How to Repair a Cast Aluminum Crankcase

by Kevin Johnston
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When you accidentally get a hole in your crankcase, your first reaction may be that the engine is ruined. Oil will leak out and your engine will not run. If the crankcase is made of cast aluminum, you should be aware that you can’t weld it, because aluminum melts at lower temperatures than other metals. However, you can repair a hole or crack in an aluminum crankcase. Using some special materials and techniques, you can fix your crankcase and make it watertight -- or better yet, oil-tight -- so that your engine can run safely.

Step 1

Use a degreaser and a wire brush to remove grease and dirt from the crankcase. Apply degreaser to both the inside and outside of the crankcase. This comes as a thick liquid you pour on and spread with a cloth. Scrub all surfaces you have applied the degreaser to. Pay particular attention to the areas where you will be applying heat as you repair the crankcase. Rub off the degreaser with a clean cloth, and rinse the crankcase thoroughly with soap and water.

Step 2

Cut a piece of scrap aluminum to cover the hole. Do this by using “C” clamps to clamp a sheet of aluminum to a work table. Use a circular saw with a carbide blade to cut the aluminum so that you end up with a rectangle that will cover the hole in the crankcase and extend at least 1 inch beyond the hole on all sides. Rub a candle on the blade of the saw to help lubricate it, but do not melt the wax. The heat from sawing will melt it during cutting, lubricating the blade.

Step 3

Heat the crankcase and the scrap aluminum patch. Use a propane torch to heat the crankcase and the aluminum scrap where the scrap touches the edges of the hole in the crankcase. Aluminum solder melts at a lower temperature than aluminum, so do not apply the propane flame directly to the solder, because it will melt away too fast. Heat the metal instead, and then touch the solder to the metal where the patch and the crankcase meet and form a seam. The solder will melt and run into the seam.

Step 4

Solder the inside of the patch. Apply aluminum solder to the inside of the crankcase where it has been patched. Place the solder along the seam formed by the edges of the hole and the patch.

Step 5

Apply liquid sealant. Car-repair sealant comes in a tube that you can apply to metal parts to stop leaks. Though it is often called a liquid, it comes as a paste. After the solder and the metal have cooled to room temperature, apply sealant to the inside seam by squeezing the tube as you run the tip along the seam you want to seal. It will form a tight seal to your metal seams on your crankcase repair job.

Step 6

Put water in the crankcase and allow it to set overnight. Check for drips the next day. If you find any, apply a second coat of liquid gasket.

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