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All Broken In?..

Ironflight

VAF Moderator / Line Boy
Mentor
It was almost a month ago that we decided to replace all four cylinders on the Valkyrie?s 1500-hour engine due to excessive oil consumption and low compression. It really didn?t take very long to get the new jugs in hand (a couple of days from A.E.R.O.), the old jugs removed, the engine compartment cleaned up, and the engine re-assembled. All-in-all, about a week for the mechanic work while doing my normal job. Unfortunately, I also had a week-long business trip and another week spent at Sun ?n Fun thrown in there, so it wasn?t until last week that we were really able to fly the airplane and break in the new Nitrided Lycoming cylinders.

The break-in philosophy was as documented by Lycoming, ECI, and Mattituck (all three have handy reference guides). 65-75% power to provide adequate but not excessive BMEP to seat the rings, shallow climbs to keep lots of cooling air going through the cowl, careful monitoring of CHT?s to make sure that things didn?t get out of hand, and richer-than normal mixtures to help with temperatures (and probably to buy another yacht for the CEO of Exxon?). As expected, the first few hours exhibited CHT?s in the low 400?s, peaking about 430, and oil temps (reflecting the heat that had to be removed ) up around 220. I tried to keep the flights confined to the early morning hours to provide for lower ambient temps, since summer seems to have arrived on the Texas Gulf Coast.

It was about hour number seven, cruising over to Louisiana for lunch at 3,500?, when I noticed a fairly rapid drop n CHT?s and a corresponding fall in Oil temps. The CHT?s went down from 425 to about 370 in a ten minute span, with nothing else being touched, and the oil dropped down to about 195. There was much rejoicing ? the break-in seemed to have occurred! We enjoyed a nice lunch and departed for Houston about 1330 local, but alas, the airplane had been sitting in the sun, little cooling had occurred, and we had to climb for altitude in the heat of the day ? CHT?s were back in the 400?s again. Oh well?patience is a virtue, we were still in the early hours of these cylinder?s lives. The next flight was later that evening, and once again I saw the break-in signature after leveling off at cruise- ten minutes of higher than normal temps, followed by a drop all around.

The next morning I launched again, and this time, there were no high temps at all ? everything appeared to be much closer to ?normal? for this airplane, and I took that as a sign that the Val waned to shake things out a bit, so we commenced to yankin? and bankin?. I had avoided aerobatics completely because the slower speed associated with a couple of G?s is not conducive to good cooling. Sure enough, through ten minutes of lops and rolls, the temps all behaved normally ? slightly elevated, but within the ?good? band.

When I landed, I noted the time on the EFIS showed just shy of ten hours since the jugs were installed ? about normal for a good break-in period. It?s too early to get an oil usage trend of course, and we?ll keep the break-in oil in the sump until it?s time for a change, but overall, it looks like the transplant has been a success and I expect the Val to go a long way on these new jugs. A great side-benefit, of course, was the thorough going-over of the entire FWF installation, with lots of little tweaks, fixes, and clean-ups ? well worth the time after six and a half years of constant flight.

Paul
 
good to hear

That the breakin is going well. Sounds like a textbook lycoming breakin. I am confident those lycoming cyl's will serve you well.

bird
 
Paul,

(and probably to buy another yacht for the CEO of Exxon?).

Nothing wrong with your break in procedure, but there is a cleaner and more cost effective way ;)

DB
 
It drags out all the flat earthers....Doom and Gloom.....The manual says this and anything else is BAD/Wrong.

The way I will break in all future engines is ........... (sshhhhh just quietly while nobody else is listening) at a power setting of say 27.5" and 2500RPM and around 50Litres/13.2USG per hour which happens to be 75% power and around 45-55F LOP. (see table below *)

The CHT's will be lower, the break in just as effective, less deposits and a whole heap less fuel used. In fact I used this power setting yesterday to demonstrate what happens.....funny enough the data backed, fact based science works! ;)

But heck.....who wants to listen to that when the OWT's are so much more believable? :D

Of course if you can't get your engine to operate like that, best to either get it to quickly or leave the red knob full bore until such time as you can.

By the way, the practise of leaving spats and fairings off during break in is NOT a good idea.

It drives me nuts after seeing our first flight or two without them compared to with them. CHT's much better with. I will never do that again, if I want to check for brake leaks and problems I will unscrew them.

Here on VAF we should take an oath to stop engine cruelty, and part of that is never break in with spats/fairings off.

Mates don't let mates abuse their engines! :)





*Table of fuel flows for different engines in the RV fleet. This is done beyond 40deg F LOP and around 75% power.

150HP 7.55GPH
160HP 8.05GPH
180HP 9.06GPH
 
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Well, geez, if you're going top give away ALL my secrets Oz...... Yes, the last couple of hours were done LOP because that's where cooler CHT's can be found at close to a reasonable fuel flow. I like to use full rich initially because you get the coolest overall temps (although cooling the cylinders with fuel is not that efficient and terribly costly) - then when I think everything is on the way, I went to the lean side. Conservative mechanically, wasteful of resources - but it makes me comfortable.

(Of course, this assumes that you have an engine/fuel system that will run smoothly LOP - some don't)

Paul
 
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.......The way I will break in all future engines is ...........

(sshhhhh just quietly while nobody else is listening) at a power setting of say 27.5" and 2500RPM and around 50Litres/13.2USG per hour .......

By the way, the practise of leaving spats and fairings off during break in is NOT a good idea.

Except at those power settings, some of us are smoking right along (I'd be over 180kts). Not a good combo around here the mountain waves and turbulence was killing me and I was unable to run those settings for very long. I'll be sans pants next time.

New motor, new airframe, rookie pilot might not be a good engine breakin policy anyway.
 
PD

I was surprised that you hadn't, but you sneeky critter you were just trying to dodge the flat earthers :D And stir up the oil execs ;) They deserve it, its not political....its fact!

Hydro guy, if your CHT's are well under control, fine, if you want the extra drag, but running around for any period of time over 400 is not optimal so why do it. I assume you were doing something like 75% power with extra drag?

Cheers
David
 
*Table of fuel flows for different engines in the RV fleet. This is done beyond 40deg F LOP and around 75% power.

150HP 7.55GPH
160HP 8.05GPH
180HP 9.06GPH

Hi David,

I haven't had the benefits of your APS education so perhaps you could explain the following to me.

Your table above confirms my understanding that HP is directly related to FF when LOP. However I would have thought that rpm is also a factor as there are higher pumping and friction losses at higher rpm.

LOP and Peak EGT have almost the same BSFC and Lycomings Part Throttle Fuel Consumption graph shows different HP at different rpm for the same FF at Peak EGT.

For example for a 160 HP I0-320 operating at Peak EGT, a FF of 8.3 GHP will produce 120 HP (75%) at 2,200 rpm but the same 8.3 GPH also at peak will only produce about 108 HP (67/68%) at 2,700 rpm presumably due to pumping and friction losses. Why would the same relationship with rpm not apply when LOP:confused:

Fin
9A
 
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Finley,

Have a close look at this graph, courtesy of another thread and APS.

KeyLOPICPBSFCCHT.jpg


Not sure which graphs you are looking at but this one represents all engines, lawn mowers, P&W radials, and yours.

As for higher RPM losses, this is true, engine losses and prop efficiency all add up, but we are splitting hairs a bit. Pick a nice smooth RPM that works for you. Balance your prop too!

As for LOP, Fuel flow determines HP, there is more O2 than fuel, so hence Lean of peak, thus fuel is the key factor. No spare fuel particles. On the Rich side of peak there is no O2 left so to speak, but ample fuel, and detonation margin notwithstanding, varying fuel flow has very minimal impact on HP. So Mass Airflow is king.

At the end of the day, splitting hairs is not relevant as you can not fly that way nor set all 4/6 cylinders that way.

Basically you have it pretty much sorted :) By the way, LOP and at 75% power fuel flow should be about 8.05GPH, so 8.3 would in theory at least be ROP, but not a lot! ;)

Cheers.
 
....Hydro guy, if your CHT's are well under control, fine, if you want the extra drag, but running around for any period of time over 400 is not optimal so why do it. I assume you were doing something like 75% power with extra drag?

Cheers
David

My CHT's were low for my break-in. I did my phase one during the winter, so OAT's were 0*F or as high as 20*F. I should have taken the pants off. 25"2400rpm with a rich mixture and I'm 175kts+ TAS. To keep good MP, I had to stay in the valley coupled with wind coming over the ridges made me uncomfortable in the turbulence and high speed. I also was fighting a unstable roll at speed(aileron hinge high 1/16" left wing)

Probably my biggest issue, I was in a 200mph plane and only had a 100mph brain. :eek:
 
Not sure which graphs you are looking at

Lycoming 0-320 Operators Manual Fig 3-10 Page 3-22.
As for higher RPM losses, this is true, engine losses and prop efficiency all add up, but we are splitting hairs a bit.
I think you are missing the point I am making. You give a definite fixed figure for 75% LOP fuel flows. I am suggesting the figure is not fixed and will vary considerably depending on rpm. For example, using the above graph, 75% fuel flows at Best Economy (peak EGT) can range between about 8.9 GPH at 2,700 rpm down to about 8.3 GPH at 2,200 RPM. LOP and Peak have about the same BSFC so I assume there would be the same range in fuel flows for LOP. The range is even greater (7.1 to 8.0 GPH) at say, 65% power as rpm can be reduced to 2,000 rpm.

I have a carb engine with a CS prop and run at 2,200 rpm at peak (or LOP if possible) up to a max 65% power and I know from the above graph that 65% power will be at 7.3 GPH so I make sure I don't exceed this FF. However someone with a FP prop that may be running at say 2,500 rpm would know from the above graph that they could have fuel flows up to about 7.75 GPH to not exceed 65% power at peak or LOP at that rpm.

By the way, LOP and at 75% power fuel flow should be about 8.05GPH, so 8.3 would in theory at least be ROP, but not a lot!

Got my 8.3 figure from the above graph and if my thinking is correct then it could even be up to 8.9 GPH if at 2,700 rpm.

I am happy to be corrected on all this.:)

Fin
9A
 
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So long as your instruments are known to be accurate, go fly and test it for yourself.

Email me the data and lets talk on the phone.
 
Our factory overhaul 200 HP IO-360 in our Mooney 201 is showing symptoms much like Paul's. Our CHTs were in the 370 range full rich (cowl flaps 1/2 open) for the first couple hours. Anythine less than full rich would go over 400 quick.

Then, they gradually trended downwards over the next 4 hours to around 350 half open and 390 closed. With 20 hours on it now, we were starting to get worried. LOP 50 degrees (10 GPH) we still could not close the cowl flaps and keep a <380 CHT. Old engine was 330 with cowl flaps closed easily and it had 25 degrees timing.

So, at about hour 20, cowl flaps closed, 75% power, 370 CHT, they dropped in the span of a few minutes to 330. Woohoo. Finally. It still creeps up to 380 at times but not as easily.

The engine has used perhaps 1/2 quart in the first 20 hours. It must be tight.
 
Break in?

I am about to contradict Paul ? something along the lines of proceed at your own peril has entered into mind.

I have been reading accounts of CHT drops being indicative of break in. I have a tough time believing it. I don?t think that the slight additional friction in the cylinders associated with unseated rings would be reflected as such a significant increase in temp at the CHT probe locations.

I think what we are seeing is formation of insulating deposits on the piston crown and combustion chamber of the head that occurs in the first few hours of operation. And the richer we run, the faster it builds up.

Many of us run lean and burn mogas. I may be wrong, but both of those operating conditions typically lead to reduced deposits, perhaps leading to increased heat transfer to the piston and head ? relative to what we might have seen running rich with LL. Our engines evolved running rich on heavily leaded gas. And the metal in our heads is already critically hot due to air cooling.

So, where I am headed with this? Perhaps ceramic coatings of the piston crown and combustion chamber would be beneficial in this day and age. Anybody with experience using them. Reno racers?
 
It's not just the rings, I don't think. There's lapping going on in the rocker box. Valve tip/rocker arm, push rod/rocker arm. Also wear-in friction on rocker shaft and valve guides. Wouldn't those account for a little break-in heat? Or would that be negligible?
 
I am about to contradict Paul ? something along the lines of proceed at your own peril has entered into mind.

Hey, no problem here - I am always learning more about aircraft engines from the folks that have been building them for decades. CHT drops have always been an indicator of break-in according to them, and it has worked well for me in the past. I can't tell you the why and the mechanism for sure, so won't debate it.

Paul
 
why do CHTs drop after break in?

Hey, no problem here - I am always learning more about aircraft engines from the folks that have been building them for decades. CHT drops have always been an indicator of break-in according to them, and it has worked well for me in the past. I can't tell you the why and the mechanism for sure, so won't debate it.

Paul
I'm starting to plan for my first engine start and hopefully soon after break in, and as usual, overthinking everything. I just found this thread, and it did trigger a question - why would CHTs drop when the rings seat?

In the many years that have passed since this discussion, has anyone come up with some ideas?

The only factors I can think of are:

1) when rings are not seated, some combustion gasses escape down the side of the piston/cylinder wall, perhaps causing more heat to get conducted to the head;
2) combustion energy is "wasted" when the gasses leak past the rings, causing less efficient power generation for a particular fuel flow/RPM;
3) the thermal insulation due to deposit buildup from carbon and lead on the head/piston theory mentioned above.

Anyone have any other ideas?
 
I'm starting to plan for my first engine start and hopefully soon after break in, and as usual, overthinking everything. I just found this thread, and it did trigger a question - why would CHTs drop when the rings seat?

In the many years that have passed since this discussion, has anyone come up with some ideas?

The only factors I can think of are:

1) when rings are not seated, some combustion gasses escape down the side of the piston/cylinder wall, perhaps causing more heat to get conducted to the head;
2) combustion energy is "wasted" when the gasses leak past the rings, causing less efficient power generation for a particular fuel flow/RPM;
3) the thermal insulation due to deposit buildup from carbon and lead on the head/piston theory mentioned above.

Anyone have any other ideas?
I am no expert on this, but your point 1) if combustion gasses are escaping past the rings wouldn't it be going away from the head? That would put combustion gasses into the crankcase and out the vent.
 
I'm starting to plan for my first engine start and hopefully soon after break in, and as usual, overthinking everything. I just found this thread, and it did trigger a question - why would CHTs drop when the rings seat?

In the many years that have passed since this discussion, has anyone come up with some ideas?

The only factors I can think of are:

1) when rings are not seated, some combustion gasses escape down the side of the piston/cylinder wall, perhaps causing more heat to get conducted to the head;
2) combustion energy is "wasted" when the gasses leak past the rings, causing less efficient power generation for a particular fuel flow/RPM;
3) the thermal insulation due to deposit buildup from carbon and lead on the head/piston theory mentioned above.

Anyone have any other ideas?

Freshly honed cylinders seal quite well and blowby or power / efficiency are not factors. Most engine shops dyno and measure power prior to ring seating is complete.

cylinder honing leaves a rough surface with millions of peaks and valleys from the surface abrasion. The peaks are very sharp and don't give a smooth surface for the ring to ride on. During the ring seating process, the friction of the flat ring surface riding over these sharp peaks, with enough pressure from combustion, will create a lot of wear and resultant heat. Over the seating period, this process will wear down those sharp peaks by some amount until they have a flat and wide enough surface to hold some oil and reduce friction. Maybe a 1/4 or 1/3 of the peak will be worn away to create this flat surface. You want a good amount of valley left to hold oil and nice flat surface on the peaks. Due to the metallurgy and other factors, the wear will stop at the point where the friction level is near optimal between the ring and cyl wall. However, not keeping enough pressure on the ring can permanently stop the seating process with valleys that are too large. This creates excess oil consumption.

As with any operation that removes metal via wear/friction you will have heat produced. Once the seating process stops, the excess heat caused by it disappears.

Larry
 
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I'm starting to plan for my first engine start and hopefully soon after break in, and as usual, overthinking everything. I just found this thread, and it did trigger a question - why would CHTs drop when the rings seat?

In the many years that have passed since this discussion, has anyone come up with some ideas?

The only factors I can think of are:

1) when rings are not seated, some combustion gasses escape down the side of the piston/cylinder wall, perhaps causing more heat to get conducted to the head;
2) combustion energy is "wasted" when the gasses leak past the rings, causing less efficient power generation for a particular fuel flow/RPM;
3) the thermal insulation due to deposit buildup from carbon and lead on the head/piston theory mentioned above.

Anyone have any other ideas?

Friction of the new rings against the newly honed cylinders and the lack of friction modifiers in mineral oil? Just a completely uneducated guess.
 
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