Square Tubed Minibike Frame project

Hey Nebraska03,

Quick fix would be to shift the motor, fromthe pic looks like the enine plate has plenty of room.
My first rides were also on a rolling frame, my little one liked it so much we spend hours running up and down the driveway :lol:
@Tanksareus- I had considered that, but there really isn't any room. The bolt pattern on the bottom of the engine (where it mounts to a frame), is snug up against the bolt holes in the plate that's welded to the frame.
Here's an idea I had:

1. Take off the scrub brake and either go with a drum or band brake.
2. Use the mounts for the scrub brake (already welded on) to install a jackshaft.
3. Put the centrifugal clutch on the jackshaft, and run the #35 chain from the clutch on the jackshaft to the sprocket.
4. Install either a different gear or pulley on the crankshaft, and also another gear/pulley on the jackshaft, and run a belt/chain around those two.

Is there any issue with running a centrifugal clutch from the jackshaft instead of the crankshaft?
@rmm727- I went out and took a few measurements and started drawing a diagram. But the distance between the rear axle mounts is approximately 8-3/8 inches, give or take a 16th if an inch. There a slight bend in the left rear axle mount.

There is also approx. 3/4" from the sidewall of the tire to the center of the rear sprocket, and 1/2" from the center of the rear sprocket to the inside of the rear of the frame leg.

And 6-1/2" from the center of the scrub brake shaft to the center of the rear axle.

@mac- Wow!! Are all those 5-bolt hole patterned sprockets?

@Harleys Papa- I think I will probably/eventually get the 4.5" Brake with the Anchor Backing Plate, but I kind of like the thought of being able to switch out sprockets with the hub setup that's on my bike.

I also took apart the rototiller gearbox that came with the engine. I did a little searching online and found an owners manual for it in a PDF file. It had a parts list and I found out that two of the sprockets inside used #35 chain, and I think might be the correct Inside Diameter to be used on the bike. It's also threaded with the same 3/8"-24 bolt pattern that is used in the driveshaft on my engine. I need to clean up the sprockets and count the teeth still, they're covered in this really sticky/thick grease which is just shy of impossible to get off, haha.
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I need updates. There is just something about this bike. This is sad but I just bought a $400 bender and bought 2 dies to go with it and all I want to do is make a square-tubed mini.:eek:ut:
Okay! Update! :laugh: I went out tonight and got a Hilliard 12 tooth Centrifugal Clutch at Tractor Supply. I put it on the shaft and it fits or seems to at least, so I bolted it on. I am gonna try and put the chain on tonight if the rain lets up. If not, I'll do it in the next few days. On another note, I had put it in the shed for the time being, and while I was gone to help my cousin move, my dad decided he wanted to spray the shed with paint. So when I returned, it appears as if my minibike has some sort of spotted grey flu. Joy... :blink: Oh well, you can only see it up close.
It's Aliveeee!!! Muhahaha!! :evil_laughter:

So late this afternoon I decided to get done what I could on my minibike. Glad I did! Spent the time working on a throttle cable (needs work still), adding a rudimentary seat and cushion, installing the chain, and played around with some adjustments. About 6pm, I got the seat on and decided to take it for a short spin up and down the driveway. It was a blast! The throttle grip on the handlebar needs work. After rigging up the cable, I would turn the throttle and the tubing/protector for the cable would move back and forth, but the cable itself (even when I electrical-taped the tubing/protector down), wouldn't adjust with the turn of the throttle grip. After an hour, I got tired of it and rigged up the throttle from the rototiller. I soon realized that I had installed it backwards? So I decided to jot down some settings in permanent marker on the seat. I also took a short video of the test run I did. The camera cut off when I hit a bump, but it's all good because I was beginning to wonder if I would be able to stop at the bottom of the driveway. All and all it's been a great day! :thumbsup:


Here's a link to the video I took. I put it on my Flickr page. Enjoy! (I am pretty sure I didn't have the choke set right, so it moved a tad slow at first).
Hey Nebraska,

Nothing beats the first ride on a bike.
The throttle cable looks a bit old, I would replace it if you can. Also try a smoother line from the throttle to the carb, cables don't like sharp bends, put in a pic hope it helps.

Have fun:thumbsup:

@Wheels1950- Haha, that would be cool, but I doubt the neighbors would approve.

@Tanksareus- First ride was great, and it gave me confidence to finish this project. :smile:

I wish I knew the original owner, to get some tips/hints on to what stuff worked best on the bike. The throttle cable that you said appeared "old" was something I rigged up after the one I bought with a kit didn't seem to stay in place. When I turn the twist grip throttle, instead of the cable inside the tubing moving, the entire tubing just moves back and forth, even when I tried to electrical-tape it in place. So I rigged up one with a bicycle cable and some plastic tubing cover from said bicycle, and then wrapped the heck out of it with electrical tape. But it didn't work either. I'll get some pics of it in a bit to better explain.

Are you suggesting I run the throttle cable along the side-bottom of the frame rather than under the seat? (The red line in the pic). I hadn't thought of that, it appears it would make for fewer bends in the cable. Hmm... :hammer:
Okay, so I took some pics and tried to do a drawing of the problem I am having with the throttle cable.

When I turn the throttle twist grip with the regular throttle cable attached, the tubing that the cable runs through moves out of the slot, instead of just the cable moving inside of the tubing.

I tried to rig something together originally with some bicycle throttle cable and some extra plastic cable tubing I had, and wrapped it in electrical tape to hold it in place, but after a certain number of bends, the plastic snapped and it bowed outward, and wouldn't turn, or turned with much effort and difficulty.

Is there an easy way to fix this? :confused: I don't mind using "unorthodox throttle methods", but I would rather have control up by my right hand for throttle adjustment, as at higher speeds, the current method I have rigged to the seat makes me a little uneasy.
Hey Ya,

Thought that might be your problem,was sitting thinking about how to word the advice without insluting your intelegence. Have learned that you just have to say it like it is , otherwise you would be here asking for help.

Throttles and cables are designed to pull and linkages to push.
Find the throttle lever on the engine and make sure is free moving, sometimes they tighen a friction bolt to hold the rpm's in a cerain position. Then you'll need to fit a tension spring to pull the engine throttle arm closed. Now you can hook up your throttle cable to the other side. When you twist the throttle on the handle bar the cable should pull on the engine throttle lever and increase your rpm's

A= outer sheath of cable
B= braket that holds outer sheath
C=throttle cable inner attached to Engine throttle link
D=spring pulling throttle link closed
You got it Tank I couldnt have have done better.
Hey Neb dont fret we all learn this stuff from trying
But hey how many people have a suicide throttle lol
Okay, thanks! I appreciate it. I sort of figured my problem had something to do with "B", the bracket that holds the outer cable sheath.

I was hoping that the electrical tape I was using to wrap the cable sheath to the frame would do a decent enough job at holding it in place, and keep allowing the cable inside to move freely, but that isn't working too well. Hence the reason I tried the bicycle cables and plastic sheathing I had to try and make it work, but it wasn't rigid enough.

I guess I'll need to find/make a bracket and then figure out a way to mount it. I also need to figure out a way to mount "C", the other end of the cable, that connects the throttle control link to the engine. I think I have a cable-pull piece from the sacrificed rototiller that will work. I'll give it a shot, take some pics and report back my findings!