The International Cessna^® 170 Association

My overhaul is almost finished, so I am wondering what the prevailing opinions about proper break-in are. Full throttle, balls-to-the-wall? How long? What's your opinion?
Greg

My opinion is to break it in exactly as the engine builder wants you to otherwise his warranty will be void. If not the engine builder then follow the cylinder manufacturers recommendations (which should be the same as the engine builder).

No warranty? No instructions from the cylinder company? Use mineral oil. Run it hard for longer periods. In other words no pattern work. Monitor oil consumption. When it stops using oil, it's broken in.

What is running the engine hard? I ran mine at 2600 rpm unless I was landing.

When I had an engine with a oil screen for a filter I changed my oil at 5 hours to get rid of the initial break-in junk. I continued using mineral oil until the next oil change at 10 hours (15 hrs total). The oil consumption stabilized but I had mineral oil to use so I ran it for one more oil change of 25 hours.

When I had an oil filter changed the filter only at 5 hours and cut it open to be sure there was nothing with part numbers in it Piece of mind really. Ran the engine hard till oil consumption stabilized, then ran it normally and changed the oil and filter at 25 hours (30 hrs total) and started using AD oil.

I've broken in 3 engines using the above basic guide.

Depending on the cylinder makeup you may never see any oil consumption. I broke in a Lycoming with Cerma-nil cylinders following the engine and cylinder manufacturers instructions and it only used 1/2 qt of oil in the first 25 hours. Essentially it was broken in in the first hour of two.

OH boy, I don't think I want to wade into this. You will probably get about a zillion opinions on how to do this. The best opinion would Probably be from the engine manufacturer/builder. Having said that, I've broken mine in by shallow climbing to 6500-7500 ft and flying at 75% power for a couple hours. At this altitude that is basically wide open throttle. If you have 6 cylinder head temp indication,(which most of us don't) keep it under design red line.

What Bruce said.
Lower altitudes will assist in heat control for the first few hours. (Denser air will carry away heat better.) Avoid long climbs at slow speeds. (Keep speed up.)
When you see cyl heat temps drop and oil consumption nil..it's broken in. Change the oil to AD and enjoy your regular flying habits.