Cams comparison

maaseyracer said:

I run the JS2, which is very similar to a PW3 cam. I run 9.5:1 compression (I am debating moving up to just past 10:1), beehive springs, BSA lifters, and RH10 conversion tubes. The JS2 is a big improvement over the stock Norton cam. It is a different power delivery experience, my opinion of the 850 was it made peak torque way too early. It felt like a tractor, and it was not the experience I wanted. (snip)

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Thanks for that. I shows well the importance to personal preference. When John Baker was building my 850 Production Racer engine at the Wolverhampton factory in 1972, we had a long talk with John Hudson, Service Manager at Norton Villiers UK/Europe at Andover. John H had worked in the road test, experimental/development, and race shops at Bracebridge Street and ditto at Plumstead Rd. and his opinion was that the best cam for getting down the road in a Commando was the stock cam. He loved the broad power curve to match the AMC 4-speed box and felt that -- unless your riding environment was substantially at high revs and fully-open throttle, the stock cam was a great choice.
The standard Commando grind, used in every Commando built at Plumstead, Andover, or Wolverhampton, except for Production Racers, Combat 750 engines, and 750 shortstrokes, is the "sports special" grind developed by Doug Hele for the 650 SS engine that began production at the end of 1961. (It was also used in all versions of the 750 Atlas engines.)

The characteristics that you didn't like were exactly why I loved it so much. That engine build included a prototype 850 head with no RH number with John's (1970s style) porting and 50 thou skimmed off the gasket face, matched 32 mm Concentrics and manifolds, standard pistons with hand-fettled valve relief pockets, and a strengthened crankshaft. With the stock 4-speed, there never seemed to be a place that there wasn't about as much power as I could use. For top speed, I think the highest speed I ever saw was ~6950 Rpm with a 24-tooth gearbox sprocket at the old Ontario speedway in California; a radar gun that somebody set up at the end of the front straight showed 137 Mph (which is a pretty good practical/versus/calculated match). On that day, I was using the "AMA"/TT full fairing and running Dunlop KR-73/76 tires.

That engine/cam combo was fast but what loved was the tractor-like smoothness. If you get up over 6500 Rpm very quickly, you need lots of long straights to make a few extra horsepower work for you. And that smooth, fat powerband is controllable!

Of course, if I had my choice today, I'd probably go with an STS/Full Auto Head, JS long rods and light pistons, a one-piece crank, a JS3 cam and BSA lifters, and big Keihins. (In fact, I did. I expect that I'll miss that old powerband but the TTI 5-speed will help.)

Blewdy Yaink said:

Thanks for that. I shows well the importance to personal preference. When John Baker was building my 850 Production Racer engine at the Wolverhampton factory in 1972, we had a long talk with John Hudson, Service Manager at Norton Villiers UK/Europe at Andover. John H had worked in the road test, experimental/development, and race shops at Bracebridge Street and ditto at Plumstead Rd. and his opinion was that the best cam for getting down the road in a Commando was the stock cam. He loved the broad power curve to match the AMC 4-speed box and felt that -- unless your riding environment was substantially at high revs and fully-open throttle, the stock cam was a great choice.
The standard Commando grind, used in every Commando built at Plumstead, Andover, or Wolverhampton, except for Production Racers, Combat 750 engines, and 750 shortstrokes, is the "sports special" grind developed by Doug Hele for the 650 SS engine that began production at the end of 1961. (It was also used in all versions of the 750 Atlas engines.)

The characteristics that you didn't like were exactly why I loved it so much. That engine build included a prototype 850 head with no RH number with John's (1970s style) porting and 50 thou skimmed off the gasket face, matched 32 mm Concentrics and manifolds, standard pistons with hand-fettled valve relief pockets, and a strengthened crankshaft. With the stock 4-speed, there never seemed to be a place that there wasn't about as much power as I could use. For top speed, I think the highest speed I ever saw was ~6950 Rpm with a 24-tooth gearbox sprocket at the old Ontario speedway in California; a radar gun that somebody set up at the end of the front straight showed 137 Mph (which is a pretty good practical/versus/calculated match). On that day, I was using the "AMA"/TT full fairing and running Dunlop KR-73/76 tires.

That engine/cam combo was fast but what loved was the tractor-like smoothness. If you get up over 6500 Rpm very quickly, you need lots of long straights to make a few extra horsepower work for you. And that smooth, fat powerband is controllable!

Of course, if I had my choice today, I'd probably go with an STS/Full Auto Head, JS long rods and light pistons, a one-piece crank, a JS3 cam and BSA lifters, and big Keihins. (In fact, I did. I expect that I'll miss that old powerband but the TTI 5-speed will help.)

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I have a set of John Hudson's tuning notes laboriously typed out by my wife from a copy lent to me by the local Norton dealer in 1975! He also states his preference for standard valves sizes, with a port optimised to get the best flow around them. It is a great guide to Norton engine assembly, whatever your planned use, and available these days as a downloadable .pdf!.

From late '75 to 1980 I owned an ex Thruxton short stroke hemi head with matching pistons, run on an 850MkIII bottom end with an ex Thruxton Peter Williams cam. The head had been ported by John Baker. Possibly the last he did whilst employed by Norton! I bought it from an ex-colleague of John's and didn't meet him.

Surprised to see JS3, but will be interested to see how that works out.

(My current bike has a TTi 5 speed, you will love it.)

Blewdy Yaink said:

The characteristics that you didn't like were exactly why I loved it so much.

Of course, if I had my choice today, I'd probably go with an STS/Full Auto Head, JS long rods and light pistons, a one-piece crank, a JS3 cam and BSA lifters, and big Keihins. (In fact, I did. I expect that I'll miss that old powerband but the TTI 5-speed will help.)

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JS3 moves that powerband up there. I have never experience the Sifton 460 the JS3 is based on a Norton, but I can tell you on a Triumph with proper setup it goes. If I were to build another Norton it would be the direction I would go, but I would probably chase a short stroke crank and an 83mm bore.

maaseyracer said:

JS3 moves that powerband up there. I have never experience the Sifton 460 the JS3 is based on a Norton, but I can tell you on a Triumph with proper setup it goes. If I were to build another Norton it would be the direction I would go, but I would probably chase a short stroke crank and an 83mm bore.

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Yeah, Jim says the JS3 is probably on the line -- but I want it to move. I was able to get a RoDy billet crank and I didn't think to ask him if he had a setup for a short stroke but I was able to obtain an STS alloy cylinder barrel (Nikasil bore) so I just went with the stock 850 size.

Blewdy Yaink said:

Yeah, Jim says the JS3 is probably on the line -- but I want it to move. I was able to get a RoDy billet crank and I didn't think to ask him if he had a setup for a short stroke but I was able to obtain an STS alloy cylinder barrel (Nikasil bore) so I just went with the stock 850 size.

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What type of crankcase are you using?

The 'standard' cam that some use in the Commando 06.1084 is actually just the same grind which became the SS cam back in 1961. The 06.1084 cam was not used for many models of the Commando, but around mid '74 it was then reintroduced as the standard cam. For the MK3 they changed the cam again, but I doubt if they fitted many 06.1084 by the time the receivers moved in. AN has the grind data for nearly all the cams since 1961, including a couple of 'exp' cams, that is how I can follow what cam became what.
For road use the 06.1084 and the PW3 are ideal, the cam I have fitted which was designed just before PW passed away is also very good despite many saying it would not allow the bike to start or even tickover. For the road use it works well, but needs a fair bit of work to get it to fit and work.

Madnorton said:

The 'standard' cam that some use in the Commando 06.1084 is actually just the same grind which became the SS cam back in 1961. The 06.1084 cam was not used for many models of the Commando, but around mid '74 it was then reintroduced as the standard cam. For the MK3 they changed the cam again, but I doubt if they fitted many 06.1084 by the time the receivers moved in. AN has the grind data for nearly all the cams since 1961, including a couple of 'exp' cams, that is how I can follow what cam became what.
For road use the 06.1084 and the PW3 are ideal, the cam I have fitted which was designed just before PW passed away is also very good despite many saying it would not allow the bike to start or even tickover. For the road use it works well, but needs a fair bit of work to get it to fit and work.

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Part numbers change for many reasons, change of material, different processing, different supplier, etc.

Presumably the profiles of these different cams was the same?

I have always been fairly certain the cam in my 850 is 650SS. I have never worried about the shape of the power band because I change the gearing to suit it. The gearing affects the carburation. When the ratios are widely spaced you lose more revs on up-changes, so there is a lag caused by the heavy crank and the tendency is to use the lower part of the needles in the carbs. That causes a slight richness in the mixture, and a loss of power. Slower taper needles work better under those conditions. I tried racing with the normal Norton box. It was hopeless - the bike was too slow everywhere. The biggest improvements with my Seeley 850 have come from using close ratio gears, slow taper needles, and increasing the trail in the steering geometry. I have power from whoa to go, but I only use the bit of the power band from 5,500 RPM to 7,300 RPM . When you use petrol as fuel, I do not think you would ever get the jetting really right. Fuel injection, programmable ignition and close ratio gears should make Commando really fly. If I had a road bike, I would investigate the set-up on the latest Royal Enfields.

Fast Eddie said:

Part numbers change for many reasons, change of material, different processing, different supplier, etc.

Presumably the profiles of these different cams was the same?

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If Madnorton's info is correct that only certain 74 850s used the 650SS profile then we have had it wrong all along.

My parts book shows the 22729 650 SS cam as being used in all 650 ss bikes, all Mercury, Atlas, N15, P11, P11A, G15CS, G15CSR, and G15Mk2. It was also used in all 88 models from 1963 onwards. Norton obviously loved that profile!

Dyno Dave's cam profile study shows that , although the part number changed, Hele's 650SS cam profile was used on all non Combat Commandos ( except PR)

Glen

maaseyracer said:

Interesting about the torque, I would have assumed it peaked much sooner, I have not studied dyno charts on these things.

I think I will be fine at 10.25:1 Plenty of clearance to the head and I am timed at 28 degrees, if it gives me any trouble I will time to 27 or 26 degrees, if I have issues there I will go back to

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maaseyracer said:

Interesting about the torque, I would have assumed it peaked much sooner, I have not studied dyno charts on these things.

I think I will be fine at 10.25:1 Plenty of clearance to the head and I am timed at 28 degrees, if it gives me any trouble I will time to 27 or 26 degrees, if I have issues there I will go back to 9.5:1.

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Thinking about this and having another look at dyno charts for the stock engine, it's not surprising that the peak might seem to be at a lower rpm.
Most of the dyno charts are for modified engines and those show less torque below 5000 rpm and more above.
I found two charts for stock 850s. They show an almost flat torque line from 2800 rpm all the way to 5600 . The line rises ever so slightly from 2800 to 5000 then tips down very slightly, but really stays almost flat to 5600 then tips down. The true peak is around 5000 but for riding purposes the torqueline could be considered essentially flat from 2800 to 5600, with the 850.

For the 850, that is a very well optimized cam for most road use!

Some riders prefer a different type of torqueline/ power output and there are lots of profiles for that.
As I age I seem to enjoy the 850 type torqueline more and more. The Thruxton R torqueline is almost identical in shape, except it is a lot higher of course. I suspect that the Vincent Rapide has a similar torqueline to the Norton 850 too, but it isn't quite as wide. That's fine because the high rpm danger point is a bit lower for the Vincent.

Once in awhile it is great fun to ride something that is more peaky in power output, a litre sportbike for example.
For travelling with a passenger plus luggage and pulling up long steep mountain passes, the high flat torqueline of the 850 Commando or 998 Vincent is really nice.

Glen

worntorn said:

What type of crankcase are you using?

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It might be "standard" but it's actually one of the first prototype 850 experimental castings. It was meant to be a perfect representation of actual production but I know that there were some detail amendments made to the design for later testing prototypes and factory production. (On the bottom, it was stamped "EX-829/2" so it may be the second 850 crankcase made).

When I built my Seeley 850, I had strong doubts about the motor. So the bike sat unraced for a very long time. When I finally got around to developing the bike by racing it, I found the 850 motor is actually an excellent design - except for only one aspect. If you want to rev the motor higher than 5000 RPM, you need to raise the crank balance factor. If the power out put decreases at revs above 5,600 with the 650SS cam, it is probably due to the crank. Mine does not do that. The bike accelerates at the same rate well beyond 6,500 RPM in top gear and feels as though the motor would rev easily to 8000 RPM. I do not know what a sensible answer might be. An Atlas crank might be better, but where could we buy them. I filled the hole which had been bored into the counterweight with a threaded steel plug. It is held in with blue Loctite, and the ends of the threads are punched. But it is probably not a good answer. The flywheel is cast iron.

With the stock cam, the torque does start to fall off faster above 5600, but the actual power peak is a touch higher at 5800. BHP doesn't really fall off much until 6200. These numbers are from Norton manuals and more or less line up with the two stock 850 dyno charts which I have looked at.
After 6200 rpm it is baseball cards in the spokes time. You can rev away and it will make a good noise but it will actually get down the road faster if the next gear had been selected at about 6200 instead.

Or perhaps a different cam had been chosen. But then we get into the crankshaft/ crankcase survival problem, which crops up somewhere in there.

Glen

maaseyracer said:

JS3 moves that powerband up there. I have never experience the Sifton 460 the JS3 is based on a Norton, but I can tell you on a Triumph with proper setup it goes. If I were to build another Norton it would be the direction I would go, but I would probably chase a short stroke crank and an 83mm bore.

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It is a lot of effort to have an 83mm bore. The bore centres need moving out as in a 1007 motor. This is what Steve Maney used to supply to do that: http://stevemaney.com/1007.html

83x80.4 would give you 870cc. It would likely be more cost-effective to go 81x80.4 for a 'square' 828cc. Or just a proven 81x89 920?

I guess my question is, what specifically does a short stroke 83mm bore achieve in return for the investment?

worntorn said:

With the stock cam, the torque does start to fall off faster above 5600, but the actual power peak is a touch higher at 5800. BHP doesn't really fall off much until 6200. These numbers are from Norton manuals and more or less line up with the two stock 850 dyno charts which I have looked at.
After 6200 rpm it is baseball cards in the spokes time. You can rev away and it will make a good noise but it will actually get down the road faster if the next gear had been selected at about 6200 instead.

Or perhaps a different cam had been chosen. But then we get into the crankshaft/ crankcase survival problem, which crops up somewhere in there.

Glen

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Bob Rosenthal is the only person I have ever known who road raced an Atlas 750 in Victoria. He fitted MAP pistons and rods which I would have thought would be heavier than normal. He rebalanced the crank to a factor in the high 70s. He was successful in A grade races before the two-strokes really got going. Then he was sponsored to race a TZ700. Destroying crankcases might be due to the low crank balance factor in Commando engines. I cannot imagine a 750 or 850 twin becoming smoother at high revs with a balance factor in the low 50s. With isolastics the vibration is probably not felt, but that does not mean it is not there.

With my bike, I have found close ratio gears seem to enable higher overall gearing to be used. There were times when I suspected the motor was revving but not pulling as strongly as it could. The heavy crank is deceptive. Sometimes there is more power there than is realised. My motor seems to be at it's best between 5,500 RPM and 7,300 RPM. The close box keeps it there at all times. But with lower overall gearing the bike does not accelerate faster. I use the crank inertia to advantage, it is not an impost. Race-changing gears on up-changes means less loss of revs. So you get a surge as the crank slows. It is when you lose revs and the gears are widely-spaced that the heavy crank is not so good. - I suspect that most guys have not tried slower taper needles in the carbs of their commandos. - With the heavy crank and widely spaced gears, they are probably using more throttle. That might mean their fuel mixture is slightly richer than is needed. Slightly rich means less power. With a road bike that does not usually matter. Reliability is more important. Better tuned motors are usually more affected by weather. That is one of the advantages of using methanol as fuel - it hides-up the tuning erroirs.

The freedom of movement that the isolastics provide in a Commando frame allow the engine/gearbox/cradle assembly to act as a counterweight to the pistons/small ends so they factor into the optimum balance factor. You can't properly discuss the balance factor of a Norton twin without specifying the frame it's mounted in.

hhh said:

The freedom of movement that the isolastics provide in a Commando frame allow the engine/gearbox/cradle assembly to act as a counterweight to the pistons/small ends so they factor into the optimum balance factor. You can't properly discuss the balance factor of a Norton twin without specifying the frame it's mounted in.

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When the isolastics are fully compressed what does the crank do which is different to when the motor is rigidly mounted ? You do not feel the vibes but the energy must go somewhere. The engine plates do not move in relation to the crankcases. The isolastics might remove some of the shock, but the engine and gearbox assembly are quite heavy. It takes more energy to rotate a crank assembly which is out of balance at high revs.

acotrel said:

When the isolastics are fully compressed what does the crank do which is different to when the motor is rigidly mounted ? You do not feel the vibes but the energy must go somewhere. The engine plates do not move in relation to the crankcases. The isolastics might remove some of the shock, but the engine and gearbox assembly are quite heavy. It takes more energy to rotate a crank assembly which is out of balance at high revs.

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The isolastics compress at a maximum near TDC and BDC, likely just after due to momentum. F=ma. Since the mass of the entire oscillating isolastically suspended assembly is much greater than that of the reciprocating mass in the engine, it doesn't need to move far to compensate the force. The fact that the engine plates don't move in relation to the crankcases just adds to the "counterweight" mass, hence less needed on the crank itself vs. in a Featherbed.

Fast Eddie said:

Part numbers change for many reasons, change of material, different processing, different supplier, etc.

Presumably the profiles of these different cams was the same?

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Among the changes in camshafts during the Norton Commando's history were introduction of oiling scrolls on the camshaft, plain parallel cam journals with oil scrolls in the bushes, the change to the 20M3S which moved the points to the end of the camshaft but retained the drilling for the timed breather, the interim camshaft for the "strengthened" cases beginning 200001 serial number that kept the points where they were but deleted the breather drillings. (Of course, the specification for "Combat cams", the PR cams, and the cams in the short-stroke engines are special and outside the discussion for "standard" cams.)
All of these modifications were done with the documentation of differing parts numbers and these show up clearly on the original factory drawings that Andover-Norton now holds. I was always told that the "grind" -- the camshaft lobe profile was unchanged for all these variants.

There was an ongoing program to reduce cam wear (and resultant damage to lifters). As the information of the fragility of the Combat engine began to come in, it was noted that there was an increase in the number of camshaft warranty claims (in hindsight, that also was the introduction of Castrol 10W-30 Multigrade oil at Castrol's suggestion that proved to turn in a straight-grade 8-weight oil after 200 Kms on the Autobahn). When I went to work at the service department at Wolverhampton in 1972, there was already a program to analyze cam wear failures and develop fixes. One ongoing program included the investigation of nitride surface treatment (sometimes called "Tuff-tride" treatment). The idea was to prevent the initial wear that makes the surface of the cam lobe abrasive against the lifter surface.
The nitride heat treatment was supposed to leave very hard, wear-resistant matrix of particles on the surface with a softer, more elastic (and thus less brittle) core material. Tests showed great promise for these cams -- when produced to very exacting quality conditions. Other designers pushed for a very hard consistent surface treatment to match the "Stellite" tips on the lifters -- the idea being that a surface that was hard as a red-headed divorce lawyer's heart would resist friction and prevent micro-damage from contaminants in the oil damaging the surface.
Every thing that was tried seemed perfect -- for a while. Then there were would be a pattern of failures. The suppliers would submit data showing that their treatment processes were perfect with consistent results but there was a big blip in early 850 Mk3 production.
John Nelson (Norton's general International Service Manager who had come to Wolverhampton after decades of work in Triumph's service department at Meriden and who was one of the most logical-thinking and insightful problem solvers I've ever met) lost many a night's sleep dealing with all this. I remember one time when we were reviewing data sheets and he remarked "I'm not sure that the issue is surface treatment -- I think that the problem is likely that instead of using EN32B-spec steel, the suppliers are actually making cams out of SH-one-T steel.")

I find it interesting there are a number of part numbers for cams, as Mad Norton says. (Preface -- He probably knows more about Nortons, their service, specs, and history than other person I know [except maybe Brian Slark but they each know a massive amount about different aspects]). Every parts book for Commando that I can find shows camshaft NM22729 for '68 -70 20M3 engines (ignition points behind the cylinder), 06-1084 for later '69 - '74 20M3S engines to '72 and standard Commando engines engine number 200001 thru '74, and camshaft 06-2608 for the 850 Mk# (some books quote 06-1084). But why would the Mk3 need a different camshaft, especially one carries a number contemporaneous to part numbers drawn for the Commando Street Scramble "SS"-model in the spring of 1971? All I can see is that the cam bush quoted to accompany the 06-2608 camshaft is only two part numbers different and it's a non-scrolled bush.

It appears that the spares department was convinced that the "standard" cam for engines with the points timing on the camshaft end was 06-1084. The provision of a different standard cam grind involving different lobe profiles, different part numbers, and different drawings must be a subject with very arcane details unknown to most.

I'd love to hear more about this mystery. Thank you, B Henderson, Carrboro NC USA