PW3 cam in 750 motor

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oldmikew said:
Just a thought, but the PW3 was surely designed for the F750 racers , presumably with the so called big valve heads and short stroke cranks.
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The PW3 was designed well after the F750 period had ended.

When Peter was racing and developing at Thruxton he produced a new cam design every week according to some, but the PW3 design used computing that was not available to him in those days. As I understood it, it was the cam he wanted to design in the '70s.

And considering the limitation that has been revealed today at high rpm it was hardly designed with only short strokes and big valves in mind!
 
jseng1 said:
Yes it is an excellent cam designed by the great Peter Williams and very popular . It works especially well - unless you rev it over 7000. Then it has "severe" valve bounce problems (even with high performance springs) as shown on the spintron.

Unfortunately Peter Williams didn't have the luxury of a spintron and slow motion cameras when he designed his cam. If he did he probably would have given it more gradual closing ramps and avoided the problem as shown in the critical video on page one of this thread. He did the best he could with the tools that he had on hand at the time and the PW3 sold like hotcakes (winning races) regardless of the valve bouncing.
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However, when designing the PW3 Peter had the benefit of computing resources he did not have at Norton in the 1970s. I probably had access to far more computing power than the whole of Norton in my daily activities from '74 to '80! I just didn't know how to use it!
 
Snotzo said:
Blue 750
are you beginning to wonder whatever has happenned to your topic ?
Perhaps you should have been warned, there are some notorious persistent thread high jackers on this forum.
I do seriously wonder whether it's worth posting any more, admin seem uninterested in doing anything to curb the practice
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Being the new joiner I don't want to complain :)
I'm happy the discussion is going and there have been some good posts on the original topic. Having never ridden a Combat or otherwise tuned Norton it's difficult to know what type of change the 2S or PW3 cam will bring. These are the cams I can source easily in Europe if I choose to go with more constrained budget on the rebuild. Obviously it's a different thing if one goes the JS kit route.

But the more I think about it, the more I lean towards the std. cam if I choose the budget route. A number of people have commented that the PW3 increases exhaust noise. That doesn't fare well here in Switzerland. Also thinking I have the early cases with the breather on the cam. These lack strengthening around the main bearing area that was later introduced. So not sure how much more the cases can take.

I have no plans to rev above 7k rpm but keep the engine working when on the move. Around here we ride mountain passes and I don't go easy on the old bikes. But it has to function as an around town ride as well.
 
Hello
Stick with the standard cam, it will do all what you want, and be the most reliable. Putting a performance cam in these engines will stress the valve gear more, with all the attendant issues that brings. Plus without doing a lot more work on the head and valve train you will not realise the performance gain with a race type cam. More noise yes, for a couple of hp more at the top end and less hp at the bottom. Hence the power band as the engine comes on the cam.
The standard cam will give plenty of pass climbing performance, I know that for a fact as i toured switzerland in 2017 and be a better behaving bike around town.
Regards
Peter
 
SteveA said:
The PW3 was designed well after the F750 period had ended.

When Peter was racing and developing at Thruxton he produced a new cam design every week according to some, but the PW3 design used computing that was not available to him in those days. As I understood it, it was the cam he wanted to design in the '70s.

And considering the limitation that has been revealed today at high rpm it was hardly designed with only short strokes and big valves in mind!
Click to expand...

I did not know the PW3 was a post F750 cam. I did wonder whether a big valve would center better on its seat and possibly be less liable to 'bounce'
 
Blue750 said:
Being the new joiner I don't want to complain :)
I'm happy the discussion is going and there have been some good posts on the original topic. Having never ridden a Combat or otherwise tuned Norton it's difficult to know what type of change the 2S or PW3 cam will bring. These are the cams I can source easily in Europe if I choose to go with more constrained budget on the rebuild. Obviously it's a different thing if one goes the JS kit route.

But the more I think about it, the more I lean towards the std. cam if I choose the budget route. A number of people have commented that the PW3 increases exhaust noise. That doesn't fare well here in Switzerland. Also thinking I have the early cases with the breather on the cam. These lack strengthening around the main bearing area that was later introduced. So not sure how much more the cases can take.

I have no plans to rev above 7k rpm but keep the engine working when on the move. Around here we ride mountain passes and I don't go easy on the old bikes. But it has to function as an around town ride as well.
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Standard cam is the one for this kind of work. When you enter the 48 'Tournante' of the Stelvio it will pick up great from low revs. It is a good all round cam in any case.
 
When I was a kid, one of my favourite things to do, was to fit the best race cam into near standard road bikes. By the time I was about 27, I'd had so many near-misses on public roads, that I went road racing. When a race cam comes on song, it usually gives a lovely adrenalin rush. With a 2 into 1 exhaust, you don't get that - but for racing it is much better. The lack of the bump in the power curve allows you to ride much faster around corners.
This discussion has convinced me I should pull my 850 motor apart and stop it's oil leaks while fitting the 2S Combat cam. I think I might order a set of beehive valve springs.
 
If you want an exercise in sheer terror - fit separate pipes with megaphones and a race cam to your commando and try riding fast around a tight twisty race circuit using the standard gearbox. If you get it wrong halfway around a corner when you are riding fast, you can end up in all sorts of trouble.
 
acotrel said:
If you want an exercise in sheer terror - fit separate pipes with megaphones and a race cam to your commando and try riding fast around a tight twisty race circuit using the standard gearbox. If you get it wrong halfway around a corner when you are riding fast, you can end up in all sorts of trouble.
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You just described a significant percentage of the Commando production racers of the '70s! Most of us just had a lot of fun!
 
SteveA said:
You just described a significant percentage of the Commando production racers of the '70s! Most of us just had a lot of fun!
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Not just Commandos in the 70s though... when you think about it most 4 stroke racers throughout the 50s and 60s had separate pipes and open megas, from Manx Norton singles to 6 cylinder Hondas...
 
acotrel said:
If you want an exercise in sheer terror - fit separate pipes with megaphones and a race cam to your commando and try riding fast around a tight twisty race circuit using the standard gearbox. If you get it wrong halfway around a corner when you are riding fast, you can end up in all sorts of trouble.
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You keep saying that, Alan, but it's been disproved by all the guys who successfully raced Commandos with exactly that setup. I raced this one for many years, and never encountered the "sheer terror" you keep going on about.

PW3 cam in 750 motor


Ken
 
Blue750
I had a Johnson J380 cam (like a modern smoother PW3) in my standard spec 8.5:1 comp 850 with mildly ported RH4 head, velocity stacks and 5 speed until it died via a damaged cam follower.
Good all round performance everywhere but on rebuilding the engine, fitted a modern standard spec Web#12 cam from Jim Comstock. This is my perfect street cam with a modified Fullauto head and I wouldn,t change back.

Great all round performance, economy and perfect in my trip through the Alps last year, never short of grunt as dobba99 and SteveA rightly say, made quick, enjoyable progress short shifting through millions of corners from Slovenia through the Dolomites and Haute Savoie and it,s relaxed at both slower speeds or motorways.
This standard type cam makes sense to your intended use as well and the Norton engineers got it spot on in my view, compliments all the usual modern ad-ons and has no trouble hitting the 7000 redline if you want.

lcrken
beautiful and functional, and I would also mention Doug MacRae,s race Commando seen in a recent post, both bikes are superb and still look like Commandos.
 
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