Hi I have a AUB engine that's been sat waiting to remove the head for several months after the new belts proved the exhaust valves had got bent. Head is now off getting sorted. Can't rotate the engine with wrench on the crank bolt to clean up the piston faces. Would putting some oil around the pistons be a good/bad idea? What else would anyone suggest?

Thats fine, its quite common for people to put a small amount of oil / 2 stroke oil / diesel / petrol around the pistons when they are siezed.

Cheers I just wanted to double check as I've finally got round to fixing my partner's car and didn't want to fook it up whilst waiting for the head to be sorted LOL

Ovbiously make sure its all clear before refitting the head to avoid conrod damage etc.. but yeah, its fine if the head is removed and your just freeing off the piston rings.