BMW airhead rocker geometry
Finally getting to the meaty end of the salt racer build.
While the crank is off getting balanced with the new pistons and rods, I had a look at the rocker geometry.
With the high lift cam (about 12mm at the valve) and recessed valve seats the geometry did not look good. With valve fully closed, the rocker nose was close to the edge of the valve stem end and moved just past the valve stem centerline at full lift. Not the best. Ideally, the nose travel across the stem end should be equidistant about the valve stem certerline.
The only way I could think to adjust this was to adjust the thickness of the spacers under the rocker posts. The stock item is 3mm. Replacing it with a 1.5mm spacer got things right as shown in the pic but only for that rocker! All the others were a bit different but acceptable with the 1.5mm spacer.
A stock pushrod was transmogrified into an adjustable one so that I could determine the correct length for the pushrods. I was going to have a shot at making my own tapered aluminium ones but just don’t have the time so it’s off to the pushrod man to have some made in 4130.
frame painted! – bike going back together
G Feeling like I’m on the home straight…frame is painted in special ‘skrunkwerks’ golden grey (stolen from Mercedes and tinkered with!).
Lots of werk fillet brazing and filling the various gussets to achieve a sculpted look. The engine case is painted in a 2 pack mat black while top engine cover and rocker covers painted in a 2 pack gloss.
skrunkwerks salt racer preview
H Here’s a sneak preview of the salt racer before it comes apart to have the frame welding finished and painted. Also some detail shots of the top secret ‘ramstein’ airbox and frame.
BMW saltracer gets a carbon bum
II’m 6″ tall. With my chin on the tank, my arse ends up a couple of seconds behind! The seat will be quite long as a result and the rear-sets even further aft.
After playing around with pencil and paper getting proportions correct, I built a CAD 3D model, sliced it like a piece of virtual bread every 16mm, then printed and pasted these offsets onto 16mm customwood. Some jigsawing and glue created what looked like a wasps bum. When sanded smooth to the glue lines, the intended shape emerged.
My friends Peter and Steve of Applied Composite Technologies made a female mold from my ‘plug’ then they laid it up with carbon/epoxy to create the finished part. The pointy end was taken off and some curves introduced so that it looked the business on the salt racer.
Mal Hewett’s Vincent salt racer
S Self built, Vincent based, he’s scooped a couple records in the Vintage class at both Lake Gairdner and Bonneville. Love the man and his machine.
ABC did a short piece on him:
https://open.abc.net.au/explore/64721