Hello everyone!

This is my first time posting, so let me know if I'm in the wrong place.

I have a 150cc off road kart that has had an engine swap. It currently only does 22mph, and I'm looking to get it up to ~35 mph. I did the math, and I found that I need a 16 tooth driven sprocket on the live axle. I want to go this route because a smaller driven sprocket will improve both my ground clearance and top speed. I have #50 chain on my kart, and the current driven sprocket has a 2 5/16" bore with 3.15" 4 hole spacing. I am trying to determine if this bore and spacing is even possible with a 16 tooth sprocket. I found a 16 tooth with a 1 5/8" bore for sale and am wondering how much material I can remove.

Any input would be appreciated!

Well, I think I answered my own question. I was able to download a CAD file from McMaster Carr of a generic 16T #50 sprocket and sketched up what the 4 bolt hole pattern and increased bore would look like.

Unfortunately, the bore looks like it might work, but the hole pattern is too large to fit on the sprocket. I considered machining an adapter, but the adapter would require the sprocket hub on the live axle to be slid over to account for the extra length of the adapter. I checked my kart, and the hub is welded on. I imagine it can't be cut off very easily. I attached a screenshot of my model.

I'm now wondering if I should change both the drive and driven sprockets to achieve the speed I'm looking for. There isn't much clearance to go larger on the drive sprocket, though.

For some reason I can't view your pictures.
I've never seen 16 teeth on a live axle. What motor are you using?
Whats the name of the buggy? Alot of carts came with 31-39 teeth on the axle.

Do you have any suggestions for how to insert pictures? I can't view it either.

I am using a 694cc twin opposed Briggs and Stratton 18hp.

I believe the buggy is something similar to a Carter Talon. The PO has a large pulley on the engine's flywheel which runs to a smaller puller on the 150cc CVT transmission. Then, the output of the CVT goes through a reverse gearbox, then a sprocket runs from the gearbox to the sprocket on the live axle. Currently, the sprocket on the gearbox is smaller than the one on the live axle.

A 16tooth sprocket is about 3.5 in.
You may not have enough material for for the bolt pattern

Moved this topic to the engine swap section since this is no longer a standard buggy engine. That industrial engine spins at much lower speeds than the scooter based engines, so your gearing is way off. No idea if you just using a torque converter or actually trying to use the CVT off the GY6 engine that was originally in place. If it was the CVT, the engagement and shifting will also be wrong for that engine speed.

PGH: Yes, my gearing is way off. I'm using the CVT off the GY6 engine original to the kart. I am certain the engagement is off. I'm not entirely sure what you mean by shifting, unless you are referring to the translation of the CVT pulleys.

If anyone has suggestions for adjusting the engagement, I am all ears.

https://flic.kr/p/2kEEYU8

Here is the CAD model I generated that shows the bore I would need and hole pattern. As you can see, this isn't going to work. Let me know if this link works; I got an error saying "It was not possible to determine the dimensions of the image." when I tried to attach the photo link.

Got the link.
Thats only a 15 tooth sprocket.
I thought you wanted a 16tooth?

I am not sure you will able to get the CVT to respond the way you want, but you will need the heaviest rollers you can find for the variator so that up shifts are quicker (belt rides up the front pulley faster) and you will want the lightest clutch arm springs so clutch engagement happens at the lowest RPM.

All right, so I made a mistake. I checked my notes, and I actually need a 19 tooth driven sprocket. Shoutout to Funnyman for pointing that out. Unfortunately, it seems like I'll have to go to at least a 20 tooth in order to get the holes drilled in the sprocket.

https://flic.kr/p/2kERZ3D
https://flic.kr/p/2kEW9BQ

I'll look into getting different rollers and springs soon.

The 20 tooth sprocket has been ordered and should arrive today. I'm hoping to get it machined this week. By my math, this should take me from 22mph to 33 mph. Hopefully I won't burn up my clutch. If it holds, I might look into changing the drive sprocket from the 16 tooth to a 22 tooth, but I'm not even sure if that sprocket is removeable. Has anyone changed it out before? Is it possible?

I did some work on the sprocket, and it looks like I'm going to have to use spacers on either side to get bolts through it without chain interference. With the driven sprocket spaced over, I'm probably going to have to do the same to the drive sprocket to get them to line up. Shown are the 4 mounting holes drilled in it. I hope to finish the boring soon.

https://flic.kr/p/2kJsKTe

You could try using a recessed Allen head bolt to clear the chain.

Do you have any suggestions as to how to do this on the hub? I wondered about that, but it is welded on the axle, so using a mill isn't really an option to counterbore the hole.

You would taper the holes into the sprocket to clear the bolt heads. You still need offsets between the hub and sprocket.

Unfortunately, on the backside of the sprocket, there isn't enough material to counterbore or countersink with the large hole pattern. Im making a plate to solve that issue, but I'm still struggling with the hub side.

I got more work done on the sprocket today. Everything fits together perfectly, and I couldn't be happier with it.

https://flic.kr/p/2kJFJXo

Like I feared, the sprocket is so small that the chain will interfere with the hub.

https://flic.kr/p/2kJBZk6

To get around this, I'm thinking about spacing the sprocket away from the hub. If I do this, either the drive sprocket will need to be spaced over, or the axle will need to be slid over. I'm doubting that the axle can be slid over enough with the steps machined in it for the bearings, but I'll try to verify tonight. That leaves spacing out the drive sprocket, and that looks like it might be a challenge. Any thoughts?

https://flic.kr/p/2kJFJXJ

You may be able to grind off the hub welds and shift it over before welding it back on.

I've considered doing that, but would like to avoid grinding and cutting if I can.

I took off the drive sprocket last night, and the reverse gearbox came apart on me like I was worried it would. Regardless, I got the drive sprocket off, and there is a counterbore already in the sprocket. I measured it, and it is reading 0.215". If I flip the sprocket around, I think it will be spaced out enough to be nearly in line with the spaced out driven sprocket. The driven sprocket is getting moved over 0.315" on the axle, but I may have some wiggle room in the axle position to allow for the extra 0.1". I'm getting really excited. I only have to wait for spacers to get laser cut, then I can put everything together to try it out.

https://flic.kr/p/2kJUffu
https://flic.kr/p/2kJYuK7

There isn't enough space for the bolt head with the sprocket flipped over, so I'm going to use SHCS like PGH recommended.

I finally have an update. The laser cutter took much much longer than anticipated, but I got my spacers back (and I got them powder coated). Here is the idea for the driven sprocket:
Hub
Spacer
Spacer
Machined Sprocket
Mounting Plate
Mounting Plate

For the drive sprocket, I'll simply putting a washer behind the sprocket and flipping it so the offset is correct. I'm really hoping the sprockets will line up correctly and the chain won't hit anything. I'm going to try to throw it all together tonight.

https://flic.kr/p/2kP3cyq
https://flic.kr/p/2kP3cyR
https://flic.kr/p/2kNYEbJ
https://flic.kr/p/2kGVD5V