New cylinders - breaking in

At any rate both Lycoming and Conti give detailed instructions for the first N hours following a major or cylinder change.

The thing they don’t quite make clear is that you need to run at high power until the oil consumption stabilises, and does so at quite a low figure, which means no really oily plugs, not even bottom ones.

The resulting extra cost in avgas can be in the thousands.

It also rules out, in an NA engine, IFR flights in the Eurocontrol system. I made that mistake in 2008 (crank swap job) when I flew UK to CZ, and some other stuff, and despite doing that trip at max power (150F ROP), the power setting was only ~ 60%, and I had oily plugs for 100+ hrs afterwards.

But for sure the first few hours are the most important. You really have to fly low level to get the power high enough.

Peter wrote:

You really have to fly low level to get the power high enough.

Unless you have a turbo

I can only tell about the IO520 with “normal” cylinders, and there I spent the 1st hour at 75-80% power, 3500ft, 24-25MP at 2500rpm. WOT only after takeoff. So, high rpm MP according to desired power. Second hour varying, between 2300 and 2500rpm. CHT maximum 400°F, EGT in cruise in the 1450-1500s. Next 23hrs normal procedure, oil change after 25hrs.

I don’t believe in flying with low RPM and a higher MP (i.e. 25/2300) for long, which may be an OWT but listening to some Conti guys it’s not so good for the engine.

RobertL18C wrote:

I don’t think these engines were designed to be babied – I run my new cylinders at 80% until the first 50 hours.

Indeed….and not just the first 50 hours…my SOP: at or just under Redline RPM and WOT for the climb (and always above 5000’)…. (normally aspirated)

Just a quick question : I want to make night circuits tonight and I wanted to try one of our 172 which got an overhauled engine (O-320) in November 2018 (I plan to use it for my big trips his year like Venice). Just checked and it only did 25 hours since overhaul.
On terms of engine break-in, I guess from this thread that circuits is not ideal for an engine this « young ». Is that true ?
Not that my club gives a damn about it but I do.

Most “experts” I have spoken to over the years say that the most critical bit is the first 5hrs or so, where you really must avoid extended low power operation (per the Lycoming instructions).

People who disregard this bit, even unintentionally (e.g. by ending up in a low power circuit in the first 1hr), tend to find glazed cylinders and these can take 100-200hrs to clear up, and (reportedly) in some cases never do clear up, leading to the “chemical solutions” – example. It happened to me years ago, but I never used the solvent approach because of seal damage risk.

Jujupilote wrote:

Just a quick question : I want to make night circuits tonight and I wanted to try one of our 172 which got an overhauled engine (O-320) in November 2018 (I plan to use it for my big trips his year like Venice). Just checked and it only did 25 hours since overhaul.
On terms of engine break-in, I guess from this thread that circuits is not ideal for an engine this « young ». Is that true ?
Not that my club gives a damn about it but I do.

On 25 hours it most probably still has the special break-in oil and I would rather not do circuits with it. Read the engine break-in instructions, i.e. this version from Scan http://www.nsf.se/documents/EngineBreakeIn.pdf and decide for yourself. Btw, the failure rate of aircraft engines is highest up to about 200-300 hours after overhaul with maximum at somewhere 100-150 hours flown. I suspect some of the occurrences are indeed manufacturing or overhaul glitches with the mechanical parts, by there may also be a part related to bad break-in procedures. Did you check the Aircraft File records by whom and how the initial break-in was flown? What is current oil consumption? There should be a report on at least the first 3-5 hours on power settings and durations flown (see break-in instructions), at least if the shop was doing that (as is advisable for clubs to make sure the initial is done correct).

( local copy )

I agree with Peter about the first five hours being critical and the first two are the most critical.

You can expect a higher than normal oil temp for the first 40 min and then drop of around 25F asthe majority of the break in happens .

I usualy fly the first 2.5 hours of a break in as it saves all sorts of problems with customers who don’t seem able to comply with the manufacturers data.

I thought this article was good advice on the topic.

http://pceonline.com/engine-break-in/

here is a good article on break-in, the how and why.