Update: ’99 Yamaha Big Bear Engine Reassembly Begins

This weekend I was finally able to get back to the Big Bear rebuild project.  The engine crankcases were resealed and joined back together.  I used a tap to clean out the old Loctite from the threads where present.  I finished the cylinder head today, which was a rusted mess.  The valves were stuck in their guides, so it took some coaxing to get them free.  The wire wheel took care of the corrosion on the valves, while I used a brass brush to clean the combustion chamber and head ports.  I lapped the valves into the seats to ensure a good seal.  Once lubricated, the valves moved easily in their guides.  The valve seals were replaced too.  The clean combustion chamber looked good.

The piston needed some work.  The two compression rings were stuck deep in the grooves, which would have reduced compression in the engine, making it harder to start.  After soaking in a penetrating lubricant, I was able to free the top ring and clean the groove, but the second ring remains stuck.  I’ll leave it soak all week and finish the piston and cylinder next weekend.  Barring complications, I should have the engine reassembled next weekend and back into the frame.

About Kevin Forth

Always learning, Kevin is an IT professional that likes to tinker with electronics, motorcycles, and whatever he can take apart.

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