Oil Pressure Relef Valve

Discussion in 'Norton Commando Classic Motorcycles' started by pierodn, Oct 11, 2017.

  1. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    I know there are a lot of same topic here.
    Please, can you explain me what the OPRV needs , as it works, and that consequences has on the oil pressure.
    Thank you
    Piero
     
  2. rvich

    rvich VIP MEMBER

    Joined:
    Jul 25, 2009
    I've taken them apart, it isn't difficult. Nothing there but a spring and a plunger. There is a shim or shims behind the spring to adjust where the plunger sits when it is not under pressure. One would think you could effectively stiffen the spring by adding shims. However, I remember Mick Hemmings commenting in his DVD that he thought this was a poor idea as he wanted to be able to pick up the valve and hear the plunger rattle when he shook it. What I don't remember is whether he suggested a stiffer spring to increase pressure. Nor do I remember why he wanted it to rattle, but I respect that he had a reason. I have never run an oil pressure gauge, but if I had one, I would be measuring the resistance to compression of the spring and finding springs of different values and testing to see what it did. I'd be interested to know if anyone has done this.
     
  3. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    Sorry, i know how it is made.
    I would like to know just what it works and when takes to work.
    Thanks.
    Piero
     
  4. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    It's a simple spring-loaded valve that opens when oil pressure has reached a certain pre-set level, and closes when the oil pressure drops below that level.
     
  5. concours

    concours VIP MEMBER

    Joined:
    Dec 29, 2011
    Are you asking what the standard pressure (PSI/bar/Mpa/kpa) set point is, at which point it let's oil pressure bleed by?
     
    Last edited: Oct 12, 2017
  6. Towner

    Towner

    Joined:
    Feb 22, 2013
    When the oil is cold the pressure can raise to a value that can hurt the engine. The purpose of the valve is to prevent the engine from to much oil pressure. This happens normaly only in the first few minutes after the engine has been started. Afterwards the oil pressure drops fast. So if you want to messure the oil pressure to adjust the valve the oil must be cold. The valve can be adjusted by shims. Normally it is adjusted by the factory and even after years it works fine. But you don't know what happened with the valve in 40 years, so it would be no mistake to check it. A good value is 55psi at 4000rpm with cold oil. One shim is about 15-20psi.

    Ralf
     
  7. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi Les,
    please again, what "opens" and what "closes".
    What changes in the oil way?
    Thanks.
    Piero
     
  8. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    If you look at the OPRV you will see it has (usually) four drill holes or 'vents' in the body. With the 'piston' (or 'plunger') and spring inserted, the vents are effectively blanked off by the piston.
    As oil pressure increases the piston is forced back against the spring pressure until at a certain point the vent holes in the body are uncovered by the retracting piston, oil then begins to escape through the vent holes so the oil pressure is prevented from exceeding a certain level.
     
    Last edited: Oct 12, 2017
  9. oldmikew

    oldmikew

    Joined:
    Jul 25, 2015
    Joe Francis one of the oldtime London Norton dealers gave me the same advice as the Mick hemming video ..it should not be shimmed out solid.. so when assembled clean if shook you can hear a slight rattle... Mine is set to blow off at 65lbs ..when cold.. though it drops off as the oil warms up... Personally I would aim for such a startup pressure for then you are assured the rockers are getting oil . they are pressure fed.
     
  10. rvich

    rvich VIP MEMBER

    Joined:
    Jul 25, 2009
    Is it the consensus that once warm the valve doesn't dump any oil? Or doesn't if it is properly set up?
     
  11. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi All.
    If i have understood well, the OPRV works only when the oil is cold because there is much pression.
    It means that when the bike starts from cold there is few oil that goes to the rockers and cranckshaft?
    But, why the oil pression is much more when the oil is cold?
    What happens if the OPRV open first or later or dont open at all?
    Thanks.
    Piero
     
    Last edited: Oct 12, 2017
  12. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    There should still be more than enough oil reaching the crank and rockers.

    Oil is thicker when cold so it doesn't flow out of the bearings as fast which causes the increase in pressure.
     
  13. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    It depends how efficient the pump is and what the relief valve pressure is but once the oil has warmed up, the Norton OPRV probably stays shut.
     

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