Campgems

A friend has a 120 Surpass IIIthat was getting a lot of fuel into the crank case. Ihad him send me the engine for a look. The diaphragm was leaking. I used a squeeze bulb and put it on the crank port and I when I squeezed it, I could feel air blowing out of the carb port. Ireversed the bulb and put it on the supplyport, put my finger over the carb port and squeezed. Air blew out the crank port. I was mulling over making a whole pump for the engine, but was having trouble envisioning the check valves setup. Not how the worked, but how to place them in the new pump. Last week one of our inventive guys at the field was showing a piston pump he made and on the end of the pump was a T and two Fourmost check valves. The light bulb went off and I started cutting plastic.

I used white Acetal for the pump body and a 1/32" silicone diaphragm cut from a sheet that I got from McMaster-Carr's. The engine has four mounting lugs on the back plate, but for some reason, the pattern is at an angle to the mounting lugs and the holes are unevenly spaced. It is a rectangle shape vs a square pattern. Ijust machined a cup that would allow four mounting screws to go through the diaphragm and then a mating center that drooped in the cup. Itore apart a Robart fueling valve and salvaged the nipples. I drilled the center of both pieces of Acetal and pressed the nipples in . I then just winged a cavity in the two pieces. Drilled them to fit the bolt pattern and use the cup part to hold the diaphragm in place while I punched the four mounting holes. I put a T on the outlet side and a check valve on each leg of the T with the flow from the tank to carb.

It works. First test was the I could get the engine started and it didn't flood the crank case. That was a bit of a problem in that Iwas trying to start with the needle to far closed. Once I found the right setting, the engine kicked right over. My tach hadn't been turned off the last time I used it, so I couldn't get any readings. Yesterday I was back out to the field and got some readings. Idle was very good. 2000 all day and very good response to the throttle. The top end was off though, only 7200. Iwas cranking a Zingler 16-8 prop. Yesterday was also a maiden for a used plane I bought and I have a 120 Surpass IIin it. I put the same prop on that engine and I could only get 7400 on the top. We flew it but it looked like it was struggling all the way. Back on the bench and I put on a 16-6 and gained another 1200 rpm on the top. Had to call it at day at that point. I've got ot order up some 15" props for tuning both the engines.

At this point, I don't think my pump is going to cause any problems. I'll get some more props in the 15" sizes and do some more testing, but I'm confident that it is a good design. And it is easily repairable.

So, Inow have an engine that runs for my Friend and a bad O.S. pump, time to see what makes it "impossible to repair". Icut the flange off the two brass tubing rivets that locks the three pieces together and punched them out. I slipped my pocket knife under one lug at the diaphragm layer and popped the back plate off. This destroyed the diaphragm because it bunched up the ears. Don't experiment with a good pump. The diaphragm had a small hole worn in the center. What I was surprised about was that it was just a flat piece of about 5mil aluminized plastic. I'm going to cut one from some garden Mylar sheeting and see how it works. I didn't tear into the check valve layer. I'll leave that for another day.I may be a couple weeks before I get a test on the "repaired" pump. I'm going out of town for a while.

If anyone would like a sketch of the pump I made, let me know and I'll draw up one. I just worked off a scrap paper with some measurements on it when I made mine.

Don

w8ye

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Don,

This is great news. Please keep us informed.