commando camshafts

Aco, check out the current issue of Classic Bike mag in the newsagent , it has a thoughtful Commando[roadbike] build by a Pommy Jaguar driveline engineer who goes in to reasoning/solutions re gearing issues, he also stays with the stock cam, but accurately timed & utilizing a modified Jag cam chain tensioner.

My gearing issues seem to have come from my lack of understanding about the torque characteristics of the long stroke 850 motor. I'm not used to running high gear ratios, then increasing them and going faster. My old short stroke Triumph usually went slower when I did that. The bike seems to be good on alcohol, even with the low comp. ratio. I've always had a problem believing in this bike, it seems absurd to me. I note that somewhere a person mentioned building a short stroke commando engine. Seems to me they would get the same result by building a Triumph motor with a squish band head ? I don't t hink the Norton 750cc SS production racer was successful ? It was probably easier on the bottom end than a long stroke motor, but I wouldn't think there would be much performance advantage ?

Youre Manx type ratios get 1st about where 2nd is standard . Close Ratios . The 1st is about 2 teeth inside the ' to small ' to get a kickstart pawl in .

Therefore , youre the equivilant of starting in second . Standard Norton Close is within 2 % of Triump Close gears , which maintan theyre kickstart facility .

Thefore ( agian :lol: ) with a five speed , you can get youre C/R 4 speed AND youre first gear back again . More or less . The Highest kick Start capeable 1st
is 2 teeth over std. first , and 2 below C/R first . So the high K/S 1st is half way between Std Commando first 7 manx first , taller than Cdo , lower than Manx.

Youd only need a six for a hairpin bend circuit , or rideing it up the back lawn . Though the old Schnaflinter was used on the continant on the Manxes gearing for 140 mph .

And you think YOUVE got PROBLEMS . :lol:



There are huge and very strong “hairpin” style valve springs and enormous coil springs to keep the aluminum followers from floating.

http://images.google.com/imgres?imgurl= ... sch&itbs=1

You will also need a considerable increase in compression ratio to go with the PW3 cam

Click to expand...

What's a 'Considerable increase' in your opinion? I have a PW3 and always felt it lacked something. My own fault really for believing all the performance improvement blurb. Yes it does but not with the kick my old 2S had at 4500 rpm. That felt like something extra but whether it actually was is debatable I guess. Mine is 750 with Combat head and 030" barrel spacer. Do you thing removing that and going back to original 10:1 compression is worth considering? I reckon I have about 9.3:1 at the moment. My head has also been overworked from what I read here and that may be the major issue. Big ports in and out. Certainly the exhausts are so far from Jim's 'D' profile they don't even bear any resemblance as such.

Is this " PW 3 " the actual " 3S " cam ? was alledged to be more a top end powerband type .Less down low (3S) than 2s & 4S . 3S for Daytona , in the 72 machines ? ?

Is this " PW 3 " the actual " 3S " cam ?

Click to expand...

Not according to Peter Williams. He intended it as a design to address the 'issues' of earlier performance cams. See here how he mentions the 3S and resulting PW3 calcs.
http://www.peterwilliamsracing.com/pw3cam.pdf

There is some scuttlebutt that the 3 in PW3 is because Axlel and then Woods 1st made this basic cam profile with easing ramps then a hand full ended up in England and the rest is history.

Aggressive cam and big ports both will like, nay need as high CR as ya can run and not detonate on the fuel and timing. The faster ya turn it the less detonation proneness. Change stack height of engine components means valve train geometry to diddle with to recenter rockers on stems.

Might try a standard small port head, even with its lower CR than CHO, for some pleasing response to hot cam and dialed in 2-1 headers.

I am surprised at the guys reshaping the combustion chamber, fitting bigger valves, porting bigger, and fitting extreme camshafts. I don't believe that approach is building on the strengths of the commando design. The long stroke inhibits the usable rev range, so the benefit of the hot cams is limited. Removing the squish band and porting bigger changes the combustion dynamics away from what should produce torque. My feeling is that I wouldn't try to make a Triumph motor out of a Commando motor. Both have their strengths, but the Norton motor is better - it contributes towards a much more ridable bike. Horsepower and top end are not the answer to everything - torque and reliability also play their part. My own 850 motor is quite silly, but it works. The 2 into 1, seems effective and I know the bike is fast enough to win, even though the motor is cheap and nasty.
I know where you guys are coming from with the big ports, hot cams, short stroke stuff. (Been there, done that with a Triumph) I still have arguments about it with a friend of mine, but I have another friend who always built his Triumph 650 motor to deliver torque,never revved it over 6,300 RPM. He has a much better racing record. My own short stroke Triumph 500 was a nasty piece of shit, I have the scars to prove it .
Here is a photo of an accident about to happen. It is of myself when I first raced in about 1967. The motor is a 650 cc Triumph engine fitted with a 63mm billet crank, extreme cams, ported to the max. The exhaust has 4 inch megaphones. It came on with a real bang at 5,500 rpm, and revved to 10,500 rpm. It had a 4 speed CR box, and ran alcohol at 10 to 1 compression. It was fitted with T1 triangular dunlops, and originally had a poor Triumph racing front brake out of a GP 500 racer. The bike was dangerously unrideable, and I crashed it everywhere . :

Indeed , CRITACALITIES . W.O.F.T.A.M.

I did it to myself, and I was lucky I wasn't killed. I don't know how to stop others from doing that silly stuff, but I suppose it is all part of growing up. That Triumph engine was great in theory, but in practice it was a really nasty bastard. It still had the long rods in it, so there was an angularity problem. On a big fast circuit, it would wind out forever, but on a tight one it was useless unless you dropped the gearing right down, dropped the tyre pressures, softened the suspension and revved the tits off it. I raced it for 12 years, however what I did not know was that a previous owner had taken it to Bathurst and bounced himself off the armco at Skyline Corner breaking an arm and a leg. I found that out several years after I had sold the bike. - All experience !
These days when I ride the Seeley it is all easy with no anxiety. I know it is very difficult to crash myself and if that starts to happen I stay in control. If I ended up on the deck it would be at about 30mph, not the big cartwheel at 100mph.
In that photo on the right hand side, the motor is probably revving at about 8000 RPM.

O.K. , who does . . .



And Why Not ,

Matt Spencer said:

O.K. , who does . . .

And Why Not ,

Click to expand...

Nourish does this for Weslakes.....

Why not on a Norton, making a cam profile to suit should be OK for teh smart guys, but fitting two sufficiently robust roller followers in one Norton follower tunnel looks a bit of a challenge....

And the sum of the benefit would be?

Compared to say JS BSA style followers (lifters)

Bearing in mind that the pushrod would still flex and the roller and pin would have play and will still wear!

Could be the difference between using 'R type' followers in a Triumph engine compared to standard radius ? Might make the bike slower. You probably should never need light valve train with the low revs the commando uses to produce it's power ? Even with the hot cams the profiles shouldn't require lightened followers etc. - just an opinion. I'd be trying to use slower lift rates, and lowering rates, and I wouldn't want a peaky long stroke motor anyway.

Mike Libby, Axtell's business partner, developed a roller lifter conversion for Commandos, but never marketed it. As I recall, he used lifters they had left over from a BSA Gold Star roller cam setup. The lifters rode in a bronze insert in the lifter tunnel, similar to that used for the BSA lifter conversion for Nortons. The bottom of the insert was machined in a way that located the rollers and kept them aligned. He did the same conversion for a Triumph flat track bike, and it seemed to work quite well, but he never ran a Norton with the conversion, at least up to a few years ago, the last time I talked to him. He had made the tooling to drill the cylinders for screws that located the lifter blocks, and had gone out to a local high performance machine shop for estimates to make the parts, but wasn't financially able to proceed. Time spent on R&D doesn't pay the bills, so he had to spend his time on work that he got paid for.

It was a nice design, but I'm not sure how much it would gain over current cam designs using radiused lifters. To get the total benefit of roller lifters you need a more aggressive lobe profile, which requires heavier spring pressure to work. I'm not sure the long skinny Commando cam is stiff enough for that. Fitting a center cam bearing, as some here have already done, would probably help a lot, but you'd still have the problem of the Commando's small lobe size, and limited room for a large enough roller. All that really increases the side forces on the cam and lifter, making the cam flex even more of an issue. In any case, I don't think we'll see Mike's conversion available in the future. I asked several years ago if he was interested in selling the design and tooling, and he was very positive about not being interested.

It's clearly possible to design something like this, if anyone is interested enough. The question is really whether it would be a significant improvement over what we already have.

Ken

When i got Peel leaned over in a corner with my elbow stirring up THE Gravel I use that long flexy camshaft to fire big bang wheel spin go lift front wheel so not using any front tire for steering leaving all corner cripples in my skinny cam wake.

Fk'n hilarious!!!!

Thanks for those comments Ken.

Somewhere in my future is a project to produce a short stroke 500 Norton engine for modified racing in NZ. After running a developed standard Dommie motor in NZ Clubmans class I want try a new class.

A friend has been running roller followers in his Velo for several years now and is very keen for me to put them in the new motor.

But Im not so keen for several reasons

- Im not sure I need it. Im aware of 500 Dommies that run up to 8500 rpm without valve control issues. In fact I have video of my bike reving off the line at over 8000 rpm without valve bounce and it has a almost standard valve train and a PW3 cam. Higher than normal spring pressure but no measurable wear on cam or followers in more than 6 years of racing. Only problem has been pocketing of valve stem ends which means valve replacement about every three years. Could use lash caps but that breaks my simplicity rule - see the next point.

- Its way more complex than the standard or BSA style solutions. One thing I have learnt is that putting more complex components inside a race bike gives more things to fail. For example I do not use a vernier on the camshaft. I use them to tune the bike on the dyno but then go through my collection of cam sprockets to find one that matches the optimal cam timing.

- Roller bearings that will fit in are not very robust. My friend checks the Velo ones after every meeting and often finds they need replacing.

- It will not be cheap and I could use the $ elsewhere to more effect I think.

I hadnt thought of the cam flex issue.

John

I don't use a vernier on the camshaft sprocket either. I simply broached two more keyways at random.

Holmeslice » Mon Sep 17, 2012 10:23 am
When i got Peel leaned over in a corner with my elbow stirring up THE Gravel I use that long flexy camshaft to fire big bang wheel spin go lift front wheel so not using any front tire for steering leaving all corner cripples in my skinny cam wake.

Click to expand...

Oh NO! Kenny you can't lean that far on THE Gravel w/o taking off more than ends of elbow and knee nor get traction enough to lift front off surface but by golly I'll take all the ribbing in the world as long as i can keep the ingenious isolastic power unit and 360's power hits to get that dang dangerous front unloaded out of any traction to matter when kicking up stones for fun. Most fun is to get spun loose before the turn leaving dark tire trace marks separated somewhat all the way around. Guess what it will look like when Peel reaches tarmac again? I see yoose racers sticking stuff way out in the breeze, jeeze Louise on Peel I'm frantically pulling body parts in on surprise contact for more clearance for gosh sakes. Don't know if her dolly training wheels should go on bar ends or cage ends yet : ) Get over on peg pogo-ing state then nail it WOT, that's when Peel gets funnest on pavement. If ya want a sense of Fast Graveling, just let half the air out of tires and remove brakes then spin rear right up accelerating into that hook back at Barbers... one after another. That's what Norris D drag cam is for in Peel, trip down power out of there! Bring on them camshaftless hot peaky 2 smokes there's a 4 stroke clunker eager to tango. Try that lazy flattracker wide cross up antics and see where that leads ya.