my 09 Yeti 575 is currently 3x9 which suits my normal riding. Every now and then it gets treated to an uplift day, and I'd like to swap the chain rings for a single ring and chain guide to stop the chain rattling around and jumping off the whole time. Is this possible with just a BB mounted chain guide? Would I have to change shifters etc? I'd probably get a clutched rear mech to help things out. Is it worth it for a few rides a year?
Easy enough with a BB mounted guide. You can also get BB to ISCG adapters. You could probably just get away with a top mount.
I like it but only you can say whether it's worth it 🙂
i went from 3 x 10 to 1 x 10 on my orange r8 pro earlier this year, i wish id done it sooner, i have a hope 34t intergrated bash/ring and hope clamp on guide, both work brilliant together, i havent had it jump off yet. i think they do a bb mount if a clamp style doesnt tickle your fancie. i was quite suprised by the weight loss by removing shifter,front mech etc.
I'm using just an MRP 1X BB-mount top guide on mine, and a single-specific chainring, doesn't really work without the clutch mech but is bang on with. Don't think I've dropped the chain once since I got it set up right- well, once while throwing the bike down a series of minor precipices during a snow ride 
Harder to do this with newer bikes and damn-fool new BBs though.
I went form 3 x 10 to 1 x 10 a few weeks back and had trouble with the chain dropping. I had a Hope BB mounted guide fitted to the top but the chain still dropped on rougher terrain! I bought a Shimano XT rear mech with that clutch thing on it and the chain hasn't dropped since!