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Hepolite rings with GPM pistons?

Discussion in 'Norton Commando Motorcycles (Classic)' started by debby, Dec 27, 2005.

  1. debby

    debby

    Joined:
    Apr 15, 2004
    Another little tech question for the group...

    I purchased a new set of GPM pistons recently and was disappointed to see they came with cheesy one-piece oil rings. I was expecting to find conventional three-piece rings like the later Hepolites use. But no! :x

    So if I bought a set of NOS Hepolite rings would they fit these pistons? Actually all I care about are the oil rings. The GPM compression rings seem ok...

    Debby
     
  2. Jason Curtiss

    Jason Curtiss

    Joined:
    Jun 14, 2003
    Deb,

    I haven’t seen a cheesy, single-piece oil control ring in over thirty years! It brings back memories of rebuilding my old Dodge pickup truck on a tight budget, using Continental piston rings and drinking Buckhorn beer late into the night. Heck, the single-piece ring worked well in my old Dodge. Thanks for the fond memories!

    One method of determining ring interchangeability would be to measure the height and depth of the oil control groove on the Hepolite piston and compare it to your GPM. If the groove is the same dimensionally in both pistons, then chances are good that the oil control ring is interchangeable between the two.

    However, the expansion rate between the pistons may be different, which in turn may require the rings to have different dimensions. I believe Hepolite is a forged piston and GPM a cast piston. And no doubt, they have slightly different expansion characteristics when run at temperature. However, the difference may not be enough to worry about.


    Jason
     
  3. illf8ed

    illf8ed

    Joined:
    Dec 30, 2003
    oil rings

    Debby,

    Now I'm confused. I thought the three piece oil control rings were the old type and the one piece were the new improved model. The new Hepolites I used eight years ago had one piece oil rings.
     
  4. debby

    debby

    Joined:
    Apr 15, 2004
    The original Hepolites, such as the ones in my old engine, had one-piece oil rings. And those big slots that gave the pistons a tendency to break. Later, Hepolite changed to the three-piece oil rings (as used by pretty much everyone else AFAIK) because of poor oil control problems.

    Reportedly ring gap is much more critical with the one piece rings and they're more difficult to seat as well. So I was really disappointed to see these.

    The GPM one-piece ring looks very much like the old Hepolite ones except there's a small spring fitted into the gap area. I'm kind of skeptical about the spring actually improving the ring's sealing ability though.

    Debby
     
  5. Scooter62

    Scooter62

    Joined:
    Dec 5, 2003
    Debby,
    Call MAP Cycle in St. Pete. Fl http://www.mapcycle.com They sell Hastings rings as well as Hepolite and I'm pretty sure they can tell you what will fit your pistons.

    Scooter
     

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