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Worn PW3 cam

Discussion in 'Norton Commando Motorcycles (Classic)' started by Fullauto, Apr 20, 2018.

  1. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Fair enough.

    The 312a sounds like a really good cam for a road Commando that has to work hard.
    How does its profile compare to a stock cam?
    Does it produce more power than a stock cam (in an otherwise stock engine) and if so in what range?

    Glen
     
  2. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    The 312a is a faily hot grind for the street when used with flat lifters. It's turnover point [where it starts making more power than stock] is about 4500 rpm.

    I like to use the 312a with a radius ground stock follower for the street. That moves the turnover point down to about 4000 and is easy on the valvetrain. [it's what is in my bike]

    Like any cam change, the power gain is going to depend on how well matched the exhaust, compression and porting is to the cam.

    And like any other performance cam change -if it's just dropped into a stock engine, your going to loose a couple horses down low and gain a couple up higher.
     
  3. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    With flat lifters

    stock vs 312a.jpg
     
  4. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Thanks for that info Jim
    So on a hot day dragging up over a long mountain pass at 70 mph two up & luggage, the stock cam might be best, or at least of no disadvantage.

    I was reminded of the mountain pass problem ten minutes ago. Its not just down to cam choices, but it's part of the package.
    A friend called looking for a 90 mm Vincent piston for one of our clubmates.Stock is 84.
    That clubmate is at aaVincent Rally in Texas on his hotrodded Vincent Comet. Overbored and stroked to 636cc, 11 to one, hot cam.
    Melted the piston yesterday climbing a hill, in the heat. Lots of damage.

    Glen
     
  5. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Yep,
    That is when a stock cam, lower compression and heavy cast pistons would be an advantage. Jim
     
    Last edited: Apr 26, 2018
  6. Onder

    Onder

    Joined:
    May 11, 2010
    Why cast v. forged? Just curious...
     
  7. jseng1

    jseng1

    Joined:
    Nov 26, 2009
    Worntorn
    I think that a forged piston with a thick crown would be a better choice than a cast alum in high temp situations because the forged 2618 alloy has a higher melting point than cast alloy. Thats why you find it in all the race bikes.
     
  8. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Cast pistons are more thermally stable, so they don't change size as much with temperature change.
    They are also usually built with thicker walls and deck since the cast alloy is not as strong as the forging alloy. So they dissipate heat a little better.
    With an air cooled motor -particularly on the street -thermal stability and heat dissipation is more important than ultimate strength.

    And JS I'm not trying to pick on you, But I am not a fan of using any hypo-eutectic forged piston on the street.
     
    Last edited: Apr 26, 2018
  9. jseng1

    jseng1

    Joined:
    Nov 26, 2009
    You can get forged 2618 forged alloy in any thickness you want on special order. You can get them in thicker walls than the available cast pistons and they will take more heat than cast pistons. See overheated and melted Hepolite cast piston below. This customer is switching to 2618 Forged alloy pistons with coated skirts and the same installation clearance as cast pistons (as Yves has done).
    [​IMG]
    Note cut Vv pockets
     
    Last edited: Apr 26, 2018
  10. Snotzo

    Snotzo

    Joined:
    Mar 12, 2013
    How does this thread suddenly switch from Fullauto's PW3 failure to a discussion on pistons ?

    Come on guys, stick to the topic. If you want to discuss piston material, start another thread!
     
    cliffa and Kvinnhering like this.
  11. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Probably my fault, I mentioned the Mountain pass and newly destroyed engine.
    When you mention heat and seizure, the mind goes to pistons.

    Glen
     
    Last edited: Apr 27, 2018
  12. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011

    Interesting comment, I meant to ask you if you can get new pistons made up for Jap & WOP bikes that don’t break the bank?
     
  13. Staytite

    Staytite

    Joined:
    Oct 15, 2011
    Hi

    Back to PW3 failures ......

    Any comments on the theory that spalling occurs during slow turning of the cam during assembly without
    Graphogen rather than use of the engine either during race or road use?

    Thanks
     
  14. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    Lots of engine wear can occur on running on a cold engine by an owner who has no mechanical sympathy i.e. high revving of the engine when cold before the oil has started to circulate throughout the engine. I once had a Honda CX500/B which I brought second hand at 50K then I got 150,000 miles out of it before I sold it, yet every time I started it from cold I treated it gently before I used some higher revs. I also changed the oil twice as often as the recommended 7K miles- I think the proof was borne out with the end result.
    RE; "spalling occurs during slow turning of the cam during assembly without" - cam needs oil at least even when engine is assembled - NEVER attempt to turn the engine over dry!:(
     
  15. Staytite

    Staytite

    Joined:
    Oct 15, 2011
    Hi Berhard,

    Please seee my original post on warnings given by Norman White that a new PW3 cam and followers must be coated
    with Grahphogen prior to an engine being turned over by hand during assembly. Apparently oil is not enough to stop
    spalling.
     
  16. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    It seems strange to me, but Norman is wanna those guys whose opinions (on Norton’s) are not to be taken lightly...
     
  17. Staytite

    Staytite

    Joined:
    Oct 15, 2011
    Hi Fast Eddie

    Exactly; and written warnings from Norman on the PW3 Data Sheet and a statement that he used Graphogen on my build sheet !

    I just wondered if failures correlated with the use or not of Graphogen during assembly?
     
  18. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    I have always used the lube supplied with a new cam or recommended by the mfgr.

    I also like the fact that my crankcases have lots of oil in them after the engine has sat long enough for the cam to have "drip dried".

    You can definitely damage a cam by too much slow rotation before the engine is run -lube or not. The cam lube only lasts for a limited number of rotations before it is useless.

    It is not so much the lack of oil spray as it is the fact that it takes speed to make the lifter hydroplane on a layer of oil. That is why you start the engine ASAP and bring it to 2000 or 2500 rpm immediately for a few minutes with a new cam. This avoids the metal to metal contact with new rough surfaces.

    The worst thing you can do is start the engine and let it idle for a few minutes with a new cam. Or kick the motor over repeatedly thinking you are priming the oil system. Jim
     
    Nater_Potater likes this.
  19. Deckard

    Deckard

    Joined:
    Jun 18, 2009
    Ah yes, more fuel to a 283 without power pack heads and a better cam was just more noise. Why not just put a Carter AFB or Holley dual squirter and totally overwhelm it! I reminisce and digress................
     
  20. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    That makes sense Jim. When trying to imagine this, it seems to me that mildly radiused tappers would aid the process a little too.
     
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