Commando Crankshaft Porn

My 850 has almost nothing done to it, and from experience I know it is still fast enough. 'There are more ways of skinning a cat' - if your bike pulls like a train and handles superbly,and if you can give it a really gods strong squirt way back in the corners you can often get the run on the guys with the big money top end motors and pass them while they are running wide. Then they need to have enough top end to out-power you down the straights and still have enough handling to get themselves around the next corner. I know this sounds cynical, however I rode an extremely under capacity Triumph against very fast Japanese bikes for many years . They can be beaten if you have the right mindset. I never won an Allpowers C grade race, however I always knew where the opposition were and what their bikes were like - strengths and weaknesses. It can be really funny if you out-ride them with a shit-heap.

If you haven't spent a big dollar on your bike, don't sweat it. One thing I always do when racing is note where the fast guys are when coming out of corners. If they are out on the ripple strips, I know I am in with a chance.

billet said:

jseng1 said:

Why go to all the trouble when I already have a cam with PW3 profile for BSA lifters - the JS stage 2. Plus it as two improvements - slightly more duration and closer lobe centers. The lobe centers are too wide on the PW3 at 107 degrees resulting in performance loss. The lobe centers on the JS2 are much better at 105 degrees. You want tho lobe centers to be close as possible without causing valve clash - to about 102 degrees but that would cause valve clash on any stock head unless the cam was very mild such as a stock cam (stock cams are at about 102 degrees).

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I have noted comments made in earlier posts about variations in the lobe centers of the PW3 camshaft, but had not an opportunity to measure one. The chance to do so came up recently, and using Cam Pro Plus equipment I was surprised to find the separation of the lobes based on the points of maximum lift was for the left cylinder lobes 109.28 deg, and 109.77 deg. for the right. I have noted that Jim Schmidt has given a figure of 107 degrees, and has indicated that in his opinion somewhere in the region of 102 ~ 103 degrees would be near ideal. My enquiries with the camshaft manufacturer in the UK brought forth the comment that they have made no variations to the lobe centers for this camshaft. If that is the case , then where does such variation come from, and are there any examples that are even wider than the 109 degrees I measured.
Is Jim's figure correct, or is the camshaft I measured correct ? The question has been put to Peter Williams for a definitive answer, but thus far he has declined to comment

The one piece camshaft is the only part of the commando design that I dislike. With a Triumph engine it is easier to progressively adjust the timings of both inlets and exhausts to optimize to suit the exhaust and gearing/handling for various circuits. I think that all that can be done is to have a standardised set of machine conditions and try various cams with different lobe centres and try to find a trend. It is a difficult and expensive path and I have chosen not to go there, I simply live with what others have done before me and advance or retard all the timings simultaneously to suit the rest of the set-up.
It would be interesting to know how the original domiracer racing cam was designed. A very capable A grader friend of mine says that it is the lift on both inlet and exhaust at TDC which is important, I don't know whether I agree with that.

acotrel said:

The one piece camshaft is the only part of the commando design that I dislike. With a Triumph engine it is easier to progressively adjust the timings of both inlets and exhausts to optimize to suit the exhaust and gearing/handling for various circuits. I think that all that can be done is to have a standardised set of machine conditions and try various cams with different lobe centres and try to find a trend. It is a difficult and expensive path and I have chosen not to go there, I simply live with what others have done before me and advance or retard all the timings simultaneously to suit the rest of the set-up.
It would be interesting to know how the original domiracer racing cam was designed. A very capable A grader friend of mine says that what is important is that maximum lift on both inlet and exhaust should be at TDC, I don't know whether I agree with that.

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You need to add this here.
most-disliked-least-useful-commando-part-edited-t18738.html

acotrel said:

The one piece camshaft is the only part of the commando design that I dislike. With a Triumph engine it is easier to progressively adjust the timings of both inlets and exhausts to optimize to suit the exhaust and gearing/handling for various circuits. I think that all that can be done is to have a standardised set of machine conditions and try various cams with different lobe centres and try to find a trend. It is a difficult and expensive path and I have chosen not to go there, I simply live with what others have done before me and advance or retard all the timings simultaneously to suit the rest of the set-up.
It would be interesting to know how the original domiracer racing cam was designed. A very capable A grader friend of mine says that what is important is that maximum lift on both inlet and exhaust should be at TDC, I don't know whether I agree with that.

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Does this friend sell valves for a living? :roll:

Sorry, on a rethink I got it wrong and I've re-edited my post. It is the lift at TDC which is important, however I believe that is just his way of setting the timing on his manx. Norton specified the lift at TDC rather than opening and closing points.

If you think about the Norton factory in the fifties and it's history. When Joe Craig and associates were building the domiracer, where would they start with the cam design ?

Snotzo said:

billet said:

jseng1 said:

Why go to all the trouble when I already have a cam with PW3 profile for BSA lifters - the JS stage 2. Plus it as two improvements - slightly more duration and closer lobe centers. The lobe centers are too wide on the PW3 at 107 degrees resulting in performance loss. The lobe centers on the JS2 are much better at 105 degrees. You want tho lobe centers to be close as possible without causing valve clash - to about 102 degrees but that would cause valve clash on any stock head unless the cam was very mild such as a stock cam (stock cams are at about 102 degrees).

Click to expand...

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I have noted comments made in earlier posts about variations in the lobe centers of the PW3 camshaft, but had not an opportunity to measure one. The chance to do so came up recently, and using Cam Pro Plus equipment I was surprised to find the separation of the lobes based on the points of maximum lift was for the left cylinder lobes 109.28 deg, and 109.77 deg. for the right. I have noted that Jim Schmidt has given a figure of 107 degrees, and has indicated that in his opinion somewhere in the region of 102 ~ 103 degrees would be near ideal. My enquiries with the camshaft manufacturer in the UK brought forth the comment that they have made no variations to the lobe centers for this camshaft. If that is the case , then where does such variation come from, and are there any examples that are even wider than the 109 degrees I measured.
Is Jim's figure correct, or is the camshaft I measured correct ? The question has been put to Peter Williams for a definitive answer, but thus far he has declined to comment

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Measuring maximum lift on the nose of the cam is not a reasonable way to assess the lobe separation angle (LSA) because very little change in lift is occurring while very significant changes in crankshaft angle are occurring, thus significant variation in such measurements can result. Likewise trying to determine lobe centerlines on the opening or closing ramps is fraught with the same issue, i.e., very little change in lift is occurring while significant change in crankshaft angle occurs. Ideally you want to determine lobe centerlines at a point in the lift curve when both lift and crank angle are changing rapidly. Try measuring it again at 0.040" and 0.050" lift to determine the lobe centerlines, and then determine the LSA from these measurements. The results at these points should all be extremely close to one another.

A friend provided some PW3 data to me which showed LSA of 106.3 deg (IN CL 103.5, EX CL 109.0) so results are consistent with the 107 given by JS.

Please let us know what you find out.

When I was building my 850 I was very conscious of the fact that the inlet and exhaust timings could not be adjusted independently except by expensive regrinding. Many years ago I had discussions with a guy whose son was successfully racing a single cylinder Honda 125 in junior dirt classes. They tried advancing and retarding the cam however got the best result by regrinding to different lobe centres. In the end it comes down to what works for you - whether you want mid-range (torque) or top end (horsepower). So the way the bike is set up to steer has an effect - if it naturally oversteers in corners you probably don't want a savage top end motor. Whatever exhaust configuration you choose, the timings must be optimized to it. My approach has been to play with what cam I already have and optimize that to the exhaust system. So far it looks as though I am heading for an explosion.

I've been looking at the cam timings of the JAP 4B 84S speedway engines. My opening points with the 850 cam and two into one exhaust are almost identical :

'Special Camwheel (Part No. 23154)

Our special camwheel with increased overlap period gives a valve timing:

Exhaust: Opens 90° before BDC. Closes 53° after TDC.

Inlet: Opens 60° before TDC. Closes 80° after BDC. '

Measuring maximum lift on the nose of the cam is not a reasonable way to assess the lobe separation angle (LSA) because very little change in lift is occurring while very significant changes in crankshaft angle are occurring, thus significant variation in such measurements can result. Likewise trying to determine lobe centerlines on the opening or closing ramps is fraught with the same issue, i.e., very little change in lift is occurring while significant change in crankshaft angle occurs. Ideally you want to determine lobe centerlines at a point in the lift curve when both lift and crank angle are changing rapidly. Try measuring it again at 0.040" and 0.050" lift to determine the lobe centerlines, and then determine the LSA from these measurements. The results at these points should all be extremely close to one another.

A friend provided some PW3 data to me which showed LSA of 106.3 deg (IN CL 103.5, EX CL 109.0) so results are consistent with the 107 given by JS.

Please let us know what you find out.[/quote]

You unfortunately seem to be unfamiliar with the method employed in Cam pro Plus to determine the point of maximum lift of a profile. Over the peak of the cam a great many measurements are taken to determine the points at precisely .003, .006 and .009 thou. Once the peak lift point has been calculated all the surplus measurements are discarded. However, Cam Pro Plus records all measured data, and to call up the data for lifts of .050 thou is straightforward. FYI the data for the 109.28 deg separation lobes at .050 thou lift is:- Exhaust 74.95 opening, 36.67 closing, and the intake 36.99 opening, 74.88 closing. This calculates out to a LSA of 109.0425 degrees (if you want to split hairs, otherwise 109 deg) This is some way off from the 106/107 , To date still no comment from PW.

Snotzo said:

You unfortunately seem to be unfamiliar with the method employed in Cam pro Plus to determine the point of maximum lift of a profile. Over the peak of the cam a great many measurements are taken to determine the points at precisely .003, .006 and .009 thou. Once the peak lift point has been calculated all the surplus measurements are discarded. However, Cam Pro Plus records all measured data, and to call up the data for lifts of .050 thou is straightforward. FYI the data for the 109.28 deg separation lobes at .050 thou lift is:- Exhaust 74.95 opening, 36.67 closing, and the intake 36.99 opening, 74.88 closing. This calculates out to a LSA of 109.0425 degrees (if you want to split hairs, otherwise 109 deg) This is some way off from the 106/107 , To date still no comment from PW.

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Snotzo,

Thank you for the thorough explanation of your cam measuring process. For clarity, are you measuring at the valve or at the lifter?

When I compare the PW3 cam timing I have to yours, it seems we are measuring two totally different cams. Specifically, your 0.050" lift opening and closing numbers equate to a duration of ~ 292 deg, which describes a huge cam (regardless of whether the data is taken at the lifter or valve) and doesn't sound anything like a PW3, which I've seen reported at ~ 270 deg duration at 0.040" lift.

The PW3 data in my possession, taken at the lifter, suggests durations at 0.040" and 0.050" lift of 271 and 263 deg respectively. Similarly PW3 cam data taken at the valve suggests durations at 0.040" and 0.050" lift of 275 and 267 deg respectively. All of this data is taken at 0 lash.

In light of the above it appears we might have a new mystery to solve. Perhaps we are measuring 2 different cams or possibly something in the data acquisition method(s) is amiss. It's also possible I have misinterpreted your comments. Let's keep after it and see if we can get to the bottom of it.

WZ507

the data measured was direct from the cam using a flat translating follower. With such an arrangement the point of maximum lift at the cam will also coincide with that at the valve, it's only the amount of lift that may differ.

If your followers are the standard flat foot type, then for sure there would seem to be a problem, but if you are using followers with a radius foot you will see a very different (shorter) duration.

The measured data I obtained was so much at variance with what I had been told or read about the PW3, that this was the reason for my initial post.

Snotzo said:

WZ507

the data measured was direct from the cam using a flat translating follower. With such an arrangement the point of maximum lift at the cam will also coincide with that at the valve, it's only the amount of lift that may differ.

If your followers are the standard flat foot type, then for sure there would seem to be a problem, but if you are using followers with a radius foot you will see a very different (shorter) duration.

The measured data I obtained was so much at variance with what I had been told or read about the PW3, that this was the reason for my initial post.

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The data I have, taken by COMNOZ, was also taken at the cam with a flat follower and appears to be in the correct ball park for a PW3. Your 292 deg duration at 0.050" lift puts the subject cam in the category of the largest Norton cams I am aware of. Thus we must be discussing two different camshafts. To help us narrow down the genre of cam you measured, what is your lobe lift? The PW3 data set I have shows a 0.380" lobe lift.

back on the crankshaft subject. it is a 13 minute video but worth it. I would hate to guess at the programing time to do this but it is amazing to watch.

https://www.youtube.com/watch?v=81UjjSH ... ata_player

bill said:

back on the crankshaft subject. it is a 13 minute video but worth it. I would hate to guess at the programing time to do this but it is amazing to watch.

https://www.youtube.com/watch?v=81UjjSH ... ata_player

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Nice, I wonder how many cranks I would have to make per month to make the machine payments. :cry:

Jim, you had better calculate how many per day, including weekends, probably 3 per hour for 18 hours, using two operator shifts to feed blanks and tools.......

But to allow you a couple of days a month to do something else, lets round down to 400 per month.....

If you spend 20 day per month writing programs for it, it should be able to do some fun stuff in 'your' run time :?

My apologies WZ507, I gave opening and closing data for 0.51 mm, not 0.050 thou. The correct data for 0.050 thou lift is:- Ex 61.84/23.47 = 265.31 duration. In 23.75/62.08 = 265.83 duration.
Cam peak lift is Ex 0.381 thou, In 0.380 thou.
Cam centerline is 109.28 at zero lash, 109.17 at 0.050 thou.

So although we have close agreement on lift and duration, the centerline discrepancy still exists.
Not too many manufacturers will tool up to produce this camshaft complete with worm drive, so I must assume the centerline variation is the result of slipshod manufacturing by the original supplier, unless there is another explanation that for the moment escapes me.

It is just possible that some users of the PW3 camshaft have a variant which could be the reason some are not satisfied with the resulting performance.

acotrel said:

If you think about the Norton factory in the fifties and it's history. When Joe Craig and associates were building the domiracer, where would they start with the cam design ?

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Did Joe Craig have anything to do with the 1960s Dommiracer :?:
Correct me if I am wrong, but I thought the 1960s Dommiracer was built by the late Doug Helne and his team- Joe Craig would have nothing to do with anything other than his beloved Manx :!:

Joe Craig died in a car crash in Austria in 1957. Doug Hele developed the Domiracer
Martyn..

Nice video. The youtube DJ's should try remixing the audio from that sucker.