Restoring old engine casings

Lacquer is ok until it gets chipped or starts to peel off. I ended up attacking my Suzuki GT550J's crankcases with Nitromors when the original lacquer started to disappear from where it was originally. And because some areas were more damaged than others, it was a bitch of a job polishing it up to a decent finish.
Buy some cheap 'T' shirts and a tube of Solvol for both sartorial elegance (initially) and the subsequent satisfaction of well polished alloy.

 

Depends how badly pitted or marked ?
Any real damage or gouges will require welding.
If normal polish will not restore to a satisfactory standard it is back to emery cloth I'm afraid.
Nothing too abrasive though probably start with 240 grit working through to 400 wet/dry
Next, for a real high polish use diamond paste with a bench grinder mop like Dozers Dad recommends or a Dremel type hand held polishing mop taking care to maintain the form.
One tip here for real shape perfection is to put black tape on any suspect areas, this highlights areas that need 'blending'
Depending on the finish you want, lacquer, anodising, chrome plating can be applied for long lasting finishes. If you go for anodising or chroming send several items to spread the cost.
OR plain simple elbow grease and regular polishing using Autosol, diamond pastes etc.
Unfortunately aluminium does tarnish and deteriorate quickly unless lacquered or treated.

 

Restored a few fork legs on my classic 2 strokes over the years.

With light gouges I blend them in with a fine file then use wet and dry up to 2000 grade and for the final finish I use autosol.
To protect them I use Belgom Alu which leaves a wax film on the surface.
I don't lacquer them.

It depends on what finish you want Andy.

Got a bench grinder like DD and I've also adopted one side for polishing mops.

Plenty of good advice in the other replies

Dave.

 

Belgom Alu ! sounds like a nasty disease.

 

I'm with Tiglet with the adapted bench grinder. These blokes do all kinds of kits for polishing. I use there bench grinder adaptor for polishing the bits of my Norton. Does a bloody good job and pretty cheap to. They also do polishing kits for drills and angle grinders and they do a bit of kit like a Dremel with loads of polishing tools for about £40-00 or so.

http://www.metalpolishingsupplies.co.uk

 

Just noticed your bench grinder is exactly like the one I have apart from the polishing adaptor.
Must be 25 + years old and still working well.
Good job you've got it bolted down with the extra length on your polishing shaft. (No crude replies please it's Sunday)