Airbox replacement - rear engine cowl
The rear engine cowl is almost complete now and I thought I'd explain a bit of my process.
I first made an mold of the shape I wanted - less the wall thickness - using templates and continually trying it against the engine for fit. It is important at this point to take into account the shrinkage factor of the cast aluminium (about 1 in 70 I was told - but was a lot more!).
Then from this simple mold I made a casting pattern by vacuum forming abs plastic, trimming it to shape and adding the detail lines on each side with body filler and then finishing it in primer.
The sand cast part was very rough when I got it from the foundery. I first trimmed it to size, then sanded the outside and finally milled the slots, for the engine breather,to match the spacing of those on the starter cover.
I sand blasted it and the starter cover to get the look similar and now have to try and age them to match the rest of the motor.
Next stage is to make the bracket that holds it on and the breather filter and ignition coil in place.