GY6 A-Block vs GY6 B-Block [232cc]

History, the GY6 engine was built upon the perfect scooter motor design technology in the 1980s. The GY6 engine is a 4 stroke single cylinder with an air or oil cooling design and it has two standard overhead valves. Somewhere between the range of 7.8 hp (5.8 kW) to 12.4 hp (9.2 kW) is the quoted standard horsepower rating. It has the capacity to produce 12,000 rpm and power more than 14 horsepower (10 kW) with customizations according to the riders. It comes with a built-in swing arm with an automated CVT transmission which is belt-driven. Originally, it was assembled in 50cc (3.1), 125cc (7.6 cu in), and 150cc (9.2 cu in) engine sizes and could be found in Honda Elite and Spacey motor scooters. But, Honda doesn’t manufacture these so-called "GY6 engines" any longer. However, you can still find these GY6 engines in Chinese, Korean, Taiwanese, and other aftermarket manufacturing scooter brands. These brands of import scooter lines include Kymco, PGO, Ricardo Motors, Roketa, Strada, SUNL, Tank, Vento, Yamato, and many others. They all use the same GY6 engine configuration as the original GY6 Honda developed.

How to tell if you have a GY6 A-Block or GY6 B-Block engine case?

First, locate the engine code. The image above illustrates the red-dash rectangular box is where the engine code is engraved. The engine code is followed by a secondary number below is the engine manufacture identification numbers which are not significant to us, really. But here what matters...

Example Engine Code “BN161QMK”

The first two letters are the acronym of the manufacturer for the make or model, "BN" means the Chinese scooter model "ZNEN," created by the Zhongneng Industry Group. The three digits and three letters that follow are the significant engine code that we cover, briefly here, and what these six-character codes mean.

The first code digit: “1”

This indicates the number of cylinders. All GY6 engines are 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. Cover more on blogshare Locate GY6 Engine Code.

The second and third code digits: “61”

This shows the uno cylinder piston size in millimeters, for example, if the engine code is "..161QMK", the piston size is 61mm. And, vary by manufacture slightly by 0.2mm, its cylinder sleeve (skirt) could be 62.9mm which allows it to slip into a 161QMK engine's crankcase bore opening 65mm. You can see there room for a bigger cylinder skirt thus it's piston size upgrade for the 161QMK engine. Which will cover further in this blogshare.

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 GY6 Big Bore Kit 50cc

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: “MK”

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...

GY6 engine code can help you determine what size cylinder the GY6 engines can handle or big bore kit upgrade available. As far as the GY6 49cc-50cc engine code 139QMB engine it will not relate to these two GY6 engine sizes: "GY6 A-Block" and "GY6 B-Block" that will be covered further here.

The GY6 A-Block consists of a GY6 125cc-150cc size engine (engine code is 152QMI and 157QMJ). And, the GY6 B-Block consists of a GY6 175cc-232cc size engine (engine code is 161QML,161QMK, or Taida Crankcase B-Block). Also, it can determine if you have a GY6 A-Block or GY6 B-Block is by the cylinder stud spacing measurements. For example, a GY6 B-Block cylinder stud spacing is 57mm commonly found in Polaris RZR 170 and GY6 180cc+ size engines as illustrated by SSP-G Cylinder Gasket 63mm below (right image): Measure straight horizontally or straight vertically center-stud-hole to center-stud-hole spacing, it's 57mm.

While the GY6 A-Block has a cylinder stud spacing 54mm (left image above) cylinder gasket 63mm which looks identical to the 57mm cylinder stud spacing (right image above) cylinder gasket 63mm. Only by caliper measurement of the cylinder gasket straight horizontally or straight vertically center-stud-hole to center-stud-hole, or diagonally center-stud-hole, or fit into an existing known cylinder with dowel pins can you start to tell if you have a 54mm or 57mm cylinder stud spacing engine block type A or B.

GY6 A-Block, vary by manufacture slightly by 0.2mm, typically has a maximum 63mm bore opening as to why you can install Taida Cylinder 61mm Piston Kit without need to bore the engine crankcase for Taida Cylinder skirt slip-in at 62.7mm bore opening. When pairing it with a Taida Cylinder Head 61mm will change your stock GY6 125/150cc size engine into an easy slip-on upgrade GY6 171cc size engine!

Since the GY6 B-Block has a 57mm stud spacing which is wider cylinder stud spacing, compare to GY6 A-Block 54mm cylinder stud spacing, vary by manufacture slightly by 0.2mm, typically GY6 B-Block has a bore opening of 65mm for it can fit an SSP-G Cylinder 63mm Piston Kit for its cylinder skirt slip-in at 64.9mm inside a GY6 B-Block crankcase or inside a Polaris RZR 170 crankcase bore opening perfectly! However, for GY6-Block if swap with a Taida Crankcase B-Block has an even bigger engine's crankcase bore opening 70mm enable it to fit a Taida Cylinder 67mm Piston Kit for its cylinder skirt slip-in at 69.5mm crankcase bore opening. And, if complete installed Taida 67mm Big Bore Kit will make it the biggest GY6 engine size available on the market, a GY6 B-Block 232cc size engine!

Most GY6 180cc+ size engines consist of a big bore kit upgrades on a GY6 B-Block 57mm cylinder stud spacing crankcase (case for short). HOWEVER, there is some daring to live on the edge-sheaving and bore their GY6 A-Block 54mm cylinder stud spacing crankcase further opening to fit a Taida Cylinder 63mm. If paired with Taida Cylinder Head 63mm they'll get the same engine displacement 180cc on the GY6 A-Block case!

In context "bore" or "boring" could mean cutting a bigger hole in the crankcase for the cylinder skirt to fit. The maximum you can bore a GY6 A-Block case safely for daily use is 65mm bore opening. However, you can still add more displacement CC power you have to upgrade longer Taida Crankshaft 66mm which will need extended Taida Cylinder Studs, Taida Cylinder Spacer, Taida Chain Guide, and Taida Cam Chain to extend in order to build a GY6 A-Block 205cc size engine max!

Important note you can not interchange cylinder stud spacing parts if they made fit a 54mm cylinder stud spacing they will not fit a 57mm cylinder stud spacing crankcase and vice versa. It's physically you cannot relocate the cylinder stud spacing as you can increase the crankcase bore opening size of the crankcase with a Taida Boring Tool. But even the boring tool will only fit a 54mm cylinder stud spacing or made only fit only a 57mm cylinder stud spacing case. So when ordering a boring tool or any GY6 engine parts like cylinders, rocker arms, cylinder gaskets, make sure it says "fit 54mm" or "fit 57mm." Which is cover in more detail in blogshare GY6 Swap [Big Bore Kit]. Now, here some GY6 big bore kit upgrades that will fit well in the GY6 B-Block.

GY6 Engine Upgrade / GY6 Big Bore Kits

Taida Cylinder Head 67mm 2V 30.5/26.5 Fit 57mm (GY6)

The Cylinder Head provides space for passages that supply air and fuel to the cylinder, allowing the exhaust to escape. The head is also where the valves, the spark plugs, and the fuel injectors are installed. Taida's Cylinder Head 67 mm has an improved oversize intake/exhaust port and a bigger 2V 30.5/26.5 valve. It can fit on the Taida 2V cylinder kit and should be used with a 57mm Taida improved crankcase and Taida Crankshaft 66mm 2V 8200 Stroker with Taida Cylinder Head 67mm 2V. Or take this complete Taida kit setup for the top-end.

Taida Big Bore Combo 67mm 2V w/Forged Piston Fit 57mm (GY6)

Taida Big Bore Combo includes a 67mm Taida Ceramic Cylinder with Forged Aluminum Piston that offers greater reliability and reduced friction for your GY6 engine. There's a forged piston that provides better endurance, as well as a ceramic cylinder that gives more heat dissipation which helps prevent overheating. The ceramic cylinder coating in this kit ensures better longevity with more heat dissipation and it can withstand higher temperatures. The Bore is 67mm in size. It also includes the Taida Oversize 2V head 30.5/26.5, the Taida T300 Camshaft, the Taida 57mm rocker arm set, and the Taida 8200 Crankshaft with stud and chain (66mm stroke). This Taida Big Bore Combo is suitable for air-cooled GY6 57mm cylinder stud spacing 4-stroke engines.

Taida Starter Motor High-Torque 4 Pole (GY6)

The Taida Starter Motor High-Torque 4 Pole "Quadrupole," found in NCY STORE, is something you should consider investing in when building a 180cc-232cc Big Bore Kit engine upgrade. With a Big Bore Kit or Stroker Big Bore Kit or an Extended Crankshaft, this Starter Motor is for the GY6 180cc-232cc BBK. So if your GY6 engine is high compression or big bore, this high-torque starter will help you get good performance. It works for any GY6 Engine Block A or B. And this starter motor torque can overpower the cylinder press brought in and make the crankshaft work accordingly. We suggest the installation of heavy gauge no.10 electrical wire on the high torque starter motor and, through the direct connections of the battery, you will need to solder or change existing wire harness connectors to protect the terminal of the new starter motor.

And there are many more high-quality aftermarket scooter parts available at the NCY STORE. So if your OEM parts fail or get bogged down, let NCY Performance Scooter Parts be your source for finding better and upgraded replacement parts for your GY6 buggy or Scooter.

To check out the latest GY6 B-Block engine performance parts and accessories, click here.


Check out the related video GY6 Decode Your Engine: