Four Stroke Top End Rebuild

Here are two videos by Rocky Mountain ATV that show how to rebuild the top end of a four stroke dirt bike. The first video covers the disassembly process. The second video continues with assembly.

This two part series demonstrates rebuild of a Yamaha WR250, but the concepts and procedures are consistent for most if not all four stroke dirt bikes. Specifications with regard to clearances and dimensions are always model specific so the rebuilder must have the service information available for the specific machine.

Engine work such as this should never be taken lightly. While most people are likely capable of performing this service, attention to detail is critical in every aspect. For an engine to perform reliably as intended, the fitment of parts must be exact and cleanliness is paramount. Further, manufacturer's recommendations must be heeded.


Four stroke top end disassembly. 11:04 minutes.


Four stroke top end assembly. 10:28 minutes.

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