Originally Posted by Mr.Firemouth

You can find your engine code below the CVT cover, beside the oil drain plug.

We'll take a look at the most common engine code: 157QMJ.
The first thing to note is that the actual code always starts with the first number, and continues for a total of 6 digits. Anything extra is a manufacturer-specific information that won't be covered here at this time.

Lets disect the code starting with the first digit:
(Digit #1) Corrasponds to the number of cylinders. All GY6 engines are single cylinder, so this number will always be 1.

(Digit #2 and #3) This is the bore size in metric millimeters, in the case of the 157QMJ, our bore is 57mm. Note that 57.4mm bore engines fall under the "57" designation.

(Digit #4) relates to the style of engine. All GY6 engines are designated "Q".

(Digit #5 and #6) The actual size of the engine. The second letter ascends consecutively for each 10cc. MB = 50cc, MC = 60cc, MD for a 70, MH = 110cc, MI = 125cc, MJ = 150cc

That is pretty much it for the standard codes stamped on most GY6 and other Chinese engines. We will add more information about manufacturer-specific codes as we find it out.

Originally Posted by jwpetersen84

So I can't seem to find out anything about my scooter motor. I do know for a fact that it is not a 50cc. It looks almost exactly the same as the 157qmj but on the case it says it is a 139qmb. What does this mean? And how do I order parts for it?i was guessing that the cylinder stud is different and that that may be the true meaning of the numbers.