Monday, May 2, 2016

Finishing the Engine

Last of the engine work

The engine was essentially complete last November, but individual accessories and the ignition system needed to be completed. This along with my work schedule plus planning for retirement left little time for serious work. But we got some done anyway.

Since then, the starter was sent away for overhaul, the ignition wires were made up and installed, the timing of the magnetos was set, and the pressure output of the fuel pump was set.


First, the ignition wires:  Each wire is a different length, and the length varies by a significant amount.

The trick is to go “by the book” plus a couple of inches to insure enough wire to strip and cap at the mag end, and enough to install a spark plug coupling at the other. This also assumes enough slack to route each wire around the rear of the engine. But ignition wire is not cheap, even in bulk, so avoiding waste is also a consideration. The spark plug ends have these nifty little 90º guides which alleviate stress on the wire.

The spark plug fittings must be matched to the type spark plugs in use. I decided to go with the surplus “tank” plugs which are available in abundance vs. the modern aircraft plugs which run about $27 each. I heard about a retired Delta pilot who wished to sell his supply of tank plugs, so I gave him a call. He just wanted to get rid of them for what he paid…50¢ each!! So, I now have a lifetime supply of new (surplus) plugs for less than the cost of one AC or Champion plug. According to Jim, they are just as good. I’m happy with that.
The wire we used is shielded, which means there is a braided steel layer around the central conductor, separated by insulation. There is a layer of rubber on the outside which is blue. They really stand out. The braided layer is stripped back enough to allow only the insulated conductor to run from the wire guide to the mag block or the spark plug.

Spark plug end:  The ends of the wires have the shielding stripped back a certain amount and a “cigarette” attached to the end. These cigarettes are just a hollow cylinder made of non-conductive plastic, with a metallic hole in one end and a spring attached to that end. The conductor is inserted through this metal hole and soldered in place. The spring provides a cushion for the conductor to make contact with the center of the spark plug, and the cap is screwed onto threads on the end of the plug. The end where the wire enters the guide has a screw-down clamp that traps the braiding. These were not such a good fit, so Jim machined a whole set of custom wire clamps on his lathe while I was on a trip. Bless his heart! They work perfectly, of course. After leaving the spark plug, the wires are routed through a tube that keeps them all together as they travel around the engine toward the magneto. After careful consideration, I decided that the guide tube would probably interfere with my planned cowl arrangement, so I removed them and took the tube off the engine. I’ll use spiral wrap, or some other product to bundle the wires and keep them a little lower so as to clear any future fabrications.

 The magneto end:  On top of each mag there is normally a hard rubber block with seven holes through which the ignition wires enter the mag  block. On these mags, we used an aluminum cap with a small section cut from the bottom which bolts to the main section trapping the shielding thus grounding it to the mag case.

The ignition block within the mag accepts each wire into a hole where the conductor is captured and the circuit is completed. This is done via a copper cap crimped to the end of the wire. the cap end is inserted into a hole for that cylinder and held in place by a pointed-tip screw that pierces the copper cap completing the circuit. Each wire has to have the shielding stripped from a precise point allowing just enough wire to enter the mag block at it’s location because once the cap (with all the wires in place) is attached to the top of the mag there is no room for movement of the wires. It is a very tight fit. Jim actually has a rubber cap with the proper lengths of wire sticking out to use as a guide.

All Done!

Setting the magneto timing is very straight forward, much like any other airplane engine. The difference here is that one mag is set to 29º before top dead center (BTDC) and the other is set to 31º BTDC. Of course, Jim Friedline has all the tools and accouterments necessary to do the job.

It was just a matter of finding TDC for the number one cylinder and backing off to the proper setting using a gauge installed on the crankshaft. The magneto is then rotated to the “firing position” and the hold-down nut tightened. This procedure actually involves some back-and-forth adjustments from the crankshaft to the magneto. A red light on the timing box (attached to the mag) illuminates when the mag is in firing position. Of course, there will always be a bit of backlash that must be dealt with, but by working “forward and back” that is averaged out.


Also, during this period since the last update, I was able to acquire a tachometer and send the old instruments off for overhaul. This tachometer is very special for this reason: when I acquired this project, a friend of mine (Van Thurston) gave me a tach face that has the Travel Air logo on it.

This was one of a group that he had silk-screened years ago. It was perfect! What was needed was a tach to put it in. This face is for a Jos. Jones tach and I wasn’t sure I’d be able to find one.

Enter Brian Karli, who built the Jenny that resides at Candler Field Museum. He had one and sold it to me for what he had in it! To say I was thrilled would be an understatement. This panel will be great, with period gauges and materials. I can’t wait to get to that part of the project. This is one thing that really stands out on an airplane like this. Keystone Instruments in Lock Haven, Pennsylvania will do the work.

"Height"  Isn't That Cool?

They also have my mag switch, altimeter (Zenith non-sensitive), and bulb-faced compass. Actually, I have two of these compasses; one of which is only good for parts.


The old inertia wheel starter I bought from Jim Friedline needed to be taken apart, at very least for an inspection. I soon realized this was beyond my capabilities, so I went searching for an overhaul shop. Needless to say, there aren’t a plethora of facilities out there doing this sort of thing. I was told of a shop in Kentucky that does good work and was able to overhaul this starter. I spoke with them on the phone and boxed up the heavy beast for shipping. It is heavy! After it arrived, I got a phone call telling me they couldn’t do that model because they didn’t have the proper manuals. Great. They did recommend a shop in Tulsa, and they were kind enough to send it back. I never even removed it from the shipping box, just sent it along to them.

When the starter came back from overhaul, I set it into place on the back of the engine to check clearances. This starter is an inertia wheel type with an accelerating motor built onto the back. These starters are period correct for this vintage airplane, give or take a few years. They also sound very cool starting. You first engage the motor which spins up the inertia wheel, then engage the wheel to the starter lug in the accessory case via an electric solenoid turning the engine. A simple inertia starter has a lug into which a handle is set and using muscle power, you spin the inertia wheel up by hand until it reaches the proper speed. This is done by ear. Then you pull a handle that engages the wheel to the engine. The motorized starter also has this hand crank lug as a backup in case of a dead battery or a bad motor. Most Stearmans have this handle lug on the left side of the fuselage, but mine will have to be on the right side due to clearance issues between the magnetos and the solenoid. An extension is required from the starter to the lug on the outside of the fuselage. Luckily, I have one in a box. It’s old and dirty, but it will work.


The fuel pump I bought from eBay and overhauled, is a very robust unit capable of quite a high output. But for this installation, I had to make sure it would not put out more than about 3 psi. This is the maximum pressure for this carburetor, since that is the pressure at which the fuel would overpower the float mechanism (which shuts off the flow of fuel into the carb bowl) and lift the shutoff valve from it’s seat, thus overfilling the bowl. There will be plenty of fuel sucked into this engine—I don’t need it being dumped overboard.

So we set up a pressure gauge and some tubing, along with a drill adapter to spin the pump. This pump is adjustable via a spring loaded screw that puts pressure on a bypass valve within the pump. When I began to spin the pump, it was putting out around 5-6 psi at the low end. I finally figured out that the spring under the adjusting screw was too strong and was putting too much force on the bypass valve, not allowing enough fuel to circulate around the pump vanes. I replaced this spring with another one I had in a “bag-o’-springs” bought years ago, but seldom used. Success. The pressure is now adjustable down to around 1.5 psi. I set it at 2 psi. This should be enough to supply fuel in any attitude. Now the pump can be installed and safetied.


This next step in the engine saga will be to remove it from Jim’s fixture and relocate it to my hangar. I sure would like to test run the engine before installing on the airplane, but this will require some engineering that I don’t have time for presently. We shall see.

When the day arrived to transport my engine home, Jim and I stood looking at the thing and realized there were just a couple of minor things left to accomplish. The tubing that connects the lower cylinder’s valve housings had to be installed and a few nuts had to be tightened with pal-nuts securing them. There always seems to be one more item. I had brought my trailer to Jim’s shop a few days prior, but a few of those “last” items set us back. On top of that, I had to leave for a trip (gotta pay for it all).

Now, with no more to do, the head scratching began over how best to get the 500 lb. beast out of his shop and onto my trailer, which was situated in the main hangar. Luckily, Jim has a chain hoist mounted on a rail with a handy little door that opens into the hangar.

Unfortunately, the little door is just that…too little to move the engine through lifted horizontally. It had to be lifted vertically to fit through the door, then swung horizontally again to set on the mount. This is the same mount on which the engine was removed from it’s last airplane. I just made a dolly, of sorts, from some scrap 2x6s with casters to make moving it around easier.

This whole process took the better part of an afternoon, but we eventually got the beast on the mount and lifted onto my trailer. The moving procedure was nerve-wracking to say the least, since any mistakes, bumps, or drops would render the last year’s work useless. Dropping a newly overhauled 1942 engine would have wrought wailing and gnashing of teeth.

The drive home was no less stressful, with the engine securely strapped to a trailer, but very top-heavy. Upon arrival at my hangar, I secured the engine from a chain wrapped around the front-end loader of my tractor, lifted it a few inches and drove it slowly into the hangar. Once it was sitting safe and secure on my hangar floor, I finally breathed a sigh of relief and had a beer. Or two.

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