This restoration article appeared in Motorcyclist magazine's November 1984 issue.

It's easy to make that engine shine brighter than ever.


Pure aluminum is virtually inert; it corrodes very reluctantly. It is also very soft and weak, a poor material out of which to make motorcycle parts. But when alloyed with other metals, aluminum can be stronger than iron or mild steel. However, the same materials and chemical reactions that make aluminum strong also leave the resulting alloy very susceptible to corrosion. Motorcycle parts made of the most common and useful aluminum alloys swiftly resemble old TV antennas if they are not protected from atmospheric and chemical attack.

Japanese manufacturers have received some unfair criticism about the quality of their alloy parts. The aluminum alloys they use for the majority of engine and chassis parts corrode more rapidly and thoroughly than traditional alloys. You can buy an old Harley, Triumph or any other British bike and be confident that any aluminum corrosion can be removed and a superlative polish restored. Modern Japanese, and now Harley-Davidson, motorcycle alloy castings can corrode so badly they cannot be restored to their original luster. But while the older materials may resist corrosion more successfully, they are not as good at their basic task, strength, as the newer ones.

Yes, they are the same part. Before, the bike looked as if it had one wheel in the shredder, mostly due to its cases. Polish, paint and cleanup made the bike worth being seen on.

Gone is the old polish of a Triumph clutch cover or of the rocker boxes of a Shovelhead. Now we get less-expensive machine-polished cases covered with a clear plastic paint. Without the clear coating, today's polished cases wouldn't make it to the dealer without at least minor corrosion. As tough as these clear paints are, they do deteriorate with time, exposure to the sun and chemical attack. When they do, the owner can have an ugly mess to clean up.


Before we start to deal with correcting the consequences of case corrosion, let's take a lobk at what you can do to prevent the deterioration from occurring.

The tough clear coat the manufacturers apply to the polished cases of their bikes can be damaged in three main ways: exposure to the sun's light, chemicals and heat. If you intend to have any fun at all, you will put your bike in the sun and get its cases hot. If you live in Los Angeles or near the beach you will expose it to chemical attack. However, there is hope.

The easiest protection is to wash and wax the bike regularly. Washing removes chemicals such as salt that attack all the painted surfaces. The sun's energetic and harmful ultraviolet rays can be attenuated by generous coats of wax. Good old hard waxes such as Classic Car Wax and Slipstream are excellent examples. Wax also keeps the majority of the harsh chemicals, such as ocean salt, from reaching the fragile clear coat over the even more delicate surface of your bike's polished alloy cases. Just don't polish too much; you might rub right through the plastic coating in time.

I have seen numerous, rather new engines with yellowed clear coatings. Thiase engines had been run very hard and had other signs indicating they had gotten unusually hot. Low oil temperatures and moderate loads help keep the clear coating on engine case parts like new.


The restoration of polished and coated aluminum parts does not require special skills. Like many other mechanical tasks, this one is a matter of knowledge and confidence.

The information in this article is the result of much experience, both my own and that of helpful and interested enthusiasts. While the products and procedures discussed have proven themselves, they are not the only materials or methods that will do. The goal here is to share with you the knowledge that. a corroded case (or bike) is not lost and that you can restore it to its former sparkling condition.

Next page
PAGE: Home 1 2