You'll probably think too messy but any fairly runny oil will stop emery cloth from clogging. Cycle oil / 3 in 1 is ok. It will also cut more efficiently. Water with a drop of liquid soap prevents clogging too, useful for painted surfaces and metal too but for rust.

A related aspect. I honed something down to remove a very large fraction of a thou with a fine ARC diamond stick and was getting no where. Dipped them in honing oil, which they no longer sell, and was amazed how quickly they removed metal. I went 2um too far expecting to have to remove more.

John

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Honing oil avaible from Axminster PT. This stuff realy does make difference. Started using it a few years ago on woodworking tools as well what a difference it made to the finish. After polishing the ferrous parts coat with Metal Guard to stop any rust forming.

One thing I'd throw into the pot – if you are cleaning up castings especially the flywheel, don't round the edges that are meant to be 'square' it can make the engine look like a cartoon toy. (Edges do need to be 'broken' to hold paint (tip from Jason…), but that's different to adding an unintentional radius).

Another is to take care with Stuart castings, some can be surprisingly soft and you can remove more material than intended quickly. I had a bit of this on the spokes of the Victoria flywheel.

Personally, I would not leave as cast some improvement usually improves things – but taking a sole plate say, to a motorcar finish can end up looking like a plastic moulding.

Steve