After 5500 trouble free miles on a completely rebuilt 46 knuckle engine (74"). I started to hear a slight noise in the front cylinder… before I got home the noise was louder (piston slap) and I could hear a squeak. Pulling the top end off I found the piston pin bushing had turned in the connecting rod and the front piston and cylinder were scuffed. Everything looked normal in the rear cylinder.
I had the front cylinder bored out 0.010” over and installed a new piston, rings, piston pin, and bushing. The rear cylinder was honed and a new set of rings installed. I drove the bike less than 20 miles and started hearing a noise like a leaking head gasket. Before I could pull over the bike started losing power and shut off. I couldn’t turn the engine over with the kicker until it cooled down. The front cylinder was quite cool... the rear was very hot.
I pulled the rear cylinder off last night. The head gasket was blown and the rear piston and cylinder are scuffed. I haven’t removed the piston yet, but the pin is squeaking in the bushing. Both times I dismantled the engine, the piston, cylinder, rod, etc seemed quite dry… though this could be from the heat.
Does anyone have any idea what might have caused this? Could the turned piston pin bushing in the front cylinder and the blown head gasket in the rear cylinder just be two isolated incidents?