55m crank on 125cc AC engine? Port matching help please!:)

Discussion in 'Maxiscooter Tuning' started by jusspb, Aug 31, 2017.

  1. jusspb

    jusspb New Member

    Messages:
    16
    I am wondering is it possible to fit and 55mm crank for an AC engine? After tuning the cases and fitting the crank I would need a spacer for the cylinder but what about cylinder head? That needs to be raised around 1.5mm aswell?
    Seen threads about LC but wondering about AC:)
    Since cylinder moves up 1.5mm more and down 1.5mm, then was thinking of 1.5mm spacer and milling malossi AC head off for 3mm.
    Any suggestions?
    Not really fond of messing with ports, but, if needed I'm in for that.
    Please give detailed suggestions when you have done this kind of work!
    No need for speculations!:) Thanks!:)

    Set atm:
    Malossi 172cc
    Multivar
    Delta clutch
    Malossi belt
    Malossi longer gearing
    28mm pwk
    Malossi mhr Reed (coming kx85cc)
    Malossi 360' manifold (coming manifold for kx85cc)
     
    Last edited: Jan 12, 2018
  2. Tamiyacowboy

    Tamiyacowboy Pippa's Owner

    Messages:
    1,850
    Rides:
    Piaggio Skipper
    i think you could run a taller spacer down on the cylinder and that would also lift the head up to. dont take my word on that.

    heres how i see it , lets say there needs a 3mm gap space change, so you lob a 3mm on the cylinder but the head needs 2mm lift to instead of running a 2mm uptop , you could just throw a 5mm on the cylinder end, its gonna lift the cylinder. if thats not possible then its just a 3mm down and a 2mm upper
     
  3. jusspb

    jusspb New Member

    Messages:
    16
    Since the stroke would be 3mm longer I understand I would need to put a 1.5mm cylinder spacer and 1.5mm head spacer and then mess with port timings?:)
    Is it correct?
    But if I put a spacer between a engineblock and cylinder I would need to but gaskets to both sides? Which would add up another 1mm if I use 0.5mm gaskets? So I would need just a 0.5mm spacer and 2x0.5mm gaskets? Could need advise who has done it before!:)
     
  4. MARSH

    MARSH Whooooo!

    Messages:
    2,340
    Rides:
    Piaggio Typhoon
    A 55mm crank would need a 1.5 mm base gasket PLUS original gasket thickness for squish band to raise the barrel due to the crank stroke, 1.5 up.1.5 down. You could use a 0.4/0.6/0,8 base gasket and have the head machined to keep port timing down. I did the head machining route when I built my 183 runner engine, keeps rpm down and a very torqey engine.
     
  5. jusspb

    jusspb New Member

    Messages:
    16
    Has anyone raised the barrel with 1.5mm spacer and then milled 3mm away from the AC cylinder head?
    Just not to mess around with port timings etc.
     
  6. Buzzbug

    Buzzbug New Member

    Messages:
    5
    006.JPG Hi yes we have done it,we use an AC motor on my daughters racing Grasskart,using a 55mm mazzer crank,ported Malossi 172 kit,1.5mm barrel spacer and modified head,I think its about 180 degrees ex timing [will check with my engine builder].Also running WC rotor,stator and CDI.Carb is 35mm TMX Mikuni using RD350 reed block on MHR manifold and modified PM59 pipe. Its quick !!.
     

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