To break-in an engine means to introduce all of the new moving parts to each other in such a manner that the contours of the metal matrix of the new mating surfaces form a compatible relationship with the adjacent surface. This relationship provides the least amount of wear with the best interaction of the two surfaces.

The basic procedure for the break-in of reciprocating engines concerns itself with the seating of the rings. In steel, nitrided, or Cermi-Nil cylinders, the rings are the harder of the two surfaces. The objective is to create combustion chamber pressures high enough to force the rings against the cylinder walls and wear into a good (great) sealing of the rings to the cylinders. We need to break-in the ring to cylinder mating surface so that the established mating surface provides the best seating without excessivley wearing the surfaces or glazing the cylinders.

The first few test runs keep the temperatures to a minimum while providing an opportunity to check for leaks and verify the installation is airworthy. During these first few test runs, the engine RPMs and engine temps are gradually increased. These runs put very little pressure on the rings; ring break-in is not the objective. Rather, these engine runs let the cam, lifters, main and rod bearings, and all the other moving parts, get to know each other. Take your time and follow these steps.

Installation

1. Install engine in aircraft making all connections
2. Check operation of all engine controls for full travel and proper operation
3. Check torque of engine lift eye hook bolts, use torque wrench. Torque to 8 ft/lbs
4. Service aircraft battery
5. If possible, leave cowling on for initial test run. A decowled engine receives very little cooling air, so running without the cowling could damage the new cylinders.
6. Flush fuel system. (Prior to connecting fuel feed line to engine)
   a. Use a clean 5 gallon bucket, hang engine fuel feed line in bucket.
   b. On gravity systems turn fuel on
   c. Select all fuel tanks (one at a time) on fuel selector valve
   d. Drain approximately one gallon from each tank.
   e. On pump feed systems, turn boost pump on and then select different tanks.
   f. Check fuel in bucket for contamination.
7. Connect fuel line to engine, do not turn fuel on

Before Test Running

1. Remove lower spark plug leads and spark plugs.
2. Service engine with proper amount of Aero Shell straight weight non-detergent mineral oil.

   NOTE: In past years, it has been common practice to use non-detergent and mineral oil during the "BREAK-IN" period because it was felt that the rings would seat quicker without the film strength additives. More recently, there has been a trend to high speed and high temperature engines, cam lobe and tappet loads also have increased to a point where it is important to use heavy duty oils which contain an EP (high pressure) additive right from the start. Rings will seat properly when moderate loads are applied as noted in the flight test section. Comment: I personally don't agree with using mineral oil. Lycoming recommends an Ashless Dispersant oil from the start in turbo-charged engines. Why? Is it because the compression pressure (manifold pressure) can be kept higher? Why not run the engine at higher than 65%-75% power?* In the 35 years that I've been building engines, automotive, marine, motorcycles and aircraft, I've never run a mineral oil. I think it's a myth. I use AeroShell 15w-50 from the very first start. Using the procedures I outline here, I've never had an engine take longer than 20 hrs to break-in. My experience has been stabilized temperatures in less than 10 hours. *By-the-way, TCM recommends breaking in the engine at as high a manifold pressure as possible.

3. Use the proper weight oil based on air temperatures and time of year. It is preferable to fill engine with WARM oil. This will lower its viscosity and insures that the oil filter bypass valve will not open up on initial engine start.

   NOTE: Let's face it, if you use a multi-grade oil from the start, the temp of the oil will not be an issue. Make your own decisions. I base mine on my experience, not because, "That's the way we've always done it."

4. Pre-oil engine by turning the engine over with aircraft starter
   ...If available, use an APU to power the starter motor
5. Spin motor over at 30 second intervals allowing rest periods to prevent overheating the starter motor
   a. During the first 30 seconds of engine spin up, you should
   ....get an indication of oil pressure on the aircraft oil pressure gauge.
   b. Spin the engine up three more times after getting oil pressure indication.
   ...Allow short cool down periods for the starter motor
   c. Check Oil level
   d. Service the engine with more oil as required to bring it to full capacity

   NOTE: Filling the oil cooler, oil filter, oil lines, etc. on a freshly overhauled engine may require 1-3 quarts more oil.

6. Check for oil leaks
7. Install spark plugs and leads
8. On gravity fuel systems, turn fuel valve on, check for leaks
9. On aircraft with boost pump, turn pump on and check for leaks
10. Check priming system for leaks

First Engine Run

1. The engine cowling should not be removed for any test run. Adverse cylinder heating may occur.
2. Begin engine test run as soon as possible while the oil is warm
   Note: Preheat engine and oil if necessary
3. Face aircraft into the wind
4. Position an observer to monitor engine for oil and fuel leaks with fire extinguisher at hand
5. Just crack throttle open! We do not want engine to start at high RPM at all
6. Prime engine as little as possible, usually two or three strokes of primer
7. NOTE: On fuel injected engines, prime to establish fuel flow and then only two to three seconds more.

Initial Engine Break-In

1. Start engine, adjust throttle so that engine idles at 800 RPM
2. Check for proper oil pressure indicator within 30 seconds. If there is no oil pressure indication within 30 seconds, shut engine down immediately and determine the cause
   a. Start and run engine for one minute at 800 RPM. Shut down.
   ....Check for leaks. ...Allow engine to cool for 15 minutes.
   b. Start and run engine for four minutes at 1000 RPM. Shut down.
   ...Check for leaks. ...Allow engine to cool for 15 minutes.
   c. Start and run engine at 1000 RPM
   d. Do magneto safety check.
   .......Turn off mags quickly to determine if P-leads work,
   ........then go quickly back to both.
   e. Run engine up to 1200 RPM for one minute, observe oil pressure,
   ....oil temperature,.fuel pressure, and alternator output.
   f. Reduce power to idle, observe idle speed
   g. Pull mixture out to shut off fuel and at the same time, observe tachometer.
   ...A 25 to 50 RPM increase should be observed on carburated engines.
   h. Fuel injected engines generally require a 10-25 RPM increase before engine quits.
3. Inspect engine for oil and fuel leaks
4. Make adjustments as required
5. Let the engine cool completely in preparation of next run

Second Engine Run

1. Preheat engine as required (if it's less than 60 degrees ouside.)
2. Start engine up and run at 1000 RPM for one minute
3. Increase RPM to 1200 RPM for seven minutes
4. Run engine up to mag check RPM
5. Do a mag check, check oil pressure, oil temperature, fuel pressure as quickly as possible

   NOTE: Keep this run at mag check RPM as short as possible, one minute maximum.

6. On aircraft with controllable pitch prop, pull prop control out for 10 seconds maximum then,
   -> go back to full increase.
7. Reduce RPM to 1200 for two minutes for cool down and then shut engine down
8. Inspect engine for leaks, make adjustments as necessary

Third Engine Run

1. Preheat engine as required (if it's less than 60 degrees ouside.)
2. Start engine and warm up for one minutes at 1000 RPM.
3. Continue to warm engine up two minutes at 1200 RPM.
4. Increase engine speed to 1500 RPM for five minutes.
   

   NOTE: Cycle propeller pitch and perform feathering check as per airframe manufacturer's recommendations. Check prop as little as possible because cycling of prop robs engine of oil.

5. Run engine to full static airframe recommended power for a period not to exceed 10 seconds.
6. Reduce power to mag check RPM. Do quick mag check.
7. Reduce power to 1200 RPM for five minutes as a cool down period.
8. Run engine up to mag check RPM to clear engine.
9. Reduce throttle to idle and check idle RPM, check idle mixture, then shut engine down.
10. Inspect engine for leaks and make necessary adjustments.
11. Remove oil filter and inspect element or remove oil pressure screen and check for contamination.
    If no contamination is evident, the aircraft is ready for flight check
    I usually drain the oil and add new at this time. New filter too.

Test Flight

1. Top oil off 100%
2. Preheat engine if necessary
3. Start engine
4. Do Not delay in getting to the departure end of the runway.
5. Enroute to the departure end of the runway,
6. Perform normal preflight run up in accordance with the engine and aircraft operator's manual
7. If the aircraft is equipped with a multiple probe EGT and you are is able to monitor EGT in addition to the above-mentioned items, abort the takeoff or return to base if any single EGT exceeds 1500 degrees.
   • Also, abort the takeoff if anything sounds, smells, or feels unusual, even if you can't quite "put your finger on it." You should be "spring-loaded" to abort this takeoff, continuing only if everything seems very close to "just right". This is a good rule for all takeoffs, but especially the first takeoff on a new engine!
8. Ring break-in procedure
   • Take off at full throttle (or climb power)
   • Monitor RPM, fuel flow, oil pressure, oil temperature and cylinder head temperature gauge (if possible)
   • In accordance with the pilot's operating handbook, reduce to climb power as required
   • Establish cruise conditions. Fly at altitudes that allow for greater than 85% power.

   NOTE: On fixed pitch aircraft, climb power is usually full throttle. Use a shallow climb angle to help engine cooling. Climb to cruise altitude (4500-7500 ft). Adjust mixture per pilot's operating handbook as required.

   • Reduce power to approximately 75% power. Check engine gauges.
   • lean engine per operating handbook (be observant of the oil temperatures; do not let it get too high)
   • Do not operate the engine for extended periods of time at a constant power setting.
     ÄAlternate power between 75% and 85% power
   • For the next two hours very the RPM, manifold pressure, and cylinder temps
     • First: Descend 1000 feet and climb back to cruise altitude at full throttle (climb power)
       Establish cruise condition at 75%-85% power.
     • Then: Descend 2000 feet and climb back to cruise altitude at full throttle (climb power)
       Establish cruise condition at 75%-85% power.
     • Repeat this during the next two hours.

   NOTE: If the engine is normally aspirated (non-turbo charged), it may be necessary to cruise at the lower altitudes to obtain the required cruise power levels. Density altitude in excess of 8,000 feet (5,000 feet is recommended) may not allow engine to develop sufficient power for a good break in. However, the cooler temps at higher altitudes may allow for full throttle operation without overheating the engine. Percent power may best be determined with a manifold absolute pressure gauge or fuel flow using Percent Power = ( displayed) gals/hr * 6lbs/gal * 2.365 hp-hr/lb

9. Increase engine power to maximum airframe recommendations and maintain for 30 minutes, provided engine and aircraft are performing within operating manual specifications.
10. Descend for landing at low cruise power settings while closely monitoring the engine instruments. .Avoid long descents at low manifold pressure. If possible, extend flaps for added drag and descend under power. Do not reduce altitude too rapidly or the engine.temperature may drop too quickly

    NOTE: To properly seat the piston rings in a newly overhauled engine, takeoff at full throttle (or climb power), lean engine per operating handbook (be observant of the oil temperatures; do not let it get too high), cruise at greater than 65% to 75% power. Do not operate the engine for extended periods of time at a fixed power setting. Very the RPM, manifold pressure (fly at various altitudes; i.e., descend 1000 feet and climb back to cruise altitude at full throttle (climb power)), and engine cylinder head temps for the first 10-30 hours. NOTE: Applying loads to the engine for short periods of time causes increased ring pressure against the cylinder walls and helps to seat the rings. This is especially important because you are "breaking-in" the engine with heavy duty oils. The deceleration (descending) increases vacuum in the combustion chamber and gives extra lubrication to the piston and ring assemblies.

Post Flight

1. After landing and shut down, check for leaks at fuel and oil fittings and at engine and accessory.section parting surfaces. Compute fuel and oil consumption and compare to limits given in.operator's manual. If consumptions vary from figures shown in manual, determine the cause before releasing the aircraft for service.
2. Remove oil suction screen and oil pressure screen or oil filter to check again for contamination
3. Check tightness of rocker box cover screws, oil scavenge, intake hoses, and exhaust system.

Return to Service

1. Release aircraft for service if all operation is normal per engine and airframe manufacturer.
2. At 10 hours since major overhaul
   a. Inspect engine for leaks.
   b. Check engine operations on ground with normal run-up.
   c. Change oil, inspect suction and pressure screens or oil filter element.
   d. Check tightness of rocker box cover screws, baffling screws, oil scavenge and
   ....intake hoses and exhaust system.
   e. Inspect lower sparkplugs for oil or oil mist.
   f. Adjust lifter clearances of all engines not having hydraulic lifters per manufacturer's.service information manual. (Example of engines without hydraulic lifters are Lycoming O-235 and O-290 engines.)
3. Repeat step 2 at 25 hours since major overhaul
4. Repeat Step 2 at 50 hours since major overhaul
5. At 50 hours since major overhaul, adjust lifter of engines not having hydraulic lifters again.per manufacturer's service information

Additional information on engine break-in.

Suggestions for Proper Engine Break-In ------------------------------------------------------------------------

Whenever an engine's piston rings are replaced whether in part or in entirety it is necessary to break in the engine. Piston rings are replaced at a complete engine overhaul or repair, top overhaul or single cylinder overhaul or repair.

When we refer to engine or cylinder break in, we are talking about the physical mating of the engine's piston rings to it's corresponding cylinder wall. That is, we want to physically wear the new piston rings into the cylinder wall until a compatible seal between the two is achieved.

Proper engine break in will produce an engine that achieves maximum power output with the least amount of oil consumption due to the fact that the piston rings have seated properly to the cylinder wall. When the piston rings are broken in or seated, they do not allow combustion gases to escape the combustion chamber past the piston rings into the crankcase section of the engine. This lack of "blow-by" keeps your engine running cleaner and cooler by preventing hot combustion gases and by-products from entering the crankcase section of the engine. Excessive "blow-by" will cause the crankcase section of the engine to become pressurized and contaminated with combustion gases, which in turn will force normal oil vapors out of the engine's breather, causing the engine to consume excessive amounts of oil. In addition to sealing combustion gases in the combustion chamber, piston rings must also manage the amount of oil present on the cylinder walls for lubrication. If the rings do not seat properly, they cannot perform this function and will allow excessive amounts of oil to accumulate on the cylinder wall surfaces. This oil is burned each and every time the cylinder fires. The burning of this oil, coupled with "blow-by" induced engine breathing, are reasons that an engine that hasn't been broken in will consume more than its share of oil.
















When a cylinder is overhauled or repaired the surface of it's walls are honed with abrasive stones to produce a rough surface that will help wear the piston rings in. This roughing up of the surface is known as "cross-hatching". A cylinder wall that has been properly "cross hatched" has a series of minute peaks and valleys cut into its surface. The face or portion of the piston ring that interfaces with the cross hatched cylinder wall is tapered to allow only a small portion of the ring to contact the honed cylinder wall. When the engine is operated, the tapered portion of the face of the piston ring rubs against the coarse surface of the cylinder wall causing wear on both objects. At the point where the top of the peaks produced by the honing operation become smooth and the tapered portion of the piston ring wears flat break in has occurred.

When the engine is operating, a force known as Break Mean Effective Pressure or B.M.E.P is generated within the combustion chamber. B.M.E.P. is the resultant force produced from the controlled burning of the fuel air mixture that the engine runs on. The higher the power setting the engine is running at, the higher the B.M.E.P. is and conversely as the power setting is lowered the B.M.E.P. becomes less.

B.M.E.P is an important part of the break in process. When the engine is running, B.M.E.P. is present in the cylinder behind the piston rings and it's force pushes the piston ring outward against the coarse honed cylinder wall. The higher the B.M.E.P, the harder the piston ring is pushed against the wall. The surface temperature at the piston ring face and cylinder wall interface will be greater with high B.M.E.P. than with low B.M.E.P. This is because we are pushing the ring harder against the rough cylinder wall surface causing high amounts of friction and thus heat. The primary deterrent of break in is this heat. Allowing too much heat to build up at the ring to cylinder wall interface will cause the lubricating oil that is present to break down and glaze the cylinder wall surface. This glaze will prevent any further seating of the piston rings. If glazing is allowed to happen break in will never occur. We must achieve a happy medium where we are pushing on the ring hard enough to wear it in but not hard enough to generate enough heat to cause glazing. If glazing should occur, the only remedy is to remove the effected cylinder, re-hone it and replace the piston rings and start the whole process over again.

Understanding what happens in the engine during break in allows us to comprehend the ideas behind how we should operate the engine after piston rings have been changed. The normal prescribed flight procedure after ring replacement is to keep ground running to a minimum, take off at full power and reduce to climb power at the first available safe altitude, all while keeping the climb angle flat and the climb airspeed higher to promote the best cooling possible. At cruise altitude we should use 65% to 75% power and run the engine richer then normal. At all times we are to remember that heat is the greatest enemy of engine break in, we should try to maintain all engine temperatures in the green, well away from the top of the green arc or red line. This means step climbing the aircraft if necessary, operating with the cowl flaps open or in trail position during cruise flight and being generous with the fuel allocation for the engine. We should not run the engine above 75% power in cruise flight because the B.M.E.P is too great and the likelihood of glazing increases. Periodic climbs at full power act to achieve a higher than cruise B.M.E.P. and helps to seat the rings. As you can see, keeping the engine as cool as is practical and at a conducive power setting is the best combination for successful engine break in.