Progress report on repaired OS pumps and regulators
07-11-2010, 10:33 PM
#1
Senior Member
Thread Starter
Progress report on repaired OS pumps and regulators
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
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
07-11-2010, 11:31 PM
#4
Senior Member
Thread Starter
RE: Progress report on repaired OS pumps and regulators
Tom,I didn't, but I can.
The Regulator on the Surpass IIwas probably OK when I took it apart. Iwas getting fuel in to the crank case and it was dificult to tune the engine because as it warmed up the mix really changed. It turns out that the seal on the pump shaft was leaking and afte things got warmed up, it starte to seal again. While the engine was cold, there was a huge amount of fuel going into the crank case, and it was pushed up the vent to intake manifold. Ihad a secondary fuel source until the seal warmed up and did it job, so suddenly it was running very lean and would shut down. My fix, or really bypass was to use two "T/s" on the pump lines wiht a small diameter conection between the intake and return lines. This reduced the pressure in the pump so the seal worked OK. Iexpect this is a short term fix, but is has been running great so far. I let the engine warm up prior to flight and I havn't had to touch the needle the last three flights. I found a note in an old RC Universe post from Austrailia where O.S suggested this bypass to fix the over rich idle miix. Seems to work well for a leaky seal also.
The Surpass III has a damaged diaghpgram from cleaning. Ii was doing the same thing as the bad seal on the SurpassII engine, filling the crank with raw fuel that was getting draw into the intake through the crank vent.
My replacement pump was nothing more that a housing of Acetal that held a small chamber with a a 1/32" Silicone rubber diaghpragm, and two Fourmost Check valves. It's kingd of cluncky, but it does work.
I'll make up a drawing of what I did for that and post it. I'm guessing you could make one for about $20 in materials and you could make 20 for about $10 each. The check valves are the expensive part at about $4.50 each. A sheet of 1/32' silicone rubber is about $7.00 from Mc Master Carr, in a 6" x 6" size. You can get 36 diaghpragms from one sheet. The Ancetal rod cost about $22 for a4 ft length which would be enough for 48 pumps. I ripped apart a Robart fueling port for the fittings to press into the pump for the two tubes, There were enough fittings for two pumps and I'm not sure what that piece cost new. The only other thing is a T fitting.
Video at 11
Don
The Regulator on the Surpass IIwas probably OK when I took it apart. Iwas getting fuel in to the crank case and it was dificult to tune the engine because as it warmed up the mix really changed. It turns out that the seal on the pump shaft was leaking and afte things got warmed up, it starte to seal again. While the engine was cold, there was a huge amount of fuel going into the crank case, and it was pushed up the vent to intake manifold. Ihad a secondary fuel source until the seal warmed up and did it job, so suddenly it was running very lean and would shut down. My fix, or really bypass was to use two "T/s" on the pump lines wiht a small diameter conection between the intake and return lines. This reduced the pressure in the pump so the seal worked OK. Iexpect this is a short term fix, but is has been running great so far. I let the engine warm up prior to flight and I havn't had to touch the needle the last three flights. I found a note in an old RC Universe post from Austrailia where O.S suggested this bypass to fix the over rich idle miix. Seems to work well for a leaky seal also.
The Surpass III has a damaged diaghpgram from cleaning. Ii was doing the same thing as the bad seal on the SurpassII engine, filling the crank with raw fuel that was getting draw into the intake through the crank vent.
My replacement pump was nothing more that a housing of Acetal that held a small chamber with a a 1/32" Silicone rubber diaghpragm, and two Fourmost Check valves. It's kingd of cluncky, but it does work.
I'll make up a drawing of what I did for that and post it. I'm guessing you could make one for about $20 in materials and you could make 20 for about $10 each. The check valves are the expensive part at about $4.50 each. A sheet of 1/32' silicone rubber is about $7.00 from Mc Master Carr, in a 6" x 6" size. You can get 36 diaghpragms from one sheet. The Ancetal rod cost about $22 for a4 ft length which would be enough for 48 pumps. I ripped apart a Robart fueling port for the fittings to press into the pump for the two tubes, There were enough fittings for two pumps and I'm not sure what that piece cost new. The only other thing is a T fitting.
Video at 11
Don
