BMX project

MinimumVK said:
So i want to present my new project that im making. Wanted to make a 125cc lifan build but lacking the funds right now and decided to make/try to make this since i had the parts: The frame is an old BMX bike that i got for free a few years ago. Im planning on making it full suspension and today i made the rear suspension. The swing arm goes through the bottom bracket and the shocks are from an old moped that are bolted onto a threaded rod welded through the frame.
I still need to figure out the front shocks and the engine mounting which is gonna be hard because of the chain routing with the swing arm at such an angle. Anyone has any suggestions on engine mounting?
The engine itself is a Tomos APN 50cc 5 speed manual that i rebuilt a few weeks ago. They are pretty strong engines and can actually do 70km/h stock but i would keep this bmx geared to do something like 45...
Thanks for the feedback!
Click to expand...
Interesting Project. Good Luck. How will you deal with slack chain when the rear suspension flexes? Chain tensioner?
 
MinimumVK said:
So today i got the engine in the frame. I aligned the sprocket so that it spins the rear wheel without binding. But then another problem came up! I had to offset the engine because i didnt want to mess with aligning the jackshafts and what not.... The transmission is on the right side and it weighs alot so the bike is very likely to tip over. Now i dont know much about physics but would gravity keep it up right at speed?
If not i think im invested in the project enough that i might make a 3 wheeler.
Whats your opinion on this? Continue like the centre of gravity will not cause issue at speed or make it more stable. THANKS!
Click to expand...
A little bit of offset isn't going to hurt. I can't tell what is going on in this picture, too close, blurry and weird back light makes it hard to see.
1716991291809.png
 
Once again you can see the results of this before going any further. Get the bathroom scales and balance the center line of the engine on thin edge of something so you can weigh each side. Then slide the engine over to the offset you need to have and weigh the heavy side. Now you know how much it's out of balance. Use some bricks or something of this same weight, jump on a pedal bike and hang it off to the side and you'll be able to feel the results of your experiment. The bike might tip over standing still, but the faster you go the less likely this will become due to the gyroscopic action of your wheels in motion. I think you'll be just fine.
 
Risk Man said:
Interesting Project. Good Luck. How will you deal with slack chain when the rear suspension flexes? Chain tensioner?
Click to expand...
I think he should take out the downtube, boost the engine up so that the motor sprocket is parallel to where the swingarm mounts. Then make a new downtube somehow.

By the way, the rear shock mounts look very sketchy to me, too.

Also you should really get some proper moped wheels that will have drum brakes built in already.
 

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