Engine Mounts for Hummels

Hummel Aviation uses a rather unique method of mounting either a half or a full VW engine in their designs. Rather than the usual "Conical" mount (usually via an accessory case), they bolt a couple of aluminum angles to the sides of the oil sump, and work shock mounts from there.
It's a bit of a chore to do this accurately. Scott Casler, the Hummel Engines guy suggests using a belt sander. Not having one, I used a vixen file, and a lot of swearing.

Here we begin.

Notice the "sugary" surface is getting brighter and brighter.















I used prussian blue and a section of aluminum plate as a surface plate to keep the surface flat, getting there.

I think it's time to declare victory. This is a junk case I use for experimenting, by the way.

This is what the inside of the case looks like. The bolt heads (AN4) have to fit down in those cavities, which are not exactly flat. I'd love to spotface in that area, but it's a PITA, and the sump walls are only about .200 in thick, so you don't want to carve away too much meat.

The solution, as far as I'm concerned, is a clever little dealie called a Stat-o-Seal. It's an aluminum (and therefore deformable) washer, with an o-ring bonded to the ID.
Between the O-ring, and the crush washer, we should achieve a good mecanical connection, and a seal the oil in the case. The aluminum angles will get a coat of whatever case sealer my engine builder likes. Self locking nuts go on the outside.