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BikeMaster CR125M Rebuild | Part 6

BikeMaster CR125M Rebuild | Part 6
By Bikemaster February 19, 2020
Above: Old, tired engine ready for refreshments.

Our BikeMaster CR125M project bike’s engine was completely beat and neglected for many years. The clutch plates were stuck and locked up, the top-end was seized with rust, and the crank was way past its expiration date. Fortunately, companies like Vintco have high quality, complete, drop-in crankshaft assemblies with bearings and seal kits to go with it. Working on an air-cooled two-stroke is very straight forward and relatively simple. However, it does take time and a little patience to strip the engine down to the bare cases.

BikeMaster has a substantial line of specialty tools (Bearing removal tool 151645, Crankcase separator 152420, Piston pin puller 152156, Seal puller 152213) that make engine rebuilds much easier. The cases can be painted after they are separated, or they can be painted after the bottom end has been reassembled. There are pros and cons to both methods. Being that we would hate to scratch a new paint job, we elected to paint the bottom end after we finished the reassembly.

Once the bottom end was finished, it was time to drop it into the frame. The freshly bored cylinder was painted with high-temp satin black paint. We wanted to spruce up the engine a little, so we machined the edges of the cooling fins on the sides of the cylinder. Again, that is part of the joy of restoring your own bike, you can make modifications that enhance the look you are trying to accomplish. Since the body components are ready to bolt on, the rest of the project should go relatively quickly. Stay tuned as we race to the finish!

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The clutch plates were completely locked together.

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Air-cooled two strokes are very easy to work on.

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A complete rebuild requires taking the engine down to bare cases.

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Fresh cylinder bore and a new coat of black paint.

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New clutch plates to send all available power to the rear wheel.

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Complete bottom end rebuilt with new hardware.

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The engine meets the chassis.

Look for part 7 of the BikeMaster CR125M Rebuild coming soon.

Go to Part 7 >>

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