Overhauled Engine Break-In

[Cruiser]

I believe you have it right. As it was explained to me, the regular oils have additives that hold the contaminates in the oil, something you do not want to happen when the engine is new and the amount of these contaminates is much greater than normal.

Mineral oil has no additives to retain the contaminates and therefore they "fall out" as sludge and are not recirculated thru the engine over and over until you change the oil. At least that is the way I understood it.

I doubt anyone can come up with data from a study that would support the claims one way or the other. Therefore, the newer "it doesn't matter" crowd can say use normal oil. For me it was a matter of it can't hurt to start with mineral oil and then change to regular AD oil after break-in. Maybe it will help a little, but it certainly won't hurt. I followed the OEM recommendation.

Do what you want, in the words of the now infamous BP engineer........ “Who cares, it’s done, end of story, will probably be fine.........."

[CoachTom]

To answer a few of the questions raised as I have an immediate need to work this through, I have found out through reading TCM Service Bulletins, ECI Cylinder break in procedure bulletins, and also Lycoming for reference: the mineral oil is used because you want the rings to "cut" through the oil and wear down the peaks of the cylinder wall created due to the honing process. You would not need AD oil because you change it and the filter out with very low engine times (IIRC: 4 hrs, 10 hrs, 15 hrs) and then transition to AD single or multi weight after break in. The two critical ingredients for the breaking in of the cylinders and rings are high combustion chamber pressure and low temperatures (hence the 85% LOP question).

The repair facility is going to break in engine for me (in flight) so I will not have to wrestle with the first few hours of fuel supply settings and excessive oil consumption as I have a 2 hour flight home. It is a necessary step for me as I do not have the luxury to spend a day or two to sit, watch, and participate in the final steps of the rebuild.

The break in point according to TCM is around 4 hours and is indicated by a drop in CHT (-50 deg) and oil consumption stabilizes.  after that i believe it just gets better.  The last figure i know is that 75% of your total engine wear occurs during break in and the other 25% over the next 1800 hours.

So as we all can see, there is many explicit directions by the manufacturers and stuff that others swear by, and it all make me sweat as I see the huge chunk of money invested in an engine rebuild possibly being wasted on cylinder glazing due to improper technique...

I guess this is clear as mud and hope to have a better answer in a few weeks after i fly it home and can relate the tale of the tape.

Cheers!

[scottfromiowa]

 

Here is a key item taken from the info provided by ksmooniac link: "If there's anything approaching consensus on which oil is best to use during break-in, it's this: To obtain the ring-to-barrel contact needed, most naturally aspirated engines will require a non-detergent or straight mineral oil.

The thinking here is that mineral oil lacks the complete additive package found in the typical ashless dispersing oil so it allows better contact -- and a bit more friction -- between the rings and cylinder walls.

This, combined with the lower combustion temperatures of a rich mixture, will give the rings the time needed to seat without overheating and losing their heat treatment."

I really think it is VERY CLEAR.  Keep Cylinder Temps Low by running Rich or lean of peak.  Use non-detergent or straight mineral oil...Not so much to remove particles, but to hone the rings to the cylinders...Fly correct power setting to ensure good manifold pressure...No power off or low power decents...

Thanks KSMooniac.  The articles were GOOD STUFF!

[craigsteffen]

Quote: KSMooniac

85% LOP would be better than any of the ROP settings IMO.  Higher power and cooler CHT (ie hi-power LOP) is optimal.  I would skip the mineral oil too and use whatever oil you plan to run.

[CoachTom]

Craig,

The percent isn't related to the air fuel mixture, but it is the ratio of power.  You are correct in the term LOP or ROP is the "distance" from peak temperature but the point i think you miss is the method of employ of those terms.  By a cylinder being ROP, it is using fuel to "enrichen" the mixture and slow the burn down as the flame spread is predicated upon density.  LOP is the opposite wherein the mixture does not have "enough" fuel in the ratio to burn and it does not generate the heat. Hence in the break in process, 85% LOP uses less fuel and creates more internal pressure on the rings since the engine is working at a higher horsepower than running at 75% ROP using fuel to cool the combustion heat generated.

The compression cycle is a very simple event and we sometimes take for granted how our automobiles through use of knock sensors and Mass Airflow Sensors adjust rapidly the fuel deployed inside of our cars combustion chambers.  Our aircraft engines are simplistic, 60 year old technology that sometimes seems on a par with a lawnmower. 

Suggest you read and research as much as you can regard engine theory as it will help you understand (just like aerodynamics helps you understand lift and flight) how the aircrafts performance varies with density altitude and its settings.

Whew... now I am out of gas after all of that. Don't be afraid to ask, there is always someone here who has the right answer or knows where to find it!

V/R

[DaV8or]

Quote: CoachTom

LOP is the opposite wherein the mixture does not have "enough" fuel in the ratio to burn and it does not generate the heat. Hence in the break in process, 85% LOP uses less fuel and creates more internal pressure on the rings since the engine is working at a higher horsepower than running at 75% ROP using fuel to cool the combustion heat generated.

[danb35]

When LOP, the only way to know how much power you're making is to know fuel flow.  With 8.5:1 compression and LOP operations, fuel flow (in gph) * 14.9 = horsepower.  For the turbos that run around 7.5:1 compression ratios, the multiplier is different; I think I remember hearing 13.7, but I wouldn't bet on it.