The big ol' o-ring at the base of the cylinder was "two-toned." Looked rather light colored (vintage white) in the groove but was a dark brown on the outside (old white). New large and small OEM o-rings from Bob's BMW. Large 0-ring is black, smaller are a translucent brown-ish color.
All four tube seals had been glued onto the tubes with that nasty 3M stuff. I recall using this yellow adhesive to seal cases and such on my old MX bikes in the 60s. That was about the only option back in the days.
Removing both pistons revealed other surprises. All three piston rings had their end gaps lined up in a neat row. That's incorrect and could be partly responsible for some of the coke on the piston crowns and cylinder heads. Spent some time removing that. The most excellent news is that the exhaust valves are in fine fettle. Absolutely no evidence of the dreaded
recession experienced on some bikes.
I used a heat gun to warm the pistons and the gudgeon pins came out smoothly. After removing the rings, all these bits were tidied up and the pistons got a wash n' dry in SWWBO's kitchen sink. I got a pass on that job.
Will wrap up the job today. The mechanics of the seal replacement was straight forward. It was the cleaning that was a time consuming PITA. You've got to know when to stop rubbin' and buffin' or else you'll never finish the seal job. Too clean and shiny is just wrong.
I'll let the bike sit with the rocker boxes off until this afternoon; then re-check torque on the six nuts. Valve lash is set and will re-confirm that, too. Today, we're off on the Trophy for an AYCE catfish lunch at the Lonesome Spur Cafe in scenic downtown Justin, Texas... home of the world's largest discount cowboy outfitters.
When refitting the piston to the connecting rod for reassembly, there's minimal space available to fit the gudgeon pin while keeping the rings within the bore. Go slowly and try not to pop out the ring/s. When slipping the piston and rings back into the cylinder, I used wooden craft sticks to aiid in compressing the sharp-edged rings.
Pad the contact point where the connecting rod meets the engine case opening. Avoid nicking the aluminum case. If that does occur, you must
carefully dress out any irregularity or oil leaks are guaranteed to happen. I also stuffed paper toweling into the tube seal openings to prevent exterior gunk from entering during the lengthy cleaning chore.
Be gentle with the Bings. Avoid hanging the carbs by their cables. So rather than go through the lengthy process of detaching and reattaching the cables, I used light line to hold them clear of the work site and plugged both openings to avoid catching any debris.
