running an engine in reverse

Discussion in 'General Questions' started by gearhead2, Jan 17, 2009.

  1. gearhead2

    gearhead2 New Member

    I have a small two-stroke 80cc engine. I'm wondering, is it possible to run it in reverse? The way i have to start the engine right now is to get the bike moving(the engine is directly connected to the wheels and it isn't a pull-start, so moving the bike is the only way to get the piston moving) and then apply the gas. So in theory, if i just cranked the engine(got the wheel moving backwards) backwards, wouldn't it start backwards?
     

  2. Old Bob

    Old Bob Member

    The ignition timing has to be changed, if it sparks at lets say 20 BTDC with CCW rotation then it should spark 20 BTDC with CW rotation, so the magneto needs to be moved to the other side of 0 BTDC from where its at.

    And it will run just fine.
     
  3. For real

    I have been thinking of mounting a HT upside down. To change the drive to the right. But I need it to go in reverse to work. How do you adjust the magnito timing
     
  4. Flapdoodle

    Flapdoodle Member

    Long ago, you could buy offset keys for adjusting the timing. I had thought about making several for my HT 80 so I could play with the ignition timing.
    key.gif

    They are small, so I imagine it would be fairly to make one by hand filing. All it does is turn the magnet so there should be very little force on it. Aluminum may work okay.
     
  5. gearhead2

    gearhead2 New Member

    so how exactly would i need to change the magneto? Sorry, i don't really have any experience with engines.
     
  6. Old Bob

    Old Bob Member

    A key could do it if the advance on the timing isn't more than the amount of material you have to remove on the key. A bracket to move magneto is used also.
     
  7. W da Huh

    I know how to change the timing on a car. Rotate the distributor. But key ?? What key? Pardon my ignorance, but please explain this..
     
  8. Flapdoodle

    Flapdoodle Member

    The offset key rotates the magnet just like you do in the distributor.
     
  9. So is the keyway on the crankshaft, or cam?
     
  10. Flapdoodle

    Flapdoodle Member

    The rotating magnet is keyed to the left hand side of the crankshaft. It is doubtful that playing with the key offset could be of help if you want to reverse the rotation, but it is how I would change the timing. I have searched the forum for how many degrees before TDC the factory setting is without success. Anyone here know?

    BTW, the smaller the shaft, the more degrees an offset key could do depending on the key size.
     
  11. cooltoy

    cooltoy Member

    Just to give you an idea, this key is 6 deg, off.
     

    Attached Files:

  12. Back in the day lots of 2 stroke singles would start backwards. The rider would kickstart his bike it would backfire and start, he'd go to let the clutch out and take off in reverse!
     
  13. Old Bob

    Old Bob Member

    Yup thats happened to me on dirtbikes, we had a bike that would do it while running if it idled down with a heavy, its was always a asurprise when trying to crawl over a log and pop! it backs up!

    Ez-Go golf carts make good use of a 2 strokes ability to run reverse rotation.

    What needs to be done whether a key modification or magneto bracket depends on the engine.
     
  14. stude13

    stude13 Active Member

    i've tried many times to find how ez-go reverses and have had no luck. any ideas or answers?
     
  15. cooltoy

    cooltoy Member

  16. stude13

    stude13 Active Member

    that looks good, but i cant sign in. i think they have the answer.
     
Loading...