Ideas for Custom Mini Bike?

[JustinJ]

I am in need of some ideas for a custom mini bike that I want to build. I am going to make a frame so looking for ideas on shapes or possibly of other bikes already built that I can copy from.

The bike is going to be used on trails, fields and in the woods.

Engine:

I am putting a 9 HP Robins-Subaru engine in it. Since I am building the frame, the size of the motor will not matter fitting in the frame.

Suspension:

I want to do a spring suspension on the front and back. I can get some springs off a midget car but may look for other springs if someone has another idea. I am not sure how much the guy wants for the springs. I would like to see some pictures or ideas for suspension on the front and back.


Tires:

I was thinking about putting 14 inch tires, since I am running a centrifugal clutch. I am open to idea on the tires. I have not seen the Doodle Bug in person but noticed on their website that I can get a tire and rim for 30.00. I do not think that I can go with a bigger tire because I'm using a centrifugal clutch and not a torque converter.


Centrifugal Clutch:

I was going to use the Comet 1" centrifugal clutch Comet Clutch - 1" Bore - OUT OF STOCK, BMI Karts and Supplies - Home I have seen the clutch on ebay a lot so know that it is still available.


Sprocket:

I was going to run a 60 tooth sprocket on the back wheel.


Drivetrain:

I know that a torque converter would be the best route but the price is too much.

Any other ideas on the drivetrain would be appreciated. I thought about a jackshaft but then thought that I would loose some low end power and more parts for something to go wrong. I did find a Jack Shaft setup for the doodle bug the other day. It looked like it help. I think it was called PMI, a bolt on accessory. I might could try something like that. I do need some ideas about the positive and negatives of having a jackshaft setup.


Price:

I want to do this cheaply but with a good design and something that will be solid and take a beating.


Justin

 

[marksteinhilber]

Look at evolution of the mini bike to the mini cross

If you want a mini bike that handles trails nicely, then look at how the mini bike evolved towards the small dirt bikes like the Honda Z50, the Gemini 50, and the Maverick in the pictures below. Over time, Bonanza BC1200 became a MX 1310 and eventually MX 1510 with a true motorcycle two stroke 100cc Hodaka engine with 4 or 5 gears. Somewhere in the middle of that evolution around 1971 - 72, you see the Bonanza MX 1310 with 8 inch wheels with knobby tires, rear swingarm, and front suspension forks, but still with a flathead engine. A similar offering from Taco was the Super 100 with Tecumseh 4 or 5 hp, or the upgraded Taco 102 or the Steens Matterhorn F-85 that had the 100cc Hodaka engines. These are basically the same frames from earlier models, but have more bells and whistles like front suspension forks with drum brakes.
If I were to build a custom trail bike with a large flathead engine, I'd look at those two bikes and possibly consider using some Gemini 50 or Honda Z50 wheels, hubs, brakes, or go with newer 50 cc dirtbike forks with disk brakes on the front. Parts like that are cheap on E-bay, and if you're welding your own frame, you can just choose the right head tube size and use the more up to date front end and wheel. The rear swingarm and shock assembly can simply mimick the vintage design as it will easily accept 8 inch or even a 10 inch wheel with the right swingarm length. With the right sprocket selection on a jackshaft, you can make a mean trail machine.

 

[JustinJ]

Hi Mark,

Thanks for the pictures. Your bike looks great. I am going to look at the bikes you suggested. You have gave me a lot to look at. I want to plan this well, so that I have nice trail and field bike for many years.