Avionics Report

September 2017 Issue




Break-In Flight Operational Tips

- Fly during day VFR conditions with minimal passengers.
- Fly during the coolest period of the day if it’s hot.
- Keep ground running to a minimum; park into the wind.
- Know and adhere to recommended power settings.
- Fly within gliding distance of the runway.

Engine Break-in Flights: Know the Power Settings

You get one shot at breaking in a new engine or cylinders. Following manufacturer and overhauler guidelines while using common sense is the recipe for success.

At some point you could be faced with flying off a new engine or cylinders. The exact procedures for attempting this sit-up-straight-in-the-seat chore might depend on the engine, the type of cylinders and what the manufacturer recommends. Still, launching for the first time with any new engine must include a solid plan for ground running, power and propeller settings, how far you’ll venture from the runway, how high you’ll fly and how long you’ll conduct the shakedown run.

To help get that plan started, we prepared this basic guide, with a little help from the pros who deliver engines. We’ll say up front that this shouldn’t be used solely as a guide for every break-in situation.

Run-In Versus Break-In

They certainly aren’t the same. The initial stage of bringing the engine to life is the run-in portion, where the overhauler preferably does this on an instrumented test stand with a club propeller that provides better cooling than a standard prop. While the initial run-in of the engine can be done on the aircraft, it is not the first choice by most engine overhaulers or manufacturers due to the general lack of environmental controls and calibrated instrumentation.

During the run-in, the overhauler goes through a series of RPM and power protocols to make sure the engine is set up properly. This is also where the engine is leak checked and the timing and fuel flow are tweaked to get it ready for the next stage: the break-in flight.

The typical run-in time for a new engine is one or two hours, whereas the break-in occurs during the next 25 to 50 hours by flying it. A technician may or may not join you for the first launch, but it doesn’t hurt to ask. Consider this a risky flight and not the time to bring your neighbor for her first one in a small airplane. Don’t laugh—we’ve witnessed the boneheaded decision—on an IFR day.

Engine Display continental

Whether you’re breaking in fresh cylinders or a new engine, it sure helps to have a graphic engine monitor with datalogging capability. Consider installing one while the engine is torn down.

Ground Ops

Nearly every engine shop we spoke with cautioned against time spent running on the ground for risk of overheating. Best to do this on a cool day (or the coolest part of the day) and to avoid excessive taxiing at low power settings.

Heat is a huge issue because the new piston rings are in the process of wearing in to the freshly honed cylinder(s), which generates abnormally high friction and heat. Excess heat can glaze or warp cylinder walls or anneal the rings. Don’t always count on older CHT gauges as your guide because they may not register quickly. There are delays in registering instant heat excursions as the temperature probe is in the cylinder head, not on the cylinder wall itself.

Nickel cyl GAMI

On the other hand, don’t rush off to the centerline without warming and circulating the engine oil. RAM Aircraft in Waco, Texas, suggests not to cycle the propeller, whether for breaking in a new engine or one single cylinder. Others recommend minimal prop cycling. We say use common sense. If the aircraft has been sitting for weeks on a cold-soaked ramp, don’t fire it up and go without briefly cycling the prop one time. The last thing you want to discover on initial climb is a problem with the prop governor.

Hopefully the new engine will have been delivered with the proper oil in it (multi-viscosity mineral oil is common), but leftover AeroShell 15-50 in the sump, as an example, isn’t the best choice for breaking in new cylinders—or even one of them.

According to RAM, the use of break-in oil and performing break-in procedures should be followed whether replacing one cylinder or six. It specifically mentioned its Nickel cylinders. For direct-drive engines, mineral oil such as SAE 20W-50 Phillips type-M can be used, and for geared engines, RAM prefers that AeroShell straight weight mineral oil is used.

This procedure should be followed for the first 25 hours of operation and can continue to as much as 100 hours, depending on the cylinder bore material used. The oil should be changed as soon as oil consumption stabilizes, but no later than the first 25 hours of operation. At that time, oil should be changed to an ashless dispersant (AD) mineral-based oil. Again, this is what RAM and others we spoke with recommend for most common high-output Continental engines. Talk with your shop about oil and change intervals for break-in.

Minding Power Settings

Round gauge

Break in a new engine with known calibrated engine gauges.

Low-powered engines are more susceptible to poor ring seating than high-powered turbocharged engines, but cylinder wall glazing is a distinct possibility on all. Babying a break-in begs for cylinder glazing. Using lower power settings just doesn’t expand the piston rings enough, leaving a film of oil on the cylinder walls. High temps in the combustion chamber oxidize the oil, the rings don’t fully seat and the engine ends up with excessive oil consumption for life.

Removing cylinder glaze requires pulling the cylinder and mechanically breaking the glaze. You don’t want to go there. The good news is lower-powered engines are the easiest to break in.

Still, it might feel unusual and uncomfortable to be flying around for 30 to 60 minutes with a Lycoming IO-360 at full power with a flat prop and rich mixture, but that’s the drill for some break-in instructions.

If it makes you feel better, remember that most flat, non-turbocharged engines were designed to run wide open for their entire life. But for bigger, higher-output Continental engines including the IO-520, IO-550 and TSIO-520, RAM has some recommended power settings for new cylinder break-in.

It says for the first 15 minutes after departing the runway, operate at full power, or no more than 30 inches of manifold pressure for a turbocharged engine with the mixture full rich. Then change RPM between full redline RPM and climb RPM every five minutes. Once cruise altitude is reached, set up 75 percent power and 100 degrees rich of peak.

N325AV Engine Removal

Most replacement engines have been run on a test cell before they’re hung on the aircraft. This limits your task to simply dealing with inflight break-in.

On a side note, you want to keep an eye on oil temperature and CHT. The general goal for a non-turbo is keeping the CHT under 400 degrees and the oil temperature well below 200, or as your manufacturer/overhauler advises is acceptable. If it’s running hot, there could be baffling or temperature probe issues, but we suggest not guessing and landing immediately.

For the descent and return to the airport, don’t chop the power to idle and glide from altitude. The recommendation is to set 2700 RPM and 23 inches of manifold pressure (1900 RPM and 25 inches on the TSIO engines). Lean to maintain approximately the same EGT as during the cruise period while maintaining a 300- to 500-FPM descent rate to touchdown.

Once back on the ground, you or your mechanic will want to uncowl the engine(s) and perform a leak check and generally look things over. Understand that the new engine might not be fully broken in after the maiden flight and you’ll still have to adhere to prescribed power settings for a handful of hours. For cylinders, one break-in flight is all that’s needed.

Do it right and with luck you’ll be rewarded with a healthy engine that has nicely seated rings and minimal oil consumption.