3,000cc Case Modifications.


Of the three popular Corvair displacement that we promote, the 2700, 2850 and 3,000cc engines, only the last one requires any modification to the Corvairs case. To build a 3,000cc engine, both the heads and the case need to be machined where the new 3,000cc cylinders are bolted on. Again the 2700 and 2850 require no modifications to the heads or case.

 Several years ago, Dan, Mark Petz, Roy and myself, got together and came up with an exact set of specifications for the 3,000cc machining, to ensure that any builder could be assured that parts sourced from any of us would be compatible. Previously there had been a number of suppliers for 3,100cc parts, and each of them had their own way of machining, and builders were often stuck with one of a kind engines, or even engines that had to have individually machined cylinders for each hole. When developing the 3,000cc engine the four of us were determined to eliminate this issue.

The single biggest factor aiding the standardization of the 3,000 over the 3,100 is the fact that the design and geometry of the 3,000 is all Corvair, compared to the 3,100 which has the piston pin and compression height of a VW engine. These compromises make the 3,100 require modified rods and custom length pushrods. The 3,000cc engine, by our design, uses stock Corvair rods and standard length pushrods. 

There are a number of other advantages to the 3,000 over previous large displacement engines, but I would like to steer back to just the machine work required for this discussion. (A 3,100 engine also required the heads and case to be machined to fit the larger cylinders.) The primary reason why we went to 92mm as the 3,000cc bore over the 3,100s 94mm bore is to improve the head gasket area and decrease the oversize required when machining the case. A 3,000cc engine’s case has the 2mm difference in case bore, this may not sound like a lot, the it is a great improvement if you need to put a helicoil or timesert in the case for a head stud. On the top, the 3,000cc’s head gasket does not break out into the head stud holes as the 3,100 does.

The above photo is from our website in 2008. It shows a highly modified 140hp cylinder head that flew 200+ hours on our 601. The head gasket area extending to the head bolt holes shows it to be a 3,100cc head. (look at the bolt hole all the way on the right side of the photo.) It has flanged VW exhaust, a modification that I no longer think is a good idea on any flight engine. This head has since flown 400 more hours on Dr. Andy Elliott’s high performance 601 XL taildragger. A strong word of CAUTION: No one should consider using stock 140 heads on any flight engine. They are notorious valve seat-droppers, and will actually produce less horsepower on typical 2,700cc engines. Flow-wise, they only make sense on high rpm 3,000’s and 3,100s. The 3,000cc engine we are building for our own aircraft has a set of Falcon heads from a 95hp Corvair. Over the years we have tested countless ideas and concepts. Some, like the heads above have limited application in the hands of the right pilot. The amount of time I spend working directly with builders gives me a very good take on what they are personally looking for in an engine. Our testing allows us to suggest which Corvair will provide what they seek.

If you are heading to College #23, and you are thinking of building a 3,000cc engine, you need to send your case in for machining to Dan very shortly. Several cases have already arrived, and Dan is setting up his very accurate tool room mill to machine these cases. The cost of this modification is $150. Dan wanted me to point out that it isn’t practical for builder to bring their cases to the college and have Dan try to machine them the same weekend. If you are planning on a 3,000cc engine, this is the week to scrub the cases, pack them carefully, and send them to Dan. We will have them ready for assembly at the College. (If your building a 3,000, but can’t make the event, you can still send the cases in for the machine work.) Again, this work is completely compatible with the 3,000cc kits sold by Mark Petz at Falcon and the kits sold by Roy.-ww

Mail Sack, 5/7/12, all topics….


On the topic of MGL, 601 builder and pilot Andy Elliott wrote:

A partial counterpoint – I have been running an MGL Ultra EFIS in my plane since day one. I was, in fact, attracted by the experimental and highly customizable nature of the system. Plus, the MGL remote data acquisition unit (RDAC) minimizes the number of instrumentation wires that have to go through the firewall, especially compared to the Dynon units.
I also knew, as an early adopter to the Corvair platform, that I would have to do some constructive engineering along the way. Note that this is much the same reasoning that led me to choose a Corvair over a Jabiru or a Continental. MGL had zero guidance on how to hook their EFIS to a Corvair (or any other distributor-driven ignition) at the time.
I claim that it absolutely *is* possible to use the ignition grounds as a reliable source for the tach signal. I have been doing that for ~440 hours, and have never had any trouble at all. However, in order to get the system to work with two ignitions, I needed to add couple of diodes to the wiring to prevent them from shorting each other out. Seemed pretty obvious to me, but perhaps not to everyone.
As William says, getting useful advice is not always easy. I get a lot of mine from him! But I would have been happy to send anyone my wiring diagram, along with the caveat that it worked for me and might not for you! I do agree that plastic sensors have little place in reliable fuel systems. I’m happily measuring my fuel flow with a Flowscan transducer. [Flowscans are all metal-ww]
That’s why they call it Experimental aviation! FWIW,
Andy Elliott

Andy: The setup in Shayne’s plane did not have the same resistors and diodes. While your system obviously works, I still prefer to have builders use a system like Chris Smith’s that is divorced from the ignition. Thanks for the input, all perspectives welcomed. -ww


On the subject of new brackets, Buttercup builder and CC veteran Daniel Kelley asked:


Hi William, will the new bracket work with Roy’s 5th Bearing?
Thanks, Daniel Kelley

Daniel: As long as your starter has a bolted on ear, not a welded one, the bracket will work. It takes a slightly different length spacer, but this isn’t a big deal. Roy makes a tail bracket for builders using his bearing that fits right up against our Gold Front Starter Brackets in a very neat installation.-ww

Corvair College #22 veteran Vic Delgado wrote:

I like it! I saw one at CC#22 on the engine you finished and really liked the simplicity and the functionality of it. Great Job William, no doubt I will be purchasing one too. 


On the post about Alan Uhr’s 601-XL(B), 601 builder and pilot Phil Maxson wrote:

Congratulations to Alan! This is a very nice looking plane. If your experience is like mine, it will bring you many hours of pleasure in the future. William’s point about relying on a proven design is right. The way to move from building to flying in the quickest and safest fashion is to rely on a proven configuration.     Happy flying!- Phil




On the photo of of the core crank decorations on the CC#23 post, Vic Delgado wrote:

Now That is a fine job of wrapping! Nice going Kendall!! LOL


On the subject of College dates, Rob Stapelton, builder from Alaska wrote to ask:

Will there be other College events later this year? If so where, when?

Rob: The schedule for the year is pretty full with Brodhead and Oshkosh this summer. The next College we have after #23 is going to be Barnwell, S.C., the same location where we had #19 and #21. We hold this College as a year-end event, and it is always on the three-day weekend in early November for Armistice Day. We don’t have the exact info yet, But P.F. Beck and his crew have said they are really looking forward to their third round as hosts.-ww





MGL vs Corvair ignition issue


In the past few weeks we had been going over an ignition issue with 650 builder and pilot Shayne McDaniels. His aircraft refused to run well on the points ignition.  He changed the points, went over the system, and even mailed it back to me to have it checked out. Just to be sure, he went over all the other systems on the engine to eliminate the possibility that he was looking at a secondary effect. The plane had been unused on the ground while he was doing some work on it and upgrading things in the panel, and the connection is not immediately apparent that the issue was being directly caused by his MGL disrupting the ignition circuit. Shane is a very experienced builder, and he had received the wiring diagram for the tach hook up from an MGL dealer. This wiring was directly responsable for the erratic ignition. When the connection was removed, the plane instantly ran perfectly. It had been a long goose chase.

Our conversion manual suggests never hooking the tach signal to the ignition. This is for good reason. If you are one of the people choosing to use MGL products, the correct solution is to use a sending unit to count bolts in the flywheel. Dan Weseman as a few sending units for this in his hangar. I am told that MGL even has a sending unit that would perform the same task. Either way, just because a company makes avionics doesn’t mean they understand ignition systems. You might think that they would be very reluctant to suggest a connection that was not tested, but it isn’t the case. I am not singling out MGL. Other companies have also made suggestions for tack signals that proved erroneous. As a builder, the best thing for you to do is choose a system that doesn’t connect to the ignition, (like the Stuart Warner tachs) or only use a system that has been proven over 100s of hours to work with the Corvairs ignition. Grand Rapids, MGL and Dynon are all successfully flying with Corvairs, but none of these are using the tach wiring that the manufacturers first recommended.

The above photo is Shane and Phyllis McDaniels’ 650 at Oshkosh 2011. The fantastic finish work was admired by legions of builders all week. This aircraft was the first amateur built Zenith 650 to be registered with the FAA. When a new model of aircraft comes out and the first one flying is Corvair powered, it speaks a lot about the popularity of the powerplant. This is the aircraft in which the MGL unit was interrupting the ignition.

In our booth at Oshkosh 2011, I stand with three pilots who flew in their Corvair powered Zeniths. From left to right, Shayne McDaniels who flew in a 2,700cc CH 650 from Missouri, Woody Harris in a 2,850cc CH 601B from California, and Andy Elliott in a 3,100cc CH 601B from Arizona. If you add in the time we put on our own 601, you are looking at 1,400 hours of ‘Zenvair’ experience. These aircraft have flown in 40 out of 50 states. We have several dozen other zenith pilots who have written their own chapter in this same story. In the eight years since we pioneered the Corvair/Zenith combination all the development and testing has long been done. Any issue that builders experience today is a case of an aircraft that isn’t of our standard configuration or is having a problem like the MGL tach connection issue.

In the foreground above is Dan Weseman’s Wicked Cleanex. Off his wing, Chris Smith flys the Son Of Cleanex. The photo was taken over a bend in the St. Johns River in North Florida in 2007. Dan’s aircraft used a Grand Rapids system, but Chris’s used an MGL. On the first flight of Chris’s plane, it had a very high oil temp indication, a very serious issue. It made little sense because Chris’s aircraft was a clone of Dan’s, and Dan never had oil temp issues. After investigation the issue was traced to the MGL unit set to read the incorrect value from the VDO sending unit. This type of issue can not happen with a mechanical system.  The MGL is a computer person’s idea of a good instrument. It can use many different sensors, but I prefer systems that are fool-proof and use high quality sensors.  Chris’s plane did not have the ignition tied to the tach, Chris and Dan made a system to have the tach signal come from a sender counting bolts on the flywheel. To be fair, most people who have studied MGL’s products agree that the things they make today are better thought out than the generation of things in Chris’s aircraft, but builders using them are still advised not to use any connection to the corvairs’s ignition system.


In the above 2007 photo, Gordon Alexander’s 3,100cc Pegzair complete and running had just passed its FAA Airworthiness Inspection. To understand something of Gordon’s sense of humor, its N-number is N129LZ. LZ129 was the Hindenburg. Gordon’s airplane was seven years of hard work in the making. Gordon brought the project down on a trailer from Minnesota to our old hangar in Edgewater, where he commenced a savage 14-hours a day for 100 days to finish it. Inspired by his commitment, Gus, Kevin and I each worked to assist him. Gus guided him through covering the fuselage. I built his motor mount, and Kevin did an enormous amount of work ahead of the firewall. It was the first Corvair powered Pegzair ever. This was probably the first corvair powered plane to have an MGL Enigma panel. I do not critique the company without firsthand experience with their products.

Our 701 testbed in the Zenith booth at Sun ‘N Fun 2010.  This aircraft was completed in our shop in 2007. It also has an MGL Enigma panel. In the weeks before the show, Dan Weseman and I worked to upgrade the aircraft with one of his 5th bearings. After Dan installed the bearing, the engine showed a drop in oil pressure. This kind of made sense because of the area of the additional bearing and the fact the engine was equipped with a stock oil pump. Changing to a high volume oil pump required pulling the engine and removing the rear case. After doing so, I was stunned to se the oil pressure was the same. Issue? The MGL sending unit had coincidently failed at the same time as the bearing was installed. I checked the system with a $19 mechanical gauge and found that there was never anything wrong with the oil system. It was $200 in parts and 9 hours of work wasted.

I mentioned this on a discussion group, and immediately found out that MGL has many ‘friends’ on the net. If you read the MGL site, the founder in South Africa has a lot to say which suggests computers and software may be a much larger passion of his than airplanes or flying. This resonates with a lot of high-tech computer people on the net, who are very quick to respond to any comment made about MGL, even if they have never met him, nor flown behind any of his products, or completed a homebuilt. One of my primary issues with MGL was they were selling a fuel flow sending unit that was made out of cheap plastic. The owner of the 701 had installed one, something that made me reluctant to use the plane at all. To any A&P, aeronautical engineer or experienced builder, selling a barbed plastic fitting in a main fuel line is indefensible. Most of the tech Computer people didn’t understand why this was an issue. The division on this is a good illustration of the two different mind sets between the groups.

People whose day job is in the IT world would be hard pressed to think of a person in their field who lost their life on the job. Yet, most mechanics and aviation professionals know several people who were killed in planes. Three of the four mentors in Grace’s flying were Ken Terry, Bob Bean, and Phil Schact. They were all killed in planes in the last 4 years. Phil, along with Bill Hess burned to death in Bills RV-8. Things I don’t know about computers are not likely to physically harm me. There are many things I try to share about practical aircraft construction that are bitter lessons, things people I knew and loved paid dearly for.

Most people know that I am a troglodyte who like mechanical gauges. I fully understand that I am a in a dwindling minority group. Most builders today like elaborate technology. It isn’t for me, but I fully accept that it is something that typical builders want. My only point is if you are in the latter group, you need to understand the issues associated with applying this stuff to your corvair powered plane, and you need to understand that the information you can trust will at times be contrary to the avionics peoples’ recomendations. Because I went to Embry-Riddle and I have worked with experimentals as a day job for more than 20 years, I personally know more avionics engineers than 98% of the people who will read this. If you work outside of aviation, let me teach you something: Most mechanics can fly a plane; Most pilots can change plugs or tires; Most ATC guys can navigate; Most dispatchers can forecast weather; Most linemen can start and taxi a turbo prop; Most glider pilots can hand prop a plane, and so on. As a general rule, people in aviation have an interest that exceeds their job description. While there are obviously plenty of avionics guys who know how to fly, build, navigate, or what ever, most people who work in aviation would gladly tell you that many avionics people think of the rest of the aircraft as a support system for the panel.

While this all may sound like mean poke at avionics guys, there is a very serious point here. If you are new to homebuilding you need to fully understand that avionics guys as a rule have the least appreciation for the bigger picture of things, in our specific case here, why shorting out the ignition on the noisy thing that makes the fan on the front turn might be bad. 

 One of my pet peeves about this is simple to explain; If we went to Shane McDaniel’s home airport and asked 10 aviators who were around and watched him spend many frustrating hours working on his plane what they thought the problem was, I am sure that 9 out of 10 of them would freely offer “the problem is that he has an old car engine in his plane.” There is little I can do to counter such misconceptions, and realistically, public relations for conversion engines isn’t a goal of mine. I don’t care what other homebuilders think of Corvairs. My only concern is getting reliable information to the builders who have chosen the Corvair as the engine that best fits their personal goals in aviation.