Engine Break-in Procedure (Flight test)
Note: Click 'Technical Stuff' on the left to go back.

When the engine is operating, a force known as Brake 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 honed cylinder walls. 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.

Installation Checkout
Engine Test Runs
Flight Test
Post Flight

Prior to First Test Flight:

1.Top oil off 100%.   Expect to puke some all over the bottom of your plane.
2. Preheat engine if necessary for temps below 50 degrees F
3. Start engine.   Do not let it IDLE. 

4. Do Not delay in getting to the departure end of the runway.
. . . Enroute to the departure end of the runway, do the following:
. . . a. Perform normal preflight run up in accordance with the engine and aircraft operator's manual

. . . b. Watch oil temperature.  It must be greater than 100 degrees F before take-off.

. . . . . . Ideally, you have a an engine monitor capable of monitoring ALL engine functions.

. . . . . . • Watch cylinder head temperatures (CHTs).  Watch for anything not considered normal.

. . . . . . • Watch exhaust gas temperatures (EGTs).  Watch for anything not considered normal.
5. Once oil temperature is greater than 100 degrees F and no anomalies, you're ready to go.

The Racetrack:

When I break-in a new engine, I like to stay fairly close to the airport.  I fly, what I call, a rectangular racetrack about 5 miles wide and 7 miles long.  The last leg keeps me on a heading for a straight in to the runway.

Leg 1: My initial climb will get me to my cruise altitude and heading into the wind.

Leg 2: For the the next leg, I'll turn 90 degrees (I usually turn left) and use the next 5 miles or so

Leg 3: For this leg, I'll again make a 90 degree heading change and maintain course for 7 miles. 

Leg 4: Is the result of another 90 degree heading change.  This puts me overhead for a straight in landing if necessary. 

Flight Test:  The take-off roll

1. If the aircraft is equipped with an engine monitor  (in addition to the above-mentioned items)

. . . Abort the takeoff roll IF:

. . . a. Any EGT exceeds 1500 degrees.

. . . b. Any CHT exceeds 470 degrees F (JPI) or 425 degrees F (EI)
. . . c. 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. Continue 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

Step One:   Climb, establish cruise condition

1. Take off at full throttle (or climb power)
. . . a. On fixed pitch aircraft, climb power is usually full throttle.

. . . b. Use a shallow climb angle to help engine cooling.

. . . c. Climb to cruise altitude (3500 to 6500 ft). Adjust mixture per pilot's operating handbook as required.

. . . 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 altitudes in excess of 5,000 feet are not recommended.

. . . . . . . . The altitudes may not allow engine to develop sufficient power for a good break in.

. . . d. If required, reduce to climb power in accordance with the pilot's operating handbook
2. Monitor RPM, fuel flow, fuel pressure, oil pressure, oil temperature, CHT and EGT (if possible)
. . . a. Be observant of the oil temperaturs; do not let it get too high
. . . b. Be observant of the CHTs and EGTs; do not let them get too high

3. Establish cruise conditions at greater than 75 % to 85% power.  Maintain for 1 minute.

4. Slowly reduce power to approximately 65 % to 75% power. Check engine gauges.  Maintain for 5 minutes.

. . . Note: 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

5. Lean engine mixture per pilot's operating handbook

Step Two:  The Cooling Descent

1. Reduce power just enough to allow the plane descend 1000 feet without adjusting trim.
. . . Note: 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

2. Establish a 75% cruise power setting.  Maintain for 1 minute.

3. Monitor RPM, fuel flow, fuel pressure, oil pressure, oil temperature, CHT and EGT (if possible)
. . . a. Be observant of the oil temperaturs; do not let it get too high
. . . b. Be observant of the CHTs and EGTs; do not let them get too high

Step Three:  Flat out

1. Now it's time to put the pedal to the metal or "Balls to the Wall" if you will.

2. Fly the racetrack at 75% to 85% power.   Maintain for 20 minutes.

3. Monitor RPM, fuel flow, fuel pressure, oil pressure, oil temperature, CHT and EGT (if possible)
. . . a. Be observant of the oil temperaturs; do not let it get too high
. . . b. Be observant of the CHTs and EGTs; do not let them get too high
4. After 20 minutes, reduce power to 65% to 75% and establish a cruise condition.   Maintain for 5 minutes.

 

Step Four:  Climbing back to original altitude

1. Go to full throttle (climb power) and climb back to cruise altitude
2. Once at altitude, reduce power to 65% to 75% and establish a cruise condition.   Maintain for 10 minutes.

Step Five:  Repeat line items 1 through 4 for the next 2 hours

1. Go to Step Three.  (Balls to the Wall at initial altitude)

2. Go to Step Two     (Cooling Descent)

3. Go to Step Three  (Balls to the Wall at lower altitude)

4. Go to Step Four    (Climb back to altitude)

Step Six:  Landing

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