Rugged off road mini bike build thread.

[jared8783]

First of all HELLO EVRYONE
Its been years since I have been on this site. I have built a couple of motorized bikes in my day. if you want to see the second bike that I buolt just look up my threads here on the forums.

will be a purpose-built mini bike for camping fishing and off road trails. I will build as rugged and durable and salad as I practically can. This bike
be used primarily for accessing camping sites that are in the deep in the woods


I will be building this by complete from scratch. That includes fabricating the frame. I'm a welder by trade now and I'm getting free one by one 14 gauge tubing from work which will be used to fabricate a friend. I have a welder my garage.

I have yet to draw up plans but I do have some good ideas and when I do draw plans up I want to run them by you guys first and get your opinions. I have selected a motor and the 212 cc Harbor Freight predator motor. 6.5 horsepower 8.1 to torque. This should be more power than I need. Therefore I plan to use a belt pulley centrifugal clutch CVT system. I remember Evan here on the forums use 79 CC Harbor Freight bicycle he built years ago. I intend on planning on figuring out which clutch pulley system using using this. I have also picked up a pair of small sprung shocks from a local off roading shop for 20 bucks. I plan on making the rear tire dealer from 12 to 16 inches wide and running a low air pressure off about 12-13 psi. I also intend on making a removable expendable rear rack to carry my camping and fishing gear.

I'm really looking forward to this should be lots of fun. Let me know what you guys think. I'll be sure to keep this thread updated.

 

[jared8783]

 

[jared8783]

11 inch wide 22 inch tall rear tire. Not sure right now what size that front tire is, and honestly I probably won't run it. I have another tire identical to that rear tire. I plan on using those two shocks for rear suspension, or I might not run any suspension at all with these tires. I will run a go kart torque converter (cvt) and a jackshaft moving the chain to the right side. This way I can center the motor much better and balance the bike. The tires being 22 inches tall I intend on having 9-13 inches of ground clearance. I plan on removing everything from the top of the motor (gas tank, air filter, muffler) so that the motor will be much shorter. This way I can maximize ground clearance while keeping the seat as low as possible to keep this mini bike as mini as possible.

Have you ever heard of a Rokon? Google it. I plan on build something of that class basically but smaller and NOT two wheel drive. Much smaller in a couple of ways though. Here shortly I plan on uploading some crappy ms paint initial drawings of what I want to do.

I have never built anything from scratch before. Any and all advice will be helpful. Equipment I have at my disposal are a flux mig welder, drill press, band saw, die grinder, air compressor, and of course more than enough hand tools for something like this. I do weld for a living so that won't be a problem. I will probably end up buying a pipe bender from harbor freight.

What do you guys think about running suspension? And maybe even modifying some moped/dirt bike forks for front suspension?

 

[RicksRides]

Welcome ( BACK) to the site.
If you need any help or parts let me know im in Osceola, just a few miles down the road.
Rick

 

[jared8783]

No way that is AWESOME!!!! Maybe we can meet up sometime, who knows even work on projects together.

Yeah it felt a little weird reading welcome to the site because I was once a pretty active member. I used to read for hours a day on this site. Built a couple of bikes, but the first was before I heard of a forum so it isn't on the site. I know this site is more about bicycles than minibikes, but it's very similar and the people on this site were great so it was my first choice for a build thread.

I have obtained a old junk chin ease scooter chassis from a local shop for 25 bucks. I will surely be salvaging the suspension forks from the chassis and who knows what else. But I won't reuse that chassis itself.


My name is Jared....nice to meet you.

 

[RicksRides]

I would really enjoy a partner in crime so to speak. Im right on the st joe/elkhart county line. Im a night owl. Up at all hours building my rides. Got a Big collection of engines Oh and Ive got the rims you need for them tires!
Rick

 

[curtisfox]

Welcome back,this should be awesome. Can't waite to see what you come up with........Curt

 

[jared8783]

Ok so for anyone who may be reading, I have come up with a minor amount of details and have learned that I need to buy a driven cvt pulley, some sprockets, pillow blocks or even weld in jackshaft mounts before I can figure this all out.

Over the weekend I came up with a very rough mock up of the frame.
Here is the crappy cell phone pic of the mock up. For all practical purposes the only four tubes that exist are the two on top and bottom running parallel from tire to tire, the rest are just holding those in place. The following numbers are very aprox. Ground clearance 9-13", seat height 25-30". and I would like to keep the wheelbase below 43 inches if at all possible.

I plan to surely run two jackshafts. One coming through the driven pulley, and one after that. Then from the second to the tire. This is because this is to be a work horse of a mini bike with really low gearing. I have already done the math for the sprockets and have the gearing numbers for both 11.68 mph top speed and 21mph top speed. I also plan on doing my best to run both gears on top of the cvt. And I will be perfectly satisfied even if i have to come to a complete stop and shut off engine to make a shift. Even If I end up running it as a one speed, I will still run two jackshafts to reduce gearing unless someone has some suggestions.


I think I could use a combination of these, idler sprockets, and two jackshafts as explained earlier, to make it a two speed on top of the cvt. Though I will surely need to come to a complete stop and shut down the motor to stop. But that's perfectly fine with me.

Like I said earlier this will be a purpose built bike. These are similar to the first two speeds on a rokon (and no I don't expect rokon performance). I went to a great off road park for the first time with a friend recently. Camped their all weekend. They allow camping and fishing and all sorts of stuff. They pretty much tell you you can do what ever you want. 750 acre park. I want this bike to get me to camping spots that cars can't reach. I want it to get from point a to b in the park. I want it to pull good logs for fire back to camp.

Most say not to run shocks on a project like this. But I really want to, and I sure will on the front. I have shocks for the rear but may decide against that and use just one of those shocks and suspend the seat or something, who knows.

If anyone has any questions about my gearing or anything else feel free to ask. I'm also open to suggestion of just about any part of it.

 

[maniac57]

Suspending the seat allows much simpler drivetrain setup and works great on something small like this. Pocketbike forks should be fine as well. Personally, with big soft tires like those, I would not bother with any springs. Just run the tires soft. It will ride great and be very gentle to the environment off road (which all parks and park rangers like)
The 212cc will be plenty of power especially if you gear it for 21mph top speed.
I doubt the multi-geared setup will be needed. Just get a good reduction and it should climb any hill you could want with the 212cc torque.

 

[jared8783]

Thanks for the offer on the wheels rick but i got some. Zi do however still need a pair oif hubs. One inch bore live axle hub on the rear and im not sure what i want on frot. They are atv rims. We should exchamge numbers. Im right acrioss the tracks from the concord mall, you are prob twenty minutes from me. And yesah everyone keeps saying no suspension. Im really torn, and inexperienced. Hey rick are there any go kart shops around?

 

[RicksRides]

yes a few cart shops but ive got a better hook up then that. Ive got some nice 1in live axle parts here.... hub, brake, sprocket

 

[FMB42]

Thanks for posting Jared (your project brings back happy "mini-bike" memories for many of us).

The torque and wide tires on your mini build should easily take you just about anywhere you want to go (and then some). Btw, my 1970 or so Taco 22 mini had a jack-shaft that, of course, allowed you to change from "low" to "high" gearing without to much trouble. And, believe it or not, that 3.5 hp no-suspension mini bike had great hill-climbing abilities (while geared hi or low). This was much to the dismay of a few "real" motorcycle riders (I probably only weighed 120 - 130 lbs. at the time tho). Something to think about for sure...

 

[silverbear]

Oh boy, partners in crime...
welcome back to the forum.
SB

 

[jared8783]

Ok progress update. I haven't really done anything more for the bike except built a steel stand for the frame to hold it while I build it and weld it. I have also decided to use a different method of engaging sprockets on the jack shaft. I'm going to have a sprocket hub machined to accept a sprocket on both sides. Honestly Ill prob have two hubs machined down so they aren't as wide, but welded together wider than a single hub. Then take two sprockets and weld them on the hub. As thick of steel as that is Ill take it to work to weld that. Ill grind the teeth off so that they are just discs. Drill several holes in the discs for rods, and matching holes in the idlers so that my home made gear engage can engage them.

As of right now I plan on drilling and tapping the hub and shaft and using a big bolt and a ratchet on the trails to shift. I figure I will use first gear rarely and kinda think it would be cool to use a wrench to shift. Plus that system ought to never break. Though I am open to Ideas on how to shift using a lever that maybe has a skateboard bearing on the end that contacts the discs. Just don't know I would keep the gear locked in with a lever.

Last weekend I spent 24 hours in my garage between two days setting up my first shop (gotta put a pic of this in the baby book). I had to boot my rust free 90 miata outside for this but it's worth it. I'll get a cover for her and perhaps warehouse it for the winter. Unfortunately I still stay with my mother so yeah, I only can have one stall. And I got two cars, two work benches, standard tool chest, drill press, band saw, and a mountain of parts for the miata. Bought a parts car years ago, stripped it and scrapped the chassis. Anyways now I have a decent work shop. Bought the steel a few days ago to build a big welding table. The top will be 3'x6'. Got two sheets (3/32" i think) and am doubling them up. I have 60 feet of 11 gauge 1.5x1.5 that I will use for the framing and I am trying to find some side crank rv jacks for cheap to install on each leg of the table so I can not only adjust level but have a foot or so of play in table height. You know where I can pick those up for cheap Rick?

I will build the table for the shop this weekend and hopefully have time left to work on the bike as well. I plan on buying the torque converter pulleys and jack shafts this weekend if I can find them.

this is the small stand you see in the pic of the garage that the mock frame is sitting on

 

[canthelpitimaguy]

That thing looks like its gonna weigh a ton, no?

 

[jared8783]

Probably, idk. Hoping to keep it under 150 lbs but really not sure. For my purposes so long as I can man handle it into the trunk of a car and strap the trunk lid down then I will be happy.

Well since my last post there has been little to no progress on the bike. Been setting up shop and building a solid welding table to work on. And my cvt pulleys have come in. I went with comet series 20 symmetrical with a 7" driven pulley. Now I can start mocking up the drive system and them mock the frame around it.

 

[curtisfox]

Something to think about: I have a friend that built one kinda like your. He used a Yamaha moped fitted a fat tire like yours but he used a 16 Harlly type tire in front because it climbs over logs easyer. He has had it for a long time now and still drives it now and then he is 82. Of corse if you don't have logs to worry about then you won't need a biger tire. I have road it and know what fun you will have..............Curt

 

[RicksRides]

Jared I see a gas welder in the pic! no more fluxcore welding?

 

[jared8783]

Curtis I WILL have logs to "worry" about, I look forward to it. This will be an off road point a to point b camping bike.

And yes Rick no more flux (for the time being that is). I do not own the welder in the photo. It belongs to a friend from work who also lives with his parents, except they won't let him use the welder there, so my home is it's home until the owner has a place he can hook up the welder at. It is an old 220 welder, weak for a 220 but obviously it kicks my flux core out of the water. I ran the breaker and wires on friday night and got that 220 going. You gotta come check it out.

As small as that flux core welder is I will prob keep it in my trunk now with my spare tire and tool bag. I never know when I'm gonna turn a wrench at a friends house and portable welding will be nice.

Also what do you guys think of the frame height in relation to the axle height as shown in the pic? Not sure exactly what I'm gonna do with height but give me your opinions on where it is at now in the most recent picture.

 

[MEASURE TWICE]

This is really great! My off road bike I got the California DMV to get me offroad sticker. One day I still intend to make it an art bike looking like a fish. I am not sure it could withstand the elements at Burning Man in the Nevada High Desert. I sure like the tires you have for the build of yours, they could probably handle very fine silt dust of the Playa without sinking in.

I'll be watching how this build goes of yours.

MT