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PW3 cam in 750 motor

Discussion in 'Norton Commando Motorcycles (Classic)' started by Blue750, Jan 16, 2019.

  1. Blue750

    Blue750

    Joined:
    Mar 17, 2018
    Hi,

    I'm looking for first hand experience of a Pw3 cam in a 750 engine with standard non-combat head. Would love to hear your thoughts if you have personal experience with the cam and can also compare to the std. Item.

    I've searched all the past posts and couldn't find much. I'm aware of the alternative offerings which I'm assessing separately.

    Thanks and regards
     
  2. freefly103

    freefly103 VIP MEMBER

    Joined:
    Apr 17, 2013
    I have one in my Seeley 750. That bike has a FullAuto head and is set up with 10.5:1 compression. To me, it's not a street cam, but a racing cam. On my Seeley, the power delivery is all above 4k rpm. Relatively unlively i.e. flat below that. I know FullAuto likes his in his street 750 set up with Mikuni single carb. I have a standard cam in my Roadster and a Maney cam in my other 750. I prefer the cams in these bikes for street riding and the occasional blat.
     
  3. acadian

    acadian VIP MEMBER

    Joined:
    Mar 5, 2010
    Do recall the lobe separation value of the PW3? Did you have valve clash issues?
     
  4. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    I have also been thinking about buying a PW3 cam. I have a Combat cam which I have not used because I believe the lift is too high. Also I have a problem scrolling the bearing surfaces. A power band starting at 4K would not be a problem, I think my 2 into 1 exhaust would make that liveable. With megaphones, it could be nasty with such a torquey motor. If you install a PW3 cam, and change nothing else, is there a noticeable boost in power between 4K and 7K ?
     
  5. dynodave

    dynodave

    Joined:
    May 28, 2003
    PW3: http://atlanticgreen.com/images/cam940.gif
    2S combat: http://atlanticgreen.com/images/cam120.gif
    open each in new window and go between them...
    I have run my 2S with 32mm carbs & manifolds into 28.5mm port head and it was awsome..
    To me they seem very similar overlap with more exhaust breathing on PW3= noisyier and more RPMs (should not have any valve tangle)
    remove the 2S funky ramp and the PW3 probably ends up has more intake overall lift too.
    Saturday... doing a club tech session on a 3S cam.
     
    Last edited: Jan 17, 2019
    cash likes this.
  6. Robert_Norton

    Robert_Norton

    Joined:
    Dec 21, 2008


    If you haven't seen this video, illustrating valve action at various RPM's in conjunction with a PW3 cam, you should watch it before making your final decision:



    .

    The video was created and posted by Jim Comstock, who is forum member "Comnoz." His website: http://www.nortonmachineshop.com/


    This thread, and others, may have useful information for you, too: https://www.accessnorton.com/NortonCommando/pw3-cam-for-850.23185/


    Also consider compression needed in order to realize benefits a PW3 or any high lift cam may provide.


    I'm not 100% sure, but I don't think all cams being sold as PW3 or equivalents are the same.


    Based on everything I've read on this website about PW3 cams, I wouldn't install one under any circumstances.





    .
     
    Last edited: Jan 18, 2019
  7. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    From memory, that cam lasted about 25,000 miles +-. The metal grinding paste that was produced from cam and follower damage wore out bearings, crank journal etc, so much rebuilding was needed, not just the cam and followers.

    One thing that came from that thread is that this was actually high mileage for a PW3.

    Given that info, it wouldn't be my choice either.


    Glen
     
    Fullauto likes this.
  8. Blue750

    Blue750

    Joined:
    Mar 17, 2018
    I've read in one of the earlier posts how well the 2S worked out for you using a standard head. How was the power delivery up to 4500rpm? I presume you ran it with an increase in compression?
     
  9. dynodave

    dynodave

    Joined:
    May 28, 2003
    The head I used was a regular/stock 71 head. The engine had no base gasket and that was all, otherwise pure stock new 1989? shenstone/norton 2S. Seemed to run real well. The original "C" head was on the bench waiting for me to do a full rebuild.
    As I've told before it was the highest HP "stock" commando run on the dyno @ the 92 INOA rally. A few full blown race bikes did better. Later when I put the "C" head back on it never seemed as strong for all around grunt.
    I did cheat and start to profile the 3S before tomorrows tech session and initial pass shows it to be incredibly similar lifts to the 2S. Maybe a touch more duration on the exhaust lobe. earlier opening but almost identical overlap (with intake) as 2S.
    The PW3 has a significantly bigger exhaust lobe than the 2S or 3S...duration and lift. Intake on all 3 are quite similar.
    The 3S profile will be posted on my webpage in a few days.
     
  10. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    I don't understand the assertion that it is necessary to raise compression to get the best out of a race cam. The cam is about breathing and cylinder filling - NOT combustion efficiency which gives a gain in power by using more fuel. A race cam probably creates a rise in combustion pressure anyway. I've used E3134 Triumph race cams in engines with comp. ratios as low as 7 to 1. They still give exactly the same power band - and the power output 7 to 1 is not much different to what it is at 11 to 1. Whatever comp. ratio you use, you still adjust the ignition advance and fuel mixture to suit it. Higher compressions require slightly more fuel but less advance, that is where the extra power comes from. In many cases, it is bugger-all.
     
  11. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    With the extra lift of the 2S cam, are there any problems with the valve gear ? I suspect that when Norton designed the Commando cams, they knew what they were doing. My near standard 850 cam is excellent. As I understand it, the problems with the Combat came from the raised comp. ratio - the machined head ? Probably also from guys over-revving them ?
     
  12. dynodave

    dynodave

    Joined:
    May 28, 2003
    hot cam & compression not necessarily linked...
    I still have my notes from my 1968 high school extra credit drafting project- 3Liter formula 1 engine design/draw. The engine design book showed the power increase ONLY for compression... increase increments. 7:1 to 11:1... motor engineers (not me) quote around 18%.

    3S profile results:
    http://atlanticgreen.com/images/cam430.gif
    2S/3S:
    http://atlanticgreen.com/images/cam432.gif
     
  13. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    I thought that long duration cams needed higher CR to compensate for loss of ‘effective CR’ ?
     
  14. dynodave

    dynodave

    Joined:
    May 28, 2003
    effective cylinder pressure/filling from ram effect...@ rpm
    effective CR is not a number but is a complex/variable math formula and would be presented across the whole RPM chart.
    not my usual language but I'll use your terminology
    a conservative cam makes a flatter torque curve resulting from flatter effective CR curve
    Hotter cam makes loss fluid ram/inertia effect @ low air velocity and peakier high effective CR curve at high rpm air velocities ram effect.

    Natural desire, but not required, is therefore additional mechanical CR across the whole RPM range.

    The principles have not changed since 1968 and my high school project. I try and teach this to my club members before they ever put a wrench to a hot rod project. I've always enjoyed motor sports and all inclusive math science physics metalurgy electronics ect. though I'm not an expert in any particular area. It was good enough to win 2 local sports car club annual racing championships back in the 70's. I built my own car suspension, engine & drove... not... "had it built" by someone. 70+ trophies tucked away in boxes. :)
     
  15. jseng1

    jseng1

    Joined:
    Nov 26, 2009
    Robert_Norton
    Your right - the PW3 lacks adequate closing ramps and suffers from valve bounce when revved. But thats been fixed with the JS2 smoothramp hardwelded or billet steel (not cast iron) profile as shown below:

    [​IMG]

    The JS2 smoothramp cam now revvs to 9000 with Bee springs. And yes this is a race cam.
     
    Last edited: Jan 21, 2019
  16. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    A cam which uses revs over 7000 RPM in a commando motor to develop it's power is pretty pointless, if you don't have a strong enough motor and the gearbox to keep it well within the revs where max torque occurs. At what revs does the JS2 cam come on song, if you use separate pipes with unrestrictive silencers ? With most cams, it is not the lift rate which causes valve-dropping, but the closing rate. The valve must be caught and lowered gently as it returns to the seat. So in some motors the cams are not symmetrical in shape, the closing rate is slower. A symmetrical cam is a compromise, the closing rate usually determines the opening rate.
     
    Last edited: Jan 21, 2019
  17. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Jim, I have watched a few videos of you riding the featherbed Norton. It looks very impressive. But you would not know how quick it really is unless you actually rode the bike. In one video, it stands up on the throttle at a fairly high speed. That could as easily be weight distribution as it could be torque. I once rode a Rocket Three which would stand up on the throttle at walking pace, but was not fast. Many road-going two strokes will stand up, but you often have to sit on the fuel tank to get them to handle. I'd really like to see some on-board video of your Norton on a race circuit, with a few other bikes around, to give some idea of the speed differences and where they occur.
     
    Last edited: Jan 21, 2019
  18. jseng1

    jseng1

    Joined:
    Nov 26, 2009
    Acotrel

    The above image of the cam profile is an older one. My latest designs are asymmetrical with a longer closing ramp than the opening ramp. See JS2 asymmetrical below (improvement on the PW3).
    [​IMG]

    I don't have any videos of my racing. That was before the day on onboard cameras. There used to be a good one of me and Fred Eiker dicing at Willow springs but it disappeared.
     
    Last edited: Jan 22, 2019
  19. chris plant

    chris plant

    Joined:
    Nov 6, 2008
    I think youre right eddie,most race cam makers specify using high comp race pistons,if you look at how the japs measured there 2 strokes, ie from exhaust port closure and not from the full swept volume of the piston,so in a 4 stroke you would measure from inlet valve closure,theres a big difference,i think they are also using same in 4 strokes
     
  20. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Perhaps if the longer duration of a race cam in four-strokes or porting in two strokes, gives better cylinder filling, so combustion pressures are already higher than they are with standard cams ? With most cams and porting regimes, there is a well defined power band which is always the same regardless of measured compression ratio. In a 7 to 1 comp. engine, the power band in terms of RPM, is exactly the same as in a 10 to 1 comp. engine. The standing waves in the inlet tract and the exhaust do not change, they are set by the timings and the lengths of the tubes. All that happens when you raise the comp. is you increase the pressure in the combustion chamber, so the temperature of the combustion process rises, so you need more fuel to maintain the balance between ignition advance and the higher compression - that is where the extra power comes from. If you are using higher comp., it is common practice to use less ignition advance, so the advantage of higher comp. can be largely negated. With race cams, you usually get more power right across the whole rev range, but much more above the point at which the cam really starts to work. With a lower comp. motor, you can get more power by running it leaner and getting optimum combustion conditions, because jetting is not so critical with the lower combustion pressure.
    I have a friend who used 14 to 1 comp. in his Manx with methanol fuel. The pistons used to collapse under the inlet valve, even though he had retarded the ignition by 4 degrees.
     

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