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The Corben Ford "A" Conversion

by O. G. CORBEN

From the October 1935 issue of Popular Aviation

This is the story of the Ford "A" Engine used with such success on the Corben Super-Ace. It really is a fine looking job and runs very sweetly in flight.

TAKING for granted that there are still a couple of you readers who venture to keep up with these articles, I will dash off a few lines on this trusty invention of Mr. Underwood's and try to explain just what to do in order to convert the old Ford motor into a suitable powerplant for your Corben Super-Ace sportplane.

For those of you who have not already secured a motor to convert, I will say that any old Ford Model A motor, which you may pick up at a used car junk-yard, will be okay providing it is in fair shape. By that, I mean, there should be no cracks in the block and the cylinder walls should not be in too bad condition. Make sure that the crankshaft is not out of round, if the cylinder is out of round it should be reground and oversize pistons installed.
The motor, on which we have done all of our experimenting, saw a good many thousand miles of service before it was given a few aeronautical monkey glands and hung on the front of the Super-Ace and I assure you that she is a sweet running motor despite her old age.

The parts taken from the original Ford motor are the block, crankshaft, camshaft, valves, timing gears, tappets, connecting rods and pistons. If you desire to have a real motor it will almost pay you to buy these parts new, from your local Ford dealer (I should get a commission after that, from Mr. Ford, however I think that he has made it possible to rig up a cheap lightplane motor so I will call it square).

I know that some of you will have several ideas which you would like to see incorporated into the motor, so that will be up to you. The plans herewith shown are the same as we have used in converting our motor which has been flown over 75 hours to date without the slightest trouble of any kind, and if the plans are carefully followed, you will have the same successful results with your motor. However, if you have any pet ideas to try out on your motor, hop to it for there is always room for improvements on any aero engine. You will note from the drawing there are quite a few special aluminum castings used in our conversion. As it would be by far too great an expense for you to have patterns made for such castings, you can buy them at reasonable prices. For further information write me in care of the Corben Sport Plane Company, Madison Airport, Madison, Wisconsin.

In view of the fact that the cost to make up their own castings, etc., would run into quite an outlay of cash, we will not take up a lot of space with the details of them and give you only the dope on the assembly of the parts and plans on the regular Ford parts that require changing, such as the crankshaft, camshaft and oil system, etc.

I believe that the drawings will give you most of the details required, so it will not be necessary to cover all of them here. The crankshaft will be the most difficult part and unless you have a drill press, I think it would be best to take the shaft to a machine shop to have the drilling and machine work, done. The shaft is case hardened and it is quite a job to drill it without the proper tools, drills, etc. The end of the shaft is machined out to receive the stub shaft which is a press fit held in place with a key. The rear of the shaft is machined to take the magneto and water pump pulley. All of this detail is clearly shown on the drawing.

All that need be done to the camshaft is to turn off 1/8 inch of the timing gear and attach the tachshaft connection as shown.

The oil system is high-pressure to all bearings and the Ford oil-pump is replaced with a Chevrolet pump. It will be necessary to, do a little machine work on the pump shaft so it will fit into the Ford block. The reason for changing pumps is that the Ford pump must be run submerged in oil, while the Chevrolet pump is of the vane type and has better pressure for force feed. This pump may also be set up in the block, making it much easier to make up the crankcase pan. The oil is piped to the main bearings as shown and then carried to the connecting rods through the drilled holes in the crankshaft.

It is necessary to plug all holes in the connecting rod bearing caps as well as old oil holes in the main bearing top halves. You will note the oil is piped to the oil pressure relief valve located at the front of the block, the oil then flows back through the valve chamber and into the pan. We found it necessary to have some kind of heater on the manifold and after much experimenting we arrived at the oil heater shown. This saves much weight and is very efficient.

The cylinder head is of our own design and has proven out very well. It is designed to eliminate all steam pockets and is reinforced to keep from cracking under constant high speed, however, the old cast iron head may be used but will add quite a few pounds to your ship and in such a case it will be necessary to cover up all the water pump holes and use the side type pump, for we find that the regular Ford pump does not circulate the water fast enough to keep the motor cool without the use of a large radiator.

The magneto used on our motor is driven by a rubber connection which not only compensates for any misalignment of the magneto but also allows for very fine timing. The water pump as you will note, is set to one side of the motor. This pump is of our own design and made of cast aluminum and will pump 45 gallons per minute which aids the cooling. The pump is driven by a V belt running from the pulley at the magneto coupling.

You will run into trouble trying to use the Ford type pump in the head in connection with the low radiator, so we recommend that you install the special pump.

Sheet aluminum is used for the crankcase pan. 20 gauge is used for the sides and the ends are made of 1/8 inch. The pan is formed and welded as shown after which the side is hammered out for the oil pump. Steel straps are used as flanges where the pan bolts onto the block.

The special oil relief valve is made up out of a standard Tee oil line fitting with a ball check and spring, using a screw for adjustment to obtain the proper oil pressure which is 30 pounds when the oil is warm.

In the next and final article we will give you the last details for completing your ship and installing the motor. While you will find that our motor conversion works out well in every detail, it is possible to use a motor conversion such as used in the Pietenpol, however, these motors weigh quite a little more and it is necessary to make the proper changes in the ship for the correct balance, etc., therefore, we recommend that if at all possible, you stick to the conversion that the Super Ace was designed around.

The original drawings from Popular Aviation, October 1928. Click on the thumbnails for a lager view.
Note: The larger files are large!