GEAR HELP (retro_racer) or anybody that can

[ironwarlock]

If I take a Honda GXH 50cc four stroke motor and gear it down 4 to 1 on a jack shaft. What size pulley would you run from jack shaft to the rear pulley to get good hill power and say 30 mph on the flats. Rear wheel is 20" schwinn spoiler rim with a 20" whizzer sportsman sheave on it. would it be a 5" pulley from jack shaft to 20" sheave?

 

[srdavo]

wow...I wanna know more of this set-up....pics?

 

[retro_racer]

The sports man sheave should be around 16".I run the same size on my bike.I'm running a larger 26" wheel though.I'm running around a 4 inch drive pully(same as the whizzers).They could run between 40 to 60 mph with this setup.My setup is about 4 to 1 on the final drive.The larger the drive pully you use the more top end you will have.The smaller the pully the lower the gear you will have.Lower gear = harder pulling,up hill,and less topend speed.
You already have it geared down some with the jackshaft setup your running(4 to 1).I would personaly try a couple of different size's here.The pullys are for the most part all the same shaft size.Are you running any type of belt tentioner? This is a big plus as your larger belt say for a 5" or 6" pully could also be adjusted to a smaller say 1" to 2" inch pully.This would give you a greater option of gears.

 

[ironwarlock]

Project is a Schwinn Springer Spoiler with custom gas tank. Will add a nice leather seat with springs and leather saddlebags. Replace the .080 spokes with .105s. Will power it with a GXH50 4 Stroke motor, belt drive 20" sheave off whizzer sportsman. It will look like my avatar. I am a machinist and will fabricate the motor mounts, jack shaft and whatever else is needed at the shop. Will keep you posted as I go .

 

[ironwarlock]

They make two sheaves.The one I have is 20" on the money. Same size as the back rim on the spoiler. I am 235 pounds so I thought i would go with the 5" drive pulley and yes i will have a tension pulley so there will be belt room to try other pulleys.

 

[retro_racer]

I wish I could be alittle more help here.I realy don't have much of the spec.s for the sportsman models.I would think that the smaller(20") rear wheel would make for less topend.Power for pulling harder at a standing start,and climing hills you should gain.
I would try a couple of sizes.Most whizzers have around a 1 1/3 to 1 primary,and a 4 to 1 secoundary gearing.So with 4 to 1 you should already be lower than that.So you just need to figure out your final drive,and that will = your topspeed.I'm thinking that the a 4",5", or maybe even a 6" pully would be a good place to start.You may have to cut some of the difference in your primary(jackshaft) back to get what you want.

 

[retro_racer]

It sounds like your on the right track.Thats for sure,and you should get a 5 to 1 with a 5" drive and a 20" sheave.
If you should need a smaller sheave let me know.I have 2 of the 16" (new whizzer sheaves),and hardware.I also have a new old stock,hardware set for the old style sheaves.We could do some swaping if you need the a smaller one.You have a realy good start on what your building,and what you want.Thats always a big help.
Are you going to use a centrifical clutch on the motor?

 

[ironwarlock]

Looks like i go with the 5" secondary to make that drive 4 to1 and just change the primary up or down as needed.

 

[ironwarlock]

Yes it will be a centrifugal clutch.
I like the sheave bolted to the rim and not the spokes.

 

[retro_racer]

Your sheave bolts straight to the rim? That is a cool setup,and yea thats why I'm running spokes that look like tention wire. You won't be disapointed with the centrifical clutch.It will realy help to get you moving.You can always upgrade to a better adjustable one too.That way you can adjust what RPM's the motor grabs.