High Volume Oil Pump


The following photo series is of testing a new High Volume Oil Pump that we had made. The assembly and testing covered about 5 hours on Friday night. When I was in my 20s, I used to make a point of donating 10% of my week’s pay to Anheuser-Busch corporation on Friday night. In the past 2 decades, I have found more productive things to do with weekends. Years ago, people saw how much time I spent at our old hangar and often said that I practically lived at the airport. After Grace and I were married, rather than trying to get me to come home from work earlier, she came up with the solution of moving the house closer to the hangar. For the past 6 years they have been 10 feet apart. Our hangar is 40’x50’, but I do most of the work in the adjoining 15’x30’ shop seen in the photos. Our hangar is a basic metal pole barn without insulation. The workshop is fully insulated and got an older central heat and A/C system installed last year. (We have a neighbor in the HVAC business who needed a Warp Drive prop.)  Although we live on a little airport, working in the small shop next to the house gives me the same feeling I had when I first got started building planes in the garage behind my house at 1235 International Speedway Blvd., Daytona.  Working in the shop makes me think about all the other builders out there working in their garages, basements and workshops, all the people enjoying the hours creating their plane with their own hands. No matter how diverse homebuilders are, they all have this in common.

Here is a shot of the basic unit. A high volume pump is basically a longer set of gears with some type of extended housing. The extended gears are from a small block Chevy V-8, and they are identical to a Corvair’s except they are .400” longer. The next time some brilliant guy in your EAA chapter tries to tell you that Porsche or Franklin designed the Corvair engine, you can ask him why he thinks the oil pump is interchangeable with a V-8. The Corvair is 100% Chevrolet engineering.

The extended housing on high volume pumps is usually a two piece affair that his held together with roll pins, it can be a little tricky to set up, and it does have some pumping losses from a less than perfect fit in the assembly alignment. It also has two gaskets in it. Above you can see that our housing is a one-piece bowl-shaped unit, CNC machined. Instead of aligning itself on roll pins, it centers itself on the two shafts, which are stabilized by the housing. This is not a new concept, this style had been made before by Corvair car racing guys. However, our unit was sized from scratch, and independently developed to serve aircraft guys. It is self aligning, has minimal pumping losses, and only has one gasket.


If you have been around Corvairs only a few years , this is a tool you may not have seen before. I built it many years ago to test oil systems. It is the back half of a Corvair case with a little sump added underneath. It has plugs welded in a lot of places to seal it, and the gauges are set to read oil pressure before and after the bypass. It has a valve to allow mimicking any bearing clearance and oil flow requirement. This part is actually a rare “RL” case from a 180hp turbo Corvair, but it is special for another reason: It flew several hundred hours in our Pietenpol. Over the years, we have tested many cases on this unit. After we moved to Gold Oil Filter Housings, we stopped working on rear oil cases for builders because most Gold Oil Systems use our replacement oil cooler bypass valve built into the Sandwich Adaptor.  This unit was very good at detecting a marginal stock oil cooler bypass, in addition to testing oil pumps.

Over the years, I have made lots of pieces of custom testing equipment, because testing is the most important element that we do. Many people have an idea about making a part. If they have time and money, or they are amateur CAD guys, they can get a machine shop to make the part. Some of these will function, and a still smaller fraction will work with other required parts in a way that fits in the final installation. Some of these parts will actually pass basic testing. But the real testing requirement is not showing it will work, but aggressively trying to find the way the part, or under which circumstances, or in which combination it will not work.  Few people understand that this is the real focus of testing. Most people who conceive of an idea, defend the concept, nurse it through manufacture, and then start testing it have a big emotional attachment to it. At that point, they believe in it. They have a very hard time trying to develop any test that will show the part or concept to be deficient or vulnerable. For testing to be of any real value, you have to run it as if it is being directed by your worst enemy, your ex-wife and her mother, and the guy at work who thinks homebuilt aircraft are crazy. For the period of testing, you have to pretend that these people have PhDs from MIT and Cal-Tech, and they want to find any flaw in your idea. You have to really let go of any emotional attachment to the concept’s success. This is really what running an effective test is all about.

Adhering to this over the years, we have tested a lot of ideas that never saw the light of day. All of the things we do make were refined by the process I just outlined. Our evolution in the development of the engine and installations was never hampered by an emotional attachment to the way we were doing it. Once a month or so, I will get a guy on the phone who will say something like “well you used to do it that way” referring to the set-up he is planning on using in his plane.  He saw in an old photo on our Web page, and is yet to understand why it evolved. His attachment is understandable, it’s how we did it once, and he doesn’t see the forces that drove the evolution. I talk a lot, but I am also a very keen listener, and in the conversation I can hear if they guy has an emotional attachment to the old way, and if he is resistant to the logical reasons why it evolved. You don’t have to build your Corvair the way we do, but when evaluating your choices, be very cognizant of the emotional attachment factor creeping in and not letting you truly evaluate the merits. Homebuilders by their very nature arrive in the field wanting to do something different. They are reluctant to be seen as conformists. This is a good concept, but it can also work against the practical goal of completing the plane. If 10 new guys all look at the logic of why we build engines the way we do, evaluate it, and then choose to build their engines that way, this is not a sign of conformity, this is critical thinking leading many people to the same point. There will always be some guy on the Net who  criticizes this and tells everyone how his engine is going to be totally different, that is once he gets started building it. 20+ years of working with homebuilders has taught me that the odds of that person flying anything are microscopic. But it isn’t primarily because his idea is bad, actually the Achilles heel of his whole concept is that It is emotionally driven by a force that has very little sustenance in it, the concern for what other people think of you.


In the background, a selection of oil pump gaskets in different thicknesses. This is how Corvairs set the pump clearance. After test fitting them, and checking for a slight drag on the pump while turning it, I settle on a .007” thick gasket and give it a light coat of spray copper before sealing it up.

Here is the unit all buttoned up, Yes, I ate dinner at the workbench.

The drill bit is pointing to the pressure regulator bypass hole. It has to be opened up when you install a high volume pump. Otherwise the pressure will be very high until the oil temp is thoroughly warmed up. The enlarged hole allows the bypass to work with cold thick oil. Without enlarging this hole it might take 15 minutes of running on the ground on a 40 F day before the oil settled down to its normal regulated pressure. Before this, an increase in rpm will raise the oil pressure. On very cold start ups you want to watch this, because even with the hole enlarged it is possible to have the oil pressure exceed 80 pounds by carelessly revving the engine to taxi it while the oil is still cold. Give the engine a chance to warm up, don’t be in a rush. Oil pressure spikes are very rough on the drive system running the pump. This is true of almost all engines, not just Corvairs. People don’t talk about ideas like this with the buy-it-in–a-box imported engines because they just wanted to buy something and use it. Since the primary motivation with Corvair builders is to learn while creating, we talk about things. Most people are happy to just have things, people attracted to the Corvair were the ones who took apart the toaster at age 10, because for some of us, we need to know why.

This plug holds in the spring and the pressure regulation piston. Make sure your piston is polished and the bore has no burrs left over from enlarging the hole. I use a copper crush washer for the gasket. I use the higher pressure spring from Clark’s. The wrench size is 13/16” but it has small fine threads, so don’t do more than 15 foot pounds or so. I do not safety these, and I have never seen one get loose. This plug is shiny because I nickel plate them.

Above is the unit in action. It is being driven by an electric drill on a priming shaft, just the way we prime the engines at the Colleges before we run them. After running through the system, the oil is returned to the center of the case by the 3/8” aluminum hard line on the right; it is entering the case where the #1 cylinder was. Notice that you can actually see the oil stream flowing in the photo. From there it goes back in the bottom of the case and is sucked into the pickup again. The new pump flowed like a river, even at very low rpm. We are going to let it run for a long time in the shop this weekend, with the drill trigger held down with a zip tie. It will be noisy, but I have my sister’s old 1970s stereo that she bought with babysitting money in the shop, a hold over from when people cared about sound.  120 watts, Ohlm speakers and an extended cut version of Exile on Main Street and I will never notice the sound of the oil pump rig running all weekend. Monday we will take it apart and look for any wear on the inside.

Grace and Scoob E were out in the shop helping with the project. Above, Grace ran the drill during the set up tests. This rear cover will have a Gold Oil Housing on it when it is finalized, but for testing, I have it set up with one of our old style oil top plates from the 2004-2007 era. You can see the built-in pressure gauges in this photo.

It wouldn’t be Friday night without a little fun. Our neighbor Roger was having a cookout and a bonfire in his front yard just down the runway. We missed dinner, but arrived in time for the relaxing around the fire with a beer phase. Most builders know that the one pound cooling fan on a late model Corvair car is made of magnesium. We brought one down and after warning those present, tossed it in the fire. It ignited after a minute of warming up. For five minutes you could have seen our airport from low earth orbit. The camera doesn’t do the event justice. It illuminated the entire southern end of the airport; you could have read a newspaper 500’ away. At most airports this would have brought firefighters, hazmat people and the news media. At our airport it brought more people with beer. As a little kid, I played with matches, built tree houses, took apart the toaster, made go-carts and was known on a first name basis at the emergency room. My test methods have gotten a lot better than childhood forays into chemistry, but my incessant need to know remains the same. I accept that the majority of people in life have a consumer mentality that tells them that simple possession is the route to happiness.  For the rest of us who know that our path to happiness is learning and creating, we have the  Corvair movement. The Harley Davidson slogan, “If you have to ask, you wouldn’t understand”’ is a modern version of George Mallory saying “Because it’s there” about mountaineering. The first statement has become something of a cliché, and many of the people saying it are concerned with what others think, but Mallory was deadly serious that he was not going to lead his life by the mundane concerns of others.  My mother taught us to be civil to everyone, but even as kids, there was a clear distinction between always being considerate of others, and leading your life by what other people think. It was an important inoculation that protected me, especially in my teenage years, from peer pressure and the things it leads adolescents to. In the long run, it made me comfortable following my own path, with little concern for what the larger group thought I should be doing. The Corvair movement is a reflection of this, and if you feel the same way, I say “Welcome aboard.”

Thank you.


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