What is the diameter of your engine's piston?

Discussion in 'General Questions' started by boyntonstu, Jan 11, 2015.

  1. boyntonstu

    boyntonstu Member

    A local motorized bike builder told me that his engines have pistons and strokes that displace 80cc.

    What is the diameter of your engine's piston?
     

  2. butre

    butre Well-Known Member

    the "80cc" engines are all actually 66cc or 69cc no matter what anyone tells you. The chinese call them 80cc engines because they're trying to lie their way into a sale.

    the bore x stroke is always going to be either 47x38mm or 47x40mm
     
  3. boyntonstu

    boyntonstu Member

    My guy says that his pistons measure 49mm.

    Is it possible?
     
  4. butre

    butre Well-Known Member

    Unless he's using a different engine than 99.999% of motorized bicycle builders, no. He's either mistaken or flat out lying if he's using china girls
     
  5. Timbone

    Timbone Active Member

    That's kind of a personal question. ;)
     
  6. Purple Haze

    Purple Haze Active Member

    The location of the wrist pin is the critical part, it sets the height of the piston in the bore. You could shim the cylinder if the ports are close, maybe do a little port matching with a dremel. Then, bore the cylinder to match the piston diameter, and have it replated. Sounds like $$$$$$. One other thing, the diameter of the wrist pin; does it match the small end of the rod? Why bother? If you gotta have a better piston, there are many sources for a custom-made piston, which I think would be much cheaper than adapting that 49mm piston, which will give you VERY little if no performance gain. Plus, a larger piston with pin will add weight, not good for crank balance. But that's just my opinion.
     
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