Engine Code: "BN157QMJ" 150cc stock, GY6 (A-Block) 54mm stud spacing longcase 20"

Locate and 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 engine'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 follows is the important engine code that will cover here, and how to decipher these 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 the non-P GY6 139QMB 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”

This shows the uno cylinder piston size in millimeters, for example, if the engine code is "..157QMJ", the piston size is 57mm. And, vary by manufacture slightly by 0.2mm, its cylinder sleeve (skirt) could be 60.2mm which allows it to slip into a 157QMJ engine's crankcase bore opening 63mm. You can see there room for a bigger cylinder skirt thus it's piston size upgrade for the 157QMJ engine. Which is cover in blogshare "GY6 Engine [Big Bore Kit]."

Another example: if it was a 139QMB the "39" would mean that it has a 39mm piston with a cylinder outer skirt of 44.78mm, which may vary by manufacturer slightly off by 0.2mm, allow it slip into the 139QMB engine's crankcase bore opening 52.5mm max. So you can see their room for a bigger cylinder upgrade for the 139QMB engine as well, cover in blogshare "About 139QMB 139QMB 49cc."

The fourth code letter: “Q”
Simply means it’s a forced-air-cooled engine. "Q" which means is not a liquid-cooled but forced-air-cooled engine.

The fifth and six code letters: “MJ”
Stand for Michael Jordan… just kidding. The “M” means the engine type is a motorcycle (motor-cycle relates to scooters\atv\buggies as well). 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 incrementally 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, you can read and decipher most GY6's engine code out there. If you still have questions on GY6's engine codes leave a comment below and we as a community of scooter riders, two or three-wheel enthusiasts, or atv\buggies can reply to your comment here on our blogshare. :) Check out the latest GY6 aftermarket performance parts and accessories, click the link here.

NEXT: If you have a question about a GY6 A-Block (54mm) vs GY6 B-Block (57mm) or the difference between. Learn more on blogshare GY6 A-Block vs B-Block [232cc] 


Check out related video 157QMJ vs 1P57QMJ: