Cylinder Overhaul - questions

Caramon13

Caramon13

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Romeo
I got a question from a potential buyer the other day, not really sure how to answer it.

My plane had the #3 cylinder repaired last year as it had compressions in the low 40s. I've had a compression check done since the work was completed and everything looked good.

The plane is making power without issue, but the buyer was wondering why/if the repaired cylinder would last as long as the other three.

Some background:

As long as I've owned the plane (which has been SINCE the cylinder overhaul), #3 has ALWAYS been the hot cylinder. I had some baffles replaced on the engine and it's cooled down a bit, but it's not uncommon to see CHTs between 420 and 440 on my engine monitor. The only way to keep it really cool is to leave the mixture full rich until near target altitude and lean back in very small increments.

The last two oil analyses have also reported higher than average amounts of chrome, iron and nickel. I have Millenium cylinders, not Lycoming.

I just did an oil change yesterday (after about 25 hours of time), sample was sent off to Blackstone Labs so we'll see if things are any different probably in a few weeks.

Anyhow, appreciate any input. Thanks!
 
Lycoming op instructions specifically state that continuous operation with CHTs over 400* will shorten cylinder life. I'd try to get the CHTs down. Been there, done that. An overhauled cylinder is no concern.
 
Thanks @Stewartb ! The CHTs are usually about 400 (ish) with full rich until altitude, then I lean back and I can keep them below 400 for the entire trip. I think it's just an airflow issue and the #3 is in the back corner of the engine area so, airflow is probably STILL an issue for me despite new baffling.

Ultimately just means I have to either leave the mixture richer than usual or shallow the climbout to keep speed up and therefore airflow going over the engine. I didn't replace the baffles themselves, just the plastic tips on the baffling, so maybe that's another option, albeit a 3 AMU option ..:(
 
Stewartb said:
FYI- http://www.lycoming.com/Portals/0/techpublications/serviceinstructions/SI 1094D (03-25-1994)/Fuel Mixture Leaning Procedures.pdf
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Thanks! I do follow those steps, but it's mostly when I get up to the 5,000 feet altitude and start leaning back for power when the CHTs start REALLY getting warm. I have to keep it richer longer than I'd like. Most flights I'm at 5500 or less, but longer trips I'm up at 9500 or so and that makes for a very slow climb with an overrich mixture.
 
Mixtures and temps are an interesting topic. I always shoot for 150* minimum leaning authority with a carbed engine. That is, in normal warmed-up cruise I can get 150*+ between full rich and peak EGT. That keeps my full power temps in control and with that I don't have lean cruise temp issues. But I fly lower than most of you so very few extended climbouts.
 
That is waaaaaaaay hot. Check your baffling. I was going through this, and just by adjusting/replacing the baffling I was able to get a 40-50 degree drop in temperature. It was cylinder #5 for me.
 
@EdFred yeah, I was flying with a buddy of mine before the baffling change and he was maintaining a pretty good climb rate above 5K, I had leaned back as per the POH and Lycoming's requirements and we were passing about 6,000 when I looked down and saw the #3 redlining at 450. Immediately shallowed the climb and it came down.

Later found out someone had messed with the mixture setting on the engine itself and it was leaned back so that even at full rich, I wasn't getting full rich fuel flow. So, that was one reason for the ultra-high CHTs at even a low altitude and high airflow.

Fixed that and added some new baffling and I can keep the #3 and #2 at about 410 on a climb, but I do get CHTs for #3 upwards of 425 ish if I even look at the mixture wrong or touch it during a climbout. It's a stupid little dance I have to play balancing angle of climb, mixture, power requirements, etc...
 
Make sure that baffling has a good seal all the way around, and that you get some airflow behind that #3 cylinder. I had to add about 3/16" gap to coax the air behind #5. Went crazy with RTV, new silicone, and Gorilla Tape to get a good seal.
 
Is this engine fuel injected? or carb'ed
 
@Tom-D it's a carbed engine. Lycoming O-360-A3A, Piper Cherokee 180C. Has about 750 hours on the engine SMOH, which was done in 2003. Top overhaul done in 2010 and #3 repaired in 2015.
 
Caramon13 said:
@Tom-D it's a carbed engine. Lycoming O-360-A3A, Piper Cherokee 180C. Has about 750 hours on the engine SMOH, which was done in 2003. Top overhaul done in 2010 and #3 repaired in 2015.
Click to expand...

This is very typical for the Lycoming 180 horse engines, #3 is troublesome, and does not cool well.
What was done to the cylinder as a repair?

When all cylinders run 400 degrees and above and you can't get them to cool down by leaning USUALLY means that the carb is way too rich. what do your plugs look like? Black and sooty? you may need a new carb.
I've even seen the wrong carb installed.
 
Tom-D said:
This is very typical for the Lycoming 180 horse engines, #3 is troublesome, and does not cool well.
What was done to the cylinder as a repair?

When all cylinders run 400 degrees and above and you can't get them to cool down by leaning USUALLY means that the carb is way too rich. what do your plugs look like? Black and sooty? you may need a new carb.
I've even seen the wrong carb installed.
Click to expand...

Tom, I do need to look at the plugs, a carb overhaul was suggested at some point by the local maintenance shop, but haven't done one.

The repair for #3 was (from the work order):

Stud assembly with exhaust guide and intake guide replaced, seats cut and lapped, and cylinder honed to ring finish. Cylinder assembled with new valve cleaned, inspected, and reinstalled. Re-installed cylinder #3, exhaust, intake, baffles. Drained oil and serviced engine with 8 qts mineral oil.

I've put on about 130 or so hours on the plane since #3 was put in. When I lean, the CHTs go up, not down, sorta confused by your statement, shouldn't the temps go up when you lean not down?

The A&P that did the work I described in post 8 found that the mixture setting was actually way too lean, which meant that even at max mixture I couldn't cool the temps down, they just kept climbing. They adjusted it full rich and now mixture will cool the temps down during climb just fine.
 
Caramon13 said:
Tom, I do need to look at the plugs, a carb overhaul was suggested at some point by the local maintenance shop, but haven't done one.

The repair for #3 was (from the work order):

Stud assembly with exhaust guide and intake guide replaced, seats cut and lapped, and cylinder honed to ring finish. Cylinder assembled with new valve cleaned, inspected, and reinstalled. Re-installed cylinder #3, exhaust, intake, baffles. Drained oil and serviced engine with 8 qts mineral oil.

I've put on about 130 or so hours on the plane since #3 was put in. When I lean, the CHTs go up, not down, sorta confused by your statement, shouldn't the temps go up when you lean not down?

The A&P that did the work I described in post 8 found that the mixture setting was actually way too lean, which meant that even at max mixture I couldn't cool the temps down, they just kept climbing. They adjusted it full rich and now mixture will cool the temps down during climb just fine.
Click to expand...
Sounds to me like you can't reach the lean side of the mixture curve, you just reach the " Red box " in Dekins writings.
Which could mean your carb is leaking internally adding fuel that you can't control.

What it the mixture rise when the mixture is pulled.
 
Look critically at your (new) baffling to make sure it tightly wraps around the tips of the cyl fins. Not much opening between the tips and the baffle will allow cooling air to flow an easier path rather than thru the fins. And check the alignment of the raw head casting fins to make sure nothing (like casting flash) is reducing or partially blocking the airflow.

Some years ago I saw an aftermarket cyl manufacturer at Oshkosh that showed very mediocre fin mold alignment between the top and the bottom halves of the head casting. The salesman was unaware of this.

FWIW my opinion is that it doesn't make a lot of difference where the head is cooled, but that the net amount of air thru the fins of each cylinder is critical.

My standard pitch. Some of you may recognize this........
 
Read some of Mike Busch's articles on cylinders, leaning, etc. Good reading, good for understanding engines and maintenance. Don't believe those that poo poo his work. Read it first then decide. His seminars are packed.
 
Tom-D said:
Sounds to me like you can't reach the lean side of the mixture curve, you just reach the " Red box " in Dekins writings.
Which could mean your carb is leaking internally adding fuel that you can't control.

What it the mixture rise when the mixture is pulled.
Click to expand...

Well, before they adjusted the mixture, there was no rise. Now I get a slight RPM jump just before engine shutdown.
 
nrpetersen said:
Look critically at your (new) baffling to make sure it tightly wraps around the tips of the cyl fins. Not much opening between the tips and the baffle will allow cooling air to flow an easier path rather than thru the fins. And check the alignment of the raw head casting fins to make sure nothing (like casting flash) is reducing or partially blocking the airflow.

Some years ago I saw an aftermarket cyl manufacturer at Oshkosh that showed very mediocre fin mold alignment between the top and the bottom halves of the head casting. The salesman was unaware of this.

FWIW my opinion is that it doesn't make a lot of difference where the head is cooled, but that the net amount of air thru the fins of each cylinder is critical.

My standard pitch. Some of you may recognize this........
Click to expand...

Thanks, I'll do that. It's kinda hard to judge since it's a one piece cowling. You almost need to pre-bend a lot of the baffles to make sure they stay where they should when the cowling goes on. I'd need a probe to see how everything is actually sitting with the cowling on since my only view is through the oil access hatch on the top.
 
Caramon13 said:
Thanks, I'll do that. It's kinda hard to judge since it's a one piece cowling. You almost need to pre-bend a lot of the baffles to make sure they stay where they should when the cowling goes on. I'd need a probe to see how everything is actually sitting with the cowling on since my only view is through the oil access hatch on the top.
Click to expand...

I don't think you understand what he's saying. If I do, it had nothing to do with the cowl. I think he's talking about the wraps on the cylinders and heads? And the crappy stuff often left between plugs in the fins. Clearance to cowls is closed by the seals and that's what you would have to check with the cowl on. But I've been mistaken a time or two......
 
Caramon13 said:
Well, before they adjusted the mixture, there was no rise. Now I get a slight RPM jump just before engine shutdown.
Click to expand...
You could still be running too rich in cruise and at high power.
It is well known the #3 cylinder on the Lycoming 180 horse power engines runs hot and fails most often, it is a matter of fuel distribution more than cooling.
 
Running slightly off "full throttle" on climb will help the distribution problem.... there were some carbs that had the throttle plate set at vertical but they should have been up to 13 deg off vertical to cause some tuberlance assuring better air /fuel distribution. and assuring that there is proper airflow around the fins in the head. I have a Cherokee 140 with a O-360-A4A power, and it runs 350 deg max CHT on #3... Use a light behind the baffling to see where the light is shinning up through the fins, that's where the air will be flowing down..
 
Careful running partial throttle in the climb....and being out of the "enrichment" zone. Being too lean at full power isn't a good thing. Partial throttle while in cruise...at a lower power setting is good for fuel distribution...also a little carb heat can help too.
 
flyingriki said:
I don't think you understand what he's saying. If I do, it had nothing to do with the cowl. I think he's talking about the wraps on the cylinders and heads? And the crappy stuff often left between plugs in the fins.
Click to expand...
Yes that's what I was saying. But in addition, you bring up a good point. Some early Pipers used felt to seal between the baffling and the cowl interior. If you try to blow thru it, it is like there's nothing there. IOW felt is an absolutely worthless cowl seal material.
 
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