PW3 Cam timing

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gripper said:
The spec sheet that Mick Hemmings supplies gives the following timings:
Inlet opens 50degrees before TDC
Inlet closes 82 degrees after BDC
Exhaust opens 84 degrees before BDC
Exhaust closes 48 degrees after BDC
These figures are taken at the valve but not sure if that is with zero valve clearance or the 0.011" normal clearance.
Looks like it's time to get the degree wheel out again and get back into the timing chest.
Click to expand...


I looked at you original post and I had exactly the same situation as you. I was getting 165 thou lift at TDC, but here's the catch: When I checked the timing with the opening and closing points, it was spot on! The two different methods of checking gave two different result about 5 degrees apart.

I left it at 165 thou ( advanced a bit) but haven't had time to road test it properly.... it's only been a year.
 
pommie john said:
gripper said:
The spec sheet that Mick Hemmings supplies gives the following timings:
Inlet opens 50degrees before TDC
Inlet closes 82 degrees after BDC
Exhaust opens 84 degrees before BDC
Exhaust closes 48 degrees after BDC
These figures are taken at the valve but not sure if that is with zero valve clearance or the 0.011" normal clearance.
Looks like it's time to get the degree wheel out again and get back into the timing chest.
Click to expand...


I looked at you original post and I had exactly the same situation as you. I was getting 165 thou lift at TDC, but here's the catch: When I checked the timing with the opening and closing points, it was spot on! The two different methods of checking gave two different result about 5 degrees apart.

I left it at 165 thou ( advanced a bit) but haven't had time to road test it properly.... it's only been a year.
Click to expand...

Hi John, did you check the lift on the pushrod or at the valve? 145thou on the pushrod will be about 165 thou at the valve
 
I had the conversation with a friend of mine who was a top A grader with the most developed manx in Victoria in the early sixties. He said that the cams should be on max lift at TDC. My feeling is that it is the opening and closing points which are important, also the gas inertia in the exhaust system, so I always compare with what I know works in other bikes of similar capacity. A 7R AJS is similar to an 850 commando in its basic dimensions. And I tend to believe that being a small single it was developed to the max for good overall characteristics, whereas the commando has always been limited by its bottom end, so probably never achieved the highest power band, nor best torque .
I might have a strange way of looking at things, however I feel there is a lot more midrange to be had from the Commando motor, better than going up in revs. Then you need the gearbox to use it effectively.
 
In my opinion there is considerable confusion in some of the posts in this thread.

A couple of things.

Just because a cam has the same opening, closing, and lift as another cam does not make it the same cam.

Please read the article titled Valve lift profile design at this location.


http://www.profblairandassociates.com/RET_Articles.html

To quote from the article


"Those of you with a mathematics bent will realise that the
numerical differentiation of the valve lift-degree profile will
produce a velocity-degree curve; the differentiation of the
velocity-degree curve gives an acceleration-degree profile; and
the differentiation of the acceleration-degree curve gives the
jerk-degree characteristics. {Just as the velocity of a car is the
rate of change of a distance-time curve and acceleration is the
rate of change of velocity}.
It will also be remembered that, courtesy of Isaac Newton,
acceleration is directly related to force and hence jerk,
which is the rate of change of force, is an ‘impulse’ or
‘hammer blow’. "

Peter Williams designed several cams including the 4 S and the PW3. The PW3 was designed using a computer at Warwick university and was very probably the first Norton cam designed using modern cam dynamic mathematical techniques. He specifically designed the PW3 to minimise this "hammer blow".

Jack Wiliams - the engineer who developed the AJS 7R in the late 1950s and Peter Williams are father and son.

http://en.wikipedia.org/wiki/Peter_Will ... cyclist%29

Peter knew a very great deal about his fathers work and spent several hours telling me about the issues his Dad had with cam design on the 7R.

The inlet cam lift at TDC should be set on the push rod. Peter designed the cam for a wide power spread. But as I said in my first post he recomended advancing it 5 deg if you wanted top end power.

If you bought the cam from Mike Hemmings ring him up for advice. He may even pass your questions on to Peter Williams.
 
I have a PW3 from Norman White, and when I asked him about valve timing he said to just put it on standard timing marks.

With just a PW3 on my standard engine, it probably performed worse than standard. I then changed capacity to 920, big valve head and as Chris has remarked on, increased compression to 9.8:1 and it was a lot better. Which of these changes had the biggest influence I don't know.

Regarding a "kick in the seat", the only cam on a Norton that has done this for me is the 2S, except when I had my 2-1-2 on my present bike, this exhaust moved the power up the rev band, but when the power started it really pulled well, but with less low down torque than a standard exhaust system.

Probably not much help to you, but just my observations.
 
I haven't played with Norton cams yet, however I recently bought a combat cam from Bwolfie. I advanced my standard 850 cam 12 degrees and when I fit the combat cam, I intend to advance it 6 degrees. This gives, I believe, the inlet opening at about 65 degrees BTDC in both cases. The main reason is that because the cam is one piece that is the earliest that I feel the exhaust opening point is tolerable. At present the exhaust closing point in my motor is pretty silly, I think it is about 27 degrees ATDC, however with the two into one pipe, it seems an error corrects an error. As far as cam profiles are concerned , years ago I bought Ed Iskenderian's book, and I felt that what he did with the computer des ign of cam profile, had much to recommend it. One of the main things about cam profile, is that it should not snap the valves shut too quickly. The old style Triumph GP cams used to do that, and they were valve droppers. I know very well that just because the same timings are used, it doesn't mean the cams are the same. But if you think about the standing waves in the inlet and exhaust tracts, it makes sense that similar capacity and stroke bikes use much the same timings for a similar torque characteristic. My intention with my commando is to always try to maximise the torque, what happens at the top end of the rev range is largely irrelevant, unless you are very rich. One of the first things I ever did when building my 850 motor was soften the cam sprocket by heating it on a piece of firebrick, then I had two more keyways broached into it, randomly spaced. With that I can get sensible timings, and are not limitted by what is intended for road use on a production motorcycle. So far I have not had to change from my original timings which I used after thinking about what happens in the two into one exhaust. The bike is easily quick enough. If you have a look at the race timings for the big four cylinder Japanese bikes of the 70s, you will see that their four into one pipes are compensated for in the cam timings . They never used the sorts of timings that were used in 500cc MV fours or Honda four cylinder GP bikes . I think that if somebody did the real deal to a Z900 and used four separate pipes they would be horrified with the result, and in any case wouldn't have the gear box required to use it. The Honda CR750 was like that.
 
Pommiejohn's post regarding 165 thou lift and correct timing figures coincides with what a friends 850 gives and that is fitted with standard timing settings.
Thanks everybody for your contributions, some are pretty well beyond me but I have managed to pick the bones out of them. My plan is to take some acceleration figures and then advance the cam 5degrees and compare the figures. Probably won't get done till after the France NOC rally and whilst I'm sure the Commando would get me there and back, I'll be wankeling my way there on my rotary. (No cam timing involved in that engine)
 
acotrel said:
At present the exhaust closing point in my motor is pretty silly, I think it is about 27 degrees ATDC, however with the two into one pipe, it seems an error corrects an error.
Click to expand...

Thats a pretty weird cam timing ?
The stock Commando cam is listed as closing at 42 degrees, and the Combat cam at 60 degrees.
Are you using some odd checking clearance ??
 
I had a 2S cam in my tuned 850 & it flew. About 4 years ago I rebuilt the motor & replaced the cam with a PW3. The bike is still in the same tune otherwise. It seems to me the bike is not as powerful now. I also rebuilt my 750 over the winter & changed the standard cam to a PW3, I expected the bike to really go, but am a bit disappointed.
The 2S cam give hell of a kick on my 850, it was a job to stay on the seat under hard acceleration in 2nd.
The only thing I can think of is that because the exhaust lift is as high as the inlet lift, is that it lets a lot more gas out keeping the compression down.
 
Flo said:
IThe only thing I can think of is that because the exhaust lift is as high as the inlet lift, is that it lets a lot more gas out keeping the compression down.
Click to expand...
Hence the need to advance.
 
i'm so glad others feel as fond of the disparaged 2S cam as I am, at least in a 10 CR engine. The most noticed to me is the Comat 2S pull after 90 in 4th, as I don't tend to WOT in lower gears long as its too easy to fly into red zone. Check out DynoDaves graphics to see most cams are slight variations of the 2S but also need other features to take advantage of them.

Got me 2 hours Combat ride in till dark, kept in legalistic rates - to report the 2S Combat in 4th is good from 30 mph to 125, thought only reached 70's today. IIRC these Amals have 260 main jets. Trixie's cam is set per factory but must try the degree process for further Nortoneering lesions.
 
Regarding a "kick in the seat", the only cam on a Norton that has done this for me is the 2S,
Click to expand...
The 2S cam give hell of a kick on my 850, it was a job to stay on the seat under hard acceleration in 2nd.]
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Exactly my experience. I had the engine down to the barrels in March and was tempted to put the std cam and tappets back in. I resisted but now wish I had. I did pull the compression plate and replace with a gasket for a bit more comp to help the cam but the only change seems to be an extruded base gasket. Oh well I still have not learned to leave well alone :roll:
 
Rohan, It IS pretty weird cam timing. If you subtract 12 dehrees from the 42 degree normal closing point for the 850 cam, it comes out that it is about 30 degrees ATDC. I cannot remember what the normal exhaust opening point is for the 850 cam, but I know it was the consideration of that which set the limit to the amount of advance I used. I achieved an inlet opening point of 65 degrees BTDC which is sort of sensible. The checking clearances were zero. I'm sorry that I am working from memory, I know I should keep records however I am definite about how much I advanced that cam in my motor (12 degrees). All I can suggest is that somebody might like to try it, and see if they can duplicate my result with the two into one exhaust. I never believed in my commando motor, but after doing this idiocy, I can only say I'm impressed. I've had problems gearing for the torque.

When I get around t o using the combat cam, I will use 6 degrees advance which will give the same 65 degree inlet opening, however the exhaust closing point should be around 35 degrees
 
Rohan, It IS weird cam timing, and all I can suggest is that it might be worth somebody trying to duplicate using a similar two into one pipe. I use zero setting clearances, and my figures can be out by 3 degrees.
My current timings are as follows :

Inlet opens 65 BTDC
Inlet closes 59 ABDC
Exhaust opens 94 BBDC
Exhaust closes 27 ATDC

With the combat cam this will be

Inlet opens 65 BTDC
Inlet closes 83 ABDC
Exhaust opens 94 BBDC
Exhaust closes 54 ATDC

I don't believe you could use those exhaust opening points with separate pipes. I've never believed in the commando motor, however I can only say I'm really impressed with mine. It's a big adrenalin rush - a serious bit of gear.
 
Seeley920 said:
Hi John, did you check the lift on the pushrod or at the valve? 145thou on the pushrod will be about 165 thou at the valve
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Hi John

Yeah that was at the pushrod. It consistently gave reading 5 degrees apart. Dead on by lobe centres, 5 degrees advanced by the 140 thou at TDC.

Since I'm hoping to convert it into a road bike now, a bit more torque would be good, so I'll leave it there and see how it goes.
 
" I'll be wankeling my way there " indeed . Thought it was a bit coarse there :shock: :lol: , for a moment .
 
I suggest there is a question which should be asked. The first commandos had race steering, and chucked a few beginners up the road after they hit 'cats eye's in the middle of the highway. Norton modified the steering on later models to make it less dependent on rider skill. If Norton had a choice of three of their race camshafts to fit to standard commandos, do you think they might not back them off a bit so that the bikes were more tractable on public roads? I wonder how many guys have simply accepted the specified settings as gospel, and used them without trying to advance or retard the cams a bit to see if they were better elsewhere ?
 
Maybe this would be a good place to repeat that the most accurate way to time a cam is by lobe centers. That's what most professional race engine builders rely on. It can get a little tricky if you have a cam with asymmetrical lobes (different profiles for opening and closing ramps), but I don't know of any Norton cams like that except some in-house Axtell cams that weren't available to normal customers.

FWIW most Commando race cams are specified at 104 - 106 intake lobe center. I've seen specs for Commado race cams from 99 to 106, but most are right around 104. The optimum setting for maximum horsepower (on a dyno, not seat of the pants) depends on compression ratio, intake, exhaust, etc., but doesn't usually vary by more than a couple degrees from the setting recommended by the cam maker. You might find something outside this range with a really extreme engine build. If so, I'd guess comnoz would be the one to know. He's certainly built some extreme engines. Feel free to chime in here, Jim!

Ken
 
'The optimum setting for maximum horsepower (on a dyno, not seat of the pants) depends on compression ratio, intake, exhaust, etc., but doesn't usually vary by more than a couple degrees from the setting recommended by the cam maker.'

Ken I defer to your much greater experience with the dyno. However maximum horsepower at peak revs is not the be all and end all. The shape of the power curve is extremely important. The length of the inlet tract , and the exhaust tract determine the lengths of the standing waves in each and true optimisation can only happen at only one RPM reading. The opening and closing points on the cam lobes set when the pulse is to occur, the shape of the lobe affects the shape of the power curve. It easy to arrange cam timing so that the motor is 'peaky' and the bike is difficult to ride, older two strokes are examples of that. The effect of compression increase is to give an overall small increase in power right across the usable rev range, increasing the revs at which the standing waves are optimised gives an increase in power due to the increased number of firings per minute, however it comes at the price of reliability. My feeling is that fattening the mid-range without increasing the revs is the way to go. I don't know how well data about midrange power (torque) is collected from dynos. Over the years in Australia, we have often been limited to about one peak horsepower reading, obviously modern dynos have much better instrumentation. My only way of knowing whether a change has been beneficial, is by riding the bike and noting its acceleration out of corners, and whether it is easier and faster to ride. As you say - 'seat of the pants', however it is the moment of truth. Rationalising gearing for the commando, I find problematic.
 
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