I’ve got one of the MRP upper chain guides on my Curtis;

If the chain does come off the ring a bit the whole device rotates around the BB which tends to then jam the chain into the device.

The BB shell is as tight as I want to go with it really.

Do I use some bearing fit or something to try and lock it in place? maybe use some emery cloth on the various mating surfaces to introduce more friction?

this is why iscg was invented.

i’ll try and be more helpfull…

i’ve got a superstar guide that does more or less exactly the same job, i’ve ‘fixed’ it using an old DMR seat-tube clamp, and an m4 (?) bolt that i found which fitted into the clamp.

linky (about £3)

luckily, there’s a hole in my guide in exactly the right position, you may have to drill one?, put the bolt through the hole, space it out with washers, and tighten it up in the seat-tube clamp.

Mine kept spinning so I put some carbon paste between it and the BB which has kept it pretty well fixed.

Can you get the guide part any lower onto the chain? that was the fix that worked for me.