Engine Break-in

[cdeerinck]

In the Lycming Operator's manual for O-360 and associated models, Section 3, page 3-1, there is the following paragraph:

New engines have been carefully run-in by Lycoming and therefore, no further break-in is necessary insofar as operation is concerned; however, new or newly overhauled engines should be operated on straight mineral oil for a minimum of 50 hours or until oil consumption has stabilized. After this period, a change to an approved additive oil may be made, if so desired.

NOTE
Cruising should be done at 65% to 75% power until a total of 50 hours has accumulated or oil consumption has stabilized. This is to ensure proper seating of the rings and is applicable to new engines, and engines in service following cylinder replacement or top overhaul of one or more cylinders.

How does one resolve the "no further break-in is necessary" with the requirement to accumulate 50 hours at 65%+ power. Doesn't that constitute "further break-in"?

Also, at how many hours does oil consumption typically stabalize?

[j-red]

at how many hours does oil consumption typically stabalize?

Excellent question and I imagine the answer will vary for each engine. Just for a point of reference, I've got about 20 hours on my overhauled o-360 and have yet to see ANY measurable oil consumption. I'm using Phillips XC 20x50 which is not a pure mineral oil, but is rated for breakin and is used by at least one top-rated shop which recommended it. 6 Qts in the sump. Oil and filter was changed at 10 hours just for good measure after the rebuild, but there was no noticeable consumption at that point, nor has there been in the 10 hours since.

[BillL]

I think the "oil consumption stabilized" is the key. Once done, no further break-in oil would be needed. CHT's should fall too, as friction drops and stabilizes along with oil consumption. Each ring/barrel material combination will have it's own break-in requirements. I take it that the Lyc factory recommendation is for plasma faced rings and nitrided steel barrel.

Maybe some of the Lyc school graduates can add more.