Refitting 50cc stock HT engine with 80cc slant head cylinder + 80cc piston

Discussion in '2-Stroke Engines' started by FoShizz, Mar 5, 2015.

  1. FoShizz

    FoShizz New Member

    I've tried searching, however, I did not come up with a complete answer. I made the mistake of purchasing a 50cc engine and now I regret the decision. Rather than buying a completely new engine, I would rather learn how to refit it to 80cc. Will this be possible, and if so, what parts would I need?


  2. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    It is not possible because the 48 cc cylinder studs are closer together than a 66 cc that you are calling an 80.

    There is no such engine size as an 80,
    A 40 mm stroke 47 mm bore is 69 cc
    The 38 mm stroke 47 mm bore are 66 cc

    48 cc has 40 mm bore.
    66 cc has 47 mm bore.

    The 66 cc engines are usually cheaper than the 48cc so it would be easier
    to sell your 48 cc and buy a 66 cc

    Where are you located?
  3. jaguar

    jaguar Well-Known Member

    the 66cc has more vibration than the 48cc which is already too much.
    you can do a lot to fix up the 48cc for more power.
  4. gobike

    gobike New Member

    Good to hear...
    Because of the state I live in, I will have to buy 50cc or under...
    It seems all the performance-Hop-up parts are listed as being for the 66cc-80cc engines, is this true, or do I just need to find the right place to buy from ?

    jaguar, what do you think are the best upgrades to do to a 48cc engine in your opinion ?...
  5. KCvale

    KCvale Motorized Bicycle Vendor

    If you can fit it to your bike the SickBikeParts multi-piece expansion chamber exhaust and an NGK plug will give you about a 1/2 horse boost.
    Same price almost as a new 66, but it stays legal.
  6. butre

    butre Well-Known Member

    the "half-breed" 66cc engines have considerably less vibration than a GT-5, which itself has considerably less than a PK-80, plus since 2010 all the engines have had better balanced crankshafts.
  7. butre

    butre Well-Known Member

    you think they're going to tear your engine down and measure borexstroke? If it were possible, putting 66/80cc parts on a 50cc engine would make it a 66/80. think about how displacement is measured?

    don't worry about the 50cc rule.
  8. KCvale

    KCvale Motorized Bicycle Vendor

    Don't fool yourself, you can just pop the head off and measure bore and stoke in no time with a metric ruler.

    The point is why would a state prosecutor pay for that if it was the only reason for the stop.
    They wouldn't.

    If you are riding like someone that is not a danger to yourself or others regardless of speed or engine size, at least my neck of woods the police have better thing other than admiring your bike before they pass on by.

    You can be completely legal, but if you are riding on the sidewalk against traffic or wreck into someone else you will be punished hard as a lesson to not ride like an idiot again including finding any violation they can with your bike if they are really mean or you have a record.

    Riding smart and safe is a win for everyone.
    Nobody wants to screw with you.
    mogogear likes this.
  9. mogogear

    mogogear Member

    Great words- courtesy is good karma for everybody involved.