Friday was good friday and so I spent some time working on the TriBSA. I've never been totally happy with the seat-unit I had for the bike. It's too narrow to fit over the shock mounts and I wanted to make sure it 'flowed' into the 2 gallon BSA tank I bought a few weeks ago. I ummed and ahhed about things for a while before making the decision to commit to modifying the seat unit...
First of all I drew a line along the centre line
Then I cut along this line with my jigsaw. Now, with the seat in two pieces I was committed to modifying it (or buying a new one from e-bay).
In order to allow the seat to sit on the frame rails I needed to make a cutaway in the front of the seat unit to clear the top tube and the tubes that form the top of the rear of the frame cradle. A quick mock up shown below.
I'm not happy with this for a couple of reasons, the first is that the bottom of the seat base is way below the bottom of the tank, the second is that there isn't much room below the back of the seat unit for a light and number plate mount (the picture above was taken with the rear wheel held in the position it would be in under full compression.)
At this point I was getting a bit tired and wasn't sure where I was going with the seat. When this happens I find it's all to easy to get despondent and make no progress so I decided to try some grinder therapy. There is a lug on the A10 frame that is used to mount the front of the seat and I was as sure as I could be that I wasn't going to use it. So I introduced it to Mr Angle Grinder. Here you can see it after Mr Grinder had nearly finished the job....
... and here is the finished job. Surprisingly satisfying I found. Seeing as I now have a tank I knew that the bolts that I had had brazed in place to hold the old Mustang tank in place were surplus to requirements so I removed them as well.
Finally I spent quite a lot of time scratching my head and trying to decide what to do with the seat unit. At the moment I'm favouring the following...
As you can see the cut-out at the front of the unit isn't required, strictly speaking the seat unit doesn't need widening either as it no longer has to sit over the frame rails but I reckon it will look better slightly widened. I'm currently trying to work out how to do the fibreglass work necessary to achieve this. In the mean time I've mocked up the seat widened by 40mm.
Which is pretty much how far I got on Friday before I got too tired to continue (I've been having some problems with my injured foot recently).