My Cox Minibike

roddie wrote:I perused quickly thorough this thread this morning before leaving for work. I really love the frame and front-end! Is this being modeled with a particular full-scale bike in mind.. maybe one you've owned or would like to own?

It looks like you have some room to make decisions on the back-end.. to maybe fit your primary-drive on the output-shaft side.. and final-drive on the opposite side.. sort of like a torque-converter/snow-mobile drive. This might help to balance the bike and give you more options with the final-drive ratio. You'd need to prepare the frame for a pair of bearings to support a cross-shaft. I'll bet you've already though about that.

The centrifugal clutch that Cribbs (Ron) spoke of.. would be an item to seek/source. Try searching Cox/Jerobee engine-drive parts on eBay.. and see if you can find anything. One of our members "overlord" (Lieven.. from France) has recent experience with the Jerobee clutch set-up.. and its' associated parts.. dis/re-assembly.. tuning etc. on a scale-model Corvette that he has, with a similar Cox .049 reed-valve engine. I'm sure he will find your project fascinating!

Please keep us up to date with your progress!

roddie wrote:

My Cox Bike wrote:
I need to find or make or find a clutch for this bike! I was hoping to have it controlled as on a real bike, but short on the precision machinery at this point. Maybe a tension system like i think this is, would work?

That "looks like" an idler.. but it's actually a band-brake that actuates when the throttle is closed. It's linked to the throttle-servo and wraps-around a groove in the clutch-bell set-up. Try searching Cox GTP Nissan/Maples throttle.. just to see what comes up. I'm not sure if the "Jerobee" models used the same clutch-system.. but I'd bet on it.

How will your cooling-system work? It looks real good.. with all that plumbing and all.. but what will you use to pump the coolant through it? The boat-modelers use a water-jacket that delivers fresh-cool water around the head, via a pick-up tube placed behind the prop for circulation. The associated plumbing carries the fresh-water in-around the head.. and expels it. A closed-system might not provide enough cooling.

Cox Hobbies used "heat-sink heads" on many of there non-aero powered models to help keep the engine cool. They look similar to the one in the above photo.. except they are totally-flat. You might be able to forego the liquid-system completely.. if it will fit within the bike-frame's perimeter.

Here's a photo of the Cox part#8477 heat-sink, designed for their "Sandblaster" model.. and used on many others.



Mounting-options are a linear 360 degrees around the glow-head. It measures 1-11/16"L x 1-1/16"W..  with the furthest point from the center of the head being 1-1/8".

I think you'll need to find a compromise between an exhaust-throttle sleeve.. and that box-header design that you currently have. An .049 exhaust-throttle sleeve will only fit an .049 cylinder that's been "milled" for it. They're usually obtained in pairs. Boxing the header could still be done.. but the sleeve would need to move within the stationary box. It may be better to keep it simple.. with reliable exhaust-throttle/open-header and air-cooled heat-sink head. You could then concentrate more on the centrifugal-clutch drive.

There are other reed-valve engine throttle-systems.. but they wouldn't lend themselves well to your 90 degree engine-layout for this bike. Those can be discussed when you build a shaft-drive bike!