The engine displaces 620 cubic inches, has a compression ration of 6.3:1 and will run on 91/115 octane fuel. It is a notorious consumer of oil and fuel, particularly when operated at high power settings. It is a Russian designed engine, originally manufactured in Voronezh, Russia and is now manufactured in Romania. It was the engine of choice for several models of Sukhoi and Yak aircraft, along with the Kamov helicopter. More recently the engine is being used in the Pitts Model 12, the non-aerobatic Murphy Moose and the Radial Rocket. As a testament to its durability, rumor has it that the engine was also used to run irrigation pumps in Russia.
|Lower end assembly||BPE fuel injection nozzle|
|Stock Russian pistons (left) and BPE high - compression piston (right)||Nose case with BPE manufactured liner|
The M14 is a nine cylinder, mildly supercharged engine, with copious amounts of low-friction, roller, needle and ball bearings. In its original configuration, it was equipped with a complex carburetor, very similar to the Bendix PS-5 pressure carburetor. The engine layout is similar to U.S. radial engines, and as such is very damage tolerant and durable. The crankshaft is similar to the Harley Davidson motorcycle, in that it is a built up crank. The M14 uses a “pinch bolt” to secure the rear crank check to the crankpin, and this bolt is stretched at final assembly. The engine relies heavily on lock plates to secure the internal fasteners. The engine is also gear, and as such, the propeller operates at a different speed than the crankshaft at a ration of 0.658:1. Therefore, when the engine is running at 3,000 rpm, the propeller is running at just under 2,000 rpm. Propellers tend to be more efficient when operated at slower speeds, and they produce much less stress on the engine.
BPE electronic ignition controllers (left) and single
M14 mag /right)
Russian power settings are different than what American engineering manufacturers use, and the nomenclature can be confusing. Wide open throttle and maximum rpm for the Russian engine is limited to 5 minutes. Wide open throttle and 2400 rpm is referred to as Nominal (Nom) 1 power and is the maximum continues power setting, which is equivalent to 80% of the basic power. Nominal (Nom) 2 power is achieved with 32 inches mercury (Hg) and 2050 rpm. Nom 2 is used for climb and high speed cruise and equates to 240/360 or 66 percent power. Cruise 1 power is set at 29 inches Hg and 1860 rpm or 50% power. This setting is used for normal cruise.
The crankcases are forged aluminum; the nose case, which houses the reduction gear, is cast magnesium; and the accessory drive case is cast aluminum as is the supercharger housing (called induction housing.)
The engine is fitted with roller tappets, roller rockers, needle bearing rocker fulcrums, a generator big enough to run the city of Oshkosh (weighing in at a whopping 12 kgs) and a carburetor of which the pilot has no cockpit control of the mixture. The carburetor is an altitude compensating carburetor, which is equipped with an aneroid that is sensitive to ambient pressure. The engine is also equipped with two magnetos, one of which has provisions for feeding a spark through the distributor section for starting. The engine has an onboard air compressor to recharge the reservoir of air that is used to start the engine and supply motive force for brakes and flaps on some aircraft. The spinning system (air distributor valve, etc.) also forces some air through the lower cylinders out of starting sequence to help clear residual oil from combustion chambers and exhaust pipes.
The “blower” is a rather unsophisticated finned wheel that operates at 8.12 times the crankshaft speed in the –P engine at 10.0 times crankshaft speed in the –PF engine. The wheel is sealed and vented to atmosphere to prevent engine oil from entering the induction path, very similar to the Pratt & Whitney R-985 engine. The wheel is used to help atomize fuel as it enters the induction system as well as provide a slight amount of boost. Some of the parts that operate the supercharger are provided lubrication through very small orifices located in the induction housing and adjoining intermediate shafts. Much improvement could be done to the blower wheel as it is rather inefficient and robs the engine of power that is not returned to the propeller. Richard Goode, well known to most pilots in Europe, has provided such an improvement that boosted the maximum inlet pressure to 46 inches Hg at seal level, and the engine reportedly produces 450 brake hp (bhp) for an undetermined amount of time. The engine is known as the M14-R.
BPE ignition coil and high-tension
|Accessory case fully assembled|
Cylinder, Ports and Combustion Chamber
The cylinders are nitrided steel with high vanadium content of a standard bore of 4.1428 inches (104.97312 mm) diameter with a long skirt that barely clears the rotating system. The barrels have some choke that is achieve at assembly from the interference fit of the cylinder heat to the barrel. When assembled, the head is heated, the barrel is cooled and the two parts are joined and secured by a modified vee-type thread. The maximum overbore of the barrel is 0.008 inches (0.2032 mm) because of the thin nitrided layer. The thread is a modified buttress thread.
The combustion chamber is a true hemispherical shape with a case, flat-topped piston. The piston is fitted with no less than five rings, the compression rings being full keystone and a sodium cooled exhaust valve with a weird seat angle. The seat angle is 46 degrees, 15 minutes, and the valve is hard-faced and made from an investment casting. New parts are not currently available through current manufacturing sources. The guides are made from a bronze, and the exhaust guide is equipped with a scraper device to clean the stem of the valve. The engine itself responds very well to modifications to improve its performance and alter the fuel and oil consumption rate. One of the hot rod “tricks” that does not work is the porting and flow matching that has been prevalent on the flat engine scene for years. In fact, it sometimes does not work on the flat engines either. If one wishes to detune an M14 engine, just alter the ports. They are very crude and inviting, but they are the only thing in the induction system that can provide swirl to the incoming fuel-air charge.
BPE Modifications to the M14 Engine
In contemplating what modifications to make to the M14, BPE looked at three factors. The first is reliability and efficiency of the engine. Secondly, BPE considered parts availability and long term viability of the engine for consumers. Thirdly, who doesn’t want more hp? Normal oil consumption on these engines has been reported to be as much as 1 to 1.5 liters in two hours; 1 liter per hour during aerobatics and the brake specific fuel consumption (BSFC) varies with manifold pressure and rpm but exceeds 0.60 pounds/hp/hour at the higher power settings. With this fact in mind, BPE developed a piston and ring combination that was aimed to improve friction loss within the engine, improve the oil control, provide some “tumbling” to the incoming fuel-air charge and enhance the performance of the engine. The end result is a three ring piston with a rail-expander type oil control ring. The ring package is a very sophisticated design that has lineage to F1 and NASCAR use. The compression rings are quite thin, being 1.5mm and 1.0 mm thick. The second compression ring has a Napier hook for oil control. The oil ring is 3/16 thick and 11/8 thick when used with a nickel-sil treated cylinder barrel. The pistons generate a compression ration of 7.5:1. You may be asking, “What is nickel-sil?” This is a process of applying nickel to a cylinder surface to restore the bore to a usable dimension. Because nickel is a non-wettable surface, a silicon slurry is burnished into the nickel to provide oil “wettability.” It is not a new process – it has been used in Europe since WWII- and its use continues to this day in more expensive European automobiles. BPE tested the process on an M14 test bed engine, owned by BPE and used for design modifications and improvements, for 100 hours with temperature and power changes interposed in the test schedule. Nickel-sil is noncorrosive (i.e. it won’t rust) and was necessary because many cylinders which have been in service cannot meet the maximum overbore limitation of the nitrided cylinder. However, do not use standard rings in a Nickel-sil cylinder! And engine equipped with BPE pistons will typically use 1 liter of oil in 8-10 hours of operation at high power, much more in line with what customers flying horizontally opposed engine expect to see. The pistons are available with either the domed top, high compression or flat top, standard compression ratio.
|Low-tension ignition harness||Supercharger in assembly|
As most operators of the M14 engine have discovered, the engine has a very low temperature limitation. BPE discovered that most of the oil temperature is generated from the propeller reduction gear. It is handling over 600 foot pounds of torque through six pinion gears. BPE also knew that some race car drivers have oil temperatures issues with their gearboxes, so we made inquiries about how they were dealing with this and discovered they use a process called “micro-finishing” of the contact surfaces. BPE measured a set of pinion gears using the three wire method, had a set of gears micro-finished and measured them again. We were unable to detect any dimensional change with the process. A set of micro-finished gears give the appearance of chrome plating, a thing of beauty for any gear-head, and they lower oil temperatures considerably.
|Supercharger components prior to assembly||Reduction gear pinion cage|
There is a sleeve in the nose case that separates gearbox oil pressure from propeller governor pressure. This sleeve is subject to accelerated wear and will allow the governor pressure to “leak off” prior to controlling the prop with the result of a prop that will not stay in low pitch. The propeller begins to “hunt” and eventually becomes uncontrollable. The initial fix for the problem was a hard chrome and grind procedure. Although effective, the process was expensive and is no longer in use at BPE. BPE now manufactures a replacement sleeve that correct the problem. Please not that this part is not shown as a replacement part in any current parts manual.
As previously mentioned, new exhaust valves are no longer available through known manufacturing sources and serviceable parts are rapidly disappearing. BPE has a repair procedure using a hard chromed and ground stem to return to service otherwise unserviceable exhaust valves. This new process required a change in guide material that we have identified and tested on our “mule” engine and have parts in service in flying engines. This should alleviate some of the problems with exhaust valves for the current time. Sooner or later, someone will be faced with having to make some high quality exhaust valves for the engine to remain a viable, competitive power plant.
|Crankshaft assembly||Exhaust valve and guide|
Because of a limited ability to make field repairs, and a lack of availability of parts (the carburetor facility no longer even exists), BPE began to employ fuel injection in its M14 engines. We knew the carburetor was somewhat restrictive to inlet air flow, and we knew from previous experience that a certain model of the Airflow Performance fuel servo was very satisfactory, so we contacted Don Rivera at AFP and arranged for an FM-300A servo and the necessary adaptors for a trial. This servo is very satisfactory for operation of the M14, provided it is properly jetted and has a proper air inlet to the servo. One drawback to the system in its original configuration is cold weather operation at high power settings. In these conditions, fuel does not evaporate well and collects by gravity in the induction housing in droplet forms, forcing the lower cylinders into an overly rich state wherein combustion will not occur. BPE, in association with others, developed a nozzle that greatly improves the fuel distribution within the engine, produces more power and results in more uniform engine temperatures. This nozzle has been thoroughly tested, flown on numerous engines and is available only through BPE.
The fuel injection system requires higher inlet fuel pressure, and BPE manufactures a fuel pump spring that allows the higher pressure of 35-40 psi.
The magnetos for the M14 engine are very reliable, although quite heavy. Magneto parts have been historically difficult to procure. The deal with this issue and provide an improvement, BPE developed electronic ignition. A full review of the product requires more space than available here, but the system coil near plug type, uses 14 mm automotive spark plugs of the proper heat range, is easy to install and maintain. The system has an advance curve tailored specifically to the engine and is approximately 20 pounds lighter than the Russian mags, conduit and harness and is self supporting. Once the engine is started using batter power for the ignition, the system will provide its own power from an alternator enclosed in both timing controllers. It uses no parts of the Russian ignition system. The high-tension wiring is spiral-wound, low-impedance and radio frequency interference (FI) is nonexistent. The system replaces both magnetos and is weather resistant. Cold temperature starting is vastly improved. Provisions are incorporated in the time controllers for electronic fuel injection to be developed at a later point in time.
BPE has designed and constructed a dedicated test cell for the M14 engine program. It is a propeller loaded test cell which has the capability of measuring reaction torque. Once the torque and speed are obtained, the BHP is calculated by the product of torque and speed divided by 5252. Brake specific fuel consumption is calculated by dividing the weight of fuel consumed per hour into the BHP. For the BSFC to be entirely accurate, the fuel temperature must be a known factor. A fully modified M14 produces between 430-440 BHP corrected.