July 26th, 2010
… a practical guide to getting the most from your new engine
The following steps are ways to ultimately increase engine longevity, performance, and minimize maintenance costs. These are all great reasons to carefully plan your engine’s break-in and maximize the time you spend in the air.
- Take-Off: Conduct a normal take-off with full power full rich conditions. Monitor the engine RPM, oil pressure, cylinder head temperatures and oil temperatures for overheating or irregular oil pressure. Make sure all gauges are in the green.
- Ascent: Reduce to climb power in accordance with the flight manual and maintain a shallow climb attitude to gain optimum air speed and cooling. This will ensure you do not ‘force’ the engine and will prevent overheating.
- Hour 1: Level flight cruise should be at 75% power with best power or richer mixture for the first hour of operation which will continue the ring seating process.
- Hour 2: The second hour power settings should alternate between 65% and 75% power with the appropriate best power mixture settings. Vary the power setting every 15 to 30 minutes utilizing best power settings. Best power mixture settings are necessary to maintain high cylinder combustion pressures.
- Cruising: Engine controls or aircraft attitude should be adjusted, as required, to maintain engine instrumentation within specifications.
- Descent: The descent should be made at low cruise power settings with careful monitoring of engine pressures and temperatures. Avoid long descents more than 15 minutes with cruise RPM and manifold pressure below 18 In. Hg. You do not want to be powering back the engine for an extended period of time. If necessary, decrease the RPM sufficiently to maintain manifold pressure.
Best power mixtures occur between 75 and 125°F rich of peak exhaust gas temperatures. Mixtures richer than best power actually reduce cylinder pressures and cylinder temperatures and can increase the time required to properly seat the piston rings.
Best economy mixture settings reduce cylinder pressures and should be avoided. Reduced cylinder pressures with increased cylinder temperatures can result in “glazed cylinder walls,” which can only be corrected by removing the cylinders to re-hone the barrels and replace the piston rings.
July 26th, 2010
… up-time, down-time, and pilot performance concerns
Most airplane owners know at a high level that breaking in an engine is an important activity. What most cannot explain is the chain reaction of outcomes that affect Pilots and Owners if break-in does not occur properly. One likely scenario includes the following events:
- “Glazing of cylinders” can occur within the first 2 hours of flight time
- Rings do not seat properly
- Oil consumption increases in excess of 25% of normal operating guidelines
- Pilots experience decrease in engine power
- Significant maintenance is required to fix the engine including the removal of the cylinders to re-hone the barrels and replace the piston rings.
- Downtime of plane incurs opportunity costs for commercial applications
- Overall value of plane is impacted at time of sale because of maintenance records
That being said, the mechanics of the process is helpful to know and it starts with the fundamental of how important piston ring seating is to proper engine break-in. Your understanding of the factors involved in the break-in process will aid in correctly operating the engine during this important time. Piston ring seating means the rings and the cylinder wall must wear-in together to provide an effective seal for the combustion chamber and to keep combustion gas blow-by and oil consumption to a minimum.
Initial Ring Seating
During ring seating, the basic purpose is to establish metal-to-metal contact between the piston ring face and the cylinder barrel. In order for this process to take place, the rings must breach the lubricating film of oil on the cylinder wall. As the rings begin to seat, the ring-to-cylinder wall surface area increases and it becomes harder for the rings to breach the protective film of oil. You can aid in this process by keeping the manifold pressures at high levels during the early stages of break-in. The higher manifold pressure, as controlled by throttle position, force the piston rings to expand against the cylinder walls, breaching the protective film of oil and allowing the slight wear that we are trying to achieve.
During initial break-in it is not uncommon to have cylinder head temperatures above the normal range. This elevated temperature is an indication that initial ring seating is taking place. As the rings begin to seat to the cylinder walls, the temperatures will drop. This usually occurs over a period of 10 to 20 minutes. Cylinder head temperatures can remain slightly elevated for several more hours until complete ring seating has been accomplished. Ideally, the rings should seat within the first 10 to 15 hours of engine operation as evidenced by stabilized oil consumption and decreased cylinder head temperatures.
Since this engine is either new or rebuilt, it has “tighter” running clearances than the engine you just retired. It stands to reason that cylinder head temperatures and oil temperatures can run slightly higher. While hot oil runs thinner and aids in ring seating, it is important that you do not let either temperature red line.