Inline 2 cyl.

Discussion in 'Performance Mods' started by MattyA, Jun 29, 2009.

  1. MattyA

    MattyA New Member

    Was looking at the 2 70cc motors i have and thought it would not be to hard a task hooking up the cranks to make an inline 2?

    Has anyone looked at this?

    With the lathe at my workshop i reckon i could get this to work, with interesting results.

    tuning them would be the hard part. as ive already ported and made the carby bigger ect.. on one of the motors.

  2. well get another stock carb or port and make the other one bigger to match.
    but i think one motor is enough for a bike.
  3. Klox

    Klox Guest

    Years ago Kawasaki had a 250cc bike called the KR250. The interesting part of the engine was that it was a tandem twin, which means that it was basically 2 single cylinder two stroke engine running in tandem in one engine casing...... Each of the two cranks had a gear at one end that ran on a seperate gear that was connected to an input shaft going into the transmission, very simple in concept.......

    You would actually need access to a milling machine as well to make this dream into reality.
    A opposing twin would be easier to build because making a crank would be much easier than an inline twin.
    Good luck!
  4. why not get a tandem bike and put 2 engines on it,one in the front and one on the back.
  5. duivendyk

    duivendyk Guest

    Could smooth things out a lot if pistons 180deg out of phase like in 2cycle twins, which were allways pretty smooth.Rather wide though.
  6. MattyA

    MattyA New Member

    Now that's thinking! Hmmmm My missus rides a motorbike, but the thought of a motorised tandum smells like danger to me:devilish:
  7. radrob

    radrob Member

  8. Klox

    Klox Guest

    that's what one would call a tandem-twin. In a typical two stroke engine design the piston moves down during power stroke, the fuel mixture in the engine casing compresses. By the time the piston crown reaches the transfer ports the compressed fuel mixture then flows into the sleeve to be compressed further by the piston on it's return stroke just before the spark plug ignites the fuel mixture. An inline two cylinder two stroke needs some kind of partition to isolate each piston (depends on the firing order and design, that's why most 2cylinder 2stroke designs have it that both pistons move up and down together) so that the gasses does not flow to areas it should not. A tandem twin is just an alternative way of engineering this needed "partition"......

    At some stage the big players in the rally world (Renault & Volkswagen) tried the approach of two engines in one vehicle. One engine driving the rear wheels and one engine driving the front wheels. The engineers discovered that in a situation where every wee bit of power matters that syncronising the two engines is nearly impossible..... thus the idea was moth balled by both manufacturers. The only way to achieve good "tuning' is to share the fuel (induction) supply to the pistons, thus in the end one can just go through the effort by increasing the displacement of the engine, it is much simpler and cheaper....
    You Americans have a saying: "there's no substitute for cubic inches".....
    Last edited by a moderator: Nov 9, 2009