floating ideas, come on in.....

popeye

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May 16, 2011
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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
popeye
 
im leaning towards the yxm 4 stroke from china via ebay as its a kit with everthing with it,
The gearbox on that kit is junk and will probably need to be replaced.

2. are there any performance parts available for 4 strokes?
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.

3. can i not flip the back wheel and use the gears that came with the bike?
No, that does not work as the gears freewheel in the wrong direction and you are not the first person with that idea.
 
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
thankyou
popeye
 
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.

http://www.bicycle-engines.com/49cc-belt-drive-complete-powered-engine-p-320.html

http://www.pistonbikes.com/product-p/4s48cc.htm

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:
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.

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.
 
AffordableGoKarts said:
Our camshaft uses .175" lift and 210 degrees duration @ .050". The stock camshaft has .160" lift. Only use this camshaft for high performance applications using our big bore carb and free flowing exhaust. This camshaft shows an noticeable increase in power from 4900 rpm on up to what ever rpm your engine can handle. The increased valve lift and duration from this cam create more horsepower and torque over stock. We set valve lash at .008" and use a synthetic oil

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.
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.
 
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.
 
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