Vortex Rok GP - Changing to 11T front sprocket

Hello, has anyone changed the front sprocket on their Vortex Rok GP to a smaller size? I’m having trouble removing the sprocket nut off the back of the clutch housing and I don’t know if there are any tricks or suggestions. The nut is gigantic so I don’t have a socket that will fit, and it seems like it’s stuck on.

That nut is tightened to a very high torque value and could also be “loctited”. You will need the right size socket and a big impact wrench or 1/2" breaker bar and a tool/ fixture to either hold the sprocket or the drum in a vise. Wouldn’t recommend directly clamping the drum in the vise. When re-assembling torque the nut to Vortex recommendation. There is likely information on this on the internet.

It’s a size 38mm socket, I use a 1/2 impact driver, only thing that gets it off and back on. Also need to use thread locker when re installing. Be careful when screwing it back on with the gun because it will take you for a ride if you don’t have a tight enough grip, or you could get a sprocket change holder that has all the sizes and it will slot into the 11t and hold it In place.

38mm is a weird size. I was on the SnapOn truck the other day looking for one. Not a stocking item. I was planning on checking the local autoparts store for one in the off chance they carry it.

To make it somewhat easier, I opted for the drum, sprocket combo from Comet. It really threw me off when they sent a new needle bearing. Foolish me put the bearing on the shaft and then scratched my head as to why the new 11t sprocket would not fit. Turns out the 11t does not use a bearing, but instead is just a brass bushing. Who knew? And better yet, why did the kit come with a bearing? Fortunate for me, I did a little search on the interwebs and an article from good old KP popped up explaining the whole thing.

God, I love this place!!!

@SahibT , where can I find this “sprocket change holder” tool you speak of?

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I know rotax makes one

I think you could find it elsewhere but eBay was the only site I could find it

Thanks for this, I was able to get this sorted with your tips.

I picked up this: Sprocket Fixation Tool (#219 Gear Holder, 11-14t) - Fastech-Racing to make it easier.

For anyone else who needs to get this done, this helped me as well:

I was careful and used threadlocker, plus the correct washer that came with the 11T sprocket.

Thanks again!


In a bind you can make a somewhat sketchy sprocket holder tool using an old chain, clamped with a vice grips.

That’s a good idea. Also found in my search for a socket that a 1 1/2 inch socket fits pretty well and more common than a metric 38 in the states. The only thing that bothers me about it is that the end of the socket is beveled and the nut is very thin, so it does not leave a lot of edge to bite. Possible I could get the end of the socket turned down so that it is flat rather than tapered.