Norris RX camshaft update

Frankly all the suggestions with modifications to inlet and exhaust sound like modifying the whole house if the new front door doesn't fit. If I can't make the RX work with current setup....then will get a cam that does work. I'm not at that point yet. Thanks, though.

Are you using standard exhaust pipes and mufflers ? The inlet tract length is not critical, but if the exhaust stifles the cam it will not be effective in producing its distinct power band. A race grind cam should produce a much different effect to a mild road cam in the same motor. It should be very noticeable when you ride the bike. If you cannot feel the cam spot with the Norris cam, you probably either have it timed incorrectly, (and a few degrees out should not cause a problem ) - or you have too much exhaust back pressure. I've never fitted a race cam to a Norton. I find the 850 cam is OK for racing, but with a two into one exhaust, and the long stroke motor, it doesn't have a very distinct 'cam spot'. Others will be able to tell you what sort of power band the Norris cam usually gives when it replaces the standard cam.
Whenever you make a change to your setup, you should be able to detect a difference. It is a matter of being conscious of the way the motor spins up, and the way it pulls, whether it gives a kick in the pants a bit up the rev range as a 'cam spot' etc. It is always better if you test the bike facing the same landscape, so you are using the same gears in the same situations. With my Seeley 850, I always practice at Winton Motor Raceway. I know the circuit extremely well, and even the most minor advantages/improvements are detectable. It is always a matter of changing only one thing at a time.

acotrel said:

Are you using standard exhaust pipes and mufflers ? The inlet tract length is not critical, but if the exhaust stifles the cam it will not be effective in producing its distinct power band. A race grind cam should produce a much different effect to a mild road cam in the same motor. It should be very noticeable when you ride the bike. If you cannot feel the cam spot with the Norris cam, you probably either have it timed incorrectly, (and a few degrees out should not cause a problem ) - or you have too much exhaust back pressure. I've never fitted a race cam to a Norton. I find the 850 cam is OK for racing, but with a two into one exhaust, and the long stroke motor, it doesn't have a very distinct 'cam spot'. Others will be able to tell you what sort of power band the Norris cam usually gives when it replaces the standard cam.
Whenever you make a change to your setup, you should be able to detect a difference. It is a matter of being conscious of the way the motor spins up, and the way it pulls, whether it gives a kick in the pants a bit up the rev range as a 'cam spot' etc. It is always better if you test the bike facing the same landscape, so you are using the same gears in the same situations. With my Seeley 850, I always practice at Winton Motor Raceway. I know the circuit extremely well, and even the most minor advantages/improvements are detectable. It is always a matter of changing only one thing at a time.

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As you said, no distictive cam spot with the Norris RX at this point. As noted rechecked cam timing last weekend and very close to Norris spec at .020" tappet clearance. The standard cam that was in there previously also has no cam spot, just too much engine pinging under load. Stock pipes and Toga stright through reverse cone mufflers. Intake is stock Amal 932/19, 932/20 with Mike Gaylord sleeved slides and stock size K&N air filter. I do know what you mean for cam spot as my first Commando was a new '72 combat purchased in 1973. The double S cam comes alive at 7,000 redline like a two stroke getting on the pipe.

To get rid of pinging and/or detonation there were a lot easier roads to go down. Thicker head gasket, a close look at timing and carburetion for three.

10:1 is probably close to a practical limit for long trips in the summer, with a light rider who knows how to keep the engine spinning and feed the throttle in as it is needed. In the absence of computerized injection and ignition the human brain has to do the work, something that younger people who did not grow up with points and carbs don't have a chance to learn.

C.R. Axtell and Ron Wood ran 9.5:1 on mile tracks and 10:1 on shorter tracks in one of the most powerful 750 Norton racers ever put together, and they were Wizards compared to most Norton tuners. And Axtell certainly wanted to win, and certainly pushed his hardware all he could.

So it is no surprise that hobbyist/mortals would run into trouble experimenting with those compression ratios. I know that racers are running higher compression now in "Norton" engines that have almost no Norton parts in them, but Axtell and Wood ran long-stroke engines that were almost all stock except for the cam, and they had it worked down to how long each stock part would run before it needed to be replaced or failure risked.

On the bright side you are learning a lot, it is an education. The Combat Commando is a novelty or collectors item anymore. It will wear it's valve gear and other mechanical parts out faster than regular Commandos just because it needs to be revved to get it's power, and it invites abuse.

Throw the Combat head and other period performance parts in a box and put it on a shelf, and put a regular head and mild cam in. Done the right way you can easily have a bike that will leave a stock Combat in the dust and will also run longer before it needs to be torn down again.

It may be some people's choice to re-live the 60s or 70s though by sitting on an over-cammed , over-ported and less rideable and reliable machine. If that is your cup of tea then maybe you are on the right track.

The 'pinging/detonation' problem has me wondering how you are riding the bike ? Perhaps you are not allowing it to rev enough. Too much throttle combined too high gearing can cause pinging, especially in high comp. engines. I never have that problem as I use methanol fuel, and the bike is always working hard spinning up through the gears on a race circuit, using a CR box. Even though your bike might not come onto the cam with a boot, you should still feel a boost in power if the cam is hotter than your previous item. I agree with Beng though. If the cam and porting are too radical, you can create something which might have higher top end when wound out, however if you try to outride someone with it, a milder motor with more mid-range could be much more effective. Personally I strongly believe in fitting race cams to four stroke motors. They give the biggest performance boost of any possible mechanical change, however you have to live with them.

God luck with your tuning. It is certainly the way to learn and it does my heart good to see you making the attempt to improve your bike. I've sometimes worried that people like myself won't exist in the future. That nobody will know the sheer joy of building their own bike, and having some success with it. I don't believe you can get that from a computer game.

Hm, on the other hand too much pinging indeed implies enough CR for more aggressive overlapped cam to wake up. My Trixie with fast rise hi torque pressure points spark adv does just fine any way I've tried her in heat high of summer on 87 octane 500 to 2000 ft elevation changes, which means some miles of steepish climbing on hi-ish throttle while wishing for over drive as so responsive to throttle hard not to exceed legal speeds too dam much. I do agree the standard head is good idea even if not milled to up CR as the velocity seems to pack mix in nicely on 2S cam so why not a RX.

BSA discovered fuel strave issues with stock Amals so if fuel level on low side that might be enough to not feed the need for speed. They cut a slot out into bowel between needle seat and needle top choke point. Need to listen to open pipes video for sense of their effect. New plug chop might be informative. If an rpm limited power drop in all gears instead of just 4th pulling to 80, then I'd suspect an issue in cam drive on the ignition curve. That is what knocked Peels insane spunk down to 5000 only in 4th but pulled pretty good to reline in lower gears. Then I discovered no cam chain tensioner left, ugh. Drove Boyer into over drive over adv like some rev limiters do for smooth cuts in rpm power.

The pinging could be a fuel issue or too much advance, however from experience just fitting a race cam to a motor using the prescribed timings doesn't usually give detonation problems. If they were there previously, and have disappeared after fitting the new cam the ignition advance has probably changed in the process. I agree with you Hobot, there could be fuel issues with this, however I would expect the usual coughing and spluttering if that was the case , not an overall leaning off across the whole rev range which you would see in a plug chop, after using the bike at full throttle. Even if the cam and ignition are timed slightly incorrectly, or the exhaust is too restrictive, the motor should not ever miss.

acotrel said:

Personally I strongly believe in fitting race cams to four stroke motors. They give the biggest performance boost of any possible mechanical change,.

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Absolutely false. Throwing a big cam into an otherwise stock Norton engine is going to be the least power gain per cost in money and time.

IF you take a stock Norton though and just remove the head, do a smart porting and valve job, put in longer intake manifolds and do some simple tuning to the exhaust it will kick the shit out of the bike with the cam change, and you will never have had to do anything to the engine below the head gasket. If you mill the head a hair for an extra half compression point and make sure your jetting and ignition is tuned you will have a really fast bike, again with never having to tear the engine down below the head gasket.

Dunstall will back me up on this, and so will Rob Muzzy, and I suspect many other smart tuners. Very simply, a racing camshaft is useless except in a racing engine that is being raced.

i've surveyed online Commando/Norton owners for reports and conditions that detonation/ping/knock detected to mainly get decades old stories of standard cam in 'detuned Combats, a few racers pressing limits in summer heats and a couple-3 of owners with oil coked chambers on poor gas = Nortons are pretty darn detonation tolerate. It timing so adv it detonates on the road then would be dangerous to ks but might not be notice on a racer roller stater that turns right thru a back fire. Still time chain issue might bother an electro brain so can't be ignored in the scope of details.

I struggled for a few years with the pinging, compensating with race gas, retard timing to 26 degrees full advance with no permanent solution. I finally bought the Starett dial indicator and magnetic stand to measure the lift and to my surprise was .330 both intake and exhaust straight off the lifters - std Commando. With 182psi compression it made sense what was going on. My solution was to change to a longer duration camshaft. As is normal the Norris RX was a solution of opportunity...found it for sale. The profile looked OK, so trying it. After last weekend's mearsurement at the valve with exhaust lift at .392 with 0.008" tappet clearance it seems this camshaft is not to spec .425 lift although the intakes are right on at .424" lift at .006" tappet clearance. Not sure if this is causing the lack of performance. The engine revs up easily in lower gears, but that one weekend of pushing top gear could not excelerate passed 80mph on a flat road. If still having this, my last resort is play with main jet size. If no joy there, my next winter project is strip the engine again and insert a combat cam. At least with the combat I can use the dot alignment for set up. With the RX cam I had to do some gear teeth and chain sprocket adjustment to get it to spec.

Do your mufflers have baffel plates in them?
if so remove them.
I had a pair of Coventery Spares Dunstal copies that gave my bike the same symptoms unll I punched out the solid baffels.

Beng, if a race cam is fitted to any engine for which it has been designed, as long as the carburation is somewhere near right , and the ignition system is OK, and the exhaust is not restrictive, the motor will develop its characteristic power band. Compared with a standard motor, it will usually be faster below the power band, and much faster in the operating rev range above the cam spot. You are correct that a lot of motors respond well to getting carburation and ignition timing right, however if you fit a race cam you have to do that anyway. Every time I've fitted race cams to standard Triumph motors, the experience has been a quantum leap forward in performance, as long as the exhaust has not been restrictive. What often contraindicates against fitting race cams is the operational rev range they give. If peak torque is up around 7000 RPM in a commando motor, it must be revved beyond the normal safe limit to use the cam to full effect. In a Triumph 650 motor E3134 race kit cams give a rev range of 4000 to 8000 RPM, a Norton commando won't cop 8,000 RPM reliably, however the Triumph will for quite a long time. Then it blows up.
I don't have a race cam for my own 850 engine. I've just bought a combat cam which I believe will be a bit better than the standard 850, however I'm concerned that I might lose the torque characteristics of my current setup. It is no good getting more top end power, if the motor won't accelerate hard right through the rev range. When I gear my bike, I always expect some lag when accelerating out of corners. My 850 doesn't have much of that. It is really difficult not to over-rev it, even though it pulls very high overall gearing. I think it would be slow on a big circuit but on a tight one, it is great.

I recently had a discussion about building a fast Norton, with a friend who raced my old short stroke Triumph in the fifties. He was still on about big ports, full race cams, short stroke - all the stuff which gives a dangerous unridable bike. The Norton commando engine is a different concept. It is obviously designed to pull, and it is extremely good when combined with the light Seeley frame and high gearing. Fitting a race cam to a road bike is often a step towards making it unpleasant to live with..

Bruce MacGregor said:

Do your mufflers have baffel plates in them?
if so remove them.
I had a pair of Coventery Spares Dunstal copies that gave my bike the same symptoms unll I punched out the solid baffels.

Click to expand...

no plates, you can shoot a bullet throught them and hit nothing.

beng said:

To get rid of pinging and/or detonation there were a lot easier roads to go down. Thicker head gasket, a close look at timing and carburetion for three.

10:1 is probably close to a practical limit for long trips in the summer, with a light rider who knows how to keep the engine spinning and feed the throttle in as it is needed. In the absence of computerized injection and ignition the human brain has to do the work, something that younger people who did not grow up with points and carbs don't have a chance to learn.

C.R. Axtell and Ron Wood ran 9.5:1 on mile tracks and 10:1 on shorter tracks in one of the most powerful 750 Norton racers ever put together, and they were Wizards compared to most Norton tuners. And Axtell certainly wanted to win, and certainly pushed his hardware all he could.

So it is no surprise that hobbyist/mortals would run into trouble experimenting with those compression ratios. I know that racers are running higher compression now in "Norton" engines that have almost no Norton parts in them, but Axtell and Wood ran long-stroke engines that were almost all stock except for the cam, and they had it worked down to how long each stock part would run before it needed to be replaced or failure risked.

On the bright side you are learning a lot, it is an education. The Combat Commando is a novelty or collectors item anymore. It will wear it's valve gear and other mechanical parts out faster than regular Commandos just because it needs to be revved to get it's power, and it invites abuse.

Throw the Combat head and other period performance parts in a box and put it on a shelf, and put a regular head and mild cam in. Done the right way you can easily have a bike that will leave a stock Combat in the dust and will also run longer before it needs to be torn down again.

It may be some people's choice to re-live the 60s or 70s though by sitting on an over-cammed , over-ported and less rideable and reliable machine. If that is your cup of tea then maybe you are on the right track.

Click to expand...

These are the standard responses to the combat engine. I share hobot's enthusiam for combat performance, so my criteria are no engine plates to lower compression, the combat head stays and yes the only reason to ride a Commando is the 70s feel, although not reliving it as I've continuously owned Commandos since 1973. I can buy a modern bike that can leave the combat in the dust as well as any other Commando, so no point there. Now how to get the RX to work properly or scrap it for the combat cam I know will work. If you think the RX is in no way going to work with my criteria, let me know your opinion and why. Thanks

I remeber reading an interview with a well known tuner many years ago. His advice on cams was " Decide which cam you need for your purpose, then fit one slightly milder"

This was my last shot that really woke up Ms Peel, for sense of exit hole size to shoot for in a 750. Open pipe sucked and completely open mega was too painful.

I agree that t he '70s feel' of a commando is important. I suggest that with any bike, you have to recognize what it is, and as a thunderbike the commando is excellent. It doesn't pretend to be a modern machine. Amongst historic racers in Australia, manx nortons are usually built with 26 degree head angle replica frames, and 18 inch wheels, and they handle like Suzuki two strokes. My question is - what does that prove ? There are not so many guys left who have ridden the genuine article, and experienced what the original setup actually does with the 19 inch wheels. I love my Seeley 850 simply because of what it is. I love that style of bike, even though it is obsolete in modern terms.
I would love to get onto a race grid a longside a Ducati 851 Pantah,an 860 or a 900, and compare the Seeley Commando with them in battle. I'd be surprised if it got thrashed.

acotrel said:

There are not so many guys left who have ridden the genuine article, and experienced what the original setup actually does with the 19 inch wheels.

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So was the "experience" that bad that it culled the field a bit?

There would not be more than one genuine manx you would find in Australia which has not been butchered in a vain attempt to make it go faster. Most of them have 18 inch wheels to get decent rubber onto them. That shags the handling. As for the manxs that handle like Suzukis - why would anyone go there ? The bike is not a modern machine, if you want that you simply buy a current model and race it. In about 1973, a mate gave me a ride on a good 1961 500cc manx, which was ex-Ginger Molloy. I found out why the old A graders used to love them so much. I'm eternally grateful that I had that experience, and I know what they were like - confidence inspiring ! My 500cc Triumph (Triton with 18 inch wheels) was faster in a straight line, however my lap times were quicker on the manx. If I got offline with the manx, just gave it more stick.
I really believe that most of the guys current doing historic racing in Australia don't value anything. If you own an original manx, you are custodian of some thing valuable. If you think forward 50 years , how will anyone know what the guys raced in the fifties, the experience won't be available because all of the old bikes will be too modified to provide it? I know the guys want to win, however surely there must be some other considerations ? You could buy a second hand VFR400 and enjoy exactly the same racing without destroying something beautiful which has a history ?

I remember that Rohan got a bit edgy when we discussed building a racer out of a Guzzi Falcone and he is quite right, the racing is not worth it.

A longer intake is critical and it really enhances those 32mm ports.

At least at 3/4 to wide open throttle, velocity stacks, especially the ones with the same 32 mm inside diameter as the carbs, not the larger ID common ones with the fine thread that screw on to the carb but the "racing" ones with the three set screws.

There's a pic here
http://www.nortonraceparts.com/roadrace-parts.html
of the ones I refer to. On these the idle circuit passages are not filtered - just holes open to atmosphere.

They can be made to work with a stock air box/plate if you reverse the rubber bellows and place them pointing inside the air box, the rubber grommet portion flanges onto the airbox plate while the other end seals against the outside of the bells. Heck of a job getting it all assembled.