While working on the MK5 I made an accidental re-discovery of a simple, cheap and effective way to get aluminium polished without resorting to power tools. I have previously mentioned the use of wet and dry sandpaper of various grades starting with quite coarse grades and then finer grades to cut the surface prior to polishing on a buffing wheel.
That is all very good if you can remove the part from the engine however in the case of the MK5 Jag there is an alloy water manifold which would require a major effort to get off the engine and I only wanted to clean it up.
Serendipity intervened and part of the water manifold was wet with penetrating oil when I rubbed it with some wet and dry. The results were quite spectacular and it subsequently took only 10 minutes to convert a grotty looking piece of alloy into something of which you could be reasonably proud . It took me back to my motorcycling days and some of the tricks I used on my “Beeza” [BSA 650 cc sprung heel Golden Flash] to keep the alloy engine and chain cover polished.
If you need to resurrect a bit of alloy such as a cam cover I suggest spraying it with penetrating oil and getting stuck into it with initially 400 grade if it is very rough and corroded.You then and work up through 600 grade and finally 1000 or 1200 grade paper cutting ” wet” all the way i.e. replenish the penetrating oil regularly. The final finish with 1000 or 1200 is reasonably good and from that point on a good shine can be achieved with cutting compound or metal polish. Note-You will get heaps of black “gunk” coming off by this method. That is OK as you are removing oxidised alloy as well as base material. Hint- where possible use a rubber sanding block to support the wet and dry paper and to avoid a “wavy” uneven surface. In short treat alloy like paint.
In previous articles I have always quoted using “dry” cutting techniques. I should have previously mentioned /evaluated wet or lubricated cutting techniques because they are usually more efficient. By the way you don’t have to use penetrating oil. Just about any petrochemical fluid will suffice for aluminium alloy including petrol, diesel, kerosene and mineral turps. For safety it would be best to use diesel or kerosene to reduce the risk of fires etc. Penetrating oil is preferred because it has a very low rate of evaporation and the oil assists in lubricating the cutting area.