Was trying to remove the big chainring last night as a tooth is broken but inadvertendly rounded of one of the bolts and its stuck! Any ideas on the best way to remove the bolt? It’s a shimano XT one. Managed to remove the other 3.

drill i out

you could hammer an appropriate sized torx bit into it.

Drill, you might need to restrain the other side somehow whilst drilling (big screwdriver or the proper tool).

Will drill easily as it’s aluminium.

Cheers for tips, will try drilling the bolt out tonight.

I did this and ended up with a little set of special drill bits that had a thread running the wrong way, so basically you drilled the appropriate sized bit into the rounded off hole, it gripped and then spun the bolt out easy as pie. I forget what their called, but any handyman shop should have them.

drilling would no doubt work but you could also try using a screwdriver on the rear of the chainring bolt. Don’t forget that this has a slotted bit on it as per the picture below (which features a Torq bolt but it’s the first pic i found).

Put a suitable sized screwdriver in and turn it round to loosen off the bolt from the rear.

Of course, it may just spin but if its been in there a while there will be enough dirt and gunk in there to give resistance so that it loosens off.

I had a similar problem – cured by applying heat to the bolt and turning as it cooled.

big rings wirk fine with broken teeth.