Just set up a new lower engine, and now the rear wheel locks when clutch is engaged

Discussion in 'Motorized Bicycle General Discussion' started by sergman89, Jun 24, 2014.

  1. sergman89

    sergman89 New Member

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    First, thank you for your time.I just bought a lower engine from thatsdax.com and then I bought a new piston as well because my old piston had an arrow shaped chip of metal missing from its top side. This will be a HUGE help guys, and I swear give me 1 more year and ill be a pro returning the favors!
    Below are all the factors I feel may be effecting this.

    The issue is that the piston seems to get stuck and locks the back wheel instead of turning over. I thought maybe some starting fluid, but that only works if the piston is moving inside.

    When I was trying to put the chain on the motor, I had to loosen the head bolts because there was to much pressure and it kept me from turning the bolt WITH the sprocket.

    Apparently there are quite a few different kinds of pistons though or its just a way for them to market. When installing the new piston and everything I only used a little bit of oil supplement to glide the piston into the upper engine.
     
  2. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Removing or even just loosening the spark plug will let the engine turn over.....
    No need to touch the head bolts.

    There are only 2 kinds of 47 mm pistons now with a low wrist pin location for PK 80's and a high location for Skyhawk types.

    Not enough info from you to answer your other questions.

    Do you have pics of your damaged piston and other parts?
     
  3. Greg58

    Greg58 Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Did you compare the pistons? There are at least two different piston that are popular. I would take the head off and rotate the engine to top dead center and see if the piston comes out of the cylinder. You do have a base gasket under the cylinder don't you?
     
  4. Greg58

    Greg58 Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Sorry MBR, but we basicly said the same thing!
     
  5. mapbike

    mapbike Active Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Pix would help so we can see exactly what you have, but I'd like to add here a question.

    You do know that all you need to do is remove the spark plug from the head to relieve th compression?

    You never need to loosen the head inorder to relieve compression for turning the engine over.

    Im not sure what you mean by "oil supplement" you should always lube piston and cylinder with a light coat of 2 stroke oil before installing piston.

    Some pistons are made with an arrow shaped indent in the piston top.

    A new engine is gonna be a little tight and be sure that with all else done right that you have the clutch cable adjusted correctly.

    Map
     
    #5 mapbike, Jun 24, 2014
    Last edited: Jun 24, 2014
  6. mapbike

    mapbike Active Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Dang......! By the time I got my response posted there were three ahead of me.... are we on top of this or what......?

    Lol....!

    Map
     
  7. mapbike

    mapbike Active Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Ditto........!
     
  8. sergman89

    sergman89 New Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    This is the piston from the original kit.

    [​IMG]


    So when I grab my rear wheel and force it to start rotating without pulling the clutch handel, it makes a "wwwwwhhhhrrrrrrr" sound instead of what im used to hearing "pump-pump-pump" ....
     
  9. sergman89

    sergman89 New Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Base gasket is the green one (when new), yes. Theres a gasket between the lower and upper engine. Also a metal gasket between the engine top (with spark plug hole) and the upper engine.
     
  10. Greg58

    Greg58 Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Remove the spark plug and rotate the tire again and see if the piston moves.
     
  11. maniac57

    maniac57 Old, Fat, and still faster than you

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    That "chip" is NOT damage. It's the piston orientation mark for assembly.
    Nothing wrong with it unless there damage the pic does not show.
     
  12. Greg58

    Greg58 Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    I'm wondering if the lower is a 40mm stroke and the piston isn't. Did you get the piston from Dax as well?
     
  13. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    That triangle mark is to indicate where the ring pins are so points to the intake side.

    All my pistons have them.
    Other pistons have an arrow that points to the exhaust port.

    There was nothing wrong with your piston.
     
  14. mapbike

    mapbike Active Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Ditto........

    Map
     
  15. sergman89

    sergman89 New Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    No I did not buy it from thatsdax, but I should of. I called them and they answered on the 4th ring, and he was so kind to answer some of my questions.

    http://www.ebay.com/itm/321415387043?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

    Thats the piston set I purchased, to be honest with you guys im not sure what a 40mm stroke means. I tried incorporating that into my search for a new piston, but I couldnt find anything.

    I did eye this piston up with the other one and visually I cannot see a difference in size.
     
  16. Greg58

    Greg58 Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    The stroke means the distance the piston travels from tdc to bdc, a 66cc engine has a 38mm travel or stroke the 69cc has a 40mm travel or stroke. MBR and Dax both supply 40mm stroke lowers. Since you are comparing the new piston to a piston that has never run on this engine dax will have to tell what you need. Did you take the head off and see if the piston comes out of the cylinder?
     
  17. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    The pistons are all the same size as in diameter and height.
    Check the wrist pin hole heights.

    The eBay add is for a "SkyHawk" high hole piston.

    The triangle marked piston is a PK 80 low hole piston.
     
    #17 MotorBicycleRacing, Jun 24, 2014
    Last edited: Jun 24, 2014
  18. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    Sounds like your replacement piston is hitting the head and stopping because the wrist pin hole is higher than the original piston.

    Put your original triangle marked piston back in the motor and hopefully you haven't damaged anything.

    PS: Now I understand why you had to loosen the head bolts to get your motor to turn over!
     
    #18 MotorBicycleRacing, Jun 24, 2014
    Last edited: Jun 24, 2014
  19. Greg58

    Greg58 Well-Known Member

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  20. greaser_monkey_87

    greaser_monkey_87 New Member

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    Re: Just set up a new lower engine, and now the rear wheel locks when clutch is engag

    The bottom end is either called a bottom end or a case, sometimes a crankcase, the part that goes on top of the case is called a cylinder or a jug, and the part that goes on top of the cylinder is called the head. The gasket between the cylinder and the case is called a base gasket, and the gasket between the head and the cylinder is the head gasket. The bolts that hold the cylinder and head to the case are called the head bolts.
     
    #20 greaser_monkey_87, Jun 24, 2014
    Last edited: Jun 25, 2014

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