Why are the engines called 66cc/80cc need info

Discussion in 'Motorized Bicycle General Discussion' started by analogtom, Mar 6, 2010.

  1. analogtom

    analogtom New Member

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    Why are the 2 stroke engines that are called 66cc/80cc called that, aren't they one or the other cc?

    I have this engine [Flying Horse, 66cc, Engine Family: 9JFHS 066?FH] and seems to be a popular engine and I would like more detailed specs on the motor. I am looking for things like spare parts sources, quality replacement parts, simple upgrades, specifications of the motor, other names the motor is called for this motor only.

    I want to have a number of builds going on soon. I want to keep it simple and have all the motors the same, for ease of repair, having parts on hand and common problems & issues I can deal with easier, etc.
     
  2. bairdco

    bairdco a guy who makes cool bikes

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    Formula to figure engine cc displacement;
    ( multiply 3.142 x radius of bore mm squared x stroke length mm divided by 1000. )

    To figure displacement for this example: 47mm bore x 38mm stroke;

    Bore diameter divided by 2 = 23.5 mm radius
    To square radius multiply 23.5mm x 23.5mm = 552.25 radius mm squared
    552.25mm x 3.142 = 1735.17mm
    1735.17mm x 38mm = 65936 cubic milliliters;
    To get cubic centimeter divide 65936 by 1000 = 65.936cc or round off to 66cc

    By western standards the volume of the engine head combustion chamber is not figured in the displacement engine rating, however some Chinese factories include this volume in their engine displacement ratings therefore making the engine appear bigger than it actually is.
     
  3. 2door

    2door Moderator
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    The difference between 66 & 80 cc depends on who your are. The Chinese, who manufacture these engines calculate cubic centemeters, or displacement, differently that we do. It is thought that they include the combustion chamber in their measurements which differs from what the rest of the world does. We measure displacement by measureing the bore of the cylinder and the stroke of the piston. The reason given by many kit suppliers as to why they use the 80cc designation is that the search engines on the Internet are set up to look for that figure. Even though there are no true 80cc engines. Most people, when they start to search for available bicycle engine kits look for the biggest motor they can find and 80cc pops up when the search. Most reputable suppliers will explain the difference on their websites.
    I hope this answers your question.
    Tom
     
    #3 2door, Mar 6, 2010
    Last edited: Mar 6, 2010
  4. 2door

    2door Moderator
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    High five to Bairdco...:)
    Tom
     
  5. analogtom

    analogtom New Member

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    Thank you gentlemen! That answers the question very clearly.
     
  6. bairdco

    bairdco a guy who makes cool bikes

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    i just copied and pasted off the grubee site.

    as for your questions about the "flying horse" motor, most of these engines have interchangeable parts, no matter what factory they come from.
     
  7. folsomfa

    folsomfa New Member

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    These motors are made by the same manufacturer in china they get they get there name Skyhawk and the like when they arrive in the us and you are right the Chinese mersure diff. than us
     
  8. mapbike

    mapbike Active Member

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    Many factories in china that actually make these engines and there are several diferences in casting quality and in tranfer port design and such, I have several china girl engines and the differences in casting from one brand to the other can be clearly seen, and even different type fasteners are used, no telling how many different litgle factories there are churning these things out over there, and it is for sure they aint all the same.

    Map
     
  9. Jumpa

    Jumpa New Member

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    Very true Map different size pistons as well.
    Is it the Gurbee that has the piston hole higher than the rest ? I found that out the hard way . Good thing I tested it out before I put any type of torque on the motor. I had my piston bottom out on me on one 66/cc

    I had grabbed the wrong piston it was about a ¼ inch to high on the center con-rod hole on the piston making the piston bottom out on the crank So no they are not all interchangeable parts. I've even seem completely round cylinders even ..I meant to ask someone on here about that too.

    How about the 66cc motors with the 6 mm head bolts , I got one of those in the mail and was not happy
     
    #9 Jumpa, Jan 25, 2014
    Last edited: Jan 25, 2014
  10. 2door

    2door Moderator
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    As a rule if the cylinder, or the cooling fins have a more round, or cylindrical appearance that is one indication of it being the smaller, 48cc engine. The cylinder stud diameter is another 'general' indicator. The 6mm stud engines were almost exclusively the lesser displacement while those having 8mm studs were the larger.

    Keep in mind that we're dealing with quality control and manufacturing practice that differs from what we are used to in American made products. There are no hard and fast rules that apply but again, generally speaking, if the cylinder fins are round, it is a 48cc. If the studs are 6mm, it is a smaller engine. That said, the ONLY way to be sure is to measure the bore and stroke of whatever engine you have to be certain.

    Tom
     
  11. mapbike

    mapbike Active Member

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    My oldest engine is my only odd ball to speak of, it was advertised as a Red Bat Kit by BGF back in 2009 and was listed as 66cc, it has the low dome piston and the 6mm jug studs, the jug and head bolt patter are smaller than any of my engines with 8mm studs and the old Red Bat is the weakest and has the worst vibes of any of my engines, never done a single mod to it but tune the carb and it has well over 2000 miles on it now and still starts every time and is very reliable and comfortable at 28mph or less pulling a 24" rear wheel with a 32T sprocket.

    I would love to have this engine set up with a better balanced crank some day but it may just end up on the shelf as a trophy of sorts since it was my first china girl engine.

    Map
     
  12. Theon

    Theon New Member

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    That May be the '70 cc' motor with a 45mm piston.
    The One with the odd ball piston is the one to really stay away from (GT5?).
    If your looking for a motor, try and find 40mm stroke x 47 mm bore.
     
    #12 Theon, Jan 26, 2014
    Last edited: Jan 26, 2014
  13. mapbike

    mapbike Active Member

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    my old Red Bat engine is a 66cc with a 47mm piston and its not a GT5, that is a Grubee engine and I have never had this displeasure of owning one of them.

    Map
     
  14. Theon

    Theon New Member

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    I didn't realize when I bought it. It wasn't labeled as such.
     
  15. Nashville Kat

    Nashville Kat Active Member

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    I think the designation 80cc may have started solely by marketing forces-

    I'm not sure when the larger engine actually came into widespread use- I think it's only been the last ten years- but before that was the 50 cc bike motor as a standard-

    then when that changed I think the sellers wanted to stress that it had more power and they simply exagerated- until people started checking the actual stats- and found the displacement 66cc

    if you think about it though- a 66 displacement is actually almost 32 percent larger-
    adding twice 16 cc difference to the 50 factor-

    so maybe there was confusion about 30 percent and people added 30 to 50 to get 80cc.

    anyway- the stud sizes are not an accurate guage to determine the size- because at first and for some time- 66's were made with 6mm studs- mine is, that I first bought in 2009- the 8 mm came out shortly thereafter, but the suppliers stores being what they are, there have been 6 mm stud 66's around for awhile- but I think there are probably all now 8mm studs new- you can still probably find 6mm motors, and surely jugs and heads to fit the bottom ends with 6mm studs, but beyond having the other set-up already- why?

    I'm stil not sure what actual advantage 8mm studs may be, except heavier in weight- and the oil companies that run all corporations always like that, because it sells more gasoline.
     

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