Oil Drain


With the manifold complete, and mounted differently from Mike's design, I needed an oil drain also a bit different. Goals for this fitting were a neat appearance, and a short profile, preserving space beneath the gear case for the aluminum external oil tank.

  The brass stem was turned and drilled. The plan was to turn the base of the stem (where it enters the gear box) to 5/16" / 0.3125" and fit a viton o-ring, which will provide the primary seal, being inserted into a 5/16" bore in the gear case. The wall of the case is only 0.100", so careful layout and planning was required to turn the o-ring groove at the correct spot.
Along with the stem is this base flange, which is reamed 5/16" for the stem, and also carries two 4-40 through holes. The portion of the flange which mates with the case is correctly radiused for a neat fit.
Here, you can see both the flange radius and the o-ring groove in the stem. There is a heavy fillet cut in the flange for a bead of solder.
Soldered up. The heavy fillet is necessary so that solder won't build up on the flange radius, which would prevent the fitting from seating fully against the gear case. The best flux for low temperature solder is the purely liquid flux which contains zinc chlorides and a bit of hydrochloric acid. This water-thin flux wets the surface better than paste, and the solder flows very well indeed. The o-ring has also been fitted in place.

In the background is a bit of ceramic batting, useful to insulate the part while heating and soldering.

To position the case for drilling, a simple technique is shown. Two cap screws are fitted in their appropriate front holes, and the whole is inserted into the mill vise, with the cap screws resting on the lip of the vise and bringing the exact bottom "belly up". Centering on the X-axis is as simple as inserting a fine drill and moving the table so as to visually align the gear case between the 2 bottom front cover screw holes at 5 and 7 oclock.
The primary hole was reamed 5/16", and the two 4-40 flange holes spotted and drilled for tapping. The holes are tapped right in the mill for accuracy with a spring-loaded tap wrench center.

Temporarily in place. The final assembly will have the flange face coated with a bit of sealant. This, combined with the o-ring, will prevent all leaks.

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