How to Bore Out an Engine Cylinder

by Tom Lutzenberger
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Aeronautical piston engine image by Andrew Breeden from

As engines get used, over time their cylinders become worn out. This wear and tear results from the ongoing friction stresses created from the piston, the piston rings and the combustion of the engine. During a major rebuild, boring out and honing the engine cylinders provides new life to the engine parts and reduces combustion problems from deposits.

Step 1

Dismantle the cylinder and remove it from the engine. Use a socket wrench and sockets and various crescent wrenches as needed to release the engine cylinder case. Remove any remaining engine parts from the cylinder so that it is completely bare. Wash it down in a large wash tub with kerosene or a similar solvent to remove engine dirt and residue. Let the cylinder part air-dry.

Step 2

Position the cylinder part in a holder so that it remains locked still when working on it with a boring cutter tool. Position the cylinder so that it is facing upside down and straight upwards. Position the boring cutter so that it is parallel with the cylinder. Allow the boring cutter tool to lower into the cylinder and perform the boring work, producing a round hole in the cylinder material. Finish the cylinder ports with a hand-held rotary or grinding tool by chamfering the intake and exit port edges inside the cylinder (only applies to two-stroke cylinders). Use a rotary burr for the initial chamfer work and a sandroll bit for the final grind.

Step 3

Attach the proper-size honing tool for your cylinder to a power drill or similar tool that will allow the honing tool to rotate at high speeds. Use a screwdriver to adjust the tension on the honing tool so that it properly fits the cylinder when inserted. Apply engine oil to the honing tool end so that it is fully covered with oil.

Step 4

Insert the tool into the cylinder and turn it on to maximum speed, holding it firmly. Move the honing tool in and out of the cylinder quickly so that it doesn't grind one spot too long. Do not pull it all the way out or you will damage the cylinder edge. Pull the tool out and check the work. Reinsert the tool and spin it the opposite direction. Pull the tool out again and ensure that the inside of the finished cylinder displays a cross-hatch pattern.

Step 5

Take the grinded cylinder and wash it completely with hot water and soap. Rinse it one final time and then dry it immediately. Do not let it air-dry or you will get flash rust.

Step 6

Apply engine oil to a paper towel and wipe it on the inside of the cylinder. Pull the paper out and look for gray or black stains. Keep lubricating with more paper towels and oil until the paper towel no longer stains.

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