Transmission system for Honda GXH50 single cylinder 4 stroke engine

Discussion in 'Transmission / Drivetrain' started by A.Chaudhry, Jun 18, 2016.

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  1. A.Chaudhry

    A.Chaudhry Guest

    Hey guys!
    I don't know much about cars and bikes, so here i am looking for some advice.
    Can you guys suggest the best transmission system to go along with Honda GXH50 engine? The compression ratio is 9.8'....
    The engine is actually used in a small urban concept car. The transmission system should be chosen on the basis of fuel efficiency and smooth drive. i know CVT is best for that purpose but which one will you suggest? and can you suggest any sequential and clutch-based transmission too?


  2. HeadSmess

    HeadSmess Well-Known Member

    depends how much money you have, space and weight requirements, etc...

    cvt has frictional losses, not actually that fuel efficient but they do allow you to find the ideal gear ratio needed at the time. the v belt they use always rubs, and thats a loss. plus the belt has to flex...more loss. the only reason they get better economy is that running the engine at the ideal rpm is better, only just outweighs frictional losses.

    gears of any type are expensive to cut... but theres nothing to stop you from tearing apart a motorbike gearbox and making a suitable box for it. at which point you may as well use a lifan/pitbike/honda50 type engine, sequential shift is great, can be had in either manual clutch or auto clutch versions. (the auto clutch actually still has a manual clutch, you just hold the gear shift up or down...) lot easier to mount, and spares/hop-ups are cheap and plentiful... can also have electric start. you dont have to make ANYTHING!

    the most efficient gearbox would be a chain box...several ratios of chain side by side (not a derailleur like on a pushbike!) with the same dogs as used in a normal gearbox. all you need is the machine tools to assemble such a thing, and as for tensioning...dont worry. online centre distance calculator will let you figure out the best ratios, all on the same centres... dunno if its the same as gears, where as long as the total teeth in any combo are the same, they share the same centre. ie, 32:32 is 64, as is 20:44, 22:42, etc... use HD #35 chain and the whole thing will be pretty compact. seal it up and keep it running in oil, last forever...

    and then theres the auto 2 or 3 speed gearboxes as used on the 1:5 rc cars.. work on centrifugal and one-way clutches, shift points are adjusted by spring tensions. once you tear one apart, the concept is fairly simple... double them up and you can have 4, 6 or more shifts without the hassle of manual shifting...

    last one...fluid coupling. or torque convertor. pretty bulky but you only need one geartrain, from output to wheel/axle... fluid couplings are used in certain washing machines, always have some "slip" but will smoothly accelerate from standstill to running speed but the torque output will always be less than the input. the torque convertor has a third memeber inside, redirects oil flow that allows for torque doubling... just like you doubled the output reduction when you take off, so fairly similar to a CVT...

    there was a go-ped that used a fluid coupling but trying to find one isnt easy...or cheap. it was not a torque convertor (despite the name) just a fluid coupling. and being a few inches across, not as efficient as one would like. torque convertors need to be big to be any good. bigger diameter=faster oil flow= better power transmission.
  3. A.Chaudhry

    A.Chaudhry Guest

    Thanks HeadSmess... that was really informative.
    Can you suggest a good chainbox transmission or a sequential that will go aong with the engine?
    We don't really have enough time to build one by ourselves...
    Last edited by a moderator: Jun 20, 2016
  4. A.Chaudhry

    A.Chaudhry Guest

    Ohh and its best if it's light weight... and the cost should be moderate...
    Last edited by a moderator: Jun 20, 2016
  5. HeadSmess

    HeadSmess Well-Known Member


    oops. new keyboard...capslock is easy to hit...

    no can do... i dont think anyone makes a chain derived gearbox commercially, i suggested it as an option if you are inclined to build anything.

    as for "off the shelf" sequential gearbox... a lifan 50cc engine will cost about $250US or so... thats engine, gearbox, clutch, electric and kickstart... a far cheaper option. it is also repeatable-in that it works, straight away, no engineering challenges other than adequate mounting to overcome. far far cheaper than trying to find a separate gearbox and mounting that to a gxh50...

    sounds like a university project....
    Timbone likes this.
  6. A.Chaudhry

    A.Chaudhry Guest

    You were really helpful, thanks!!
    Yep it is a university project. We are actually planning to change the transmission for better fuel efficiency and smoother drive.
  7. bikejock

    bikejock Member

    Staton inc. used to sell a Honda GX50 rack mount kit with the engine & everything. but last I checked they were sold out. Real bummer but I settled for a GX35 for my bike. I was a able to fit my old Grubee 4G transmission to it out of curiosity. The bolt pattern & clutch size is exactly same as the 50cc Chinese clones on the GX35.

    In my experience with the GX35 it's pretty light weight. Just light enough to where I can use my regular side kickstand without it tipping over. For the speeds I can do about 32mph tops & gas mileage is even better than the 50cc engines. Acceleration isn't all that great & it struggles on the inclines since I use a friction drive. I thought about getting a gear box & chain drive setup someday to replace the friction drive to help top speed & climbing.
    Last edited: Jul 30, 2016