How to Polish Motorbike Engine Casings

Aluminium engine casings and covers take a battering from weather and road salt. They turn dull, grey and often white with corrosion. Polished up, they transform the look of a bike, whether it is a classic restoration or a daily rider.

On or off the bike?

You get the best results with covers removed, so you can reach every curve and won’t get compound on the rest of the bike. If you polish in place, mask surrounding paint, rubber and wiring, and never polish near a hot engine.

Strip any coating first

Many casings are lacquered or painted from the factory. Polishing compound won’t cut through lacquer, so strip it first with a suitable remover. If the surface looks patchy and blotchy even after cleaning, there is probably lacquer on it.

Step by step

1. Degrease the casing thoroughly.
2. Remove corrosion and deep marks with wet-and-dry paper, working up to a fine grade so the surface is smooth.
3. Cut with a coarse mop and brown compound from an aluminium polishing kit. For large flat covers, an angle grinder polishing kit saves a lot of time.
4. Refine with the stitched mop.
5. Polish with the soft mop and blue compound until the reflection is sharp.
6. Wipe off the black residue as you go.

Keeping the shine

Bare polished aluminium dulls over time. A metal sealant or wax helps, and a quick buff with a soft mop brings it back. Some riders clear-coat polished covers, which protects them but will need stripping again for a future polish.

More in our motorbike and classic car brightwork guide.

Questions

How long does it take to polish an engine cover?

It depends on its condition. A cover with light oxidation is much quicker than one that is heavily corroded and needs sanding first.

Can I polish magnesium casings?

Some older bikes use magnesium, which needs different care. Check what your casings are made of first.

Why is it still blotchy after polishing?

There is probably lacquer left on the surface. Strip it and polish again.