Running China Motor backwards ?? Successfully ??

Discussion in '2-Stroke Engines' started by ToyTruck, Jan 5, 2013.

  1. ToyTruck

    ToyTruck Member

    Has anyone Successfully run a 2 stroke motor backwards ??
    Any issues apart from adjusting the timing ?

    Anyone have ideas for re-timing ?? Offset key way obviously won't work . Is it possible to re cut a new keyway

  2. Racie35

    Racie35 Member

    might be easier to cut a new slot in the couldnt file a keyway enough to move that far.....or maybe move the ignition magnet or pickup?
  3. crassius

    crassius Well-Known Member

    saw one that ran backwards on the work stand once - seemed to run well that way, but I didn't stay around long enough to see what they found was wrong with it (it was intended to run normally)
  4. ToyTruck

    ToyTruck Member

    Thanks for the info ....
    The motor will be rack mounted on a DownHill MTB
    No room for jack shaft and I want to keep my rear disc
    So the plan is to run the sprocket in behind the freewheel cassette

    The sprocket fits so now I need to figure out the timing mods
  5. BigBlue

    BigBlue Active Member

    I assume China engine means a pocket bike or Cage engine and not the China Girl or Happy Time. You could probably run a RC ignition system with a hall sensor as a pickup.

    You might want to look into the Tophat system from Kings that allows your to have a sprocket and disc to be mounted on the same mount:

    Another thing, how do you plan on starting the engine?

    Good Luck,

    AKA: BigBlue
  6. ToyTruck

    ToyTruck Member

    Sorry , I meant the Happy Time engine .... Waiting for a kit to arrive
  7. keatonx

    keatonx Member

    i have made weed eater generators and would put power through the generator motor to start it. one time i hooked up the wires backwards and it tried to start, but backfired real hard out both ends of the engine (carb and muffler). My friend and i made a friction drive weed eater bike and we bump started it backwards. it did the exact same thing. Different engine, but you will likely have the same problem. it will run fine if you fix the timing, but may not last too long. the piston rubs mostly on one side of the bore due to the crank position during the power stroke. Its hard to explain, but it wedges into that one wall because the con rod isnt straight at TDC when the explosion occurs. Therefore the engine is designed to get alot of lube and cooling in that area. reverse the rotation and the piston wedges against the other wall, which will have less lubrication and cooling than the other, original side. i dont know how substantial this is, but it will likely happen to some extent.
  8. ToyTruck

    ToyTruck Member

    Thanks , that's something I will keep an eye on ....
    I have already fitted the motor , and am just trying to set the timing now.

    Any other suggestions as to where to set the timing at ???
  9. Old Bob

    Old Bob Member

    Mirror image of what is was before.

    If you don't know, then set it about 25 deg, BTDC.

    And don't worry about wrist pin offset.
  10. ToyTruck

    ToyTruck Member

    Thanks , I got it running and it seems good enough.

    Although it does stumble a bit at high rpms ...
    I am thinking it may be fuel issues as my tank is probably not high enough to give a good gravity feed.
    The filter is about 2 inches away from the carby and seems to always have fuel?

    Could the timing affect the rpms as much as I am seeing ?
    It does seem to rev right up on a good downhill!
  11. BigBlue

    BigBlue Active Member

    Last edited: Jan 15, 2013
  12. ToyTruck

    ToyTruck Member

    Thanks for the info

    When I posted up asking for help , I was hoping someone would have done it before and could have just shown me a pic and it would have been too easy LOL

    All I ended up doing was removing the magneto and the woodruff key , then finding TDC working back to about 15 - 20 deg BTDC to find the position of the magneto when it fires for NORMAL engine rotation.

    So then I moved the crank to the New 15 -20 deg BTDC for the new rotation and put the magneto on , remembering that the engine now spins the other way.

    I am sure this makes sense to those who have messed with timing.

    Long story short I got it running , did half a dozen short test runs less than a minute. Did four 5 / 10 minute runs then when I was almost home ..... The motor locked up ..... Cooked the crank bearing on the magneto side ..... HAHA

    New bearings ordered .....

    This motor is the 4th kit I have bought and the only one to fail .....
    I am going to assume it just failed and had nothing to do with reverse rotation ....

    Will find out soon enough
  13. jaguar

    jaguar Well-Known Member

    What kinda oil you using and at what ratio?
    Something has to be way wrong to ruin that bearing.
  14. ToyTruck

    ToyTruck Member

    The oil is a Castrol synthetic race oil

    Running the recommended run in mix.

    Thinking back now , it had a squeal intermittently the whole time ...
    I just put it down to clutch squeal ...
    One of the times I heard it really bad , I had just done a 10 minute ride and because I didn't support my muffler , it cracked down both sides of the bend , I just assumed the squeak was the cracks as the muffler was shaking .

    Everything else looks good , so I will replace the bearings and try again
  15. Fabian

    Fabian Well-Known Member

    When the engine is running backwards the thrust is on the opposite side of the piston face. Considering pistons are cam ground, i'm not sure if this has an effect on the way the engine operates.

    Does running the engine backwards require different port timing compared to an engine designed to run in the manufactures intended direction of rotation???
  16. ToyTruck

    ToyTruck Member

    The piston looks fine , no wear or damage ???

    The motor is stock standard.
    It was odd because , I adjusted the timing a couple times . And each time the seal popped out a bit behind the magneto .
    I pushed it back so it was flush , set the timing correctly then started running it.

    It's actually ironic , because the two previous kits that are running fine had real bad quality control ... This one looked perfect haha

    I built my mount so if it is a bad way of installing , it won't take much to spin the motor round and add a jack shaft .

    I appreciate the help with failure diagnosis , because I don't want to keep rebuilding after half a days riding !!
    At this point I am going to get rid of my fuel and start from scratch with fresh 16:1 mix and just hope that it was a one off bad bearing.
    I was lucky that it was barely running when it locked up

    Fabian , do you really think port timing could affect anything ??
  17. ToyTruck

    ToyTruck Member

    I should add that I had oil dripping of all over the motor ....
    I am sure it was not a fuel issue , but I want to rule it out.
  18. ToyTruck

    ToyTruck Member

    Here is a pic of my bike , plan is to raise the back of the tank and extend / lower the carby

  19. jaguar

    jaguar Well-Known Member

    could be that the crank was wobbly which put extra stress on the bearing. Best to visually check it when its apart.
    the odd location of the engine puts extra stress on the tire/wheel when hitting bumps. Also it puts additional weight on the rear which already has too much weight (since bicycles are incorrectly made that way). I would of mounted the engine closer to the shock.
  20. ToyTruck

    ToyTruck Member

    As far as the motor goes I am thinking it was either one of those things OR I possibly did some damage with it miss firing while I was getting the timing right .

    Thanks for the suggestion to check the crank , I am tempted to do some porting mods while its apart .

    As for the bike , as the rear suspension compresses , the seat and my back get very close to the engine , it does make it more unstable .....