Whether you have a motorcycle, outboard engine, some sort of powersport vehicle or an ATV, boring an engine’s cylinders is an important step in the engine rebuilding process and is an economical way of repairing damaged and worn out cylinders in engine blocks. The process (if done properly) literally restores your engine block back to factory specifications (or larger with big-bore kits) giving you tight tolerances and restored horsepower and compression for a fraction of the money it would cost for a new engine or powerhead in most cases.
Cylinder boring is a process where a specialized machine and tooling removes the damaged material from the cylinder walls by spinning a special carbide tool inside of the cylinder. This tool cuts away the damaged area and smooth’s the cylinder walls so that the piston can move up and down with minimal friction and allows for maximum compression.
Before talking about the process of cylinder boring I would like to talk about when and why it may be necessary. Obviously an engine seizing would indicate that the engine block may need to be bored or sleeved, but also loss of horsepower and/or compression would also show that it may be time to repair the cylinder and replace the pistons and rings. When talking about ATV’s, powersports and motorcycles there are many scenario’s that cause damage to the cylinder walls. One of the main causes of engine seizure or loss of compression is sand in the air filter that gets into the engine. It usually leaves vertical scratches all over the piston and cylinder walls. We have seen people bore out there cylinder and then put the engine all back together and forget to clean out the air box and burn up the brand new piston and sleeve/cylinder in minutes. The other common situation is not properly breaking in the engine or properly warming up the engine. When you turn on your engine and start racing it the piston that is moving up and down at a high rate of speed will create friction and therefore heat up. If the pistons or rings heat up to quickly they may crack or break into pieces leaving deep gouges in the cylinder walls.