Mike Busch, author of “the big book on piston engines,” has a helpful article in the Jan/Feb 2019 issue of COPA Pilot, the Cirrus owners’ group’s magazine. Busch explains why engines need to be run hard for a few initial hours and then offers a concrete procedure:
Break in the engine by running it as close to maximum continuous power as possible without allowing any CHT to exceed 420F for Continental cylinders or 440F for Lycoming cylinders. Run it this hard for an hour or two until you see the CHTs come down noticeably , indicating that the lion’s share of the break-in is complete.
This requires running at nearly full throttle at a low altitude (the engine won’t generate more than about 75 percent power after climbing to an ordinary cruising altitude of 6,000 or 7,000′ due to the lower density of air molecules up there).
This is timely for me because we’ll be breaking in a new engine for the Cirrus SR20. After 14 years and roughly 2,000 flight hours it seems prudent to swap out the engine, despite the fact that it hasn’t given any signs of ill health (this is contrary to Busch’s recommendation to wait until the engine tells you it is sick and then maybe only replace one cylinder).
Maintenance shops say that they hate dealing with Continental and love Lycoming, which might be one reason why Cirrus has switched to the Lycoming IO-360 engine for the more recent SR20s. Our little cluster of T-hangars also contains at least one story of a Continental engine that failed after a few hundred hours due to manufacturing defects and terrible support from Continental (instead of sending out a new replacement engine for the nearly new aircraft, the best that Continental would do is take the old engine back, try to fix it, etc. That would have resulted in months of downtime at a minimum. So far the wisdom of the shops has been proven correct. We had some issues with our order and couldn’t even get a return phone call from Ernesto Rodriguez, the customer support manager at Continental. I kind of like the idea of the 200 hp 6-cylinder Continental engine in the SR20 as offering greater smoothness than a 4-cylinder engine (what Cirrus is buying now from Lycoming), but one notable feature is that the per-mile cost of engine reserve actually becomes higher for the older SR20 compared to the SR22 (they both use 6-cylinder Continental engines and the cost of overhaul or swap-with-reman or swap-with-new prices are almost identical between the 200 hp SR20 engine and the 310 hp SR22 engine, as you might expect given that the mechanical configuration is pretty similar other than dimensions). To minimize interactions with Continental and save about $12,000, perhaps the smarter thing to have done would have been to wait for the engine to get sick and then ship it to one of Busch’s favorite field overhaul shops (see previous post: https://philip.greenspun.com/blog/2018/08/13/euthanasia-for-aircraft-engines/).
Why do engines need breaking in? Busch has some interesting figures showing the grooves in a new cylinder that are supposed to make the barrel “oil-wettable”. These have a spiky top that you want to grind down with hard usage to slightly flatter. Busch says that ordinary Philips 20W-50 “might be a better choice for break-in oil” than the traditional straight-weight Aeroshell W100.