What prevents a HT from running in reverse?

Discussion in '2-Stroke Engines' started by mickey, Nov 9, 2007.

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  1. mickey

    mickey Guest

    What prevents a HT from running in reverse? I know that the spark would be retarded rather than advanced but I would think that could be fixed. Further, what prevents a HT from being mounted upside down or with the case vertical? Its got no sump and the carb could be flipped over. Could RH power be as simple as that?
    Last edited by a moderator: Nov 9, 2007

  2. minibiker

    minibiker Guest

    if you were to make it run backards the intake exhaust would be switched and would have to make a fancy attatchmet for carb mpipe and the wdhole engine in general
  3. mickey

    mickey Guest

    I don't think so. Its a 2stroke, one power pulse per revolution. It shouldn't matter which way its revolving except for the spark advance. The intake and exhaust is determined by the location of the ports in the cylinder.
  4. mickey

    mickey Guest

    I'm picturing it mounted so that a straight line drawn through the axis of the crank and clutch would be parallel to the seat tube and near vertical.
  5. jpilot

    jpilot Guest

    An HT should run fine in either direction. They're piston ported so they don't care which way the crank is turning. Ignition timing would be the only issue.

    Some of the ultralights I used to fly ran the engine upside down. They did fine except clearing a flooded start condition required removal of the spark plugs to clear the cylinder. Plugs tend to foul easier on inverted engines also.

    I've found nothing whatsoever regarding ignition timing on the Happy Times. If there is any advance built in (in the normal direction of rotation) it can't be much or the thing would kick back when trying to start it.
  6. mickey

    mickey Guest

  7. VTBikeman

    VTBikeman Member

    If you reorient the magnet in the magneto to be the at the same orientation AFTER top dead center as BTDC the motor should run backwards. Don't switch the north and south poles of the magnet or the ignition will fire at the bottom of the stroke.
  8. Hi,

    I can't remember the username offhand but somebody took the cylinder of a HT engine and turned it around (so in standard mounting position on the bike, the carb was now facing forward and the exhaust was pointing rearward)....They reported power was down....I think it had to do something about the direction of engine rotation relative to the ports / gas flows inside??....I am thinking in addition to the possible retarded timing issue of the engine running backward this would be an issue as well....

    Of course new mounts would have to be figured out as well....VERY interesting thought though.


    I like the thinking tho....
  9. VTBikeman

    VTBikeman Member

    I don't think there is anything to be gained by turning the cylinder around unless it facilitates intake and exhaust mounting. You may have to rotate the piston 180 if the skirt is not the same on both sides as the skirt is part of the valve. I don't know how it would affect the intake breathing as the intake sits in the crankcase before it goes to the cylinder. I haven't tried it because I don't need to but I think it could work as I stated. You could go 30 mph backwards.