One of the first questions people ask when talking about Twin Navions is "What kind of engine does it have?" It's a natural question. Most think there's a Lycoming O-360 tucked inside those cowls. Close, but not quite.

This article focuses on the TEMCO-Riley D-16A, since it's the one powered by the most obscure engine. The D-16 uses an O-320 and the Camair 480 uses a six-cylinder Continental O-470 and there are tens of thousands of those working around the world.

Background:

Let's first explain where the O-340 came from and why it's so closely connected with the Twin Navion.

Engines used on the X-16, D-16 and D-16A Twin Navions:

O-290-D
125hp @ 2600 rpm
type certificate E-229

O-290-D2A
140hp @ 2750 rpm (135hp max continuous at 2600 rpm)
type certificate E-229

O-320-A1A
150hp @ 2750 rpm
type certificate E-274

O-340-A1A
170hp @ 2700 rpm
type certificate E-277

When Roger Keeney and his team of engineers began working on the first Twin Navion conversion, they approached the four major engine manufacturers of the day; Lycoming, Continental, Jacobs and Franklin. The last two were closing shop, and Continental was concerned more about how their image would be affected should they decide to support the group's effort. Only Lycoming supported the group, and they were willing to bend over backwards to assist.

The team decided it would be quickest, and easiest to take an existing engine installation and incorporate it into their Twin Navion. Have you looked at those early D-16 photos and thought, "That cowl looks a lot like a Super Cub?" That's because it was. They pulled out a parts catalog for the PA-18 and ordered two of everything from the firewall forward. The engine happened to be the O-290-D.

The X-16 had zero single engine performance, and the first thing Jack Riley did when he bought the rights was to increase the power. To do so, they installed 140hp O-290-D2A engines. They still used the Super Cub cowls. Although performance improved, you could only hold about 1,000 to 1,500 feet if you were at sea level.

Other boosts came when they replaced the fixed pitch propellers with variable pitch units, and later fully feathering constant speed units.

In early 1954, a second attempt was made to boost performance, and finally register single engine performance when Riley Aircraft installed the 150hp Lycoming O-320-A1A. Again, the performance improved, but not to the 5,000 foot single engine service ceiling that Jack Riley was pushing in his sales.

When TEMCO-Riley began working on upgrading the D-16 to the D-16A, they too wanted to increase power. Here's where the story of the Lycoming O-340 begins.

With the D-16A program, Jack Riley had the chance to finally meet the 5,000 foot single engine service ceiling. To do so Riley approached Lycoming and asked them to supply a more powerful engine. Their response was to apparently show him their concept drawings for the 180hp O-360. It was exactly what Riley wanted. The problem was it was still years away from production. An interim solution was to upgrade the O-320 line. Taking a narrow deck O-320, and adding longer barrel cylinders. A longer stroke on the piston connector rods increased the compression to 8.5:1 and an extra 20hp was obtained.

Although the O-320 and O-340 engines were very similar, the O-340 was just a little wider. The solution was to simply widen the D-16A's cowlings.

When the first D-16A began flight tests for its certification in May 1954, only one O-340 had been built. It was partnered with an O-320.

Since the O-340 was the most powerful engine in Lycoming's four-cylinder line, a number of other aircraft manufacturers selected it to power their aircraft. The O-340-A1A engine (approved July 1954) used in the D-16A is the basic model. The -A2A (January 1955) has no provision for a hydraulically operated propeller. The -B1A (November 1956) lowered the compression to 7.15:1 and developed 160hp.

Some examples of aircraft using Lycoming O-340 engines include:

• Oakland Super V
• Brantly B-2 and B-2A helicopter
• Cessna 170 (STC - KWAD Company)
• Piper Apache (STC - McKenzie Flying Service, Inc.)
• Various homebuilt aircraft

Operating the O-340:

The O-340 behaves no differently than either the O-320, or the O-360; it's still a carbureted four-cylinder, horizontally opposed engine. Unlike some earlier piston engines, it produces full power, 170hp continuously.

Maintenance:

As it's been mentioned before, the O-340 is no different than either of its O-320 or O-360 brothers. The same goes for the care and maintenance. The difference is in some of the unique parts used.

Some of the parts/modifications unique to the O-340 are:

• Larger center and rear crankshaft bearings.
• Larger bearing chambers in the crankcase, making it a -30 case.
• A unique crankshaft.
• Shortened connecting rods.
• Shorter connecting rod bolts (can be cut down from longer bolts).
• Unique air intake pipes, caused by the step down between cylinder and crankcase.
• Longer push-rods and push-rod tubes.
• Carburetor limited to prevent full throttle.

Parts Catelog:

Textron/Lycoming O-340 Parts Catalog

Alternatives:

Should someone be unable to find parts for the O-340, there are a number of alternatives that could keep their plane flying.

Lose 20hp:

There are two D-16s that have had their O-320 engines modified to produce 160hp. They use the same engine mount as the D-16A, and see a reasonable improvement in performance over the 150hp Twin Navion.

Down grading from 170 to 160hp shouldn't cause any problems, although performance will drop slightly.

Add 20hp:

As my father had originally attempted in 1975, upgrading to the 180hp O-360 engine would be an ideal solution, and a nice boost in performance.

Since the Twin Navions don't use a dyna-focal engine mount, one would have to look for the same engine installed in the Bellanca Scout, the O-360-A3A2.

We understand that the cowls were designed to cool a 200hp engine.

An Uncertified Option:

Engine Components, Inc. (ECi), is making two new versions of an O-340, based on their PMA'd O-320. Although the displacement is the same, there are major differences. First of all, the ECi O-340 is uncertified. Their added displacement comes from a modified piston rod.

ECi says their O-340 puts out either 177hp or 185hp. Either one would give a nice boost in performance.