The 212 in our '47 C-8 had its original single diaphragm fuel pump but I had a new double diaphragm unit that I wished to install as part of a general overhaul. The D/D pump requires an adapter plate to accomodate the inverted mounting flange orientation, as compared to the single diaphragm pump. I have plenty of information about how to install it as described in the Mechanical Procedure Manual but I don't have the actual spacer/adapter. It describes the spacer/plate/gasket "sandwich" and gives part numbers for each item but, not surprisingly, no dimensional data. Why should they when I can just go to my local Hudson Dealer (Olympic Motor Sales) and get them by p/n?
I originally had made a plate by mocking up the pump on a bare block with cam installed to determine what the plate thickness should be to get the pump arm follower surface centered on the cam eccentric. Although that process yielded an acceptable wear pattern on the follower, I was having fuel delivery issues when driving the car. My speed was limited to about 40 and hills were out of the question. (the electric pump I had installed as a priming/back-up pump took care of the issue temporarily) Pressure was on the high side at 5-1/2 psig but volume was in the dribble range. I suspected that my choice of plate thickness was the issue so I removed the pump and removed the lower (fuel side) housing and found the smoking gun. A slight dent in the diaphragm center disc matched up with the screw head for the valve retainer indicating an undesireable contact, limiting the stroke. That limitation was enough to drop my effective stroke to dribble-output level. A bit of head scratching lead to making another adapter plate from 12 ga. instead of the 3/16 material on my first try. Result: quart/minute volume and 4-1/2 psig pressure (the pressure is unrelated to the stroke length under no-flow conditions, unless, of course, it's zero). Although I believe I've solved the problem, I wonder if anyone can tell me what the original part thickness is. I'm just curious as to how close I got. I'd have never guessed that it was that critical. I only reduced the total assembly thickness by .079", but due to the geometry of the mechanism, it made quite a difference in relative stroke position.
There....I wrote another book.