In my last column, Breaking in a new engine in the Aug. 24 issue, I discussed the mechanics of breaking in an engine. In this column I will discuss some of the steps every pilot should take during break-in.
The first decision is what oil to use for break-in.
Here, again, you need to refer to the manufacturer’s recommendations as a starting point. Lycoming recommends breaking in all naturally aspirated engines on straight mineral oil and all turbocharged engines on AD oil. (There are special requirements for the O-320H model engines.)The difference is in the cylinder pressure required to produce adequate ring force against the freshly honed cylinder wall to wear in the surface.
The biggest concern about break-in of the cylinder is glazing. This was more common with the old hard chrome cylinders when pilots would “baby” their new engines so as to not hurt them.
The lack of adequate ring pressure and friction resulted in the rings not knocking off the little peaks left from honing, leaving more oil in the valleys, which can coke up, leaving a varnish or glazed surface.
With a turbocharged engine there should be adequate cylinder pressure to seat the rings even if someone tries to “baby” their engine.
Additionally, some of the new types of chrome processes leave a much different surface so they may not recommend using mineral oil for break-in.
So always check with the manufacturer and rebuilder for their recommendations. It will make life much easier in case of a problem.
The second step is operation. If your new engine is from the factory or a large rebuild company that has a dynamometer, then the first step of the break-in has been completed.
When new pistons and rings are installed, the coefficient of frictions is very high until the smoothing out of the cylinder wall is done. Much of this can be done on the dyno run.
If this is a field overhaul, then the first few hours of the break-in will be done in the air.
In this case it is important not to overheat the engine on climb out. So on the first flight, take off at full power, then climb out watching the oil and/or cylinder head temperature (CHT) so as not to overheat the engine because of the added friction from the new cylinders.
If you just have an oil temperature gauge, do not go over 240°F during climb out.
Most of the old timers will just cruise around or near the airport to check out the engine at high load, like 75% power.
After these first few hours, change the oil and filter to get rid of all of the iron filings. This will have been done at the factory for a new engine.
Run this second change of oil for 10 to 15 hours and monitor the oil temperature and the engine performance. Then change the oil and filter and run this change for about 25 hours or so.
If after this third oil change, the oil temperature is down to normal range and the oil consumption has returned to normal, I would consider the engine to be broken in.
I do not recommend oil analysis on these first few changes because of the low hours. An analysis will usually come back with a warning about high iron from the break-in process.
For the lifters, if you use the STP additive for assembly, then you will have some zinc-containing additive to help the cam and lifters run in. Others have used the Lycoming LW-16702 additive for cam lubrication during break-in, this is especially true for O-320H models.
An added point is if you break in your engine on straight mineral oil, the lack of an ashless dispersant tends to allow more varnish coating on the lifters. This reduces the possibility of rusting during the life of the lifter.
A final point is fuel. All of the test results and the experience of many people in the field indicate that it is very important to do the break-in period on a fuel with some lead content.
This does not mean that you have to use straight 100LL.
For 80/87 engines with a proper STC, you can run a mixture of, say, 25% 100LL and 75% mogas. This will give you the same lead level as the original 80/87 fuel.
You can use this mixture for the entire life of the engine, but it is much less critical after break-in.
I know people get tired of the “follow the manufacturer’s/rebuilder’s recommendations” line. But there are enough model to model variations that it is very critical to follow whatever recommendations the people who are warranting your particular engine give.