floating ideas, come on in.....

Discussion in '4-Stroke Engines' started by popeye, Aug 26, 2011.

  1. popeye

    popeye Member

    hi, ive been lurking round here for a little old while now im very shortly going to start stockpiling the parts i will need for the build, i was origonally going to buy a ht motor and put it on a tadpole trike but after hacking up a few bikes ive decided that im no good at fabrication so itll be a shop bought 2 wheeler and im leaning towards the yxm 4 stroke from china via ebay as its a kit with everthing with it, so on to my questions....
    1. what kind of speed will this motor on stock gearing pull?
    2. are there any performance parts available for 4 strokes?
    3. can i not flip the back wheel and use the gears that came with the bike?
    4.is there a kit available with the nesasasasasasasasrrrry [nevr could spell!] bits to mount up a say gx160 engine? honda clone
    any hoo many thanx in advance

  2. cobrafreak

    cobrafreak New Member

  3. popeye

    popeye Member

    thanx cobrafreak ill be right back ;]
  4. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    The gearbox on that kit is junk and will probably need to be replaced.

    AffordableGoKarts.com is the only place that sells a full range of performance
    parts for the 50cc 4 Stroke Honda or Huasheng clone.
    AGK is the only place to buy a reground cam for that motor.
    They also sell hop up parts for the GX 160 and similar including a engine mounting plate.

    No, that does not work as the gears freewheel in the wrong direction and you are not the first person with that idea.
  5. popeye

    popeye Member

    now that's a well reasoned and concise answer MBR thanks for your time, as you seem to know what your on with, i don't suppose you would advise me, on a mid priced [reliable] plug and play kit/ a list of parts i.e. honda engine comet g.box etc please? i would value your oppinion as i am just about to order the bits i need but am not sure what i want all i do know is a happy time engine is a lot of faffinf around with rebuilds and generally poor running from what ive read anyhow
  6. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    A Grubee 4 stroke kit with the 4G gearbox is a pretty good kit to
    get started with.
    They were very hard to find a while back but a few sellers have them
    in stock now.



    There are a few variations on the Huasheng motor and Grubee gear box.

    This gearbox http://www.bicycle-engines.com/tbelt-transmission-honda-p-341.html

    on this motor http://www.bicycle-engines.com/49cc-powered-stroke-engine-shaft-p-157.html
    is a better solution than the kits above but you would have to get all the other
    parts that come in the kit.
    You can also buy the real Honda from Small Engine Warehouse for about $130 more.
    Last edited: Aug 27, 2011
  7. popeye

    popeye Member

    thank tou mbr ill go have a look at those and see where i want to go from here
  8. Old Bob

    Old Bob Member

    Regrinds are a waste of money. you can not make the necessary changes in timing and lift by altering the stock cam on a uni lobe design.
    A piddly increase in lift of only .015" is worthless.
  9. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Hi Bob
    I have wanted to ask you what you recommend to increase the
    performance of a 4 stroke 50 cc Honda GXH 50 or it's Chinese clone.

    I too questioned the value of a reground cam and got the explanation
    quoted above.
    The cam is plastic and the reground cam sells for $39.

    Do you know of any successful porting work done on a Honda GXH 50?
    Thanks for your insight.
  10. Old Bob

    Old Bob Member

    I haven't dug into the 50cc indepth, but the same approach I use on the 31 and 35 will work.

    I determined early on that hot rodding a GXH50 is not a good idea as it lacks the bottom end oiling to support a substantial increase in rpm or load.It does not mean that you can't perk it up a little but doing a full package with cam, high CR piston, porting etc will have it running well outside of the 7500 rpm limit Honda recommends.

    Honda did a pretty good job on valve sizes, the exhaust ports are very good from the factory.The intake port is where you need to do most of the work.
    You have to calculate a few things after measuring.
    Measure the lift at the valve stem.Measure the valve head diameter.
    Then calculate the curtain area of the valve using 45 degree seat value.
    You can measure seat width on used valves easy enough or if new use some dykem blue and spin valve in seat to mark bluing.
    Curtain Area = Lift * PI * ((Valve Diameter)-((Seat Width)*2*COSINE(SeatAngle)))

    This value is the largest you want any part of intake the port to be.

    On the exhaust side,just deburr and chamfer the intersection of the port runner and valve pocket on the inside corner.

    Match a carb venturi to approximately the same size as the valve curtain area.

    Don't indiscriminately hog out the exhaust port.
    Don't try to lap the valves to improve sealing
    Don't use aftermarket piston rings.

    The problem with "regrind" cams is that the base circle is reduced to make the change to lift, this messes up the rocker arm geometry in the valve closed position and leads to early valve guide wear.
    On the Uni lobe cams you need to add material to the lobe especially in the area that controls the overlap period. You need to be 50 degrees of overlap or more to make significant difference,without a high CR piston simply adding duration and some lift doesn't get you anywhere.
    Its possible to design a cam that has more lift and overlap, but with stock opening and closing points so that you would not need a high CR piston.
    This type of cam is what cam makers were seller as torque/mileage cams in the 70s -80s, they do work well and are what the 50cc needs,but you aren't going to get it from a regrind.

    Intake and exhaust length tuning is worth exploring as well as tuned air boxes.
  11. popeye

    popeye Member

    see this is why i started this thread to get the 4 stroke disscussion going because im currently saving for my kit and am unsure what to get, i do have another question if anyone is able to answer id be gratefull, do you have to have a gear box? as in can you not run a sprocket off the clutchstrait to the back hub? maybe with a properly large back cog?
  12. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Mini Bikes do this but they have very small diameter wheels and the rear sprocket is still very large.

    A Honda GXH 50 on a 26.5" wheel bike running a 9 tooth on the clutch
    would need a 150 tooth sprocket on the rear wheel to give a top
    speed of 36.9 mph at 7800 rpm.
  13. popeye

    popeye Member

    thanx for the reply mbr unfortunately im a little hard of thinking and i dont speak maths verry well at all but i run a 24in rim so thats even worse then? will a mini moto g.box/cvt work in our application i asked you once about the yxm engine kit on ebay and you said the box on it was junk, could it be replaced with the mini moto cvt/g.box as its a 2 stroke piece of kit or is that unimportant?