When i got the seat pan and the tail piece(see previous post), I immediately began to wonder how to mount the two together. BMW’s R100S seat and cowl is a great design and works well with the hinges. But this is a Short Wheel Base model and we are going with the fiberglass tail piece. The tail piece mounts to the subframe through the saddle mount bag loop at the rear of the subframe and a small ‘tang’ that goes into the main frame tube.
The suggestions I got for mounting the seat pan to the tail piece were:
Velcro
Industrial Velcro
Upholstery with snaps (no thanks)
And then finally… i found out about Well Nuts. BINGO!
Well nuts seem perfect because they act as a thin rubber buffer between the to parts. Also when you tighten them they pull the pan snug onto the tail piece.

To do the job, you are going to need about
– 7 Well Nuts
– 6/32 screws to match the Well Nuts – about .75 inches long
– Fender washers for the Screws
– and a 5/32 and 5/16 drill bit.

Well Nuts purchased at the local hardware store (who has lots of my money):

Screws (I went with Stainless Steel):
Fender Washers:

The first step was to mark 3 holes to mount the rear of the seat pan to the tail piece.

The holes are drilled with the 5/32 bit. Just big enough to get my screws through.
The Well Nuts in the photo will eventually live in the seat pan.

Then snug up the upholstered seat onto the tail piece as best you can, and mark through the holes.

I started by drilling holes into the seat pan with the 5/32 bit. BE CAREFUL. DRILL SLOW. If you ram the drill bit through the seat pan, it will go through the other side and ruin the upholstery.

After i drilled the holes in the seat pan, i mounted it to the seat and ran screws through the tail and into the pan to make sure they lined up.

i then widened the holes with the 5/16 bit. AGAIN. DRILL SLOW AND CAREFULLY.

Time to insert the Well Nuts into the rear of the seat pan:

Now that the seat pan is attached to the tail piece, I marked 4 additional holes for some extra reinforcement.
NOTE: Make sure these holes do not conflict with the subframe cross member that contains the fender mounting bracket.

With the seat pan attached, I drilled (5/32 bit) carefully and slowly though the tail piece straight through the seat pan. i did this for all 4 holes so they would match perfectly.

I then widened the holes on the seat pan ONLY with the 5/16 bit:

All done. 7 screws all lined up. Seat pan is securely attached to the tail section.