66cc Vs. 68.5cc engine What different?

Discussion in '2 Stroke Bicycle Engines & Kits' started by Lecheroandpuertorro, Jun 7, 2011.

  1. Lecheroandpuertorro

    Lecheroandpuertorro New Member

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    Hi friends
    i have a 66cc in my bike with angle fire head one day i test the compression and the gauge read 150 psi i dont know this number is good but i need to know is good or no.The solution for me is visit a friend and check your bike he had a 68.5cc engine when i check the compression WOW 250 psi i check other 66cc engine and i read 150 psi now i believe 150 psi for a 66cc is normal but now my question why the 68.5 engine have 250 psi and the 66cc have 150 psi? i check and the engine in the outside is same as 66cc i believe if he have some differences that is inside the engine. i ride the bicycle of my friend and she have good torque more that mine and he ride the bike with 87 octane fuel and i ride my bike with 93 octane but dont see result with high octane but this is other history.Please any friend in the forum i need help to know the different of this 2 engines.
    Thanks....:-||
     
  2. rohmell

    rohmell Active Member

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    150 psi is a good number for the 66cc engine.

    I can't believe an extra 100psi is coming from the extra 2.5cc of the other engine.(must be a buster to pedal start)
     
  3. rustycase

    rustycase Gutter Rider

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    Could be squish band, head gasket thickness, piston configuration, or ring condition.
    Or all of the above.
    Take your pick.
    150psi is respectable.
    Ride it like you stole it!
    rc
     
  4. Lecheroandpuertorro

    Lecheroandpuertorro New Member

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    thanks for the answer but i like to know if the 68.5cc have more stroke or more bore than 66cc.let me know if you have this info for this engine.
     
  5. mapbike

    mapbike Active Member

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    Best of my knowledge the "68.5cc" is still just the same ole 66cc and being called a 68.5cc, I know BGF on ebay sells soem of his engines with the claim "68.5cc" and I have one that was claimed at that size and it has the same everything as the other 66cc engines best I can tell, I think it is just another sales gimic just like some call the 66cc an 80cc which it isn't.

    Just my $.02

    Peace
     
  6. rohmell

    rohmell Active Member

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    Pop the head off of your engine and measure the diameter of the cylinder, then go to your friend with the 68.5cc engine and measure his cylinder and see if same or not.
     
  7. Lecheroandpuertorro

    Lecheroandpuertorro New Member

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    i dont understand one point i measure the compression of two 66cc engines and the measure is same 150 psi and i measure the 68.5cc engine and have a compression of 250 psi my friend is a maniac with your engine and dont head off only for a suspect i need a biker with this two engines and with the experience of disassembly this engines and compare both spec...i believe this person exist in this forum...thanks my friends
     
  8. mapbike

    mapbike Active Member

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    No matter where you look you will never find any parts listings for a "68.5cc" engine.

    49cc 66cc are the most common and 66cc is the biggest of the China Girl 2 smokers.....

    Myself and many others have rebuilt these engines from the ground up and there is only a 66cc engine that gets called 68.5cc, 70cc or 80cc

    As to the 250lbs compression I have no answer for that.

    Go to this link and scroll down, read and you will see this engine is called a 66cc, it's called a 80cc and in the final description it is refered to as a 68.5cc engine, the truth of the matter is that this is a 66cc engine and this is the biggest displacement of this type engine that is made

    80cc Motor Bike Motorized GAS ENGINE KIT black X-80BK | eBay

    I dont see one of these engines being capable of being roll started if the compression was actually that high, that is about like diesel compression ratios and not typical for one of these loosely built chinese engines, that kind of compression would require a much better built engines than these are to have any durability in my opinion.

    Peace
     
  9. jtgolden

    jtgolden New Member

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    is that a slant.... and do you recommend that motor for a first time builder?

    Thanks!
     
  10. mapbike

    mapbike Active Member

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    Here is the one I would choose between the two, I just used that other kit for referance for the point I was making about the advertised 66cc-68.5cc-70cc-80cc.

    80CC BICYCLE MOTOR gas ENGINE KIT MOTORIZED silver X80A | eBay


    This is the engine that I will be putting on my next build, and a good friend of mine has this same kit and he got an excellent engine, very smooth and strong. all of my engines that I have bought came from BGF and I've had good results.

    Peace
     
  11. thatsdax

    thatsdax Member

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    for the China good times in frame 2 strokes. BMEP of 90lbs -110lbs is typical. Any compression higher will only serve to beat itself up since these motors were not deisgned to take such high compression and make such big power. The fatories have lowered compression on these motors in order to exchange high power for a longer life. . 125-150 BMEP is really getting high and premium gas is on order. Once you get above 150 BMEP, then you are talking super high compression and fuels other than pump gas are now in order. If you are getting 250 BMEP, try checking agian. Make sure throttle is held wide open when checking.
     
  12. ducedave

    ducedave Member

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    is the compression gauge working right? some gauging tools work best between (A-B) not (C-Z) 250PSI would blow the head piston head gasket spark plug head studs rod rod barrings AND WOULD SUCK SMALL ANIMALS OFF THE SIDEWALK AND SPIT THEM OUT CRISPY!!!!!!
     
    #12 ducedave, Jun 10, 2011
    Last edited: Jun 10, 2011
  13. Lecheroandpuertorro

    Lecheroandpuertorro New Member

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    with the same gauge i measure the 3 engines and the same same day i believe is work great the owner of the gauge is a aircraft mechanics he measure the compression of the rotax engines in the ultralight airplanes but its possible dont read with precision.In Puerto Rico the most popular engine is the motoubaik 66cc but the engine of my friend(the engine with 250psi of compression )is not have brand and this engine is very superior in torque i ride my friend bike and the different is day and night.thanks
     
  14. ducedave

    ducedave Member

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    Cool!!!!!!
     

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