A while back, I posted that I had rebuilt the Regulator on an O.S 120 surpass IIengine. I have also made a replacement pump for the O.S120 Surpass III and I've just rebuilt the stock pump for that engine.

My Surpass II has had four flights and is a great running engine. My only complaint is that I have trouble shutting it down. More servo setup is required. That bugger will tick over at 1500 for a long time.

My Home made pump for the 120 Surpass IIIseems to be a success also. I've run three tanks through it on the test stand and it looks good. This week, I'll put it in my 2M pattern that the Surpass IIis in and see how it runs in the air.

I pulled the stock pump apart, and found a hole in the center of the diagram. I'll let someone else tell you how it got there. The diaphragm was a curious mix. It looks like a 2mil piece of Mylar with a half mill stainless steel foil bonded to it. It is very stiff, with no expansion rings. I've been in a dilemma on what material to use for a replacement. The other night, we had some Thai food from Trader Joes's that comes in a foil package that you boil. That package is a plastic/aluminum compound that is just about the same thickness as the stock Diaphragm. The material stands up to boiling watter without problems or changes in size. Iput a piece in a jar of 15% nitro fuel for a couple days and there was no effect on it. It is all but impossible to tear unless you make a cut to start the tear. I made a new diaphragm from this material and I'll try it out this week. My biggest problem so far is finding some 3.5mm OD x 3mm ID brass tubing to make new riveted sleeves from. Guess I'll jut bolt on the plastic without the brass sleeves for the test. Itried machining some tubing, but it managed to be off centered a slight amount, so it wouldn't flare like it should to rivet the pump back together.

Ithink I need a couple hours flight time on both the home built pump and the repaired O.S pump before I can call them a success, but for now, they look good.

Don