Honda engine & 4G Belt drive runs jerky

GoldenMotor.com
G

gcw

New Member
May 9, 2009
6
0
0
IL
This is my first MB build. I started out with the Honda engine and Grubee Stage II Gearbox. The gearbox was very noisy so I installed the 4G Belt drive. The belt drive is very quiet and the bike runs very smooth up to 18 MPH, but at 18 and over, the bike is a bit "jerky". It kinda feels like it is not getting enough gas, but the motor is just purring along and doesn't sound like it is starving for fuel. I've replaced the fuel filter, but that didn't correct it. I think it may be in the centrifical clutch. When I start the bike on the center stand the back wheel spins. If I try to start it with the back wheel on the ground it wants to take off. I've got the idle set as low as it will go and still keep running. I've checked the clutch and one of the pins on the clutch plate was out too far and not letting the plate retract all the way. I thought that was my problem so I tapped it in just a little so the plate will retract all the way. However, that did not correct the problem.

Also, when I had the Grubee Stage II gearbox the bike would run around 33 MPH, but now with the 4G belt drive it will only run about 25 MPH. Has anyone else noticed a loss in speed when they switched to the belt drive?

Thanks in advance for any suggestions on correcting my problem.
 
MotorBicycleRacing

MotorBicycleRacing

Well-Known Member
Jul 28, 2010
5,844
109
63
SoCal Baby!!!
www.facebook.com
gcw said:
I think it may be in the centrifical clutch. When I start the bike on the center stand the back wheel spins. If I try to start it with the back wheel on the ground it wants to take off. I've got the idle set as low as it will go and still keep running. I've checked the clutch and one of the pins on the clutch plate was out too far and not letting the plate retract all the way. I thought that was my problem so I tapped it in just a little so the plate will retract all the way. .
Click to expand...
The bushing on the clutch is low quality Chinese junk and is grabbing

You can buy a true oilite bushing from Mc Master Carr to replace it.

What sprocket sizes and gearing are you running?
Wheel xize?
 
O

ocscully

New Member
Jan 6, 2008
373
1
0
Orange County, CA
The loss of speed is due to the added reduction of the 4G drive at 5:1 reduction vs Type II Gearbox 3.7:1 reduction. To get the top end back you need to go to a smaller rear sprocket. The clutch and clutch bell on these drives have some problems. One is the bushing already mentioned. It can cause the bike to want to take off when starting and also acting real herky/jerky at idle. Second is the fact that the clutch stall speed/engagement rpm is way to low. I replaced the 40lbs/in. coil springs in mine with a set of 60lbs/in. springs. These new springs made a major improvement in how the bike operates. Another weak area on this clutch is the joining of the 20t driver to the clutch bell. Mine came apart on me on Monday. It appears to have been held together with only a press fit? Although I was informed by Jeremy from bicycle-engines.com today that they are supposed to be silver soldered together. He also said the the pins you spoke of are the reason that my clutch bell came apart. They can keep the shoes from retracting? He suggested pulling them and adding a bit of JB Weld to the tip and gluing them in place?

ocscully
 
G

gcw

New Member
May 9, 2009
6
0
0
IL
Thanks for the replies. My original oilite bushing froze up so I had to replace it. Today when I tried to take the clutch bell off, the bushing was again froze to the bell. I will need to get another one again. Has anyone had any success at replacing the oilite bushing with needle bearings?

My original clutch bell also came apart with the 20t driver separating from the clutch bell. It appeared to me to only be pressed on and not welded or soldered on.

I will try some JB Weld or some loctite on the pins on the clutch shoes to hold the pins in place. They seem to work their way out and that is probably what causing the bike to want to take off on start-up. Where did you find the heavier 60lb/in clutch springs? I've looked for some but haven't been able to locate any.

I like the general idea of this belt drive, but it seems to be poorly made and not holding up very well. I've only got about a 100 miles on it and it has came apart twice on me.
 
O

ocscully

New Member
Jan 6, 2008
373
1
0
Orange County, CA
I bought the springs from a http://www.centuryspring.com/pdfs/12-229.pdf The 60lbs/in springs I finally settled on are their part# J-37. The problem with this particular source is that they have a $40.00 minimum for orders placed online or over the phone. They have no minimum if you order and pick up at their Will Call Desk. Since they are some what local 50 miles north in LA, I made a trip up and bought several sets of springs at various spring rates to try out. The springs only cost $2.50 ea.

My solution the the clutch bell separation issue was to have a local fabricator weld the two parts together on the inside surface of the clutch bell.

I've purchased several of the american made oilite bushing from McMaster Carr but have not used them yet. I'm still using the stock bushing. If you find a source for a needle bearing that can replace the stock bushing be sure and let us know.

ocscully
 
G

gcw

New Member
May 9, 2009
6
0
0
IL
Thanks for the info on the springs. If I ever get down that way in LA I will get some of the springs. I'm still looking for the needle bearing and if I do come up with a source I will post it. In the meantime I've ordered 2 oilite bushings from McCalister-Carr. Hopefully those will last longer than the China-made ones. I had thought about spot-welding the clutch bell and will do so if this one comes apart.
gcw
 
You must log in or register to reply here.
Top Bottom