The carburetor mount was made from a 0.75″ x 1.3″ x 2.4″ piece of Aluminum 7075-T6, while the lock cylinder was made from Ø5/16″ yellow brass. I change the lock cylinder to a full split cotter, adjusted the outside perimeter of the carb mount to better match my rear cover casting, and reduced the size of the mounting studs to #10 to better fit the overall scale of the carb mount.
You might want to refer to the rear cover build log and start the carb mount before doing the rear cover to save yourself a little time.
You’ll need to make the split cotter lock cylinder first so that the cove cut can be made when the bore is machined in the aluminum mount. To start the lock, I faced off a piece of the rod to 0.810″ and drilled and tapped it #6-32 through. My tap wasn’t long enought to tap all the way through, so I tapped about 3/4 of the way from one side and 1/4 from the other.
The side where I went in 3/4 of the way will end up as the tapped half of the cotter and is marked black for my reference.
Since the block is 1/8″ oversize in thickness, I’m clamping on a little less than 1/4″ so I can profile the mount boss in the next operation. With the block clamped, I drilled for the #10 mounting studs, and roughly drilled the center bore to 7/16″.
The mount boss was then profiled to the finished width of 0.812″ and the lock cylinder installed with a #6-32 screw and washer from each side of the boss to hold it securely in place for machining at the same time as the carburetor bore.
I have also added a 0.052″x45° chamfer for a 1x15mm o-ring to seal the carb body to the mount.
Using a 1/4″ chamfer mill, I’m profiling the carb mount with the straight side of the cutter and using the tip to machine a chamfer wherever the carb boss on the rear cover doesn’t exactly match the profile. You can just see a little bit of the chamfer cut on the left side.
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