I’m building a motorcycle from scratch in my garage

I've planned to do this project for a long time, and a couple years ago I just realized that I could actually do it. I'm building an off-road motorcycle - kind of like a cross between a dirt bike and a mini bike. In case you didn't know, mini bikes look like this:

Mini bikes are junk; everyone knows they are junk. They are mass produced in a factory in China and sold here for under a thousand dollars. It's mostly kids that play with mini bikes. Most of them don't even have suspension in the back, and they use 212cc engines from Harbor Freight. I don't want a mini bike.

The next step up from a mini bike is a dirt bike, and here's a photo of a dirt bike. This is a great bike, and they are very good quality.

Dirt bikes cost five to ten thousand dollars, and the math doesn't make sense to buy used. I could buy a dirt bike if I wanted one (CRF450x is an awesome bike), but I'm not interested in jumping and breaking by back and my leg and maybe my arm. Dirt bikes are built for motocross, and that's jumping. They have some trail oriented bikes like the crf450x, but it's the same as the motocross version just with more gears and wider gear ratios. Another reason I don't want a dirt bike is because they tall, and when you fall over, it's a long way to fall. Most grown men can't even touch both feet on the ground when sitting on a full sized dirt bike - this is because they are built for jumping so they need a lot of room for the suspension to compress.

I'm not doing any of this jumping stuff, mini bikes are junk, so what do it do about an off-road motorcycle? No one builds one like I want, so I'm going to have to build it myself. This is not an economical endeavor by any means; I've already spent more money than a dirt bike costs, and I'm not even close to a functional bike yet. But I'm just getting warmed up.

Let me explain a little bit about the design. Picture an ATV like a Yamaha Grizzly 700, and now picture it cut in half long ways. That's the easiest way to picture what I'm building. It's an ATV with two wheels. I've gone with 25x10x12 tires in the rear and 25x8x12 in the front - just like what's on one side of an ATV.

This is already in progress - using 1 1/4" DOM tubing with .095 wall thickness. It's the perfect balance of strength, size, and weight.

The rear suspension will be like all motorcycles - a swing arm and a single shock. Up front is where it gets interesting. I don't want to use forks on this for a couple of reason. 1) Forks are expensive and they are long, and they would make my motorcycle ride very high to get the amount of suspension travel that I need (same problem as the dirt bike). 2) I can't make them myself - obviously.

After a great deal of research, I've going to use an experimental virtual steering system that will allow me to use swing arms just like an ATV. And drawing some inspiration form a guy named Robert Horne (read about the Rohorn Racer on Odd Bike). He built a recumbent racing motorcycle with an interesting suspension system. It seems to work for him, so maybe it will work for me. It should solve my issues; I'm just worried about the wheel moving more than it should. This should allow me to put the front wheel close to my frame, and it will track up and down instead of backward at an angle like forks do.

This is a prototype, and I'm using the Wildcat 460cc engine from EC Carb. Check it out at that link, it's a big block in the small engine/go kart racing world. I can easily tune it to about 30hp, and that's enough for the first version of this bike. It should do about 70 with the right gearing, and I'm not sure I even want to go that fast. I mainly want torque, and this engine has some torque in the low end. It should be enough to turn over that 25x10x12 rear tire. It will be on par with the power of a Honda Rancher just driving one wheel instead of two.

If I was going to be cheap, I would get a comet 780 torque converter like everyone else does with their big blocks. But I'm better than that. I want something with a little bit more strength, so I have a secondary clutch for a Polaris RZR 900. It will definitely work. The problem many people have is the try to use a 40 series on these big block and the secondary isn't strong enough, so it just immediately pulls it apart and shifts into higher gear - not what you want. The only caveat to this is the input shaft has to be custom welded. I had to buy an input shaft for a Polaris 900 with a spline end that will fit this secondary, then I had to cut it off and will eventually weld it onto another shaft. But that's a problem for another day. 

Here are the tires I'm using - pretty standard 25" tall atv tires. Now I decided to use the Can Am bolt pattern 4x137mm wheels. This give a fairly big center hole so that I can fit the sprocket hub through it. Most motorcycle wheels do not have a detachable hub; atv wheels do. I'm not wanting to weld the wheel to the hub assembly; I would rather it be removable. So for the rear, there will a sprocket hub, the wheel hub, and then the brake rotor hub in that order. So I have to be able to get the wheel between the sprocket hub and the brake rotor hub hence the large center hole. I could have gone with Polaris wheels which have an even bigger center hole, but they are 4x156. I would have to make a bigger wheel hub, and that's more weight for no justifiable reason. I'll see if this works.

I'm using just a few tools for this project to do the cutting, bending, and welding.

I've also got some other tools like drills, levels, clamps and such. The main useful thing is the fabrication table with the holes in it to clamp work pieces.

Follow me on Instagram for updates on the build:
@cowboybenwade