BMX project

[cloakedvillain]

The forward half of a kiddie dirt bike makes a great starting point.

At that point, why not stretch a chinese pitbike and throw some ape hangers on it? They use heavy gauge mild steel instead of butted alloy steels. You can feel the difference in a hawk versus a drz200 or klr250.

 

[Chainlube]

At that point, why not stretch a chinese pitbike and throw some ape hangers on it? They use heavy gauge mild steel instead of butted alloy steels. You can feel the difference in a hawk versus a drz200 or klr250.

I'm working off a 125 dirt bike. Don't really want the swing arm. The rest is steel.

 

[Flight Risk]

A good way to deal with a swingarm suspension on this would be to put a jackshaft right through the pivot of the bottom bracket. Extend a bolt a few inches and put a couple sprockets on it. Sprockets can be the same size on a shared bearing. Chains remain the same length.

 

[michael whiteman]

This is a good idea. It will also allow you to change the overall gear ratio easily. My idea only used two idler sprockets and no shaft. On my current build I put a couple of sealed ball bearings with 5/8" ID in there along with a shaft all purchased on Amazon. They were 16x35mm but I'm sure yours will be different. 5/8"collars are on Amazon also. Remember, if your drive chain is a #415, Stanton Inc is the only place that sells the modified small sprockets. Or you could grind down one yourself.

 

[MinimumVK]

Well im slowly getting this thing together. As you can see i had to make alot of modifications to the frame (and yes the paintjob isnt the best but it looks nice from 10 meters away!). Before fully welding the engine mounts i was thinking about the chain alignement and room to fix stuff on it. I decided that i would make an off-set sprocket for the chain to get a bit more clerance. In return i would get room to remove the sparkplug and even the whole top end without removing the engine out the frame since i didnt want to stretch it any further. It also needed to be level for the dipstick reading to be correct and the transmission oil to reach all the gears. Tank is a 10L tank of a Tomos T12 Colibri that i had and its mounted on rubber hangers. For now i will have MTB style handlebars, front 203mm hydraulic and rear 180mm cable disc brakes and the normal seat. Rear brake will be mounted on a disc brake caliper adaptor so that it can move and be adjusted with the chain tension. Getting by with the parts i have at home without buying anything for it (except for engine parts because its valuable) Overall its coming together nicely. I still need to make some parts so it should be done in a couple of weeks.

 

[cloakedvillain]

The front wheel being bigger looks funny, but so does the tank. Coming out good either way.

 

[michael whiteman]

Boy, you've been busy. I don't see where the jackshaft will be on the painted frame. I like the original layout when it was white. Your butt is going to be really tired when you run that tank empty.

 

[Chainlube]

Ha ha, you said it before and I read it, but you also said Lifan 125. I'm think 4t and it's a 2t 48cc. I love it even more now.

 

[Wrench]

Boy, you've been busy. I don't see where the jackshaft will be on the painted frame.

Jackshaft goes thru the swing arm pivot

A good way to deal with a swingarm suspension on this would be to put a jackshaft right through the pivot of the bottom bracket. Extend a bolt a few inches and put a couple sprockets on it. Sprockets can be the same size on a shared bearing. Chains remain the same length.
View attachment 214201

Your butt is going to be really tired when you run that tank empty.

Is that something you have experience with LOL

 

[michael whiteman]

On mine I put sealed ball bearings in the bottom bracket including a 5/8" shaft with keyway. Would you then put a sealed BB in each swing arm? That will keep the dirt out and also have enough surface area on the balls to support all the forces acting against it. I hope we will get to see close up pictures of this one when it's finished.