Piston Ring Gap

Discussion in 'Mech Tech' started by Deefer66, Nov 17, 2019.

  1. Stock Bentley says.

    [​IMG]

    So 0.012" or 0.3mm minimum

    But Hastings say..

    [​IMG]

    Which comes out at 0.015" or 0.38mm

    From other guides have different fist and second ring gaps:

    First 0.004" per inch dia, second 0.005" per inch dia.

    I'm using AA pistons at 96mm which comes to 0.015' and 0.018" (0.381 and 0.45mm)

    Anyone got any definitive guidance?


    Sent from my SM-G930F using Tapatalk
     
  2. Use the instructions that come with rings
     
  3. Didn't get any...

    Sent from my SM-G930F using Tapatalk
     
    davidoft likes this.
  4. davidoft

    davidoft Sponsor

  5. 0.3mm on the one I checked first .. if I need to open up is it fine sandpaper on a lollipop stick?

    Sent from my SM-G930F using Tapatalk
     
  6. 77 Westy

    77 Westy Supporter

    The Hastings chart is generic for water cooled engines. Ring gap also depends on the type of engine and the type of pistons. I have Keith Black Hypereutectic pistons with Hastings rings in 96mm AA Biral cylinders and used the KB 'suggested' clearances for an air-cooled engine for the top ring.

    Top ring gap 0.028”, 2nd 0.018”.

    Don’t have the ring gaps too tight, especially the top one, if the ends touch the ring will seize in the bore – and you don’t want that.:)

    Piston ring gaps KB Hypereutectic.jpg
     
    Last edited: Nov 17, 2019
  7. 77 Westy

    77 Westy Supporter

    Ring gaps must be square and parallel – I made a simple jig and used a small grinder.
    IMG_4889 (Medium).JPG
     
    Valveandy and Deefer66 like this.
  8. Second ring gap tighter than top?
    Some have it other way around. Is this just varied opinion, material, usage or manufacturer.

    Might just aim for both same just over minimum values one I build the bespoke mini grinder!

    Sent from my SM-G930F using Tapatalk
     
  9. 77 Westy

    77 Westy Supporter

    The top ring runs hotter than the second and expands more.
     
    Deefer66 likes this.
  10. Well I guess as they're the AA Hypereutectic pistons it'll be the same then!
    That's a healthy gap.. still under the wear limit on a stock though

    I have also asked AA for their guidance by email just in case ..


    Sent from my SM-G930F using Tapatalk
     
  11. Word of the day: hypereutectic.
    Must find a conversation to throw that one into!
     
    77 Westy and Deefer66 like this.
  12. Going to be difficult to say nevermind fit in a conversation!.. but it might make you sound like you know what your talking about.... I don't I'm just copying text and hoping

    Sent from my SM-G930F using Tapatalk
     
    Valveandy, andyv and 77 Westy like this.
  13. 77 Westy

    77 Westy Supporter

    I’d be interested to hear what they say.
     
  14. mcswiggs

    mcswiggs Supporter

    Jim at Stateside gave me the the following advice for the 96mm Hasting rings he supplied me with;

    The top piston ring must be file fitted (gapped) to 25 thou This is measured 1” down from the top of the barrel. Use 2 pistons to square the ring and file a little at a time then debur the edges.
     
    77 Westy likes this.
  15. Not sure if it's a property of the Hypereutectic piston (got to use that word again) or just that they put the rings a bit closer to the top of the piston but the rings get hotter so need a bigger gap, up to 40% on stock... (even though Jake Raby doesn't agree apparently)

    Sent from my SM-T580 using Tapatalk
     
  16. AA response...


    Hello Dilwyn

    They try to get them all set up on .0045” per inch for the top ring and .004” per inch on the 2nd

    So they should be .017” top and .015” 2nd


    Jonathan

    AA Performance Products


    Sent from my SM-G930F using Tapatalk
     
    77 Westy likes this.
  17. 77 Westy

    77 Westy Supporter

    So, the definitive answer for Hypereutectic pistons is between 0.015” and 0.028” with the top ring gap larger, or smaller, than the second. :)
     
    Deefer66 likes this.
  18. Perhaps your KB pistons run the rings a little closer to the combustion face so get hotter that way?
    They did get a little worked up over at 914world about it!
    Also found a tech article saying bigger gaps didn't really change blow by up to 0.0065" / inch and then only marginally.
    ...Then there's the whole rings spin in the grooves so don't bother setting gap position it'll change before long discussions!

    Sent from my SM-G930F using Tapatalk
     
    77 Westy likes this.
  19. 77 Westy

    77 Westy Supporter

    This is the KB piston I’m using.
    IMG_4839 (Medium).JPG
     
  20. Maybe a smidge closer than on an AA...[​IMG]

    Sent from my SM-G930F using Tapatalk
     

Share This Page