So there I was, standing in my motorcycle shed, a 14MM tap in one hand and a new 14X1.5MM filler plug in the other. I was staring at the stripped drive shaft filler plug hole on my 1986 R80 and realizing that the only way that a 14 MM tap was going to re-thread that hole was if I pulled the final drive and reamed the hole first. It was also looking likely that I would either have to dismantle the final drive unit itself or grind the taper off of the tap to provide enough full threads for the new plug.
Phooey. That's a lot of work just so that the R80 wouldn't have a rubber cork for a filler plug. It also seemed possible that bad things could happen to a perfectly good final drive during that much surgery.
I took a second look at the filler hole and realized that while it looked to be stripped smooth, it still had some residual threads, especially near the bottom where the previous owner and BMW's 12 MM filler plug couldn't reach. A quick trip to the hardware store for some metric taps and dies, and I formulated a plan to sleeve the hole which a hollow plug threaded 12X1.5MM on the outside and 10X1.5MM on the inside. The standard 10X1.5 bolt stocked by my hardware even had a smooth raised lip for the gasket to seat on.
This is what I came up with, sorry for the crappy photo, but it's hand held in poor light without a flash. Glare from my flash unit made the part unrecognizable. This is the sleeve and the new plug: