The Cessna 120-140 Association Forum

Hi,
My C90-14F is in the process of being overhauled. I have heard about keeping CHT's below certain limits during break-in. My 140A doesn't have a CHT gauge. Do I need to worry about CHT since I can't monitor it? I live in the pacific northwest so the ambient temp will likely be pretty mild (50-60F) when I do the break-in.
Thanks,
Josh

Josh,

I can tell you that my new Melleniums ran fairly hot when I was breaking them in and I still have a higher #2 temp if I don't keep an eye on it even after 150 hours. The old factory Continentals ran really cool on the other hand.

If you are breaking them in soon I think you will be better off, my temps in the winter time always are pretty stable/cooler and in the low 300's after leveling off from climb out.

Glad to hear you are hopefully nearing completion of the overhaul, it's always a long slog waiting for DIVCO and parts....

Thanks for your input David.
Josh

All those gauges to watch will give you ulcers. Here's my take on break-in, worth at least twice what you're paying for it.

First thing to do is make sure your baffling and seals are in good condition. Then, follow the instructions of the overhauler or the cylinder manufacturer, or both. Keep an eye on the oil temp gauge, keeping in mind that it will run a little high during break-in. After your first 1 hour flight at high power, there's not much point in worrying unless you have chrome cylinders, which require many hours of hard running to break in. The whole purpose of break-in is to first knock off the rough spots without overheating (the minutes long runs at idle or slightly higher) and then seat the rings without glazing the cylinder walls (the high power run(s)).

Thanks John. I will definitely follow my engine shop's break in directions. From what I've heard though, it sounds like no less than 75% power. I figure that means flying fairly low (2000'ish MSL) and wide open throttle. That means I want to pick a cool/cold early morning so the air is smooth since I will be way above maneuvering speed the whole flight. And the cool air will help with keeping engine temps in check.

I'm with you on keeping things simple.


Josh