news Eddie, please read this link. https://www.gofundme.com/nigelandandye
I wont comment, Nigel did a lot of work on my Jim Lee 8 valve that got me out racing & always gave advice & stopped for a chat.

all the best Chris

With 4 valves per cylinder, the valves are much lighter, so higher revs are more easily achievable - the problems them move elsewhere. If you short-stroke the crank, there is a problem with power delivery - 'torque wins races'. A high revving four-stroke motor with megaphone exhausts which has most of its power in the top 2000 RPM is probably the worst case scenario, even though it might be good in theory. Overall 4 valves per cylinder usually give about a 10% increase in power across the whole rev range. So it is worth doing if there is a race class which would accommodate it, and it doesn't cost too much. If you think about 500cc JAWA speedway motors, the best two-valve is almost as fast as a good four-valve.

Chris, Fast Eddie,
Thanks for the info on Dave Degens and Nigel HS. Chris beat me to it with the link to the gofundme page and it seems having Nigel do the mods will not be an option. Although I’d seen his bikes many times in the paddock over the last 30ish years when spectating at CRMC events I’d never had the chance to talk to him, but a very nice guy by all accounts.
Any ideas on who else in UK might be able to do this kind of work? A google search shows that there are companies in USA bronze skulling Japanese m/c 4 cylinder heads for drag racing but it would have been nice to find someone who’d done the Weslake heads before.
Jim – re 11,000 rpm
The 500 Weslake (and Degens ) engines which both rev to 10,000-11,000 rpm have some inherent advantages over the Norton valve train. The cams are gear driven and better supported, the push rods are much shorter, especially in a short stroke like the Degens engine and they have 4 springs ( 2 per valve ) operating on one pushrod/cam follower. At one point Dave Nourish started using stronger valve springs which coincided with his introduction of roller followers which were a lot heavier than the stock Triumph ones he previously used. However I don’t believe any spintron type analysis was done so who knows what banging and crashing is going on in the valve train at these rpms.
A drawback of high spring pressures and rpms is that on the Weslake/NRE heads the valve seats get bashed back into the head. This gets worse as the head ages and softens with temperature cycles. The head softening leads to 3 deleterious effects – 1 -the valve seats move and get pushed back in the head, 2 -the groove for the copper ring compression gasket deepens and eventually the head contacts the barrel leading to loss of sealing pressure and 3- the helicoils for the head bolts under the exhaust ports pull out. The #3 problem I have fixed myself with bronze insets but the other 2 are more problematic. There is very little metal surrounding the valve seats and to repair them I’d have to have the head welded thereby softening it more. If I was able to have it re-heat treated I’d still have the problem of it going soft again (in about a couple of seasons). Hence my interest in the bronze skull as a permanent solution.

Back to Nortons -I was wondering if anyone has experienced Norton heads going soft? I’ve read on this site of plenty of people having the front studs pull out which is possibly an early symptom. However, I haven’t heard of any racing Nortons having their valve seats move around – the Norton racers I have known seemed to retain their valve sealing pretty good over time.

As far as high revs and high compression are concerned, I don't go where I don't need to go. Do your event promoters do fuel checks ?

Hi

Pip Hingham? the sprinter was the first person I read about doing bronze skulls that was in his drag race bike one of the GS1000 type bikes although I dont know what capacity it ended up at.
Dave Degans would be the man to ask but I am sure he wont give you the namme of who did his skulls.
However I do remeber being told that someone in the vintage club did this to his bikes. I cant remember the bike this was done on!!! but it was 50s eraor earlier.
Will post & ask on the BHR site.

ps The Daytona with 4mm valve stems, offset ball lightened rocker arms, light weight followers & springs with less poundage resulted in an engine where the cam did not get worn out. Dave told me the race springs sold with higher spring rate pressure caused lots of problems & wore out cams quickly. ie every second season.

Chris