Sprocket vs Spokes a bolting odyssey

[Ryokukitsune]

I bought a generic china 49cc motor kit a few years back and I'm just now getting around to getting it up and running. Till now I didn't have a bike to put it on without some serious mods to the frame so I put it off. Now I have a pretty big framed hard tail mountain bike that is just about perfect for my mounting solution (hose clamps) but I'm running into a problem with the rag mounted sprocket.

On both the 9 and 5 bolt sprockets the holes line up with two spokes crossing on one of the holes and I can't seem to find the correct orientation to mount it so it won't put unnecessary stress on my spokes. I've already got a taunt one just waiting to snap and I'm worried that installing the sprocket is going to cause that to happen sooner rather than later, though there is nothing I can do about it as that eventuality will come soon enough regardless.

My real question is how I'm going to solve this little problem because I've managed to bolt on the sprocket but I'm not using all the bolts. Instead of using all 9 I'm using 6 in groups of 2 in a triangular pattern with a space between each group.

Geometrically it should be strong enough not to slip at all and other than being a bit more delicate to true I've managed to get it secured without running into the issue of the spoke obstruction.

I'm wondering if this is good enough to run my motor with or if I'm just asking for problems down the road. As I have no experience with motors I don't know if the minimal anchoring is going to just chew threw my spokes the second it gets some torque from the motor or if it will eventually twist my wheel out of shape due to inadequate torque distribution a crossed all of the spokes.

Has anyone tried this? Douse anyone know what I'm doing wrong with the mounting?

I would post pictures but I don't have a camera the most I can do is post this graphic (quick and basic render of the setup in Maya, minus the spokes and wheel)



Uploaded with ImageShack.us

 

[azbill]

it sounds like your wheel is 32 spoke,,,
a 36 spoke is best for the rag joint
a clam-shell sprocket mount might be your best solution

 

[2door]

it sounds like your wheel is 32 spoke,,,
a 36 spoke is best for the rag joint
a clam-shell sprocket mount might be your best solution

I concur but, check with the vendor before ordering a sprocket adapter. I believe most of them are designed for a 36 spoke rim.

Also I'm a little concerned about your proposed engine mounting method. "Hose clamps"??

You need to clarify that for us. If you're talking about those stainless steel, worm gear clamps used on radiator hoses, they won't hold your engine in place. You need to explore some other options in that regard.
Photos would really help.

Tom

 

[Ryokukitsune]

I've had my reservations about using the house clamps but they seem to be holding strong enough and once I get everything tightened down I plan on basically flooding them with pipe solder. The initial mechanical connection should be enough to ground them and after that the pipe solder should be good for transferring heat into the frame (though it has to compete with the impedance of the rubber gasket [recycled garden hose] between the frame and 6” lengths of pipe I'm using to widen the foot print of the bracket). I'll make a mock up later to show what I mean but rite now I'm a little busy with chores around the house so it might be a few hours/days before I inevitably forget about it =P

on the issue with my wheel, yes I do have a 32 spoke rim/hub. If it comes down to that being a deal breaker I'll just do without the darn thing and go out and buy a used wheel with 6 hole disc break lugs and buy a sprocket that can screw into that, I won't screw up my true and it would be about as expensive as getting a 36 spoke wheel and making the current setup work.

As for the question about how safe the bolting pattern on the sprocket is, I haven't seen anyone really answer that. its kind of important so I'll ask again, douse anyone think my triangular pattern is going to screw up my spokes/wheel?

 

[Andyinchville1]

HI,

Strength wise 6 LARGE bolts to hold the sprocket would be plenty (after all the Top Hat and some sprockets mount direct to disc brake hub using 6 SMALLER bolts without breakage issues)....

The part that would concern me tho is if the metal mood shaped pieces supplied with the kit would be supported enough to properly distribute the clamping load on the spokes....missing the extra bolts would negatively affect that aspect of the sprocket mounting.

Maybe as an alternate solution, you could use smaller nuts and bolts so that they all fit in between the spokes?.....the main idea being you need to ensure the backing plates are all clamping properly.

Hope this helps you.

Andrew

 

[Ryokukitsune]

valid points, I guess without any horror stories it will come down to experience on this one. since I have none it'll be a bit of an adventure on my part. I'll give it a go and tell you guys how it goes in few weeks, once I get this project up and puttering... I'm pretty sure I have 8 mil bolts because they are wider than the 6 mil screws I took off the bottle lugs.

hopefully this won't catastrophically fail on me, i highly doubt it but its still possible. if something douse go a wry I'll just invest in a HD double walled wheel with disc breaks so I can buy the appropriate sprocket without screwing up my true. at least a week after I get it running I should know for certain if there is going to be a problem because I'll be keeping an eye on my spokes for twisting.