Engine Code: "BN157QMJ" 150cc stock, GY6 (A-Block) 54mm stud spacing longcase 20", Chinese scooter model "ZN150T-9" manufacture by Zhongneng Industry Group


Decipher GY6’s Engine Code

Where do we locate GY6's engine code and how do we decipher what each character means?


GY6’s engine code is located on the lower-side of CVT, just beside the oil drain bolt. The first set of numbers above is the scooter engine code. The secondary number below is the scooter's unique identification numbers (engine registration numbers).

Example Engine Code (above) is “BN157QMJ”
The first two letters are the manufacture acronym for its’ make or model, "BN" means the Chinese scooter model "ZNEN" manufacture by Zhongneng Industry Group. The three digits and three letters set that follow are more important engine code that will cover here, and how to decipher their meaning these main six-character codes.

The first code digit: “1”
Corresponds to the number of cylinders. All GY6 engines are a single-cylinder with single-piston, so this number will always be uno—one.

NOTE: If you have a letter “P” after example “1P”, stands for (P)air valve horizontal engine. The P series engine has a taller cylinder head and a shallow recess cam seating that gives it a slightly more performance than non-P GY6’s engine code. However, if both cylinder and cylinder head is swap out it will be identical to non-P GY6 engine. So, parts are interchangeable as long as both are replaced cylinder and cylinder head from 1P and non-P. But why? Because their so more upgrades available for non-P type engines include performance camshaft, etc.

The second and third code digits: “57”
Corresponds to the bore size in millimeters, for this example 157QMJ, the bore is 57mm. At the cylinder sleeve (skirt) outer diameter the bore is 57.4mm which falls under the same reference digit "57" still. If it was a 139QMB the "39" means it's a 39mm bore, with a cylinder outer skirt of 39.4mm perhaps, varies by manufacturer. Still will fall under the "39" digit code.

The fourth code letter: “Q”
Simple means it’s a GY6 style engine. Why not “G” right... but that the way it is Q. :/

The fifth and six code letters: “MJ”
Stand for Michael Jordan… just kidding. The “M” means the engine type is a motorcycle (motor-two wheels). The sixth letter thereafter is code for engine displacement size measure in CC (cubic centimeter). See the table below. Notice as each alphabetical order B-to-Y so is the engine displacement CC increases. In incremental 10cc, 15cc, 25cc, 50cc and 100cc.

  • MB = 50cc
  • MC = 60cc
  • MD = 70cc
  • ME = 80cc
  • MF = 90cc
  • MG = 100cc
  • MH = 110cc
  • MI = 125cc
  • MJ = 150cc
  • MK = 175cc
  • ML = 200cc
  • MM = 250cc
  • MN = 300cc
  • MP = 350cc
  • MQ = 400cc
  • MR = 500cc
  • MS = 600cc
  • MT = 650cc
  • MU = 700cc
  • MV = 750cc
  • MW = 800cc
  • MX = 900cc
  • MY = 1000cc
  • YG = 1100cc
  • YL = 1200cc
  • Y? and so on...

Engine Manufacturer will engrave more characters, added acronym (code) in front as we see in the first picture but also in the back of the engine code line for their added specific GY6 variant makes/models' acronym like the example below.

Engine Code: “VE157FM2A”

  • VE = Vento Scooter
  • 157 = Uno-Cylinder 57mm
  • F = Natural Air-Cooled
  • M = Motorcycle Type
  • 2A = 2nd Gen, Series A—just guessing?

That’s it. Now, your ability to read and decipher most if not your own GY6's engine code. However, if you still don't know what scooter engine you have, leave a comment below and we can help answer your question right here on our blog-share. :) Check out the latest GY6 aftermarket performance parts and accessories, click the link here.


Check out related video 157QMJ vs 1P57QMJ: