Snap! (Post # 151)

Snap!

The vent valve before restoration with cardboard "hood" taped on.

When it happened, I thought "no big deal" It's plastic.  I'll just glue it back together.  Little did I suspect how long it would take and what I would have to do to restore it. Because it was something that did not affect how The Alfatross ran or what it looked like--it was practically invisible, hidden away behind the glove box under the dash--I did not start to obsess on it until most of the "important" issues had already been addressed. 

The butterfly valve, control shaft, and broken paddle handle.

But when I did finally take a long hard look at it I realized that the "butterfly" valve controlling the flow of ventilation into the cabin on the passenger's side was probably a cylindrical prefabricated unit welded into the firewall as a single piece. The butterfly itself was made of a round rubber disk trapped between two stamped steel plates spot welded to a central shaft. The shaft was bent into an "S" shape at the bottom ending in a short paddle-shaped lever made out of what looked like black bakelite plastic. Notches in a steel plate welded to the bottom of the cylinder locked the butterfly in four preset positions ranging from completely open to completely closed.

I used the stump of the handle and the part that broke off to make a mold.  
That was the easy part!

You could take the nut and washer off the top of the butterfly shaft, but the butterfly was still trapped inside the vent pipe because it was spot welded to the shaft.

I got around that by grinding the spot welds down until I could pull the shaft out from the bottom--after marking the shaft orientation with respect to the butterfly angle! I knew I would have to make a mold of the handle but that was going to be a little tricky because part of it was still attached to the shaft and would have to be supported and aligned just right throughout the process.  

The clear Alumilite cast after drilling but before attaching it to the shaft. 

I used the wrong approach on my first attempt at casting a new handle. I thought I could keep the part of the handle that was still attached to the shaft and just replace the part that broke off, but the bond between the original material and the new cast was weak and broke again almost immediately. 

The finished and painted final assembly

On the next attempt I cast the entire handle using an epoxy resin called Alumilite. After removing the original bakelite part of the handle still attached to the shaft, I discovered that the shaft inside was cleverly flattened to resist twisting forces. I drilled a hole in the cast for the shaft, injected epoxy to lock it into place, and inserted the shaft at the correct angle.

The vent tube with butterfly valve secured with pins through the shaft.

Putting it all back together was pretty straight forward. I inserted the butterfly into the tube from the inside, ran the shaft through it, lined up the holes in the shaft with the ones in the butterfly, then inserted pins through the holes from the engine room to hold it in place.

A "foot's eye view" of the "re-manufactured" vent valve under the dash and behind the glove box.

Looking back on what I just wrote in a few minutes reminds me of how long it actually took, all the fiddling around to figure out how to do it, and all the wailing and gnashing of teeth when it didn't go as planned.  Maybe I should have started with a "Don't try this at home, folks!" warning.