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Norton 4 valve per cylinder pistons?

Discussion in 'Other Norton Motorcycles' started by APRRSV, Jan 17, 2017.



    Jun 26, 2016
  2. dynodave


    May 28, 2003
    Common enough mod is to make RH AND LH cutouts so they can be used on either side. That way you can sell 2 LH pistons as a pair.
    The 650 I just rebuild had this setup because OEM pistons are so hard to find. My friend sourced a pair of LH (in 1992) and had to do this to get a set.

    I'd be asking if he is selling them as a pair that can be seen, AND if are they the ones with the cut slot under the oil ring....
  3. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    The extra cutouts will drop the CR significantly.

  4. Rohan


    Aug 26, 2010
    Those cutouts are so close together that they couldn't function as a 4 valve anything,
    the valve pairs would be impossibly close together - indeed overlapping each other in pairs.

    I'd imagine the redundant cutout would soon carbon over, so you'd soon get most of your compression back.

    That really is cheapskate engineering !
    Reminds of the story where a batch of Vincent heads came out that had been twin plugged.
    That set all the pundits into a spin...
    Seems the apprentice had bored the plugholes the wrong side, and then was instructed to redo it correctly,
    so the whole batch wasn't wasted...
  5. annajeannette


    Sep 5, 2014
    four valve heads are nothing new you can trace back to 1915 when Indian motorcycle built there broad tack racers V twins with four valve heads to improve performance and only month after Harley Davidson followed suit Both machines where improved and ridden By my late Great Uncle Freddie Dixon with got him a track speed record for 1920 on the brooklands bowl he lapped brooklands the ten mile lap at at 103.237 and this was on the Harley Davidson with new modified heads 55 degrees angle 4 valves per cylinder hemispherical head made at park garage stockton on tees Dixon motors garage, Only then to be broken a year later by bert Le-Vack riding a 1000cc Brough Superior and they had No brakes back then these where hard men
  6. annajeannette


    Sep 5, 2014
    my great uncle freddie did improvements on geared oil pumps and had patents for them and later speedos and a patent for airboxes and carbration , and tuning of carburettor, and the Four wheel drive and four wheel steering patented in 1936 and disc brakes were patented in 1923 under RA research, witch My later Freddie Dixon was the senior Engineer he was also senior engineer for Douglas and later 1930 on Riley cars witch by 1933 he had achieved 200 hp out of a 1500cc riley engine bench tested witch was fitted to the Riley Red Mungel racing car See Haynes books Man with a Heart of a Lion Freddie Dixon By David Mason this book would make a very good feature movie , of very hard men of the 1920s and 30s
  7. Triton Thrasher

    Triton Thrasher

    Feb 10, 2009
    Before about the late 1920s, four valves were sometimes used because they didn’t have the metallurgy to make good valves big enough.

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