Got my Jack Shaft installed, now set screws keep shaking out

[BrianI]

Hi All,

Originally I bought this go cart with just a direct chain drive. It looked so cool with it's oversized tires that I never considered how little power it would have. After learning some about it, I opted to go with a jack shaft; thus changing my gear ratio from 5:1 to 10:1 (where there is a 12 tooth sprocket on the clutch, a 20 tooth jack shaft sprocket, then on to a 10 tooth sprocket which is tiny, and then on to a 60 tooth sprocket on the wheel).

I had to move the engine, which involved cutting that white plate that you see pictured, and then welding up a jack-shaft assembly (yes, I know, I'm a sucko welder ) which bolts to the white plate, and which I cut slots in. The engine also bolts to the white plate with slots, and between all the slots, I can tension the chains. I was never able to bolt everything tight enough to keep the chain on the wheel sprocket from coming right off when I drive it (I'm too big for it, and I'm taking it up 10 degree hills, but I never get a chance to even smoke the clutch before it pops off!). So last weekend I welded a piece of angle iron to the white plate, sent a couple bolts through the jack shaft assembly in order to control the tensioning better, and to hold it in place to prevent the assembly from shifting and popping off the chain. Well, that worked for a few minutes, but then the set screws on the 10 tooth jack shaft sprocket fell out and the chain fell off again.

So, my question is: any suggestions to keep the chain on? When it works, it still has little power, and it is too fast in my opinion for my kids, so I'm all for increasing the gear ratio (which would likely result in less stress on that little sprocket), but I can't find reasonably priced sprockets. I mean, you can get an 80 tooth sprocket for the wheel for like $26, but above that the price goes way up. And I didn't see a wider selection of jack-shaft sprockets (for example, it would probably be better to have a 15 tooth and 30 tooth sprocket on the jack shaft). I could always go with a torque converter, which is why I went with the jack shaft because I figured it would be easier to add the torque converter later if I had to, but that's a last resort.

Any suggestions would be appreciated. I'm off to add hose clamps around the sprocket to see if that helps

[x-bird]

couple of tricks. carefully mark the shaft where the set screws make contact and drill a shallow dimple. I started off using blue and red loctite on the set screws but have since gone to fingernail polish. i put it in the set screw hole and around the edge of the sprocket where it will wick in between the shaft and sprocket. to disassemble, a little heat from a propane torch does the trick. one issue i see is that you have a lot of unsupported shaft length , you really should add support bearing next to that sprocket on the end. you can also ad lock collars on either side of the sprocket.

[BrianI]

Hi X-Bird,

Those are great suggestions, thank you. I was considering welding that little sprocket on to the shaft, but it may be too much for my little welder. So I'll try your suggestion first about predrilling and using nail polish. If that doesn't work, yeah, I agree with you, there is clearly too much unsupported shaft. I'll probably buy new supports in that case and make an entirely new assembly for it.

As for the support bearing on the end, that may not work because the sprocket is so small that the chain would likely rub against it. Maybe if there were a small collar and then a support bearing, so it wouldn't rub against it. Really, I wish they had a wider selection of jack-shaft sprockets; 10 tooth to 20 tooth is less desirable than say 20 tooth to 40 tooth. Even 15 to 30 would be better.

Thanks for your reply!

[x-bird]

with your tire in place, where are you putting the driven axle sprocket? Your layout has me a little confused as to where you're fitting it all. looks like your 10T on the jackshaft is in line with the middle of the tire.

[BrianI]

Well, you should be confused; looks like I uploaded the wrong three pictures last night. These new ones may clear things up (i.e., the ones I meant to post).

[BrianI]

It's a 60T sprocket on the wheel itself. Pictures of the whole go cart are in my photo album.

[SYCARMS]

Looking at the first pic it appears the chain does not line up completely, may be an optical illusion. The chain has to be perfectly lined up to both sprockets. Lets say the rear is 1/8" out further than the front, this would cause the rear sprocket to move towards alignment causing set screws to loosen as the shaft is gouged from sprocket being forced to move. This will loosen the screws in the process.

[BrianI]

Thank you for your reply.

I'm reasonably sure the chain was straight (I cut a specially shaped piece of wood to test if the chain is 90 degrees to the shaft). The motor might not be perfectly parallel with the other chain, but that wouldn't cause this problem (but I nevertheless have to find a way to make that aligned).

[BrianI]

Hi x-bird (and All),

Success! I drilled into the shaft a bit per your suggestion, then used lots of crappy nail polish, and it held together great!

Today was the first time I put the cart away while it was still working. And it was the first time I could run it in a field (as opposed to our gravel road; which is easier, but much more dangerous for the kids).

Thanks again for your suggestions.

[SYCARMS]

Glad to hear it is running.

[OLDKID]

Good Deal ! Hope it serves you well !
NEXT !!! ONE IS NEVER ENOUGH !