M20J CHTs

[PT20J]

I recently swapped out an IO-360 A3B6D for a factory rebuilt IO-360-A3B6 on a 1994 M20J. I've accumulated about 12 hours on the new engine. I've been running at 25"/2500 rpm, 50-deg ROP at low altitudes to break in the cylinders. The airplane has a JPI EDM 700 with new CHT probes. The factory probe is on cylinder #3 with an EDM ring probe under it (no spark plug gasket probe), and there is good agreement between the factory gauge and the EDM on #3. The baffles are all in good condition with new tight-fitting GeeBee seals. All 9 EDM probes (4 CHT + 4 EGT + oil temp) read within a degree of each other before engine start. I consistently get the following CHTs (+/- 5 deg): 1-360, 2-380, 3-360, 4-375. EGTs are: 1-1390, 2-1410, 3-1400, 4-1420.

This isn't a big spread, but I'm curious if others see similar. It's interesting that the even (left) cylinders are hottest. On the other hand, that side has the engine air intake, the cabin air intake, and the oil cooler, all of which I would think would take cooling air away from the cylinders.

 

[carusoam]

PT,

who’s break in procedure are you following?

The reason I ask... modern NA break in procedures usually use WOT and max rpm and variations of rpm every 15 minutes or so...

Have you performed a gami spread test?

Before  comparing cylinder cooling... start with comparing cylinder heating.... a tight gami EGT spread is a good place to start...

PP thoughts only, not a mechanic...

Best regards,

-a-

 

 

[PT20J]

I don't want to get too far afield here as I'm mainly curious about the CHT spreads -- and especially which cylinders are hottest and coolest -- on other IO-360 M20Js. But, just for background: 1) The engine is a factory rebuilt with a 2-year warranty, so I am using the break in procedure recommended by Lycoming. The engine was run in a test cell before delivery, so much of the initial break in was done already. I've just been running at 75% to keep the peak cylinder pressures up. 2) I haven't run a GAMI lean test because the fuel flow transducer has become intermittent. However, the flows must be fairly well matched as the engine will run 60 deg F LOP before it starts to lose a lot of power and get rough.

Skip

[Shadrach]

There is no reason to abuse an engine during break in. 

On 11/25/2018 at 8:47 PM, PT20J said:

I recently swapped out an IO-360 A3B6D for a factory rebuilt IO-360-A3B6 on a 1994 M20J. I've accumulated about 12 hours on the new engine. I've been running at 25"/2500 rpm, 50-deg ROP at low altitudes to break in the cylinders. The airplane has a JPI EDM 700 with new CHT probes. The factory probe is on cylinder #3 with an EDM ring probe under it (no spark plug gasket probe), and there is good agreement between the factory gauge and the EDM on #3. The baffles are all in good condition with new tight-fitting GeeBee seals. All 9 EDM probes (4 CHT + 4 EGT + oil temp) read within a degree of each other before engine start. I consistently get the following CHTs (+/- 5 deg): 1-360, 2-380, 3-360, 4-375. EGTs are: 1-1390, 2-1410, 3-1400, 4-1420.

This isn't a big spread, but I'm curious if others see similar. It's interesting that the even (left) cylinders are hottest. On the other hand, that side has the engine air intake, the cabin air intake, and the oil cooler, all of which I would think would take cooling air away from the cylinders.

 

Hi Skip,

Temperature spread appears healthy. All other things being equal #3 is often the hottest. Break-in should be at high power, but it need not be abusive. What is your reasoning for running 50 ROP at low altitude? Your temps are acceptable but that’s not an optimal break in setting. The goal is high but generally even cylinder pressure through out the combustion stroke. This is why most manufactor’s suggest varying RPM. It’s an additional tool to ensure the ring is seated to the cylinder wall through out the stroke. 50ROP at low altitude gives good power but is just about the highest peak pressure you can generate with a mixture setting.  I’m not suggesting the engine won’t break-in being opporated as you’ve described, I’m just wondering why you’re doing it that way.

Edited December 11, 2018 by Shadrach

[jwilcoxon78]

Those are close to the numbers I see.  Interestingly, prior to overhaul, my #3 cylinder was the hottest.  Now, and some 300 post overhaul, my #2 is generally running 380-390 (cruise vs climb). 

[Shadrach]

6 hours ago, jwilcoxon78 said:

Those are close to the numbers I see.  Interestingly, prior to overhaul, my #3 cylinder was the hottest.  Now, and some 300 post overhaul, my #2 is generally running 380-390 (cruise vs climb). 

Perhaps whomever did your baffle seal work understood the airflow challenges for the right rear cylinder and addressed them at installation. 

Edited November 26, 2018 by Shadrach

[Bob - S50]

Those numbers actually look better than mine.

Are they with the cowl flaps open or closed?

When we were seating the rings after a top OH, we ran with the cowl flaps open, 75%, LOP and saw CHT's right around 300 +/- 20.

[Shadrach]

3 hours ago, Bob - S50 said:

Those numbers actually look better than mine.

Are they with the cowl flaps open or closed?

When we were seating the rings after a top OH, we ran with the cowl flaps open, 75%, LOP and saw CHT's right around 300 +/- 20.

^^^^^^This is how I would do it if I were breaking in a new engine today and were based at my current drome. WOT at 1700' AGL, lean enough to keep temps under 330. vary the RPM between 2400 and 2700 and readjust mixture as needed on the lean side of peak.  This time of year that's probably in the low 80% power range with cool CHTs, high mean cylinder pressure with lower peak pressure.  Ideal for seating rings.

Edited November 26, 2018 by Shadrach

[PT20J]

Most everyone seems to be focusing on the break in process. I appreciate the comments, though I realize that opinions vary on the best way to break in an engine. I did not intend to imply that I thought there was a problem with the engine. The engine is doing fine -- minor wear metals in the filter after a 10 hour oil change, oil consumption down to about a 0.1 qt/hr. and CHT spreads are only 15-20 deg F. It runs well from 125 ROP to 50 LOP.  

I just found it interesting that the two hottest cylinders were on the left side and wondered if anyone else had seen anything similar. The spreads (not the absolute values) are pretty consistent regardless of mixture or power settings. 

Skip

[carusoam]

Skip,

You have run into an avid group of aviators... they are focusing on the beginning of a long conversation... where there is no easy answer...

1) Break-in procedures have been modernized with time...

2) They start with a few hours at the factory...

3) continue with a few hours around the airport after the Engine has been mounted...

4) They continue over the next period of hours flying fast and low changing power settings based on elapsed time...

4.5) The break-in can be considered completed after about 50+ hours according to engine manufacturers... it is often 90% complete by watching CHTs on your engine monitor.  When rings seat, CHTs come down into normal ranges....  Often, coming out of the factory, on a factory reman, you might not ever see high CHTs because the seating has happened in the early runs before leaving the factory...

5) When it comes to discussing CHTs, MSers want to know a few details before just hazzarding a guess...

6) CHTs are a related rates discussion... comparing the rate of heat generated to the rate of heat removed by the cylinder... if EGTs are high on one side, CHTs can be expected to be high on the same side... Raw EGT numbers are difficult to use, but peak EGTs usually give the answer we need for the discussion.

7) If somebody gives you an answer that says just check your cowl seals... or buy cowl seals from GB... they may be giving you a good answer, but they can give you a much better answer by asking a few questions first...

8) With only four cylinders, it is more of a challenge to say the left side is doing something than the right side... there are so many interactions between them all...

9) Getting all that discussion out of the way... If all your cylinders peak at the same time, let’s focus on cooling issues...

10) have you done any seal tests?  Dark room, flashlight from outside the seal, camera inside the seal looking for light?

11) have you changed any seals around the front, like alternator or starter...?

12) Are you suspecting that the rings haven’t seated on one side of the engine?

A Typical challenge of a new engine mounted after OH can easily be the sealing of old seals or new seals that aren’t fitting properly...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Shadrach]

On 11/26/2018 at 2:00 PM, PT20J said:

Most everyone seems to be focusing on the break in process. I appreciate the comments, though I realize that opinions vary on the best way to break in an engine. I did not intend to imply that I thought there was a problem with the engine. The engine is doing fine -- minor wear metals in the filter after a 10 hour oil change, oil consumption down to about a 0.1 qt/hr. and CHT spreads are only 15-20 deg F. It runs well from 125 ROP to 50 LOP.  

I just found it interesting that the two hottest cylinders were on the left side and wondered if anyone else had seen anything similar. The spreads (not the absolute values) are pretty consistent regardless of mixture or power settings. 

Skip

It's hard to say much about temps during brake in other than acceptable or unacceptable.  Your's are acceptable and appear to be functioning in a well sealed cowling. A 15-20df spread is close enough as makes no difference, so you've got that going for you...which is nice.  The engine should definitely run well from 125-50 ROP, thats about as combustible a mixture range as exists on the spectrum. Not a lot of difference in power, probably a more noticeable difference in CHTs, and certainly noticeable difference in fuel burn.

Edited December 11, 2018 by Shadrach

[graham28105]

Shadrach, you mention that the #3 is usually the hottest. That's the way it is on mine. Why is that?

[Shadrach]

4 hours ago, graham28105 said:

Shadrach, you mention that the #3 is usually the hottest. That's the way it is on mine. Why is that?

Because number three is butted up against the baffle seal wall. Cylinders on the right side of the engine are oriented with their fins facing forward. Mooney attempted to account for this by putting a pocket behind the cylinder to allow airflow around the barrel. It’s sufficient but just barely. If not aligned it’s even less effective.

Here’s an old thread from years ago that I started on the subject. Scroll to post 15 for images of what I’ve explained above.

 

Edited December 11, 2018 by Shadrach

[jonhop]

Ross @Shadrach,

Thanks... #3 is my hottest cylinder and I have recently replaced the upper baffle material at last annual. I found light bleed while it was on the ground beforehand and my A&P suggested that it could be blow by... Baffle replacement improved temperatures quite a bit but #3 is still hotter than the rest and keeping it under 380° F in climb-out or LOP in cruise above 10K feet is tough. Now I have something else to try...

[jaylw314]

On 11/26/2018 at 11:00 AM, PT20J said:

Most everyone seems to be focusing on the break in process. I appreciate the comments, though I realize that opinions vary on the best way to break in an engine. I did not intend to imply that I thought there was a problem with the engine. The engine is doing fine -- minor wear metals in the filter after a 10 hour oil change, oil consumption down to about a 0.1 qt/hr. and CHT spreads are only 15-20 deg F. It runs well from 125 ROP to 50 LOP.  

I just found it interesting that the two hottest cylinders were on the left side and wondered if anyone else had seen anything similar. The spreads (not the absolute values) are pretty consistent regardless of mixture or power settings. 

Skip

My hottest cylinders are #1 and #4 (360-380 deg F on hot days), #2 is usually about 5 deg F cooler, and #3 is about 20 deg F cooler.  #3 might be inaccurate because it uses the bayonet ring probe, and the factory CHT meter is ridiculously useless without gradations--I can only guess it reads somewhere between 300 and 350 deg F.  

The fact that #1 and #4 are hottest makes absolutely no sense to me, as is the fact that #3 is (probably) the coolest by far.  Clearly, the fuel flows are ok because my GAMI spread is under 0.5 gph.

I thought maybe #4 was hotter simply because it is next to the oil cooler, but after the shop RTV'd the gaps around the cooler and did some baffle work, it is still the hottest (although all the cylinders were about 10-15 deg F cooler after).

This really bugged me for the first couple years, but I think I'm at the point where I'm telling myself to just deal with it since the engine runs fine 

[carusoam]

Jay,

have you verified the sensor locations?  Some engine monitor sensors are not quite properly matched to the cylinder numbers... 

That would explain a big part of the difference you are seeing....

Best regards,

-a-

[graham28105]

Thank you Ross.

[jaylw314]

8 hours ago, carusoam said:

Jay,

have you verified the sensor locations?  Some engine monitor sensors are not quite properly matched to the cylinder numbers... 

That would explain a big part of the difference you are seeing....

Best regards,

-a-

That's an interesting point, I'd never thought of verifying that.  I think #3 is correct, though, because it helped me identify a lead-fouled plug correctly, and since everything else looks good, I'll probably be lazy and wait until something else goes wrong...

[PT20J]

In my case, I installed new bayonet CHT probes in 1, 2, 4 and a 3/8" gasket probe under the factory probe in #3. We sealed the gaps around the baffles with RTV and put new GeeBee baffle seals on which we took great care to fit tightly. The left side has the air filter and the oil cooler which may take cooling air away from cylinders 2 and 4. That's one reason why I was curious what others see for CHT spreads on M20Js. I figured if this was normal, I'd stop investigating. It seems from this and other threads that CHT distributions vary a lot from airplane to airplane.

[Cyril Gibb]

On 11/26/2018 at 2:00 PM, PT20J said:

Most everyone seems to be focusing on the break in process. I appreciate the comments, though I realize that opinions vary on the best way to break in an engine.

Your relatively small CHT deltas are probably the envy of many Mooney owners.  Doesn't seem to be an issue.

What may seem to be thread derailing are merely opinions on the break-in technique that you use, mentioned by yourself at the outset.  You're absolutely correct that there are a range of ideas on the best way to break-in an engine, as there are about mixtures/flaps/oils/additives and a myriad of other topics.  As with those other topics, it's helpful to outline to potential newbies reading the thread that they should investigate the alternative ideas for themselves, and make their own informed decisions about what is "correct" for them.

I would imagine that the comments re: break-in are mostly directed to other less experienced owners looking for guidance, that they should keep an open mind and research alternative views.