make a 26cc rc engine run in reverse?? for motorised bike and a goped??

Discussion in 'General Questions' started by joshua97, Jun 20, 2013.

  1. joshua97

    joshua97 Member

    hi i have a motorize bike project, its a friction setup I'm making (engine on right of bike), using the rear end of a hoped sport, basically i need the Chung yang 26cc engine to run n reverse (so bike goes forward) the way iv built it makes it too hard for me to mount engine on other side etc, i was told all i have to do is retime ignition?? ,but if in reverse with the bolt holding the spindle to crankshaft come lose (will i need to change crankshaft to left thread?)... i also have a goped geo sport with the engine on the right side to that needs a new motor? what if i put another cy 26cc on the goped but use the ild goped motors magneto on the cy26cc to adjust timing??? i really don't know what I'm doing in terms of running them in reverse :-/ so any help is greatly appreciated, thanks :), josh

  2. 5-7HEAVEN

    5-7HEAVEN Active Member

    The most logical solution to me is to mount the engine on the opposite side.

    Keep it simple.
  3. joshua97

    joshua97 Member

    yea i would love too, But the way the motor is mounted at the moment and the tank swell, would mean that i have to weld some sort of mounts to frame etc, but i know i can reverse motor rotation easily, as the goped had a Zenoah engine that ran in reverse as well, but thats blown and not rebuildable :( . i know its a case of retiming it but how- i don't know.
  4. 5-7HEAVEN

    5-7HEAVEN Active Member

    Pictures would be nice.
  5. joshua97

    joshua97 Member

    How do i add pics to a post? Haha
  6. HeadSmess

    HeadSmess Well-Known Member

    any piston port/reed valve engine can run backwards. so yep. you gotta retime it. how? most coil units are designed for one way operation. maybe the zenoah coil will fit?

    otherwise, good luck :)

    theres a standard convention amongst small motors to spin the same way. so im dubious of any zenoah running "backwards". then again, marine uses the other end of the shaft and so spins "backwards". zenoah makes marine!!!

    starting...starters only work one way. if it has centrifugal good luck clutch starting...

    good luck finding 1 left handed crankshaft for an engine that has only ever been built right handed. hard enough tracking down an OS FS26 LH crankshaft and cams, which were actually manufactured!

    you say you built it... obviously you have overlooked a fundamental design criteria. back to the drawing board. sorry :jester:
  7. Big Red

    Big Red Active Member

    I gotta agree with HeadSmess, HUGE design flaw. But, Pitbike and goped engines run the other direction and they're a dime a dozen. When I was a newbie I checked out putting a goped engine on a bike. It's hard to do because it runs backwards from a chinese bicycle engine.
    Good luck bro,
    Big Red.
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  8. 5-7HEAVEN

    5-7HEAVEN Active Member

    I run two goped engines on my bikes. One is a Tanaka 47R racing engine, the other is a CY460 engine. The Tanaka is rare and expensive. At $255, the 460 is moderately priced.

    Both, like all goped engines, spin counterclockwise.

    LOL, I know why Big Red thinks they run backward.

    Many gopeds run the cheap Mitsubishi clone and bolt them to 5:1 trannies.

    The trannies REVERSE the engines' rotation. that's why my crankshaft faces to the right, on my bike.
    Last edited: Jun 22, 2013
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  9. HeadSmess

    HeadSmess Well-Known Member

    the problem with crankshafts and saying clockwise, or widdershins ( :p) is its all dependant on which end you stare at them :(

    HT engine, spins opposite direction to wheels due to single SPUR gear redux.

    straight shaft brushcutter spins same way as a bent shaft, but gearbox at end reverses rotation, so cutter head rotates opposite direction.

    a pit bike engine spins the same way as the wheels. the primary gear shaft spins backwards, secondary gear shaft or output shaft spins same way as wheels.

    ducati, i believe, spins backwards.

    most car engines rotate one way looking from the front.

    all model aeroplane engines rotate one way except for the occasional small runs on counter rotaters for twin and quad engine setups. then you have to try and find suitable props in both hands.

    pusher props on planes are reversed to standard props, as the engines mounted "backwards". the shaft spins "the wrong way" to just put a tractor prop on, unless you got that counter rotater set.

    for some reason pushers and tractor props cant be used together on twins.

    the mustang p82 uses two rolls royce merlins. one is a specially made one for running backwards. they only made something like 700 counter rotating sets. restoreres now have to get them cast individually. and get the props specially made. but when you can afford half a mil on just one engine, i doubt moneys the issue :)

    somewhere on youtube theres videos on reverse gearing...where both gears mesh but rotate the same way!!!!
  10. 5-7HEAVEN

    5-7HEAVEN Active Member

    Okay, goped engines spin in the same direction as Happy Time/China Girl engines.
  11. Big Red

    Big Red Active Member

    Yeah they do. But the drive gear is on the other side. And ya just can't 'turn it around'. And a 4 stroke gearbox won't fit on it without modifying it. You could always jackshaft it to the other side. Or possibly use a freewheel on the pedal crank (SBP) and drive it from the pedal side.
    Big Red.
  12. joshua97

    joshua97 Member

    the goped sport runs the opposite way to the chinese bike engines (spins left) the cy 460, does that spin to the left? if yes ill get one of them for the bike and for the goped. but the cy26cc engines i have run to the right but then bike and goped will go back wards haha. and no clutch, just direct spindle drive, and no pullstart is used either. as for retiming a 26cc cy to go in reverse do u know where i can gets reverse magneto? so it fires properly? thanks, or any details on a left spinning engines? cheers
  13. 5-7HEAVEN

    5-7HEAVEN Active Member

    Please don't not mistake the engine crankshaft with the 5:1 transmission drive gear on a goped engine.
    The 5:1 goped transmission bolts onto the goped engine. It is NOT part of the goped engine.
    If the drive gear is on the other side, just 'turn it around'.
    Just turn the engine around or swap the 3:1 tranny with a 5:1 tranny.
    You can bolt on a 3:1 tranny and face the clutch to the left.
    A 3:1 tranny does not reverse engine output rotation, like the 5:1 tranny does.
    Run a 10t on the 3:1 tranny, a 50t wheel sprocket and you get 15:1.
    Or you can run the 3:1 tranny, jackshaft it to a 24t sprocket.
    On the right side jack a 10t gear to a 44t chainring.
    With a 24t inside chainring and 12t 8th gear, final drive is 15.12:1,
    with a 1st gear (34t) of 42.84:1.

    Orrrrr you can just 'turn it around'. Face the clutch to the right. (I did this.)
    Install a 5:1 tranny w/an 11t sprocket.
    Chain that to a 72t chainring.
    With a 24t inside chainring, final drive is 16.36:1.
    First gear w/34t is 46.36:1.

    You're right, I don't know how a 2-stroke engine would fit a 4-stroke gearbox.
    However a 4-stroke engine w/a 76mm clutch will fit a 3:1 or 5:1 gearbox.
    Last edited: Jun 24, 2013
  14. 5-7HEAVEN

    5-7HEAVEN Active Member

    Correct me if I'm wrong.
    If I stare at the engine clutch, what does "spin left" mean, clockwise or counterclockwise?
    CY460 engines spin CCW. as does Tanaka, Mitsubishi, Robin/Subaru and pocket bike engines.
    I know this for a fact, as I have run all of these engines.
    I will presume that most goped and weedwhacker engines spin CCW.
    You must remember that the 5:1 pocketbike/goped trannies REVERSE the drive gear's rotation.

    I cannot say this any simpler.
    Last edited: Jun 24, 2013
  15. joshua97

    joshua97 Member

    theres no transmission on the engine, its a goped sport geo (thats the same engine/setup i need for bike) its just a spindle on the crankshaft-held on by a bolt. that runs on the wheel :)
  16. MusiCALpuLLtoy

    MusiCALpuLLtoy New Member

    a 2stroke WILL run either direction
  17. joshua97

    joshua97 Member

    when u stare at cloth its clockwise, if u are behind engine, pullstart at ur legs and clutch facing front, it rotates left or anti-clockwise. i found out its a zenoah GZ25N14 (Geo) Engine after much searching haha, heres a link to the parts for it, so u can see motor
  18. 5-7HEAVEN

    5-7HEAVEN Active Member

    If you cannot relocate the engine, remove the spindle and put a belt or sprocket drive.

    Then the tire will turn correctly.
  19. joshua97

    joshua97 Member

    thanks, but the only was is to get it to run in reverse, i don't wanna do any modifications. i know u can run them in reverse with only changing timing, how do i do hat tho? just a different magneto? any mag recommendations thanks
  20. HeadSmess

    HeadSmess Well-Known Member

    how many times can we say this? do you not read anything these people are posting?


    anything normally fitted with a small engine is designed with the point in mind that all engines of similar design, regardless of manufacturer, all rotate in one direction. be it a generator, a brushcutter, a pump, or a motorised pushy.

    you proved you arent a designer by ignoring the basics.

    run it on nitro, and give it a glow plug. then it doesnt matter, cus it doesnt have spark ignition.

    yes, two strokes will run both ways (as long as they are piston or reed ported). so will standard diesel fourstrokes if you can live with exhaust being driven back through the aircleaner... both these motors can do it just by "bouncing back" against compression. a petrol 4stroke will do it with cam changes. get over it, its well documented in boats and early cars.

    kickback is well known in aircraft with no starters. watch the old movies carefully. they smack the prop backwards against compression so it kicks and starts running the right way. works on RC 4strokes, doesnt on RC twostrokes(which can seldom run backwards as they are normally ported through the crankshaft, a variation of drum induction. cox049 etc are the exceptions) so the same can apply when stalled. they kickback against compression and will start running backwards under the right conditions.

    a cox 049 can splutter at 25000 rpm and suddenly its running in reverse without you realising til its throttled down!

    the majority of manufacturers stick to a standard pattern, and dont deviate.

    other than flipping the motor which involves a redesign, and awknowledging you made a fundamental booboo, you could try circuit forensics.

    depot your magneto. work out its internals. then reassemble, in reverse.


    pretty basic.

    all you gotta do is bear in mind if its a N or S pole first, which way the coils are wound so will it produce a negative or positive charge current triggered by a opposite trigger current. and then make sure the magnets line up to cause firing at the correct time still, which they wont because the magnetos are usually assymetrical, so always have the advance built in by design.

    i have an old kawasaki brushcutter here that uses a symmetrical magneto. that can be flipped and still wont run both ways as the flywheel needs to be flipped somehow...

    you want the last suggestion?

    re locate the keyway on the crankshaft/flywheel.

    the easiest and most logical option. work out where it is in relation to TDC and add or subtract twice the existing advance to get the new location.

    that should work but you may experience polarity issues with the charge currents... some systems will, some wont.

    you still havent explained how youll start it in reverse... cus a pullstart wont work anymore.
    Last edited: Jun 25, 2013
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