If you have Gone to the Trouble of Disassembling the Engine, you will want to Polish it to a Beautiful Finish | News

During a normal engine overhaul, not a restoration, various parts are thoroughly inspected after disassembly and cleaning, and assembled while replacing parts as necessary. It is important to know that, instead of polishing thoroughly, it is better to refresh parts that are difficult to polish from the outside, so that the engine will look more beautiful and clean after assembly.

The difference in beauty at a glance

The top surface of the crankcase was cleaned of corrosion stains with a wire brush and polished with several different non-woven sheets. A full restoration job would probably require sandblasting followed by a finishing glass bead shot, but for a normal overhaul, a simple finish to a suitably casual beauty should be sufficient. The engine drive sprocket area is covered with grease and sludge, so it needs to be thoroughly removed and the aluminum surface thoroughly cleaned before assembly work. The crankcase was dirty due to age-related deterioration and corrosion, but if sandblasting was not used, it could be made to shine like this. The luster will be further enhanced by finishing in the order of coarse, medium, and fine grit.

Practicality of wire brushes and non-woven sheets

Use brushes of various shapes and sizes to scrape off dirt and grease stuck in small areas.
Brass brushes are useful for removing corrosion without deep scratches on aluminum.
Use a nylon brush for easy cleanup and a brass brush for tough stains. It is effective to fill a spray bottle with “kerosene” and spray it directly on the stain, then polish and rinse it off while dissolving the sludge and grease. Use brushes where necessary. After removing the dirt, wash the entire crankcase with degreasing cleaning parts cleaner spray and let it dry.
In addition, here we set a round cut non-woven sheet (Scotch-Brite) in the cup of a mini-disc grinder to polish the surface.

Air and power tools improve workability by far!

This non-woven sheet is useful for removing burns from frying pans. If you use different products with different grain sizes and gradually increase the number of grit (increase the product number number), you can polish to a luster finish that shines brighter than the crankcase in practice. The workability will be overwhelmingly improved with a mini disk.
This time, we polished the crankcase using a fine grit of Scotch-Brite (non-woven fabric sheet), but you can get a whiter and shinier shine by pre-finishing with a coarser grit and then gradually increasing the grit size. Even if only a fine grit is used to finish, the beauty will be like this. For more detailed and difficult-to-polish areas, there is a back trick of using a rounded Bonster. For flat surfaces such as the top of the case, this is fine, but for uneven surfaces such as the back of the crankcase or around the drive sprocket, wrap steel wool (Bonster) around a steel core with a cutout at the tip and use it as a polishing rod with a hand drill to get a finish beyond imagination.

There is also the means of an electric drill + non-woven wheel bar

In this case, the non-woven sheet was set in the cup of a mini-disc grinder and polished. When a mini-disc is not at hand, a combination of an electric drill and a non-woven wheel is convenient. If there is a difference in diameter and grain size, it is possible to polish in a flexible manner. In any case, remove dirt and grease before proceeding with the work.

Hairline finishing is basically rubbing in the same direction.

If you are so inclined and polish it to a shiny shine, it may somehow float in comparison with other parts. In such cases, a hairline finish can be achieved by preparing a non-woven sheet and “polishing only in one direction” (one-way = same flow direction). If the polishing is unified in the same direction, the beauty will stand out after the assembly is completed.
This is an attractive technique.

POINT

Point 1 – If you’ve gone to the trouble of disassembling it, let’s take it one step further and pursue the improvement of the finished product.

When overhauling an engine with a strong restoration element, the crankcase, cylinders, and cylinder head are often sandblasted, and there are many opportunities to use shiny glass beads as the finishing touch. The alumina finish used as a base finish has no luster at all and, on the contrary, is easily corroded and stains stand out.  For these reasons, glass bead finishing is by far the most common choice for engines with aluminum surfaces. When sandblasting, the parts must be thoroughly cleaned after treatment. No matter how fine the masking is intended to be, it is the sandblasting media that gets in.
Therefore, after blasting, all threads and oil passages should be thoroughly cleaned and air-blasted repeatedly, and if possible, an ultrasonic cleaner should be used.

Let’s practice crankcase polishing. This is not a thorough polishing like buffing, but a simple case polishing using a non-woven sheet and a non-woven bar to remove dirt and grime at the same time. When overhauling an engine, each part is cleaned and inspected before assembly, but for crankcases and other parts that are difficult to polish in a complete engine, a simple polish at the time of disassembly will make the engine look considerably cleaner after assembly.

The crankcase of a Honda horizontal engine was used as an example, and it took only a few minutes to polish it with a mini disc rotor using a non-woven cloth sheet. Even including the finish polishing, this level of shine can be obtained in a dozen or so minutes. Of course, it is necessary to prepare tools before the work, but with a certain amount of tools and a non-woven polishing sheet, the crankcase can be finished more beautifully than expected. When you carry-out engine disassembly and assembly, please try a simple polishing operation for the crankcase.
Of course, do not forget to clean the parts after the work.