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Piston Rings

Discussion in 'Norton Commando Motorcycles (Classic)' started by swooshdave, Jul 11, 2019.

  1. swooshdave

    swooshdave

    Joined:
    Apr 15, 2009
    Rings installed. Circlip facing up. Oil ring not over lapping, you can see the red and green marks. Inside bevel on top two rings facing up. Does it matter where the two oil scraper rings have their gaps at? And where do you like to set the top two gaps at? @comnoz mentioned it doesn’t make too much difference as they are going to move anyways. Planning on putting them in nearly dry bores so they bed nicely. What else am I forgetting?

    [​IMG]
     
  2. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Joined:
    Dec 3, 2012
    Did you deburr the top rings so they do 7 rpm with no drag in the ring land ? :D
     
    concours likes this.
  3. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    The oil ring rail end gaps should be 1 inch away from the expander end. One gap to the left and the other gap to the right, so there is roughly 2 inches between the rail end gaps.
     
    swooshdave likes this.
  4. swooshdave

    swooshdave

    Joined:
    Apr 15, 2009
    And then how dry should the bore be? Wiped clean or wiped with a bit of oil?
     
  5. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    From your picture it looks like the circlip is are in ‘back to front’ as it look like I can see the ‘rounded edge’ face of the circlip (I could be wrong here though).

    My understanding is that these style of circlip is are stamped out. The stamping process creates one face with a very slightly rounded edge, and one face with a very clear and sharp edge. The sharper edged face should go against the pistons as it helps it ‘bite’ and increase security of the circlip installation.
     
    Time Warp likes this.
  6. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    I’ve personally never put pistons in a Norton dry, so I may be missing a trick here!

    But I suspect that it’s a practice done more commonly in modern racing engines, which have modern oil pumps.

    The Commando pistons and bores are fed by splash. On a freshly rebuild engine I worry that it would take quite a while for the crankcase oil content to reach the point whereby the ‘splash’ is serving its function.

    (Same argument for the cam. Which is why I always lather the cam and followers in assembly lube).

    Whilst I can see the logic re the ring bedding in process, I worry what’s gonna happen to those soft alloy pistons being pushed and dragged up and down freshly honed (and thus rough) bores.

    I’d be happy to hear from those who can demonstrate that I’m wrong though...
     
  7. MexicoMike

    MexicoMike

    Joined:
    Jan 31, 2010
    Well - when you say "splash" it's not actually splash like an old Briggs and Stratton lawnmower motor. IOW, the crank does not dip into the oil (once any wet-sumped excess is returned to the tank!). Oil is "sprayed" ("splattered" might be a better word) onto the walls by the oil from the crank journals. So oil is almost immediately deposited on the cylinder walls when the engine turns/the pump supplies pressure.

    When I last rebuilt my Commando, I installed the pistons/rings totally dry. The only lube present was a wipe of WD 40 on the bores to prevent surface rust after honing/cleaning with soap/water. So far (8 years later) no sign of oil use/no smoke at all. Not claiming a one-time result proves anything but I wanted to try it and if was rebuilding another one I'd do the same again.

    Some folks that I used to work with building automotive race/performance engines now use ONLY the dry method. But, as I often say - do what you are comfortable with!! :)
     
    Fast Eddie likes this.
  8. kommando

    kommando

    Joined:
    May 7, 2005
    Bore dry with a drop of oil on front and back of piston well below rings is how I do it.
     
    swooshdave and Fast Eddie like this.
  9. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    From the photo, it looks like you’re right.
     
  10. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    All good points ref the dry piston assembly guys.

    I guess the caveat being ‘do what you’re comfortable with’ !
     
  11. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    Modern engines are the ones that don’t need it.
     
  12. cliffa

    cliffa

    Joined:
    May 26, 2013
    +1 on that. The “sharp” side should face outwards on grooves which have a semicircular cross section. It will offer more resistance to the clip creeping out under side load. Of course if the groove is square cross section it makes little difference.
     
  13. cliffa

    cliffa

    Joined:
    May 26, 2013
    I thought dry run in was more to do with the materials used for the liner and rings ?
     
  14. kommando

    kommando

    Joined:
    May 7, 2005
    Modern engines are already run in as the dimensional tolerances off the machines are so good so the rings touch the bore all the way round, that allows a good surface finish to the used, that plus most engines are water cooled and so less heat distortion. On old engines the tolerances are not as good so the rings only touch in a few area's, so the surface finish is deliberately rough so the rings wear to the shape of the bore. The dry bore accelerates the wear in the first few seconds of running in and guards against glazed bores ie the rings are still only touching in some area's but the bore is too smooth to wear the rings to fit the bore.
     
  15. swooshdave

    swooshdave

    Joined:
    Apr 15, 2009
    [​IMG]

    So here are the two circlips. From the photo which one has the sharp side up? I know the answer because I can feel the difference. The holes (which are mostly what you can see in the previous photo) are rounded on both sides.
     
  16. cliffa

    cliffa

    Joined:
    May 26, 2013
    The left one.
     
    kommando likes this.
  17. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    First, to clean the bore of any metal residue left in the pores, you take a few pieces of paper towel dipped in a little motor oil and wipe the bore. You will see the paper towel gets black. Continue the wipedown until the paper comes out looking pretty clean.
    I then do the same thing with the piston.
    The oil left on the bore and piston after wiping it down with a dry paper towel is enough for the assembly.
     
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  18. cliffa

    cliffa

    Joined:
    May 26, 2013
    I see what you mean now Dave, it looks as thought the holes were stamped (punched) the other way round to the circlip itself.
     
  19. swooshdave

    swooshdave

    Joined:
    Apr 15, 2009
    Would you have washed my barrels after you bored and honed them? Should I give them some soapy warm water then wipe down?
     
  20. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    I would have washed the barrels after I bored them and then wiped them with a little honing oil to keep them from rusting.

    They will still benefit from an oiled towel wipedown.

    You will be surprised at how much crap is on the towel on the first wipe.
     

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