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18: 650 SS engine

Discussion in 'Other Norton Motorcycles' started by pierodn, Oct 4, 2018.

  1. pierodn


    Nov 10, 2012
    The 650 SS engine had the same crankcase, cranckshaft, rods of the 99 600 Dominator?.
    Thank you.
    Last edited: Oct 4, 2018
  2. norton bob

    norton bob

    Nov 29, 2013
    No,No!! A very few of the last run of 88/99 motors were reputed to have been fitted into 650 cases as 88/99 cases had run out. 650 crank and rods are a different stroke and big end size to the 88/99 motors. 88/99 cases are identical to each other and are pretty much the same as 650 cases except 650 cases have a bulge at the back to give clearance for the extra crank throw and big end bolts. 650 barrells and 99 barrells are interchangeable with a bit of work to give pushrod clearance, they are not identical though . 650 ones may be stronger. 88 motors have been bored and fitted with 99 pistons to make a 525 motor. My 99 runs with 650 pistons as that was all i could find , a bit confusing . I have considered cutting and welding a bit more space in my 99 cases and fitting a 650 crank and rods which will also allow me to use my 99 head barrels and the 650 pistons. Now I have really confused you. There is not much wrong with the 88 motor ,tough as old boots ,smooth and will rev and be up with bigger bikes at the end of a run.
    Last edited: Oct 4, 2018
  3. annajeannette


    Sep 5, 2014

    Hello yes your confusing yourself 650 and 600 model 99 are Not interchangeable the 650 barrel will fit the model 99 600 but the model 99 barrel will not fit the 650, if you try you end up splitting the barrel from april 1961 the 88/99ss model had the Norton Manxman 650 crankcase and cam and followers and push rod , But Not the Crankshaft they had there own 88 are 72mm stroke model 99 are 82mm stroke with 1.5 inch journals where has the 650s had a 89mm stroke and 1.75inch journals and the 650 pistons will be ok in an model 99 but you cannot fit model 99 piston into a 650 has they have longer skirts and you wreck the motor ,big time and you cannot fit a 750cc barrel on 650cc cases has the studs are further back by 1/8th on the barrel ok
  4. worntorn


    Dec 22, 2006
    I believe you can fit 99 pistons into a 650 for a very high compression setup.
    I was told of this by two old time Westwood Norton racers.
    The 99 pistons have a bit more height above the wrist pin than 650s. According to the info I was given, this results in an 11 to one CR, maybe ok for racing on 110 octane, not so good for the road.
    My 650SS is running 8.9 to ones , although at .060 over the ratio ends up being more like 9.5 to one.
    No detonation problems so far.

  5. annajeannette


    Sep 5, 2014
    well you try running 99 piston in a 650 the motor will not last five seconds the model 99 piston have longer piston skirts you have cut of about an inch from the bottom of the skirt , to make them fit so the piston skirts doesn't hit the crank center weight
  6. robs ss

    robs ss VIP MEMBER

    Aug 16, 2016
    Good info Anna - but you could try phrasing it in a bit more friendly way.
    Glen was only trying to be helpful!

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