2013 Franklin 1 New

7/17/2019 2013 Franklin 1 New

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Getting the Most from the Franklin engineBy Steve Brousseau

From its very beginnings in the Bell 47 helicopter, the Franklin engine has been the target of criticism for amultitude of reasons. It is generally viewed as being underpowered and difficult to start (especially in coldweather). Bell 47D, D-1, and Bell 47G owners often complain about oil leaks that are difficult to detect andstop after tireless efforts.

When the military began with the 47D in the late 40s with the H-13 designation, helicopters were new andunfamiliar to the mechanics faced with the challenges to keep them flying. It took considerable time formaintenance personnel to get the required training and experience on how to maintain helicopter engines. Whileit generally agreed upon that the military had to come up to speed quickly with helicopter technology, time andexperience were not on their side. When the Korean War broke out in June of 1950, the Bell 47’s Franklin enginewas quickly put to the test under combat conditions, along with the typical wartime problems with spares,supplies, and lack of experienced personnel. As a result, these problems contributed to an overall lacklusterreputation of the Franklin.

When properly maintained and understood, the Franklin engine is a solid and reliable power plant for the Bell 47.From one Bell 47 to the next, each engine has its own idiosyncrasies. If you are an owner or operator, there aresome simple and low cost solutions that will allow you to get the most from these engines. As both an owner andoperator, I have found answers that deal with some of the issues that are most often the subject of conversation

around the Franklin, as covered in this article.

Bell 47G with Franklin 6V-350, 235HP engine (Photo by Steve Brousseau)

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Franklin engine models

The Franklin engine came in several versions rated from 178HP to 235HP. Model numbers and power ratingsinclude:

• 6V4-178 at 178HP

• 6V4-200 at 200HP

• 6V-335A at 210HP (as used in the Bell 47D, D1, G, and H)

•

6VS-335 (turbocharged 210HP version used in Bell 47G3)• 6V-350A at 235HP (upgraded 210HP; Bell 47 “ Super G” with retrofitting to earlier models)

The remainder of the article will cover the common issues and solutions:

• Oil system and points of leakage; oil consumption, oil pressure, oil filtering

• Valve cover variations and recommended gaskets

• Starters and starting techniques

Oil system and points of leakage, oil quantity, consumption, pressure, and filtering

No aircraft engine should leak, but Franklins do leak in varying degrees! No matter how small the leak, once theoil sprays around the engine in flight, it’s hard to tell where exactly it’s coming from. There are three likely places where oil will escape:

1.

From the manifold crossover drain located between the oil sump and the accessory case.2. From the engine breather hose located below the engine cooling fan, and3. From the valve covers, with or without oil drains, covered in the next section

The photos below show these parts of the engine.

Manifold crossover drain behind brass fitting (Photo by Steve Brousseau)

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Engine breather hose (Photo by Steve Brousseau)

About the manifold crossover drain

The presence of an open drain on the manifold crossover has raised a number of questions as to its real purpose.According to engine experts, the purpose of the drain is to discard excess fuel from the manifold at startup. It isalso associated with the oil pressure relief and must be removed if an oil pressure adjustment is required. Anover-primed and flooded carburetor will expel the fuel to the low point in the manifold and subsequently drainout. In the Franklin, however, residual oil that seeps from the oil system will also find its way here. This drain isintended to stay open, as it is very narrow in diameter and will have little or no impact on the induction system.

There is also some question as to whether the drain should “self-seal” at startup via a check valve (a small ball inthe drain assembly that seals the outlet). Other engine owners actually have the drain capped off with an AN-typefitting. Once the cap is removed, the drain then allows oil and/or fuel to escape, if present. On Lycomingengines, the manifold crossover uses an AN-type fitting with a check valve. At engine startup, the valve closes.At engine shutdown, the valve opens and allows fluid in the pipe to escape.

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If the drain uses a fitting larger than the one originally called for, a “lean condition” would exist due to theadditional air entering the intake manifold. To compensate, the carburetor would need to have a mixture settingon the rich side to compensate for the air vacuum entering the open drain. If the drain is capped off and closed,the opposite would occur and a possible “rich-condition” would exist. Slowing pulling on the mixture lever atengine shutdown will normally indicate if the engine is going to a lean mixture as the engine RPM will increase between 50 and 100 RPMs. If there is no or very little change, then the engine is running excessively rich.Removing and examining the spark plugs will reveal this.

If your engine has the drain valve permanently capped off, fuel and oil will build up in the crossover pipe,requiring that you open the cap on occasion to allow fuel and oil drain off.

Oil quantity

Another interesting detail has to do with how much oil you added to the sump. If the sump of overfilled, even byas much as a quart, the engine will discharge the excess oil through the engine breather hose. As a general rule, ifyour engine calls for 10 quarts at the oil change interval, the stick should read in the “9” vicinity on the stick afterinitial run up. Subsequently, keep the level at 9 quarts at every pre-flight. In the case of the 6V-350, which callsfor 8 quarts at the change interval, the stick should read in the “7” vicinity on the stick and maintained there.

When I originally acquired my Bell 47G (with the 6V-350), I made the mistake of continually adding oil to the8-quart level on the stick. After flights, the center frame and tail boom required extensive cleaning to remove the“blown-out” oil. At the 7-quart level on the stick, 8 quarts would drain into the oil pan at the change interval.After learning this lesson, the oil blowout stopped and I now fly with a clean engine and center frame.

Oil pressure and consumption

The Franklin manuals indicate an oil consumption rate for each of their engines. For example, a consumption rateof ½ -pound per hour indicates that after every hour of flight, the engine consume approximately a half-quart ofoil. In my experience, this is absolutely true. A Franklin engine, like most aircraft engines which are of a vintagedesign will consume oil. As oil is consumed, oil pressures will begin to decrease. For example, if the sump isdown one quart, a normal reading of 60 PSI at 3100 RPM will show between 50 and 55 PSI with less oil in thesump. Similarly, the engine idling oil pressure will be less. If 35 PSI is normal pressure at idle with a full sump,

the reading will be less if the sump is down one quart.

On cross country flights involving multiple stops over three hours, I carry an extra quart of oil in my flight bag.Remember that unlike the later 47s with the Lycoming engine, the Franklin has no reserve oil tank. So unless youcan buy aviation grade oil at your destination, it is a smart practice to bring a quart or two along with you.

Oil filtering

The Franklin engine has a marvelous oil filtering system that uses a layered pancake series of screens enclosed ina sealed funnel-shaped canister. This is far superior to the oil screen used in the later Lycoming engines.However, at the oil change interval, it is a good idea to inspect the condition of the crush gasket on the bottomretaining nut. A kinked gasket will result in oil leaks. The gaskets only cost a few pennies from your airport

maintenance shop.

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Oil filter on lower right; angled breather hose in foreground; note the drop of oilhanging at the tip of the hose (Photo by Steve Brousseau)

ADC, Inc. produces an oiling filtering kit that you can add to the Franklin, installed just aft of the oil cooler. At$900 or so, it is an outstanding design with an extremely fine micron-type filtering screen. This provides anadded measure of filtering and a state-of-the-art design. It is popular with the Lycomings (due to the poor filteringdesign on the VO-435.) ADC does make an oil filtering kit specifically for the Franklin. ADC does run ads in publications such as Trade-A-Plane containing their product and contact information.

Valve cover variations and recommended gaskets

There are two valve cover designs available for the Franklin: those with and those without oil drain outlets. The

purpose of these drains is to allow oil to return from the valve covers back to the sump. Without the drains, oilwill settle in the covers and cause smoky engine starts as the oil is burned off. Some engine experts claim thatimpurities captured by the oil and leading to acidity can cause damage to the valve guides and create valve train problems. A Franklin engine expert might be able to provide additional information.

The drain-equipped valve covers are getting hard to find, since top valve cover only requires a downstream drain.The original fittings at the sump are also difficult to locate, but suppliers like McMaster and Carr have angledfittings that will work.

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Valve covers with oil drain pipes (Photo by Steve Brousseau)

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Lower valve cover with return line to sump (Photo by Steve Brousseau)

Real Gaskets of Tennessee manufactures FAA-PMA valve cover gaskets for the Franklin. These are similar tothe rubber canning jar gaskets that my grandmother used to use every fall when canning tomatoes and peaches forthe winter. They are resusable and provide an excellent seal around the valve covers. If your existing covers areleaking, then you need to replace them with RG-17727 from Real Gaskets. They have a Web site atwww.realgaskets.com. These are best gaskets that I have ever used.

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Standard valve cover gasket on left; FAA-PMA gasket from Real Gaskets on right(Photo by Steve Brousseau)

Engine starters

The original engine starter for the Franklin engine uses a very antiquated design found in cars, trucks, and tractorsmanufactured in the 1930s. This design requires a combination of foot pedals, cables, and pulleys that make up amechanical solenoid for energizing and turning the starter. When the foot pedal is depressed, an actuator lever onthe starter is pulled to make contact with electric push button that closes the 24V circuit, allowing power to flowfrom the battery and circuit relay to the starter. During this sequence, the starter bendix drive moves up toengage the engine flywheel and turn the engine for starting.

While this system is generally reliable, it is obsolete by today’s technology. In the event of an engine failure inflight requiring an autorotation entry, any attempt by the pilot to restart the engine would require moving his right

foot from the flight pedal area to the rear of the box beam to engage the starter pedal. However, because thesystem uses dual pedals protruding both sides of the box beam, a co-pilot or passenger present could assist byapplying the left foot to the starter pedal, leaving the pilot-in-command free to control of the aircraft.

The stock starter with the Franklin is the Delco-Remy 1109662. With the introduction of the turbochargedBell 47G3 using the Franklin 6VS-335, a fully electric version of the starter was installed using the Delco-Remy1109697. This eliminated the obsolete starting pedals and cable system of the mechanical solenoid.

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Delco-Remy 1109662 mechanical starter on left; Delco-Remy 1109662 converted model1109697 electric starter (Photo by Steve Brousseau)

Original Delco-Remy 1109697 electric starter (Photo by Steve Brousseau)

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Bell 47 D, D1, and G helicopters can be upgraded to use the electric starter by adding an starter key to aconvenient location in the cabin, or by even upgrading the collective control with the late style G2 starter buttonand landing light box. Following the electrical schematic from any one of the later Bell 47 helicoptermaintenance manuals will guarantee the proper electrical connections. Additionally, you will need to remove themechanical pulley tabs from the short cross tube immediately forward of the solenoid for adequate clearance.

Another interesting point concerning the Delco-Remy starter is that it has an oil drain plug. This gives you the

option to drain the old oil from the Bendix drive starter well at your oil change interval.

Aviation-grade oil drain plug on Delco-Remy 1109662 (Photo by Steve Brousseau)

If you are interested in more information on the electric starter conversion, please contact me at the e-mail addressat the end of this article.

Engine starting techniques

All Franklin engines are different in some way. This is especially true when starting the engine. Franklins arevery sensitive to outside temperatures and a difference of a few degrees can make the difference between an easyand a hard start. Generally, two full rolls on the throttle and a 45-degree roll will do it under ideal temperatures.But in cold weather, preheating is must, so be prepared to lower the carburetor heat lever to act as a choke duringstarting. I use a 115,000 BTU industrial job site kerosene heater to get the engine intakes warm before rolling thecopter out of the hangar. Even a pre-heat of only five minutes is enough to prepare the engine for an easy start onthose cold winter days.

Every Franklin requires its own starting technique. With a little practice and experience, you’ll quickly figure outthe required starting technique for the outside air temperature on the day of your flight.

And one final tip

These old engines require as much lubrication as possible from the 100 octane low-lead fuel that we use today.There was a time when aviation gasoline had far more lead in its composition for valve and valve guidelubrication. Use discretion when leaning the engine, as significant leaning can lead to valve problems and majorengine repairs.

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About Steve Brousseau

Steve owns and operates Bell 47G-2A1 (N1380X), originally a G-3B1, and Bell 47G (N140B), originally a Bell47D-1, out of Fitchburg Municipal Airport in Massachusetts where he is an Airport Commissioner, member of theFitchburg Pilots Association (EAA Chapter 1454) flying youngsters in his Bell 47s as a flight leader in the EAAYoung Eagles program., as well as promoting aviation and the Bell 47 at charity and fund-raising events.

Steve is also a Gold Member of the Bell 47 Helicopter Association and a member of the New England HelicopterCouncil.

For additional questions or comments, contact [email protected]. .

Other articles:

• Running the Texas No-Bar Kit

•

Selecting the Bell 47

• A short history on N140 Bravo

Disclaimer: The information in this article is the result of years of research, studying Bell 47 parts andmaintenances manuals, service instructions, airworthiness directives, technical bulletins, as well as what I haveexperienced first hand. I believe the information to be accurate to the best of my knowledge and should only beused as a set of evaluation guidelines (things to look for) when considering the purchase of a Bell 47 helicopter orrelated components.

This is an information-only copyrighted article and is not to be copied or used without my express writtenconsent. Photo credits are used.

2013 Franklin 1 New

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