Lycoming vs Savvy / Busch for Engine Break-in

[merlin]

Hello...
I am planning to break-in my field overhauled Lycoming io360a1a this morning on my M20-F.  I am hoping to reconcile Lycoming instructions to run 75% power with Mike Busch AOPA article to run with as much power as possible keeping the CHT below 440 degrees.  I have read lots of previous threads about this and most suggest as much power as possible, but scratching my head as to why Lycoming says "75% power".  

Thx... hopefully back in the sky after 6 months down for major overhaul!

[ShuRugal]

Lycoming says 75% power because that's what they've always said, and if they change that guidance the lawyers will tear them apart for having given less than optimal guidance in the past.

Busch has the advantage of being able to report on test data gathered using modern testing equipment and techniques, combined with the advantage of not being liable if someone breaks their engine because they misunderstood his advice.

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[N201MKTurbo]

I don't think there is much difference. They both want you to run as much cylinder pressure as possible. In reality, keeping it below 440 CHT will probably limit you to 75% or so.

[ArtVandelay]

75% power worked fine for me, but maybe not non steel cylinders.

[N201MKTurbo]

The bottom line is they don't want you to baby the new engine. The rings will seat better if they are forced into the cylinder walls by high cylinder pressure. The exact power setting isn't that important, just as hard as you can get away with.

[kortopates]

Rich is right, Mike is responding to the many clients we see that did baby the engine and the rings have not yet fully seated after a number of hours. Mike then suggest to run as close to 100% power as they can for a hour. It has saved a number of clients from having to pull new cylinders, but it doesn’t always work.


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[PT20J]

15 minutes ago, kortopates said:

Rich is right, Mike is responding to the many clients we see that did baby the engine and the rings have not yet fully seated after a number of hours. Mike then suggest to run as close to 100% power as they can for a hour. It has saved a number of clients from having to pull new cylinders, but it doesn’t always work.


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I would suspect that it would work if the rings had merely not seated, but not work if blowby had glazed the cylinder walls.

Skip

[Shadrach]

1 hour ago, merlin said:

Hello...
I am planning to break-in my field overhauled Lycoming io360a1a this morning on my M20-F.  I am hoping to reconcile Lycoming instructions to run 75% power with Mike Busch AOPA article to run with as much power as possible keeping the CHT below 440 degrees.  I have read lots of previous threads about this and most suggest as much power as possible, but scratching my head as to why Lycoming says "75% power".  

Thx... hopefully back in the sky after 6 months down for major overhaul!

If they didn’t, No one above 5000msl would be able to break in engines in the summer.

I don’t think 75% has ever been a limitation, it’s a minimum.

Edited August 26, 2021 by Shadrach

[kortopates]

I would suspect that it would work if the rings had merely not seated, but not work if blowby had glazed the cylinder walls.
Skip

You’re right it’s a matter of degree, but it’s worked even with some glazing detected by borescope. But as you point out it sure can get to point where it’s too late.


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[N201MKTurbo]

If you pull the cylinder and hone it again and put it back with the same rings, it would probably break in. The honing is what causes the rings to wear and conform to the cylinder.

[PT20J]

Piston rings are springy because the cylinder bore changes dimension with temperature. To seal well, they are designed so that combustion gasses force them down against the bottom of the piston groove creating a gap to admit gas pressure behind the ring to force it against the cylinder wall during the power stroke. Higher power creates higher pressures.

However, higher power creates higher temperatures as well, and during break in there is more friction that also increases temperatures. Keep in mind that a lot of Lycoming engines go into airplanes without CHT gauges. Likely, the 75% recommendation is a tradeoff between getting high enough pressure and keeping the temperature reasonable.

Skip

[merlin]

Thanks everyone!  Maiden voyage went great!  #3 got up to 411 degrees and I was getting nervous but then trended back down.  It has been a long 6-monty hiatus from flying but so happy to have a sound airplane / engine to fly again.

[takair]

Glad it went well. I have had great luck following Lycoming SI 1427C.  While they discuss some initial power settings between 65% and 75%, part of the break in is at max allowable power:  “If the  engine  and  aircraft are  operating  to correct specifications per  the Lycoming  Operator’s Manual, increase  engine  power to  the  maximum airframer  recommendations and  hold  for 30 minutes.”  

[Guest]

8 hours ago, merlin said:

Hello...
I am planning to break-in my field overhauled Lycoming io360a1a this morning on my M20-F.  I am hoping to reconcile Lycoming instructions to run 75% power with Mike Busch AOPA article to run with as much power as possible keeping the CHT below 440 degrees.  I have read lots of previous threads about this and most suggest as much power as possible, but scratching my head as to why Lycoming says "75% power".  

Thx... hopefully back in the sky after 6 months down for major overhaul!

I’d follow the instructions of the person/ company who you will be looking to for warranty coverage.

Clarence

[carusoam]

+1 for what the warranty says…

For fun you can probably compare the Continental guidance for break-in…

Essentially…

1) max power, for highest possible ICPs…

2) max FF, for best internal CHT control.

3) alternating rpm every 15 minutes, for changing the travel of the pistons.

4) for hours at a time, for minimizing the climb to altitude cooling related issues.

On the East coast that means… go out over the ocean, and speed along at 1k’ above sea level and change the rpm every 50 miles or so…

 

Avoid glazing…

Avoid wearing in a step near the top of the cylinder….   So max rpm is important to use… but not continuously…. It turns out the pistons and the rings travel slightly differently depending on the rpm they are actually running at… 

 

I was so looking forward to collecting data, and seeing the rings break-in…. Knowing that the full break-in can take 50 - 100 hours….

I saw none of it…. The first two hours were run in a test cell… the next two hours were flown by the mechanic hanging the engine on the plane… by the time I flew the fifth hour… cylinder temps were all in the normal range already…

Bring somebody along that has done this before…  because at 1k’ paying attention to the flying is a full time job.  Having somebody watching the engine monitor is pretty helpful too… in the event something starts to get out of hand….

Review the data… see if the JPI data shows a step where the CHTs start to behave better… share here if you can.

PP thoughts only, not a mechanic…

Best regards,

-a-

[Bartman]

Congratulations on the successful First Flight !

[A64Pilot]

Actually most ring break in will occur very quickly, almost certainly in the test cell if one is available. there is some final breaking in, but if they don’t in the first few hours, it’s very likely they never will. That first hour or so in a field overhaul is the most important.

If you look at the side profile of most rings you will see an angle on the inner upper edge, this is why they have a up and a down, they aren’t symmetrical, usually there is a dot indicating top.

The purpose of this angle is so that cylinder pressure will force the rings against the cylinders improving compression and decreasing blow -by. So running at high power means high pressure of course and high pressure seats the rings.

‘Some engines like Continental for instance have less spring tension and rely more on the cylinder pressure to blow out the rings and make them seal, this is why compression checks on Continentals are less reliable, they are called low tension rings. Low tension rings free up a surprising amount of HP due to less friction, and run cooler for the same reason.

Low tension rings have forever been a hot rod thing, due to decreased friction, further making me believe that Continentals are more “hot rods” motors. Well that and hearing a big bore Conti idle of course.

[JWJR]

My 75 POH says do not lean for ground operations- some Lycoming operational instructions are outdated. I would call Lycoming and discuss your thoughts/ intentions with their technical folks.


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[carusoam]

Proof that our lawyers are better than their lawyers…

Go MS!

Best regards,

-a-

[kortopates]

2 hours ago, JWJR said:

My 75 POH says do not lean for ground operations- some Lycoming operational instructions are outdated. I would call Lycoming and discuss your thoughts/ intentions with their technical folks.


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You could call but easier to just download and print Lycoming published break in guidance per SI 1427C. They're free to everyone.

https://www.lycoming.com/content/service-instruction-no-1427c

Edited August 30, 2021 by kortopates

[FLYFST]

So what about factory rebuilt engines? Is it correct that Lycoming ground tests have essentially completed the break-in before Lycoming ships the engine?


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[PT20J]

3 hours ago, FLYFST said:

So what about factory rebuilt engines? Is it correct that Lycoming ground tests have essentially completed the break-in before Lycoming ships the engine?


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I think so. We installed my rebuilt IO-360-A3B6 during an annual inspection. Since a compression test is required for an annual, we did a cold compression test after installing and filling with oil and priming the oil system, but before running it. Compression was 79/80 in all four cylinders. During early flights, I never had high CHTs or a sudden drop in CHT supposedly characteristic of ring seating.

Skip

[A64Pilot]

I think if we looked we would find somewhere that  Lycoming doesn’t recommend continuous cruise power settings above 75%, and that’s where the 75% comes from.

75% is certainly enough, and has been said is about all your going to get anyway even at sea level if you leave yourself enough altitude to compete an Emergency landing if that brand new engine quits.

Just don’t lean it, leave it full rich, and be darn sure your at the max allowable fuel flow, not just within acceptable limits, a lot of cooling comes from wasting excess fuel and you want the cooling.

At high power running rich won’t result in fouled plugs and carboned up exhaust valves etc, the engine is hot enough to stay clean

[A64Pilot]

11 hours ago, JWJR said:

My 75 POH says do not lean for ground operations- some Lycoming operational instructions are outdated. I would call Lycoming and discuss your thoughts/ intentions with their technical folks.


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I think that comes from there have been many accidents from taking off leaned out, one fatality in my neighborhood was, with a 10,000+ hour ATP in his Bonanza.

At least that’s how I interpreted the accident report, pretty gruesome read too. took me a little while to understand how his blood toxicology had such high levels of CO when his passenger had none, then I realized he must have been alive and breathing until the fire got him. while the crash killed his pax.

‘So I always say, if your lean on the ground, lean the snot out of it. lean it so much that it won’t turn more than about 1500 before it starts missing, that way you can’t take off leaned out. At taxi power you cannot hurt an engine from excessive leaning, so don’t worry about leaning too much, you can’t.

[ShuRugal]

.
‘So I always say, if your lean on the ground, lean the snot out of it. lean it so much that it won’t turn more than about 1500 before it starts missing, that way you can’t take off leaned out. At taxi power you cannot hurt an engine from excessive leaning, so don’t worry about leaning too much, you can’t.

Yep. Lean for max idle rpm after startup. I like to tweak mine so that it can't taxi uphill unless I enrich it a bit. Post flight taxi neck to the hangar, I'll put throttle fully closed and use mixture to control my power for taxi. Lean to peak RPM, then lean further if I need to slow down.


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