Updated: first published November 2020
There's been a lot of sheet metal work on this bike - the magneto cover, the faux swinging arm and the silencer which was completely missing. It's one of those pressed sheet metal affairs quite widely used in the 70s and 80s on bikes when it can be hidden and some (think the last BSA and Triumph unit singles) where it cannot.
Here's one from eBay:
Now, these come up on eBay from time to time but at over £100 a go I was never going to buy a new one, or even a second hand one but I have a welder, a bandsaw, a brain and a calculator and making one couldn't be too hard could it? Of course, because it was entirely missing I had little idea of scale so I took this library picture and scaled off it:
Where C is the speed of sound and Lc is the length of the chamber. I plotted the results of the calculations:
Using the same technique as that used on the cardboard model, I have split the hemispherical corners ready for bedning: