Wrong piston?

Discussion in 'Motorized Bicycle General Discussion' started by Daniel sheffield, Oct 11, 2019.

  1. Daniel sheffield

    Daniel sheffield New Member

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    Hello everyone just join the forum can’t wait to get information from people who know what they’re doing. I currently have a 66cc bike kit that I am trying to do performance upgrades on to get better speed, so when I took the head off I noticed that the deck height was around 2 mm. I checked the crank and I have a 40 mm crank which from what I could find online should put my deck height at zero.
    could I have the wrong piston in the stock engine from factory.
     
  2. Greg58

    Greg58 Well-Known Member

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    Probably not, there are only two piston types I know of, there’s a big difference in the two. How many base gaskets does it have? Sometimes two are used to get the port timing correct.
     
  3. Greg58

    Greg58 Well-Known Member

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  4. Daniel sheffield

    Daniel sheffield New Member

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    It has only one base gasket. I did some lite porting with a file to round some of the sharp edges but want to get more top end out of it. I have gutted the exhaust but left the cap on and trued the mating surfaces between the head and cylinder. Tops out at about 33mph but gets hot. Running about 20:1 oil. Need it to do 30 mph consistently for a 12 mile one way trip to work.
     
    #4 Daniel sheffield, Oct 11, 2019
    Last edited: Oct 11, 2019
  5. Greg58

    Greg58 Well-Known Member

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    If it’s getting hot it may be lean, have you done a plug chop? Google it, there’s a few how to online.
     
  6. Daniel sheffield

    Daniel sheffield New Member

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    Ya it’s choco brown if not rich
     
  7. Greg58

    Greg58 Well-Known Member

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    Is it new or fully broken in? It will get better with time, also what rear sprocket are you using? Smaller sprocket increases top speed but hurt low end torque.
     
  8. Daniel sheffield

    Daniel sheffield New Member

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    About 5 tanks in. 44 tooth. Going to get a 36 with hub soon and designing a expansion chamber to make using stock exhaust
     
  9. Greg58

    Greg58 Well-Known Member

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    20/1 is more oil than most of us run, I've been running 32/1 in my bikes since 2011. I didn't like oil dripping on the shop floor where I parked.
     
  10. Daniel sheffield

    Daniel sheffield New Member

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    Yeah I just figured it would aid in break in kind a like four strokes, and because it’s running so hot and I have to travel such a long distance I like the idea of the engine having plenty of oil. not too worried about the mess
     
  11. Greg58

    Greg58 Well-Known Member

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    I went from a 41 to a 38 on my 66cc bike and it made my ride a lot better, if you drop down on the sprocket and add a good expansion chamber you can see several mph.
     
  12. Daniel sheffield

    Daniel sheffield New Member

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    Would you recommend going to a high compression head to help with the heat and case matching the ports for better flow
     
  13. Greg58

    Greg58 Well-Known Member

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    A lot of the performance heads on the market do little to increase performance, they can help cooling. Proper squish band clearance will help more than higher compression.
     
  14. Daniel sheffield

    Daniel sheffield New Member

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    My problem is the piston sits so low in the cylinder that I feel like my squish clearance is too high
     
  15. Greg58

    Greg58 Well-Known Member

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    I would check the compression first to have a baseline, a stock engine should be 90-100 psi minimum for good performance. To get top rpm
    you need a degree wheel and use base gasket thickness to adjust port timing, then decking or gasket thickness to set squish.
     
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  16. Greg58

    Greg58 Well-Known Member

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    You can lap the cylinder fairly easy, I use sandpaper on a true flat surface. I do ever head and cylinder to check flatness.
     
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  17. Greg58

    Greg58 Well-Known Member

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    A thick piece of glass with sandpaper taped to it is what a lot of people use. I sand the cylinder using both hands in a circular motion, different grit paper till I finish with 400 or finer.
     
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  18. Daniel sheffield

    Daniel sheffield New Member

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    I’ll try getting a gage will post an update soon
     

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