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:
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.
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.
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.
A while back, we purchased some fiberglass parts from Craig at Boxer Cafe. Craig has been great to work with and talk to. He even made a custom front fender specially for us.
As with building any custom bike, the parts you buy may not be perfect. They usually require some modification. But they are a great starting point.
The seat went to Autos International in San Diego for upholstery.
Thankfully, somebody in the upholster shop has a keen eye and noticed that the seat pan is slightly uneven. The tail sections (seat Cowl) and seat pan are not symmetrical parts but should fit the bike without uneven gaps and without looking crooked.
Again, I’m glad the seat came back into my hands because I also realize that the foam was a bit too high. It made the seat just a bit too tall. I’m only 5’9″ and the bike’s owner is a bit shorter then I am. So some foam has to go so we can touch the ground with both feet.