leaning during break-in

[prkaye]

At what point during the break-in phaase is it ok to start leaning the engine aggressively? Is CHT the only consideration? I have about 7 hours on the engine now (plus 2 hours in the test cell) and CHTs have consistenly been mid 350's in cruise since first flight on this engine. Is it ok to start leaning now, if CHTs stay below 380? I've been spending a fortune on Avgas the last week!

 

[Majorpayne317641]

Your break in is most likely already done. The official answer is when oil consumption stabilizes. More than likely the break in of the rings and cylinder walls was complete in the first 2 hours. I did an in air break in with no engine stand test run, it was super cold out so I did max power for the first two hours. Oil consumption stabilized within the first flight essentially. It’s very similar to how you build and break in a race engine for cars. I didn’t know that at first since it was my first aircraft engine I broke in myself.

 

[BoydBirchler]

Lean for best power. Full rich can wash off part of the oil film during break in and cause problems as bad as too lean. If CHT's are below 400F you are safe.

 

[wcalvert]

Like was already said, your break-in is mostly complete. Start flying it like you're planning to fly it and learn what it can do. Massive benefits from leaning, including on taxii, so no need to delay.

Be sure you understand the details and theory behind leaning so you'll get the most benefit with the least risk. There are some great articles and books out there that discuss it all.

Question: F/I? with balanced injectors? You'll be amazed at how they can run deep LOP.

Have fun!

 

[lr172]

I like high cyl pressure for 20+ hours on a break in. No issues leaning to best power which is where I break mine in, but I wouldn't go lean of peak until after full break in, which most experts say is around 20-25 hours. Oil consumption stabilizes after ring seating, but ring seating is not synonymous with break in completion. All of that said, after ring seating, I have no issues with moderate periods of less than 75% power, but try to maintain that as much as possible.

 

[prkaye]

Thanks guys! I flew for an hour today leaned-out to just RoP. CHTs still good, and it was nice to be burning about 25% less fuel than i have been for the last week!
Thanks again for all the advice. This IRAN was very, very expensive, but has been an amazing learning opportunity.

 

[Carl Froehlich]

Thanks guys! I flew for an hour today leaned-out to just RoP. CHTs still good, and it was nice to be burning about 25% less fuel than i have been for the last week!SNIP

Your spark plugs and exhaust valves will be a lot happier as well.

Carl

 

[prkaye]

Related question - would you also say that it's safe for me to transition back to auto gas at this point?
I know i'm probably being way too over-cautious about this break-in, but it was such an expensive repair - almost double what i originally paid for the freshly-overhauled engine 15 years ago!

 

[lr172]

I can't think of any reason that auto gas is any less beneficial to a break in, at least after burning a tank full of 100LL to get some lead on the valves/seats.

 

[prkaye]

I can't think of any reason that auto gas is any less beneficial to a break in

My guess is that 100LL was recommended at the beginning of break-in when the cylinders are potentially much hotter, to mitigate risk of detonation with lower-octane fuel?

 

[lr172]

k

My guess is that 100LL was recommended at the beginning of break-in when the cylinders are potentially much hotter, to mitigate risk of detonation with lower-octane fuel?

Still pretty far from detonation. FAA runs these at redline (500 CHT, etc.) and most still don't detonate with 100LL, but might with 93, I suppose. Most engine guys want to see 100LL to get lead on the valve/seat. It is mostly a hold over, as the modern stuff doesn't need lead lubrication, but the older stuff did.

Larry