GOOFIT Big Bore Cylinder Rebuild Kit for GY6 50cc 139QMB Racing Scooter Parts 64mm Valve

Very good product. Tip of the trade here. Kit comes with oilpump, same as original, if your oilpump works just set the oilpump aside and install only if needed. Did install an A9 cam with this kit. Recommend the cam. The head is small valve, did porting and valve shroud ( the valves sunk in a bore and the bore shrouding the breathing dremel out the shroud and dremel out the port. however AVOID ENLARGING THE CHANNELS, very little wall material on some spots.just try to takendown the big wart that is cast to hold the pressed in valve bushing.On a 50cc base engine this head will do the same as a big valve head, so keep the head and dont be dissapointed that its a small valve head.Engine displacement. You will get a bit over 80cc with the 50 mm bore.(Formula: Radius X Radius X Stroke X Pi (3.14)) or as with this kit 25 X 25 X 41.4 X 3.14 = 81.44....or 81.5cc. Its called 100 cc kit but everyone and his brother markets it that way.Carburetor, Do NOT buy a 24 mm carb, its overcarbed and you will have issues. An 18 or 19 is perfect you might get away with a 20. If you have a cheap sealed carb, toss it and get a carb you can adjust, and open up to change Jets. With this kit, you might want to start with a main jet around 80-83 somewhere. Watch Youtube, plenty of videos on how to install and tune. My scooter is now doing a bit over 60 mph and have a very good response and pick up. I do recommend you put in a 2000 rpm torque spring (the red one) with this kit. Run as high octane as you can get hold of because you will bump up the compression pretty significant with this kit. A word of warning, many buys a race CDI and have a hard time starting, and don't know why. Many of the race CDI don't retard the timing on very low RPM (as when youre starting), if you want to put a race CDI on your scooter, find one with advancing and retarding curve, otherwise you blame this kit, or get into a long carburetor fix, that doesnt fix anything. Stick to the stock CDI (stock CDI will retard at start) until you have found an advancing/retarding CDI. This kit comes with more gasket you will need. And the parts are well done. I would take my time to mirror polish the top of the piston, and the combustion chamber, careful not to damage the valve seat. The valve seat has a 3 angle valve cut already when it comes so nothing is needed with the valve seat. You can , and I recommend that, grind the valve and get a vitnessmark where the vakve will seat, and do a back cut on the valve up to and close to that mark. You can also make the circumference of the valve head , the edge..make ut round, and you will get a better flowing valve. If you have a steady hand, you can put a piece of protective leather around the valve stem and put the valve in a hand drill, and work the valves with a file.All in all, this kit rocks, and if you do all those little extras, you will beat all big valve heads.Im very happy with this kit and I strongly recommend it.You can just bolt it on and get a much faster scooter or do all the small tweaks and get a rocket.Word of warning...you will have a bigger engine, and thus you will have more heat. When putting on your cooling shroud, be very anal, it will pay out, go over small cracks and openings with black silicone.Good luck to you all

I have a little bit over 100 miles on this kit. My 50cc Tao Tao did about 27mph stock(40mph on the speedo). With this kit and an upgraded and rejetted carb, it's now hitting just under 40mph (55mph on the speedo). Acceleration is night and day. I can takeoff quickly and keep pulling. Hills are no longer a problem, and I have lots of hills around me.Installing the kit was pretty straightforward. It took me about 7 hours, but I was really cautious. My stock motor had 69mm valves and the kit requires 64mm valves. Since the kit included the rocker arms, I assumed that to be the case. I switched the arms onto my old base, and installed the kit. If you use the stock head, it will fail quickly. IMO, this is the most common cause of failure.The rest of the kit went together really well. The metal in the engine is soft, so be very careful not to strip anything. I have a few "troubled" threads already, but they're still holding. The piston was a bit tight, but a little motor oil made it workable. Yes, getting the wrist pin clips on and off are the toughest part.The BBK has no EGR, so you basically ignore that whole system. You can remove it, but I left it all on and connected.My carb is jetted at 85 main and 33 pilot, and I have a pod filter rather then the airbox. The BBK had me go up about 3-5 jet sizes. I am choosing to run it a bit rich to give it a longer life.I haven't tried the included 8g rollers yet. I'm planning on optimizing the variator next.I have found it more difficult to star the scooter in colder temps after the install, but it will start off a jump. This implies to me that the stock 4ah battery may need an upgrade. On warm days, it'll start right up.Will update if anything changes or blows up.

The first thing you need to know is that having the right tools and space will make this installation much easier. Speciffically a drill bit and slide hammer, and bench vice for removing the old tapit sleeve from the valve assembly or just purchasing a kit with a new one ready to go instead of fighting refitting old stuff (((serioisly this would have ended the rebuild had I not been in a garage)))) Secondly I snapped the large silver compression ring and had to order a replacment 50mm set, you may double your ring order to be on the safe side or else be very careful seating the rings. You will need a magnet extension or wire to pull the chain up through the case, the a9 cam does fit this kit but again you will need to reseat the tappits on the valve assembly. All the gaskets worked, i needed a few particular wobbly extensions to get the fan shroud back around the engine not alot of space to fit a wrench or screwdriver. Took a few more days than I originally planned but my little taotao atm50 will through my 275lb ass around fine I can hit 45mph and pull away from city traffic fine so well worth the effort and money even with the setbacks, I can even wheelie it a little if the slope is right.

Cylindre et culasse en centimètres cubes très bien mais dommage pour moi il est trop gros pour mon scooter 139 QMB 50 cm

Wrong zize poston and cylinder

I bought this bore kit for my wife's 50cc as her scooter piston had gone and thought it would be a cheap up grade and was surprised with how much performance it gained on a stock engine it went from 30mph stock to 45mph gps speed with out any other mods and left my 50cc behind I was so impressed I bought a second one and fitted it to mine I'm running 6.5 roller weights and a performance variator and getting 55mph the only down side to this kit are the 9 gram rollers that are included are too heavy and a shame it does not come with 6 or 6.5 gram rollers but very satisfied

Me sirve pero pensé que traía el árbol de levas, ahora lo he tenido que comprar separado

Alles komplett angekommen und auch Verbaut. Geschwindigkeit von ca. 50 kmh auf 65 gestiegen, Drehfreudig und bis jetzt nach 4000 km noch nix gewesen.