1. Seal up motor as best as possible.
2. Steam cleaner turned up to 'scorch'. Most times you'll get off all of the multiple layers of badly applied aerosol paint - but the factory paint won't be so co-operative. Sometimes the finish is such that you can simply spray straight over it and have it look OK (not awesome), but usually not. I guess some work with the wet and dry could blend the edges and make for a better job.
3. Unseal the motor, inc the gearbox oil drain plug and pour WD40 into everywhere that water got in (and you'll be surprised where it does and does-not get into).
4. Reseal the motor and clean off the WD40 that dribbled out everywhere.
5. Paint.
6. Remove and clean/replace all of the nuts/bolts with painted heads. Not doing this makes the engine look like bodgy shit, no matter how go a job you've done on the rest of it.
Nothing beats doing it properly - the above is fine for a dunger, but the few times I've done it, it leaves me feeling dirty and wrong and unsatisfied.
So then I go to Plan B:
Strip the egine down, and clean the parts in the parts washer at work, and then dry bead blast them if they need more 'love'. If they've gone anywhere near the blaster, then they go back through the parts washer for as many cycles as I can stand before I do anything else to them.
Then mock assemble the motor and hit the external parts with paint, and leave them to dry for as long as possible.
Wet blasting gives a better finish than dry blasting, if the cases are to be left unpainted.
