Rebuild A Motorcycle Motor

Motorcycle motors don’t last as long as those on cars.

Motorcycles tend to rev higher than car motors so they don’t last as long. You may need to rebuild a motorcycle motor with as little as 25,000 miles on it or if there’s been significant damage done, regardless of mileage. Every part in your motorcycle’s motor has exact, factory specifications. The need for a rebuild means parts are damaged, worn or both. The process for rebuilding a motorcycle’s motor is to return each part to factory specifications, assembled in like-new fashion.

Instructions

1. Remove the drain bolt with a wrench and drain the motor oil into a catch pan. Replace the drain bolt. Use a ratcheting socket wrench and an impact driver on stubborn nuts and bolts to remove the motor from the chassis. Place the motor on a free-standing motor mount or workbench. Disassemble the motor. The process will vary depending on your motor’s configuration, but generally you will remove the head, cylinders and pistons first with a socket wrench and socket extensions. Once the top end of the motor is disassembled, disassemble the bottom end or the “cases.” You’re more likely to run into screws during this process. If they don’t break loose with a little pressure, don’t strip them; use an impact driver to tap them loose. Clean and inspect every part as you go. Carefully organize and label each part as you remove it.

2. Inspect and evaluate each part for damage and wear. Use micrometers to determine if there is excessive wear in the cylinder. The machine specs will be in your owner’s manual, but aftermarket manuals, such as Haynes or Chilton’s, often provide better tips for rebuilding.

3. Take any damaged or worn parts that you can’t replace to a machine shop, along with any engineering specs the machinist may need to do the repair.

4. Replace any worn parts and bearings. Some engine rebuilds are done because of a major failure, such as a broken rod. Some are done because the parts that touch and wear from friction simply wear out over time. Either way, it’s easier and often less expensive to return your motor to factory specs by replacing parts rather than repairing them.

5. Reassemble the motor after you’ve repaired or replaced all the damaged or worn parts and surfaces, including the pistons, rings, valve spring, valves, valve seats, camshafts, main bearings, crankshafts, rod journals and rods. Reference your motorcycle’s shop manual for a particular assembly sequence as well as for the torque specifications. Apply assembly lube to all parts that endure friction, such as the camshaft. Use a torque wrench to tighten each bolt to factory specs as you complete the reassembly. Then reinstall the motor. Remember, after a rebuild, it’s like a new motor and needs to go through the same break-in process as a brand new bike. In the break-in process, ride the bike conservatively as all the new parts seat. After you ride it a couple of times, recheck the torque specs on the head bolts.