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Two-Stroke Top End Rebuilding
By Eric Gorr
Cylinder and Exhaust Valve Cleaning Tips
Does your cylinder have burnt-on mud on the outside, heavy brown oil glazing on the cylinder bore, or gooey oil on the exhaust valves? If so, here is a tip for cleaning those parts without flammable cleaners. Go to the grocery store and get a can of aerosol oven cleaner. This stuff is great for cleaning the carbon from the exhaust valves without completely disassembling them. CAUTION: Oven cleaner attacks aluminum, so don't leave it on the cylinder for more than 20 minutes. Oven cleaner can be used on both steel and plated bores.
The oven cleaner will help loosen the oil glazing on the cylinder walls. Then, you can use a Scotch-Brite pad to hone the cylinder walls in a crisscross pattern. Wear rubber gloves when you use oven cleaner and flush the cylinder afterwards with soapy water. This will neutralize the acid in the oven cleaner and break the molecular bond of the oil, so the debris can be rinsed away. Sleeved (especially Kawasaki cylinder bores) are vulnerable to corrosion after cleaning. Spray some penetrating oil on the cylinder bore to prevent it from rusting.
Caution: Certain types of cylinders corrode quickly after the cleaning process, so spray the bore area with penetrating oil to displace the water.
Honing the Cylinder Bore
Many people have emailed me with questions regarding honing cylinder bores. If you want to buy a hone to deglaze bores or polish off small scratches, then a ball-hone is the best choice. Ball hones are manufactured by Brush Research in Los Angeles, under the brand name Flex-Hone. These hones are available under different labels and they are most easily available from auto parts stores. Buy a size that is 10% smaller than the actual bore size. These hones are available in several different materials and grits but the profile that bests suits both steel and plated cylinders is aluminum oxide 240 grit. A ball hone cannot remove material from the cylinder bore, especially on the hard nickel plated bores. However a ball hone can polish down the peaks of the original hone scratches and increase the bearing ratio. In other words the piston will be touching a greater percentage of the bore. Sometimes that makes the piston wear quicker but if you have to ball hone the bore to remove scratches, it's a compromise. The one type of hone that you should never use on a two-stroke cylinder is a spring-loaded finger hone. The sharp edges of the stone will snag the port edges and most likely damage the hone and the cylinder.
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