Proper engine break-in is equally as important as a proper rebuild. Here, we'll go over a checklist to make your build will last, as well as a step-by-step break-in process.

Putting in the time and money to rebuild your motorcycle engine is both a critical job and a prideful accomplishment. The feeling of an engine failure right after a rebuild is a sinking one, and will most likely stir up a mixture of frustration and disappointment.

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We want to help as many people as we can avoid that feeling. So, we've put together a review checklist for your rebuild, followed by a general engine break-in procedure, because your motorcycle should bring joy and fun to your life, not take tufts of hair out of your head.

We'll start with a quick review on the motorcycle top end rebuild. Be sure these critical steps and precautions have been taken. If you find any concerning discrepancies, it's worth it to pull back apart and double check.

  1. Be sure that you have proper piston to cylinder clearance. Recently, a cylinder was bored with requested .0035” clearance. This machine shop has been in the area for over 30 years. When complete, it looked like it was tighter. He slipped the piston through the cylinder a few times and said, "It's okay." He was asked to check again, which he refused, and said that it was correct, and that he was too busy. Back in the Brew Bikes shop, it was double-checked, and clearance was .0015”.  Yes, way too tight. Don’t just take someone’s word that clearance is correct, always double check it!
    Always double check your piston-to-wall clearance.
  2. Was the honing of the cylinder properly done? Honing is required to be done after boring, and if the cylinder was not bored, it still is needed to deglaze the cylinder for proper ring break-in. Different honing tools are better used for different applications, with common tools being brush hones and flex hones. Safe grits and hone materials depend on the cylinder finish, so check your manual or with the cylinder shop for a recommendation. Be sure that the crosshatch is at 45 degrees. The proper crosshatch will retain the proper amount of lubricating oil while allowing the rings and piston to break-in. Too little of crosshatch or too much will not allow the rings to break-in correctly and never get the proper sealing they were designed for.
    Read our full guide to cylinder prep.
    After proper honing and deglazing, your cylinder wall should have a consistent, 45 degree crosshatch.
  3. If the bike is a 2 stroke don’t forget to chamfer the ports. If it has a bridge in the exhaust port, most pistons require this area to be relieved. READ the piston specs, and if you don’t understand, be sure to reach out to Wiseco for specifications.
    Read our guide to relieving the exhaust bridge in 2-stroke cylinders.
    A critical step in 2-stroke cylinder prep is port edge relief and exhaust bridge relief. This will help ensure smooth piston and ring operation, and combat accelerated ring wear.
  4. Be certain that the ring gap is within specification. Don’t assume it is correct, check it.
    Always double check your ring end gap. With your compression ring in the cylinder, measure the end gap with a feeler gauge to ensure it's within the spec included in your piston instructions.
  5. Proper cleaning of the cylinder. Before you start cleaning make sure the gasket areas are clean with no residue of gasket or sealers. First, use a cleaning solvent with a brush and then again with a rag. This is not enough, and you will need to clean with dish soap and water. Using a clean rag you will be amazed on how much grit from the honing is still in the cylinder. Be sure to clean the piston also.
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