"Hoot."- theses are the cheapest and least durable. There have been numerous threads describing complete failures after a short period. There are Three types, a linear gear, helical gear and an updated version that uses a chain. The chain version is supposed to be much better. Grubee Stage III and II gear box- These are better that the Hoot but are noisy and the engagers break. It is a gear mesh and the box is filled with oil which some say causes more friction. Grubee G4. This is the latest Grubee gearbox. Its belt driven and available with and without an engager. There have been some bad reviews about this box being too wide and the freewheel breaking. From member "Blow By U motors": First of all, it is my personal opinion that the 4G T Belt Drive engine kits are the most reliable V mount 4 strokes Kits out there. There are pros and cons for both engines, Honda GXH-50 is of course Japaneese high quality and offeres more tourque that the Clone but the Honda is not built for installing in bicycles at all. If you use original equiped Honda you will have to take the engine apart and remove the govenor plus the carb will not except a throttle without modification. The best way to deal with that is to buy a Huasheng carb for $40 and your problem is solved. Except for the price most Honda`s sell for $400 or more un like the Huashend 142F-cc 49cc engine the prices start at $170. The Huasheng engine unlike the Honda is ready to go right out of the box and the only down fall of this little screaming deamon is that is made with Chineesium metal and that means be carefull of how tight you turn them bolts. Huasheng engine is by far the best value and I have heard reports of over 50,000 miles and still going strong. If your going to have a problem with this engine it will be right away not later on and they come with a 6 to 7 month warranty and that is more than enough time find any problems. Now when it come to the two different 4G Tramsmissions tappered shaft Huashend plus Huasheng also has five eights shaft and Honda five eights shaft and in this case the advantage gose to the Huasheng tappered shaft because the clutch bell has a bearing. Now the Honda on the other hand has a brass bushing called a cc bushing that requires soaking the bushing in oil for 24 hrs, it is very brittle and easily damaged. Trans for the Honda also comes with a problem matic clutch that requires special tuning, ie; springs and washers but once this is dialed in the clutch engages right off idle. Unlike the Huasheng Tappered shaft the clutch dose not start engageing untill 2100 RPM. There is one more thing that gose in the Honda`s favor with the 4G trans and Honda as a the pair are three quarters of an inch more narrow that the standard 4G with the Huasheng tappered shaft engine enables you to use the one piece wide crank with the Honda of which is more narrow than the 3 piece wide crank that comes with the standard 4G kit. I will say this about the 4G T Belt Drive engine kit with the Huasheng engine and that is this I have sold more than 200 of thses kits and I have only had to deal with shipping damage. Also this is the kits that I use in all my high end custom built bikes. BUT it dose not matter what engine you use with the 4G T Belt Drive transmission you are going to get a winner. EZM Q-matic - claim to fame is that its all american. the box was designed by member "Quenton Guenther." The claim is that its the best box on the market but you have to pay for it. It's quite expensive. The EZM 'Q-Matic' is a automatic with a max-torque made centrifugal clutch. The EZM 'Silent-Drive' is a manual version. Both are a belt drive primary and chain secondary design (the manual is easily converted to a belt secondary. At this time, the manual 'Silent-Drive' is only available with a kit. The auto 'Q-Matic' is available in kit form or as a stand alone replacement for Honda GXH50, and HuaSheng 142f as well as a few other 4cycle engines with a 5/8" drive shaft. The drive is only 2" from the mounting flange of the engine. EZ Motorbike Firebelly WhisperDrive- From Evan aka tyrslider. "Cake to install and icing to operate, this 1 speed automatic is brimming w/ style and sophistication; A window into the works lets onlookers gaze w/ wonder! The WhirlyGazer Technology also helps you, the rider, check o/a condition at a glance. 3 HD High Speed Sealed Bearings on the Primary Shaft Inspire Total Confidence. The throaty 4 stroke sound through the FBC signature SS pipe is nothing less than assertive. Be the 1st on your block to Command Respect! Currently in Production the "WD" is a simple and economical 4 stroke kit made (not sourced) almost entirely StateSide. All componants are made right here in the USA except as listed here: the bearings and final drive chain are made in Japan and the sprocket, throttle and grips are made in China. Depending on the motor you use it is likely made in China. The "WD" comes w/ Drive System, Engine Mount, Wide Cranks, FBC SS Exhaust, Chain and Rear Sprocket. $440 W/ HD Rear Axle Grubee MB Wheel (W/ FreeWheeling Rear Sprocket). $540 FBC AirFilter and Chain Tensioner available at $20 each w/ order of "Base Kit". You Buy Only What You Need! Will work w/ many engines including Lifan, B&S, Honda GX100 and most notably the Harbor Freight 2.5 HP ($109.99 but often on sale for $89.99)." YouTube - ShellyBelly WhisperDrive YouTube - An evening in front of the FireBelly! YouTube - FireBelly WhisperDrive in true technicolor extra reality TV Sick bike parts shift kit- $189 This kit is designed to fit the Honda or Huasheng engine using the Hoot or Grubee Stage 2 or 3 gear box. This kit will allow the user to shift gears using the bike's standard rear derailleur. Sick Bike Parts Staton- Staton-Inc motorized bicycles, bike kits & gear drive kits. They've been making kits since 1984, long before any of the other companies listed were even conceived. Its a Gear mesh that's machined in the US and is intended to mounted on a rack.. Lifetime warranty on the gearbox. They sell a Nuvinci CVT kit that looks really cool. I personally have Robin Subaru crank shift kit with the gearbox. The box is bullet proof but is a little noisy. Staton gave me some new thinner type grease that seems to do a better job with noise but leaks out and has to be wiped down every so often. CVT- I've heard of people taking them off of pocket bikes and retro fitting them to their motors. I don't think there are any company specifically making them for 49cc honda's and Huasheng Thats dax I'm quoting Thats Dax "59 bucks and 9 shipping will get you this gear box. Mounts right up to Titan, and others that share the 76-78 mm" "Automotive Technology for the Gear box drive system, and some other engineering combinations yields a simple yet super reliable, smooth , quiet, and very powerful " affordable go karts affordablegokarts: Jackshaft Assembly for 79cc HF EngineI got the chance to meet the owner of AGK and he seemed to be a really cool guy. he was vary enthusiastic about MB's. This trans is for a 79cc Harbor freight engine and I don't know if it will fit the honda or HS engine. I handled the jack shaft at the "Death Race" and it seamed pretty durable. looked hand made (USA manufacturing )the owner (wish i could remember his name) expressed a concern about the engine case fatiguing over time but his bike was really fast on the track.