Engine breakin

J

JOhnH

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I have about 12 hours, including bench time, on a rebuilt O360 in my 1977 Cessna 172N.
So far we have been making 2 hour flights at around 2-3000 ft at 2550 rpm (+-50rpm) and full rich.

CHT in level flight has not really gone down significantly on any cylinder yet. Maybe a tiny bit. It seems to fly very well.

According to the JPI 700 monitor:
#1 CHT runs around 399degrees
#2 CHT runs around 383
#3 CHT runs around 412
#4 CHT runs around 422

Oil temp runs around 204
OAT is high 80's low 90s.

CHT for #3 & #4 exceed 450 during takeoff (for just a few minutes).
My mechanic is mostly concerned about #2 not running hot enough to set the rings.

We are planning a trip to from FL to N.C. next week. We plan to fly around 5,500 ft msl. My question is whether we should lean it as normal or should we leave it full rich and make an extra fuel stop?

We expect to have about 25 hours on the engine when we return and will have the oil changed at that time.
 
The rare instance mine has gotten over 400F I was looking for molten aluminum to start spewing out from the lower cowl, I would freak if mine got to 450 even during break-in. Despite what the manufacturer says is the limit
What is the cylinder wall, steel or ?
 
Sounds like chrome...

If it is, someone should have their head whacked...
 
One should work hard to not exceed 400F during climb, or at any other time. This is done by trimming ASAP to a reasonable speed.

On the TB20 (with the engine 300hrs after an OH) I have to trim to 120kt more or less right away, to keep the hottest cylinder below 400F, or 420F if departing in hot places e.g. at +35C.

The same applies when running in a new engine, but the temps will be harder to keep down.
My mechanic is mostly concerned about #2 not running hot enough to set the rings.
Click to expand...

IMHO there is no basis for this concern at all. What you need to set the rings is plenty of cylinder (combustion chamber) pressure, which is why one flies at a higher power setting than normal.

It can take a suprisingly long time for a new engine to settle, in terms of oil usage. The cyl temps settle sooner. Mine was oiling the lower plugs in a couple of cylinders, for about 150-200hrs. Now it is clean.
 
You want to get the rings to seat quickly before they and the cylinder walls glaze. To do that, you need high power settings, 75% at least and even some full-power time. We follow Lycoming's recommendations for all the engines we install, and the oil consumption is down to normal by the time 50 hours comes up.

Too many folks are afraid to run them hard. It will be difficult to do with OATs high, because the temp limits might be exceeded and the density altitude could be too high to get 75% power. Consult the POH and see just what power settings you need to get 75% and 65% at the altitude and temperature you're operating in.

Lycoming's recommendations: http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1427B.pdf

Dan
 
Dr. O said:
Sounds like chrome...

If it is, someone should have their head whacked...
Click to expand...

I had chrome cylinders on a rebuild once. They never did break in. Replaced them with steel and it broke right in and everything went perfect. I hate chrome cylinders. I wouldn't put them on a lawn mower.

I'm just sayin' ..... :skeptical:
 
JOhnH said:
I have about 12 hours, including bench time, on a rebuilt O360 in my 1977 Cessna 172N.
So far we have been making 2 hour flights at around 2-3000 ft at 2550 rpm (+-50rpm) and full rich.

CHT in level flight has not really gone down significantly on any cylinder yet. Maybe a tiny bit. It seems to fly very well.

According to the JPI 700 monitor:
#1 CHT runs around 399degrees
#2 CHT runs around 383
#3 CHT runs around 412
#4 CHT runs around 422

Oil temp runs around 204
OAT is high 80's low 90s.

CHT for #3 & #4 exceed 450 during takeoff (for just a few minutes).
My mechanic is mostly concerned about #2 not running hot enough to set the rings.

We are planning a trip to from FL to N.C. next week. We plan to fly around 5,500 ft msl. My question is whether we should lean it as normal or should we leave it full rich and make an extra fuel stop?
Click to expand...

Keep in mind that I'm just a drag racer that doesn't really know much about Lycomings, but

1) CHT shouldn't have anything to do with the rings seating. Rings need combustion pressure to seat properly. In cars you do it by accelerating and decelerating lightly.

2) The rich fuel mixture can wash the oil off the cylinder walls and cause scoring. If it wasn't for your high CHT, I'd be concerned.
 
Capt.Crash'n'Burn said:
Keep in mind that I'm just a drag racer that doesn't really know much about Lycomings, but

1) CHT shouldn't have anything to do with the rings seating. Rings need combustion pressure to seat properly. In cars you do it by accelerating and decelerating lightly.

2) The rich fuel mixture can wash the oil off the cylinder walls and cause scoring. If it wasn't for your high CHT, I'd be concerned.
Click to expand...


!. CHT can rise some when the rings are generating considerable friction. The cylinder barrel is attached to the head, after all. Mostly, the oil temp will be higher.

2. Gasoline washing oil off cylinder walls happens only when the engine is flooded. At those rich mixtures the fuel won't even burn. Rich mixtures are used in flight to help cool the engine; the excess fuel absorbs heat through evaporation and the richer mixture burns without approaching detonation, which can raise CHTs.

Gasoline will combust only at mixtures of between 8:1 and 18:1 (weight of air:weight of fuel). Inside the fuel tank the mixture is far higher than 8:1 and so the electric fuel gauge sender, which is a wirewound potentiometer in most older aircraft and which makes sparks when it's failing, doesn't set off the vapors in the tank. The danger is when the fuel cap is off and the mixture near the filler neck leans enough to explode if a spark gets to it. Or if the tank has been drained but still contains fuel vapors. We're awful careful around tanks when they're opened up in the shop for any reason.

Dan
 
So if I fly at 5,500ft, should I lean or not?
 
JOhnH said:
So if I fly at 5,500ft, should I lean or not?
Click to expand...
Personally, I wouldn't fly until I found and fixed the problem causing those excessive CHTs. Full rich and 75% power at 2500 feet shouldn't run anywhere near that hot, breaking in or not. And until the engine is broken in I'd stay low with high power and a fairly rich mixture (but probably not "full rich" if slightly leaned will result in CHTs in the 380F range). At 5000 feet it's very likely you need to lean as the combination of WOT and high altitude will enrichen things considerably.
 
JOhnH said:
So if I fly at 5,500ft, should I lean or not?
Click to expand...

From Lycoming Service Instruction 1427B:

1. Start the engine and perform a normal preflight run- up in accordance with the engine operator’s manual.
2. Take off at airframe recommended take off power, while monitoring RPM, fuel flow, oil pressure, oil temperature and cylinder head temperatures.
3. As soon as possible, reduce to climb power specified in operator’s manual. Assume a shallow climb angle to a suitable cruise altitude. Adjust mixture per pilot’s operating handbook (POH).
4. After establishing cruise altitude, reduce power to approximately 75% and continue flight for 2 hours. For the second hour, alternate power settings between 65% and 75% power per operator’s manual.
NOTE
If the engine is normally aspirated (non-turbocharged), it will be necessary to cruise at the lower altitudes to obtain the required cruise power levels. Density altitude in excess of 8,000 feet (5,000 feet is recommended) will not allow the engine to develop sufficient cruise power for a good break- in.
5. Increase engine power to maximum airframe recommendations and maintain for 30 minutes, provided engine and aircraft are performing within operating manual specifications.

Note three things: (A) Item 3 asks you to lean as per POH. Lycoming does not want you to run it rich. (B) You can't develop enough power at higher altitudes. (C) The last half-hour calls for maximum power; that means redline RPM, and max MP if it's a CS prop, provided the POH allows such operation. Some engines have a time limit on full power, and the POH will talk about that. You'd use the lower power for the half-hour run. An O-320 in a 172 has no limit, and I run them at 2700 (which takes full throttle) for that time. A 172 scoots along pretty good at that setting. And burns a lot of fuel, too. Don't lean it too much.

Dan
 
JOhnH said:
Nickel. "Four new Titan Cylinder assemblies with nickel barrels." Was that the answer to the question you asked?
Click to expand...
I have no personal experience with nickel but what I've read says this should break in pretty much just like steel (unlike chrome which is difficult to properly seat rings on). I'm wondering if there's any chance you have the wrong ring material. I think that steel rings are required for nickel but I'm not sure. If that's true any someone put in chrome rings (as required for steel cylinders) it probably would explain the high CHTs and lack of break-in at this point.
 
gismo said:
And until the engine is broken in I'd stay low with high power and a fairly rich mixture.
Click to expand...


I'm not all that shot up about flying low with a new engine that's running hot. Altitude gives me a choice of spots to set it down if needs be.

Have we considered that perhaps the CHT gauge is out of calibration? It only takes a pot of boiling water to do a single-point cal check.

Jim :cheers:
 
Have we considered that perhaps the CHT gauge is out of calibration? It only takes a pot of boiling water to do a single-point cal check.
Click to expand...

Jim, can that be done with a cht probe? (the water will boil taking it into the low 200s but the important range here would be 300-500F)
I know you can with an oil T probe...
 
Let'sgoflying! said:
Jim, can that be done with a cht probe? (the water will boil taking it into the low 200s but the important range here would be 300-500F)
I know you can with an oil T probe...
Click to expand...


If it's off at 212°F it'll be off at higher temps. I'd give it a shot. However, this is a multi-point system and I doubt that all four probes are off that much. The high CHTs are likely due to the high OAT.

Dan
 
weirdjim said:
I'm not all that shot up about flying low with a new engine that's running hot. Altitude gives me a choice of spots to set it down if needs be.
Click to expand...
"Low" as in low enough to produce 75% power or about 6000 MSL unless the OAT is high.

Have we considered that perhaps the CHT gauge is out of calibration? It only takes a pot of boiling water to do a single-point cal check.

Jim :cheers:
Click to expand...

Certainly possible and as you say easy to check. You can even get a pretty good idea looking at the gauge on a hot day with as cold engine.
 
Do a three point check. A container of ice and water mixed, a cold engine should read ambient temp and a pot of boiling water 212. That should give you a pretty fair ides of gage calibration.
 
Dave2 said:
and a pot of boiling water 212.
Click to expand...

Almost. I just taught a class at a 6000' elevation college and forgot to take into account the fact that water boils at a lower temperature at high elevations. Rule of thumb is to subtract 1.5°F for each 1000' up. Embarassing when the prof makes a boo-boo like that.

Jim
 
I scanned through most of the posts but didn't see the suggestion of swapping probes to see if the high temps follow the probes or stay with the cylinders. Also, remember that #3 and #4 are the rear cylinders, check the flexible baffle between the underside of the top cowl and the solid baffles, make sure the flexible portion is tall enough and is pointed forward to seal the gap when the compartment is pressurized. Were new baffles installed when your engine was hung? See: http://www.airforms.biz/catalog/index.php?cPath=21_57&osCsid=3145e11f3710ab6f41a5f84741394a38 for any pieces you may be missing. It sounds like the front cylinders are getting cooling from ram air but no air is moving through the top of the plenum and down through the rear cylinders.

For your flight, I'd fly at 2700 rpms with what ever mixture setting would allow me to keep those CHT's below 400. If full rich at 5000 ft, 2700 rpms doesn't keep your CHT's below 400 AND your baffles are in perfect condition, I would suspect lean mixture or a low fuel flow issue. Check the rubber connectors between the intake tubes and the sump.

You're not far from Zephyrhills (realatively) give Charlie a call or stop in for a vist. http://www.zephyrengines.com/homepage.html One of the most reputable engine shops in the country.
 
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