Engine Transmission Question

[Gbrebes]

Hey Everybody,

I am in the process of building a Roadmaster frame with a Briggs and Stratton 5hp engine.

I have really been studying and doing a lot of thinking/figuring about the type of transmission to use on this build and I thought you all might be able to offer some advice. I was originally going to copy msrfan's style of using two belts and a Whizzer automatic clutch with a rear sheave on the back wheel.

Muchos Gracias to msrfan for your help and a copy of your book. It is very helpful.

But then I found out about the current price for the automatic clutch (around $300?, the lowest I saw on ebay was 170 something and it was incomplete), and I started trying to figure out less expensive ways. Also the auto clutch seems to be a little "rare", so it seemed like it might take a long time to procure one.

Anyway, I have been thinking about a centrifugal clutch with two chains and a jackshaft, but I am not sure how I will fit my regular bike pedals into the equation.

I have also considered the EZmotors Q-matic transmission. I used to think it was expensive, but now that I find out how much different clutches and transmission systems actually cost, it doesn't seem so expensive.

Does anyone know if the Q-matic will bolt onto a 3/4" shaft like my Briggs engine?

Then I have even considered a manual clutch with a suicide shifter to engage/tighten the one belt. I don't think this is legal in California, but it would be so vintage and cool.

I guess I am leaning most towards the centrifugal clutch, just for cost reasons. But I wouldn't be able to pedal start, I was thinking of using a kickstart like briggsbiker.

But if you all have any insights, suggestions, I would really like to hear them.

Thanks,

Gilbert

 

[Build-a-beast workshop]

bicycle brake-handle, run the cable to the tensioner/idler pulley.tension the pulley to press the belt down and use the cable to lift it, i've seen some who use the cable's pulling action to press the belt down, so they'd have to hold it to drive, but i guess it's preference.lifting the pulley off the belt with the cable (and getting one of those locking brake handle's from the china kits for when ((if)) you peddle) looks like the way to go.should be able to bump start it with that configuration. or just go on ebay and buy a "max-torque" 3/4 bore centrifugal clutch for 15-30$$, its the same one the ezmotorbike kit uses. but both of those solutions involve alot of work/fabrication/beastification/customization.if you've got a mounted briggs you must have a welder and the trimmins to do it.

 

[Gator Wrestler]

I would use something simple such as a jackshaft to obtain about a 12 to 1 reduction. If the engine has the mounting holes I would use one of these
Torque Converter Backplate, www.bmikarts.comBMI Karts and Supplies - Home
This clutch will do 3/4" Bore Clutch, www.bmikarts.comBMI Karts and Supplies - Home
it's for #35 but you can get one for #40 chain.
You want to build a jackshaft like this
Torque Converter Backplate & Jackshaft, www.bmikarts.comBMI Karts and Supplies - Home
You could go with a Torque Converter if you like, the 5HP B&S has enough torque.
The hardest part will be moding the frame to accept the engine. Most of the rest is just a matter of choice.

 

[Quenton Guenther]

Hi Gbrebes,

The Q-Matic has been used on many B & S motors including the Animal series.

The front shaft can be 1/2", 14 MM, 15MM, 5/8", 3/4" 0r 1".

Can withstand up to 10 HP motors with stock clutch, and up to 28 HP with upgraded Max Torque racing clutch.

Easily setup for low RPM motors.


BTW the Max Torque clutch made for EZM isn't the same unit as sold on go cart sites or EBay. It is specially designed by Max Torque to our specifications and is certainly more pricey.


Have fun,

 

[msrfan]

Hey Gbrebes, any centrifugal clutch you put on the motor shaft will require a pull rope or kick start. Even using a slipper clutch like Whizzers they're almost impossible to pedal start without a compression release. You can get an dirt bike comp. release and tap a new hole it the head for it. It should do 40-50 mph without a transmission depending on your overall drive ratio. Belt drive so much quieter and requires hardly any maintenance. Just hard to ride in the rain without slipping. Very simple in fabricating and operation compared to torque-a-verters or transmissions.

 

[Gbrebes]

Thank you all so much for the responses. Msrfan, I definately hear you on the ease of set-up, less noise, and easy maintenance of the belt system, and to me it makes the bike look more like an old motorcycle, its just that automatic whizzer clutch that is holding me back. They seem hard to come by and pricey. I am sure they are worth it, I'm just a little cheap I guess.

That's when I started looking into the manual/suicide belt clutch solution. This looks really cool, but maybe difficult to operate at multiple stop lights and probably illegal in California.

Anyway, still puzzling it over. I will have to make a decision soon though, as I am preparing to cut and stretch my frame soon, the most challenging part of the build so far.

Thanks again everyone,

Gilbert

 

[msrfan]

Hello Grebes. You mentioned briggsbiker's kickstart motor. I just remembered, he has a Max Torque belt clutch on his jackshaft. Very inexpensive compared to a Whizzer autoclutch. It's more compact than mounting it on the motor and the engine pulley is approx. the same size as the clutch pulley so it engages at the correct rpm. Just a thought.

 

[Gbrebes]

Thanks for all of your help msrfan.

I have looked many times at briggsbiker's build pics and I am wondering. Is the Max Torque clutch mated with an extra pulley for the primary belt (the one from the engine to the jackshaft?) Do you have any insight as to how this is done? Or does the clutch have two separate belt pulleys?

I am sorry to always be asking questions, but I just don't have a lot of experience with self-building motorbike transmissions.

Again, thanks for the help. I have a dream that someday when I finally get this bike running, I will drive it out to Costa Mesa or Corona (I am not sure where you live) and come meet you and shake your hand for the help that you have given. I'll just have to figure out a way to take streets all the way.

Gilbert

 

[msrfan]

That will be a good day, Gilbert. Keep plugging away at it and you'll get-er done. Briggsbiker's primary drive is a pulley on his motor shaft going to a pulley on the jackshaft. Next, and inboard, is his clutch on the same shaft. The final drive belt goes from the clutch to the rear wheel. The jackshaft is supported by two pillow block bearings. You can view this on his second photo of his thread titled "briggs kick start motor bike". Dale.