So, despite not having a clue about mechanics at all, and my bike having been sitting in parts for the last week, I’m nearly done, but think I’ve hit a snag.

Got the raceface narrow/wide single chainring in what was the middle position, and as I am not great with hills, splashed out on a Hope 40t sprocket expander in place of the 17t. I think I have set up the rear derailleur (Shimano Zee, FR version), but the chain moves a biiiiiiiig way across/sideways from the top two cogs, especially the top one (40t) and doesn’t sound great!

There is very slight slack in the chain, is it worth removing an extra link and see if that keeps it on more? Any other ideas? Is this normal with a single chainring?

How have you sized your chain?

Normal way would be round the big sprocket and the chainring but not through the RD and then add 2 links. any tighter than that you risk ripping the RD off.

Also how have you got your crank BB spacers (if any) set up to change the chainline? Might need to move the cranks over a bit to help the chainline.

I sized it by putting it around the largest sprocket, but put it through the RD as well (pulling it tight). Will have another look without and adding two. I don’t think there were any spacers on my crank arms when I had them off, but to be honest don’t think I checked for that, will get them off again and have a look. Thanks for the tips! I really wish I knew what I am doing!!

Double check for the chain sizing before you shorten it. That is the normal procedure though.

Shortening the chain is not going to help with the chainline though.

If you have a screw in external BB then there are normally spacers between the BB cup and the frame.

So unscrewed the BB and moved 2x spacers to the other side, or at least I tried to but can’t get the right thread and am scared of trashing it, so will have to man up and see if there is a bike shop near me that can sort it all out pronto in the morning. So very annoyed right now.

Check the threads are clean, it should screw in gently by hand. Check you are screwing it the right way (normally an arrow on it)

Tried again this morning but it wasn’t having it. Took it into a shop in town, unfortunately they’re closed tomorrow so it’ll be Monday at least until I can collect it again. Wish I’d done that to start with!!

Did you check you had the right cup on the right side?

Drive side is a left hand thread, non drive side is a normal right hand thread.

Should be some arrows on the cups.

I would suggest moving just one spacer at a time and checking the chainline(assuming they are 2.5mm each)

Another thing to check is that you are pushing the cranks fully home. Assuming they are shimano then make sure you gently tap them home so they but up against the bearing cover. Don’t try and use the plastic pre-load bolt to try and pull them home as it is easily damaged. It is just there to lightly pre-load the bearings before you tighten the clamps on the non drive side crank arm.

If you have rear suspension make a note of what pressure you’re running in the shock, then let all the air out of it & compress it fully when measuring for chain length.

Thanks, had tried all of that, was the correct side and turned it the right way! Seemed to ‘drag’ when starting to tighten and I just didn’t want to force it, then I was getting more and more annoyed, never mind.

Being a short cage mech, even though you have the Zee FR, it is going struggle to work well with the 40t ratio expander. The mech will be mega stretched in the big ring and sound horrible! Designed to work with a 36t cassette at the most. Would work better with a longer cage clutch mech.

I’m using a One-Up 40T sprocket with a Zee FR mech without any problems but I did move the chainline 2.5mm to the left, which has nothing do with the 40T sprocket, of course, but improved the way the chain ran on the Race Face n/w chainring.