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Discussion Starter · #1 · said:
What is a GY6?

The Honda Motor company has been said to have perfected the scooter engine design in the 1960s. Building upon that technology a newer motor, the Honda gy6 engine, was produced in the 1980s. This is a 4 stroke single cylinder, air or oil cooled design that comes standard with two overhead valves. Stock horsepower ratings can be found quoted in the range of 7.8 hp (5.8 kW) to 12.4 hp (9.2 kW). The engine is capable of producing 12,000 rpm and power upwards of 14 horsepower (10 kW) with modifications according to end users. The GY6 engine has a built in swing arm with automatic CVT transmission that is belt driven. This engine was originally manufactured in 50 cc (3.1), 125 cc (7.6 cu in), and 150 cc (9.2 cu in) engine sizes and was found in the Honda Elite and Spacey line of motor scooters. Honda no longer uses this design on their scooters, but Chinese, Korean, and Taiwanese copies of this engine are readily available. Current brands of import scooter lines that use the Honda GY6 cloned engine technology include: Kymco, PGO (imported by Genuine Scooter Company in the USA), Ricardo Motors, Roketa, Strada, SUNL, Tank, Vento, Yamati, and many others.

I'd like to note that Honda had their parts made in china under their management and quality control and when they were done with with the GY6 and or the Honda mini bike design it was cheap and easy for for the Chinese manufacturers to buy the licenses and reproduce the parts and vehicles and to great success too. said:
How do I know if I have a GY6?

If you look just under the left side engine cover, right above the kick stand, there will be a series of

engraved letters and numbers. If you see QMB139, then you have a 50cc GY6, if you see QMJ157, then you have a 150cc GY6 engine said:
Hey MO! How do I know what engine I have? I have heard all this talk about 1PE40QMB and 157QMJ blah blah. It seems so darn confusing to get parts for these Chinese bikes! What can you do to help? -Lost in Las Vegas.

Chinese bikes and ATV's can really be confusing, that is why scrappy dogs was started. There are two identifications to remember by using this site for help, not only to know what you have, but to get what you need. The first is the engine type. While this site uses a simplified directory at the left, you really need to know the engine number to get your parts right. This engine number is typically in two parts on the same stamp location. Most of the time the numbers are stamped on the left side of the engine, under the belt cover, near the front close to the engine mount to the frame. The bottom number is the reg. number, the top number is the one to pay attention to, this is the engine identification number. It tells you what you have. Below is a picture of a number plate for a 50cc 4stroke, also known as a 139QMB.

The engine number is very significant, and reveals alot. Take for example a popular engine, like the Honda Monkey (chinese copy) The number stamped on it is a 1P39FMB. The first number is the number of cylinders, the second, a P, is code for a horizontal engine. The next 2 numbers, 39, is the bore diameter in mm, 39mm bore. The next letter, F, indicates that it is natural (not forced) air-cooled style. The next letter designates that it is a motorcycle engine "M". The next letter reveals the full engine displacement. B is code for a 50. C for a 60, D for a 70, F for a 90, G for a 100, H for a 110, I for a 125, J for a 150, and so forth. Notice that the size graduation increase is indicated by an increment in the alphabetical letter? It's no coincidence. It's amazing to me the cooperation in standards of China. There is also prefix letters on many, designating the manufacturer, like Quinjiang (we have them all on file), which stamps there acronym, QJ, as the first two letters in there code. It's also very revealing, as the QJ139qmb is quite different then the other 139qmb's. It uses the 1E40qmb (2T) transmission components, and the engine case is a little different. There are also suffix numbers at the end, which designate iteration levels, like -3 in the photo below, which denotes that it is the third design, or improvment. Call or email us if you have any questions. We love to help. Here is the Chinese engine code chart with the example of the JOG 2stroke engine number 1PE40QMB-4

Some engines have the number plate on the upper rear side of the belt cover. GY6 engines are on the fron, bottom, left had side near the centerstand pivot. 2stroke JOG's are near the rear wheel like Honda Spree elite and DIO. They are often on a sticker on the belt case. Sometime the airbox needs to be removed and alot of grime washed off on the 2strokes. By federal law they are stamped on the engine case and are there, even if you don't see it at first inspection. Either way it will help you significantly to know this. said:
How do I know if my 150cc GY6 is a long or short case? I want to change my belt and it has no indication on it?

With a few exceptions, the 125/150 GY6 has two belt sizes: 743 for the short case, and 842 for the long. If you have a 10 inch rim on the rear with a tire that is 3.50 wide or less, it's a short case. The belt cover will also measure 16 inches from end to end. If you have a 10" rim with a 4.00 wide, or a 12 or 13" rim, you have a long case. The belt cover will measure 17 1/8" long. Another easy way to tell is simply to count the number of retaining bolts for the belt cover, the short case has 8, the long one has 10.

I did some measuring today and it seems this also applies to 50cc GY6 scooters as well. said:
QJ139QMB-3 and QJ1P39QMB-3 anomaly engine tech facts

Hey MO! I've got this QJ engine in my Baja Sun City SC50, it's also found in the Vento Triton, and MotoMojo Roadster 50. I'm just confused about what parts fit what?

Yes, that is a pretty unique engine. We call it the QJ anomaly. This engine is fundamentally the same, with these differences:

1) The aperture in the crankcase for the cylinder is slightly smaller, making big bore kits difficult without some modification

2) The belt size is unique, using the 836-17-30.

To confuse things a little, it seems the Vento and MotoMojo uses an 891-17-30 belt.

3) The QJ anomoly uses 21mm 2stroke JOG engine variators, rollers and rear clutch pulleys.

4) The belt cover is unique also

5) These are often fitted with disc brakes in the rear, making some of these components difficult to acquire.

6) The carburetors that are fitted on these use a different type than standard 139qmb. We would recommend changing the carb to the more common type.

Other than these differences, it is essentially a standard 139QMB engine.

MO! said:
MO, I've noticed that there are a few different heads types and other parts on GY6-125/150 engines. I thought they were all the same? All these engines had the 157QMJ in the engine code. What gives!

Yes, there are a few different types, but are easily distinguished, and thankfully most are interchangable. The standard GY6 engine parts your will find on our site fit and work perfectly. There are two variations that I will identify now.

GY6 Scooter Version B - This engine is found in alot of higher priced quality scooters like Zhen, Lance, Fly, etc. The engine number will be BN157QMJ, and will have a 16" rear wheel ( although some Lance Duke Tourings have the smaller wheel BN engines, which are standard parts, with some other exceptions). This engine is made by BenNeng of the Zhongneng Industry Group. This engine has alot of non-interchangable parts, like the variator, head, stator, etc. The head on these is taller than a standard GY6 head, and has longer valve stems. The stators are 12pole DC types. The belts are longer than standard, and are often 906. The cylinders however will fit from standard parts. Our big bore kits will fit -B models. The performance 4 valve head will fit these without use of the longer chain and retention studs, as this engine already has them.

GY6 ATV Version B - This engine is found almost exclusively in ATV, Buggy, and Go-Cart's. Externally they look identical to a standard GY6, with one prominent, yet subtle difference. They have two bolts holding the cam cover down, while the standard GY6 has 4. The other differences are internal, and on the top end only. The cylinder retaining studs are slightly wider spaced than a standard engine, not allowing the use of standard heads and cylinders. The apperature in the crankcase is larger than normal, which allows a larger big bore kit without machining of the case, but the kits that fit are nearly impossible to find. One last thing on Kazuma ATV engines, model KZM157QMJ. Nothing fits these except Kazuma specific parts. The QJ157QMJ and QJ156QMJ by Quinjiang is also a unique oddity.

MO! said:
What is a CVT transmission?

Peer into a planetary automatic transmission, and you'll see a complex world of gears, brakes, clutches and governing devices. By comparison, a continuously variable transmission is a study in simplicity. Most CVTs only have three basic components:

* A high-power metal or rubber belt

* A variable-input "driving" pulley

* An output "driven" pulley

The variable-diameter pulleys are the heart of a CVT. Each pulley is made of two 20-degree cones facing each other. A belt rides in the groove between the two cones. V-belts are preferred if the belt is made of rubber. V-belts get their name from the fact that the belts bear a V-shaped cross section, which increases the frictional grip of the belt.

When the two cones of the pulley are far apart (when the diameter increases), the belt rides lower in the groove, and the radius of the belt loop going around the pulley gets smaller. When the cones are close together (when the diameter decreases), the belt rides higher in the groove, and the radius of the belt loop going around the pulley gets larger. CVTs may use hydraulic pressure, centrifugal force or spring tension to create the force necessary to adjust the pulley halves.

Variable-diameter pulleys must always come in pairs. One of the pulleys, known as the drive pulley (variator), is connected to the crankshaft of the engine. The driving pulley is also called the input pulley because it's where the energy from the engine enters the transmission. The second pulley is called the driven pulley because the first pulley is turning it. As an output pulley, the driven pulley transfers energy to the drive shaft.

When one pulley increases its radius, the other decreases its radius to keep the belt tight. As the two pulleys change their radii relative to one another, they create an infinite number of gear ratios -- from low to high and everything in between. For example, when the pitch radius is small on the driving pulley and large on the driven pulley, then the rotational speed of the driven pulley decreases, resulting in a lower “gear.” When the pitch radius is large on the driving pulley and small on the driven pulley, then the rotational speed of the driven pulley increases, resulting in a higher “gear.” Thus, in theory, a CVT has an infinite number of "gears" that it can run through at any time, at any engine or vehicle speed. said:
What is an AC or DC CDI?

CDI modules can be generally divided into two:-

* AC-CDI - The AC-CDI module obtains its electricity source solely from the alternating current produced by the alternator. The AC-CDI system is the most basic CDI system which is widely used in small engines.

* DC-CDI - The DC-CDI module is powered by the battery, and therefore an additional DC/DC inverter circuit is included in the CDI module to raise the 12 V DC to 400 V DC, making the CDI module slightly larger. However, the vehicle that uses DC-CDI system has more precise ignition timing and the engine can be started easier when cold. said:
AC/DC CDI Comparison


1,884 Posts
Discussion Starter · #2 · (Edited)
So now that we have covered some of the basics lets get to the good stuff like mods and after market.

Just like the other minis pretty much the same applies for mods except for a real tranny the GY6 has a CVT and drives gears.







Big Bore Kits, B.B.K.


Drive Gears

CVT covers

Crate engine

Etc, Etc

Each mod does something different the CVT is more complex than the other mods as there are different aspects to such as springs clutches and rollers each changes aspect of the CVTs operation.

The CDI is probably the easiest of of all the mods for the most part there are 2 variations you will for sell the orange compact CDI it's the same size as the stock CDI and looks exactly the same as the stock CDI except for it's orange. The orange CDI SUPPOSEDLY eliminates the rev limiter and gives you a slight timing advance and supposedly this helps out in the mid range of the power band. The second version is the RACE CDI it's a bit bigger almost the same size as the less common DC CDI it's usually in an anodized finish and is the same as the first except it advances the timing a little more than the first and supposedly ads more power to the mid and top range of the power band. It's also said the these CDIs won't fix a poorly running GY6 and if anything will make it worse. The bigger DC CDI found on some scooters is pretty much the same thing except for appearance as far as i can guess, most sellers offer DC variation of the performance CDIs as well as the more common AC version. EDIT: you probably will get no gain or any noticeable boost from a CDI.

Another common mod is of course the carburetor. This one isn't as simple as the CDI as there are more variation and a lot more claims. supposedly from what i have read the stock sizes are 17 and 18mm and supposedly 20mm. The 20mm is one of the common performance options, basically the claim is that this 20mm is of better quality than stock. the 22, 23 and 24mm carbs are little more straight forwards there are bigger than stock and some of better quality how ever the 24mm carb requires a aftermarket air filter as it won't fit the stock air box, at least not with out modding the boot that clamps on to the carb. My guess is the same probably applies for the 23mm too. The carb sizes also go in to the 30mm sizes for the bigger GY6s and BBKs. Obviously an aftermarket carb gives you more air and fuel thus giving you more power.

The exhaust is straight forward pretty much any offering gives better performance it usually has bigger header pipe and a better flowing unrestricted muffler and is usually louder than the stock pipe. Most offering have CC rating and seems to be pretty generic fitting most models and CCs such as the 50 and 150cc engines.

For the actual engine we have the performance head and big bore kit (BBK) and for the bigger GY6s suck as the 150 and above stroker cranks. The performance head from what i can tell actually has few variations. From what i can tell some are stamped out in china and some are done here in the USA on top that some have different MM diameters on the combustion chamber. The performance head is usually a good match with a BBK.

The BBK comes in quite a few flavors from 60cc to 100cc and 160cc to 200+cc for the bigger GY6s. Some of the bigger ones require case boring just as like other minis like the CRF and the monkey bike. Most of the time if a BBK requires a case bore it's stated as so. Bigger BBKs will require a larger carb and of course and exhaust.

Another way to add a few more CCs is to get stroke cranks it adds more travel to the the piston and cylinder and ads more power. The stroker requires more room for the extend travel in the cylinder and or in the engine cases.

Lets not forget the camshaft it plays big role and can have a real impact on performance. There are different flavors for the Cam it can add power to different parts of the power band. Usually it's either the low end torq for acceleration of the line or the mid and top end of the power band for top speed. It adds power by leaving the valves open longer and opening them further and certain points in time depending on when and how far it changes it adds torq and or mind and or top end power.

Of course if you want you can just get the whole shabang and get an entire engine. There is catch the you can't just shove a 150cc GY6 in to a 50cc GY6 frame there thing like space and wheel base that need to be taken in to consideration, it's not all the different that with any other mini. Wither bigger engine you will probably need a bigger exhaust and or carb if doesn't come with them. From what i can tell they come stock and have room for improvement there are people and places that can probably sell it to with aftermarket of your choice pre installed as well.

Now that you have all that power you need a way to put it ot the pavement that's where the CVT and drive gears come in.


Found some quality performance parts,
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