Predator 212 build - sprocket adapter slips and destroys spokes. Help!

[RB55_2018]

Hello All,
I recently built a Predator 212cc motorized bike. It's been working great; I'm loving the CVT transmission and lower end power of a 4 stroke. I was able to reach 55mph on a flat surface. The torque from the 212cc 4 stroke engine is incredible. I was able to do wheelies with a 36T rear sprocket and climb very steep hills with no issues whatsoever. However, the high torque also caused my hub adapter to slip, bend spokes, and destroy the back wheel. I have had a lot of experience with motorized bikes before and never had an issue with a hub adapter slipping when I used this procedure: file the halves of the adapter so they do not contact each other when placed on the wheel, roughen up the surface of the hub adapter a bit with sandpaper, clean the hub and adapter surfaces with 95% isopropyl alcohol, apply blue threadlocker to the screws, and apply a retaining compound to both halves (I always used Loctite 660) before installing the adapter on the hub and tightening the screws as much possible with a pipe on the Allen key for more torque. Unfortunately this was not enough to stop the hub adapter from slipping with the 212 engine. I don't want to use mag wheels since I've heard that they are basically poor-quality Chinese junk. I've even heard of the wheels flat out snapping in half when going around a corner and launching the rider above the handlebars. On some downhill sections, my bike reaches 60 mph and it would be an absolute disaster if the mag wheels broke (maybe even lethal).

What should I do? I've heard that the rag joints are even stronger than hub adapters if used properly. Any advice would be appreciated. Thanks!

 

[Wrench]

Sure would like to see some pic of your 212 build

 

[Member 30571]

What should I do? I've heard that the rag joints are even stronger than hub adapters if used properly. Any advice would be appreciated. Thanks!

I got 1000 miles on my rag joint and I never had to re tighten the 9 bolts

 

[RB55_2018]

Here are pics of my build:

 

[RB55_2018]

I got 1000 miles on my rag joint and I never had to re tighten the 9 bolts

I'm just afraid the sheer torque of the motor is too much for a rag joint setup, but I might be wrong. Honestly if I could I would just TIG weld the aluminum hub adapter to the hub but I only have a stick welder. A aluminum welding rod might work though? Idk

 

[Member 30571]

WOW, Thats very nice !!!!

 

[Chainlube]

Seeing that you're not running a chain to the pedals, why not just a motorcycle wheel and tire. You will probably have to stretch the frame a bit but no biggie.

 

[mark20]

You could drill a hole in the middle of the adapter, then tap a m8 screw thread and tighten it down, that would make more griping area for the sprocket.

 

[RB55_2018]

Thanks for all the suggestions so far. The frame very strong; it's made of solid steel. I’ve carefully inspected it after 70 miles and I haven’t seen any damage. The cantilever brakes are, surprisingly, sufficient for stopping at high speeds. They definitely require more force or pull than disc brakes but work well enough for me. Here’s what I’ve seen and my opinions:

1. Properly installed rag joint (@Member 30571) - could anyone give me their opinion on this? Honestly I have no clue if it would actually hold up to the massive torque this engine produces or just snap all my spokes like spaghetti sticks . A new rear wheel is only $50 but I hate having to wait for parts to come in so I want to get it right the first time.

2. Welding the aluminum hub adapter to the hub - anyone done/tried this? Is it a good idea at all or would it just ruin everything?

3. Drilling and tapping an M8 bolt through the adapter - I like this idea but I don’t know if it would improve grip. @mark20 have you tried this before? I did find a higher strength Loctite retaining compound that might help a bit with slippage but I still don’t think it would solve my problem. The fundamental issue here is that there are two smooth circular metal surfaces with no shaft key, and a high amount of torque is applied to one while the other resists the torque. Friction can only go so far. Screwing a bolt through an adapter half would increase clamping force on the opposing side but I don’t know if it would be enough to stop slippage. Maybe I could drill a small hole (without going all the way through the hub of course) that the screw could go into so it would lock with the hub? Or even use a Dremel to make a small keyway? No amount of torque from the engine could break that connection. Just don’t know if the hub is thick enough to make that work. Any opinions/thoughts would be greatly appreciated here.

4. Motorcycle/Dirt Bike wheel (@Chainlube) - would love to but I’m not a fabricator and have no clue how I would do this. I also don’t have fancy or expensive equipment, just basic garage tools.

5. BMX wheel (@Don_Parsons) - I have no experience with these. I’m using 26” tires FYI. Wouldn’t mind using a smaller rear wheel if I had to but would prefer not to. Is there any difference between BMX wheels and normal bike tires aside from height and width?

 

[RB55_2018]

Addition: I found one last method that might work. Essentially, I would rotate the rear wheel so the freewheel threads (currently unused) would face the left side instead of the right side. Since I’m not using pedals and the wheel has cantilever brakes, the orientation actually doesn’t matter. Then, I would use a left-handed freewheel adapter along with some large washers and thread it onto the freewheel mount. Lastly, I would drill holes into the sprocket so I could bolt the sprocket to the freewheel adapter. This would self-tighten and utilize the wheel’s built-in mechanism for holding a chain. Below is an example of a kit they sell to do this:

Freewheel Sprocket & HD Axle Kit w/Brake

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