Engine break in

I'm sure this has been hashed out to the nth degree already, but I wanted to start a little discussion about engine break in. Most of my past research and experience has been, run it medium hard but mainly steady (no pattern work or stalls, etc) but to overall keep it cool. So, today I was talking to the owner of a new-to-him RV-6A and he said his mechanic told him to run it hard and run it hot. So, which is it?

1. Run it hard and run it hot?

2. Run it hard and keep it cool?

3. Keep it cool and try not to do too much on-and-off power, but to keep it steady?

You didn't mentioned which engine, but here's a great article by Lycoming about breaking in:

https://www.lycoming.com/content/hard-facts-about-engine-break

I am in the run it HARD but do not let it get too hot or hot for long. I want oil temp below redline and not let CHTs stay above 400 for long. Typically I have seen 400 CHTs first 1 to 1.5 hour flight but not after that. Running full power, I typically have seen CHTs drop 20+ degrees and stay below 400 right around the 20-minute mark with steel cylinders. All bets are off with Chrome or Nickle-Carbite. My preference is new Lycoming cylinders or new aftermarket steel.

That's pretty much how I've understood it. But, the main question is, why are people being told to run it hot?

break in

Run it hard keep it cool. below 400 if possible, absolute limit 425 and only for a few seconds.
Mahlon Russell protocol for ground runs.

10,000 opinions on this

What you are mostly concerned about is cylinder glazing which is oil cooking onto the cylinder walls which can ruin the rings ability to seal effectively.

High MP helps apply additional pressure onto the rings and thus helps reduce oil on the cylinder walls and speed the breakin process.

If you can keep the heat down (and we don't really know what the cylinder barrel temps are), the ring seating will take place eventually.

The CHT's drop as the insulating carbon layer builds up on the piston crown and cylinder head surfaces. If the rings were developing enough friction and heat to raise CHT's, the cylinders/pistons would likely scuff and score.

Breakin is indicated by the drop and stabilization of oil consumption more than any drop in temps.

Just another opinion.
Tim Andres

Break-in

Had trouble getting my engine warm enough on the first flight. OAT was about freezing. I climbed out at 100 mph. EGT's were in the 1400 to low 1500s and CHT's from 270 to 305. Added air dams in front of cyl's 1 and 2. This brought all CHT's over 295. The CHT's have never been over 370 on a hot summer day during climb. A friend with another RV-8 had a similar experience. Why are cooling results so different for various builders? My break-in was slow. Because of low temps? My Lycon IO360 M1B has 10:1 comp. and dyno'ed at 214 HP, so there was plenty of heat to be carried away. Van's stock cowl seemed to do that job well... What accounts for the differences in cooling?

bkervaski said:

You didn't mentioned which engine, but here's a great article by Lycoming about breaking in:

https://www.lycoming.com/content/hard-facts-about-engine-break

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Yes, and the key quote on power levels -my highlight...

A new, rebuilt or overhauled engine should receive the same start, warm-up and preflight checks as any other engine. There are some aircraft owners and pilots who would prefer to use low power settings for cruise during the break-in period. This is not recommended. A good break-in requires that the piston rings expand sufficiently to seat with the cylinder walls. This seating of the ring with the cylinder wall will only occur when pressures inside the cylinder are great enough to cause expansion of the piston rings. Pressures in the cylinder only become great enough for a good break-in when power settings above 65% are used.

Full power for takeoff and climb during the break-in period is not harmful; it is beneficial, although engine temperatures should be monitored closely to ensure that overheating does not occur. Cruise power settings above 65%, and preferably in the 70% to 75% of rated power range, should be used to achieve a good engine break-in.

Almost impossible with a fixed pitch at 3000 ft MSL in the AZ desert...

Jesse said:

That's pretty much how I've understood it. But, the main question is, why are people being told to run it hot?

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Because they are listening to the wrong people?

Mahlon's approach (essentially what you'll get from all the good engine builders - including Lyocming) is high power, and keep temps under the 425 limit. They break in great if you do that.

It's science, not magic - facts and explain actions count, opinions don't.

Paul

Cht

Here is what I have in my notes:
On the ground during initial runs, keep CHT's under 350 deg f to prevent glazing of cylinders. Once you are flying, keep CHT's under 400 deg f for first 25 hr or until oil consumption stabilizes. Cruise Power when flying should be over 65% with 75% being ideal. Engine times less than 65% doesn't count towards the 25hr as there isn't sufficient pressure to seat rings.

Jesse said:

why are people being told to run it hot?

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For the same reason they are told to always run ROP, not to walk under ladders, and avoid risky behavior on Friday the 13th. Most people just cannot help themselves from freely passing on information, regardless of it's accuracy. It makes them feel knowledgeable, eventhough the source of the knowledge is suspect (they typically don't know enough to know it though). In most cases, the knowledge was passed on to them and wasn't obtained through diligent research.

While newer plateau finishes don't require much breakin, for old school bore finishes like we typically see in aviation, running it hard is pretty important for proper ring seating. Engines should be run at operating temp and not cold. However, there are only negative consequences for running them hotter than std operating temps.

Larry

lr172 said:

Engines should be run at operating temp and not cold. However, there are only negative consequences for running them hotter than std operating temps.

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In my reference to "cool", I am talking about standard temps, in the 300's in other words. By "hot" I am referring to prolonged running over 400 or any running over 420.

This is the type of discussion I was hoping to start.

tim2542 said:

What you are mostly concerned about is cylinder glazing which is oil cooking onto the cylinder walls which can ruin the rings ability to seal effectively.

High MP helps apply additional pressure onto the rings and thus helps reduce oil on the cylinder walls and speed the breakin process.

If you can keep the heat down (and we don't really know what the cylinder barrel temps are), the ring seating will take place eventually.

The CHT's drop as the insulating carbon layer builds up on the piston crown and cylinder head surfaces. If the rings were developing enough friction and heat to raise CHT's, the cylinders/pistons would likely scuff and score.

This is incorrect. The heat is coming from the barrel and migrating to the head. A good, non-oil burning engine run at peak or LOP with 1000 hours will have VERY little carbon deposits on the head. I pulled cylinders at 150 hours without a trace of carbon. A bit of lead deposits around the exhaust valve, but not a speck of carbon. Heat of the piston crown is not reflected in the CHT measurement.

Breakin is indicated by the drop and stabilization of oil consumption more than any drop in temps.

Just another opinion.
Tim Andres

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The high cylinder pressures (i.e. running it hard, high MP, etc.) actually helps to apply force against the back of the ring thereby forcing the ring face hard against the rough barrel surface, ultimately creating a very smooth and polished interface. Its not about keeping oil off the surface (in fact you want as much oil as possible during this critical phase). Breakin is fundamentally over when the rough barrel surface becomes smooth on it's plateaus (the wearing takes the rige down to a plateau on a mid-point of the ridge)(though very fine polishing of that interface is still taking place for many hours). Same way that finer grades of sandpaper eventually stop abrading a surface once its sand particles have flattened and become smooth. The honed barrel is not a flat surface, but millions of ridges caused by the honing abrasives. You initially want aggressive wearing of the barrel surface, creating polished plateaus on each ridge. This creates the flat surface for the ring to ride on and still leaves some ridge left to hold oil. When you don't have enough pressure on the rings, only the very tops of the ridges become polished and this leaves too much ridge area and therefore excess oil in the deep ridges. This is one reason for high oil consumption. It also reduces the effedctive barrel surface area leading to lower compression.

You only get a short period of time before the barrel surface becomes polished and the weaing stops. Therefore, it is critical that the engine is run hard in the first hour. All of that metal wear creates a lot of heat and is why you see high temps initially that drop after about 30 minutes (the wearing stops). It is easy for the temps to get too high during this initial phase on an air cooled engine, therefore it is a balancing act. If you let it get too hot, you'll glaze the barrel wall and that fills in the ridges causing an oil burning engine as well as halting the ring/wall wearing (i.e. breakin)

I should add that this no longer applies to automotive engines, as they use a more advanced honing process that puts the plateaus on the surface and breakin in is over in a few seconds. I have seen some info from lycoming saying that breakin is no longer required and makes me wonder if they have started doing plateau honing.

I should also add that many don't see this phase, as their engine had it's initial breakin on the builders dyno or breakin cell. If it ran for an hour at the rebuilder or lycoming, this initial ring seating was done before you got it. The long term fine polishing does require pressure to work, but it will happen eventually and it is not as crtical that it be done at continuous high power, though that is preferred.

Larry

Jesse said:

In my reference to "cool", I am talking about standard temps, in the 300's in other words. By "hot" I am referring to prolonged running over 400 or any running over 420.

This is the type of discussion I was hoping to start.

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I am unsure exactly what temp is too high to prevent glazing (The significant threat from heat during breakin). I would lean on someone like Mahlon for that experience. I do have some experience though. During a period of distraction early in my first flight (first 15 minutes) I notice one cylinder peak up to 450 and another to 430 before forcing it richer (a story for another day, moral of the story is full rich during first hour). The barrel that hit 450 was heavily glazed and need a new hone job. The one that hit 430 showed almost no traces of glazing.

Larry

When you don't know......

It was 1985... PA28-151... new ECI top end. Picked it up at STS (in November) and departed in a full power climb (no cht egt etc. only had oil temp) and waited for the oil temp to hit redline. Leveled off and circled the valley at just under redline for an hour going from 2600 to 2300 rpm every 15 minutes. Landed and put it away. From then on It was flown in my normal manner.

Oil consumption was 1 quart in 50 hours till it was sold in 2003. Comp tests were always over 75.

How hot did the cyls get??? I have no idea. I would never do that again.... what I didn't know then.

Why don't the manufacturers . . .

I've always wondered why don't the manufacturers do the break in before they sell the engine. It seems to me that the big guys have all the right equipment to go ahead and break in the engine before selling it. I know this adds cost but it may be an optional service they can provide if "one" wanted to pay for it...

Sorry Jesse that didn't really answering your question - - - I've had 3 new engines since I've been flying and been told to fly it full throttle as much as possible but keep Temps below 400 like most folks that are responding.

Ironflight said:

Because they are listening to the wrong people?

Mahlon's approach (essentially what you'll get from all the good engine builders - including Lyocming) is high power, and keep temps under the 425 limit. They break in great if you do that.

It's science, not magic - facts and explain actions count, opinions don't.

Paul

Click to expand...

+1 after reading all this , could not have said it more nicely.

I think I have posted this before here, but if not this is an article I wrote about break in. Just a review of the what and why...or at least the what and why in my opinion

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 to 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. 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.
After an engine is overhauled or has a major repair it is run in a test cell to ensure operating characteristics and to begin the break in process. However this process may take as long as 100 hours of operation to complete. You, the pilot, are in control of engine break in for 98 % of the time that it takes to occur. This is a serious responsibility when you consider the expense and aggravation of having to remove, re-hone and re-ring cylinders that have glazed and not broken in.
Hopefully, understanding what engine break in is, as well as what is happening in the engine while the rings are seating and how our flight procedures effect the break in process, will help us to achieve the quickest and most efficient break in after piston rings are replaced.

Jesse,

Good stuff here. I just replaced all cylinders on my IO550 (due to SAP AD).

I went with Ram cylinders. Their break in procedure is to limit ground ops; no cycling of prop. Max power obtainable for 15 minutes then at least 75% for the next 45 minutes varying rpm every 5 minutes. Of course keep temps low (below 400 if possible). Engine is broken in at that time. This worked fine; oil consumption 1 qt/25 hrs and CHTs below 380 even in climb. YMMV

ps: You'll probably have to "g up" the plane to keep speeds reasonable!

Reading Malhon's excellent article I found this portion interesting...

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. 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.

65% to 75% power is ideal - makes me feel better living in the AZ desert.

I guess this is one time when more is not better.