CHT temps too cold?

[Justin Schmidt]

3 minutes ago, MikeOH said:

@Justin Schmidt

So, if I understand you correctly, some engines, when overhauled, had their data plates changed to 20 degrees?

Further, are you saying Lycoming now ships new engines with 20 degree data plates??!?

If the shop or owner wanted to do that SI yes, I would have hoped they asked the owner. Of the particular models listed in the SI, yes. I, also, believe there is a list of all engines and what their timing is which is what would be coming from the factory

[MikeOH]

So, if I call up Lycoming and order a brand new IO-360A1A for my M20F will I get one with a 20 or 25 degree data plate?

Does it depend on what plane I'm installing it in?

Do I have to prove what plane I'm going to install it in before they will sell to me?

I believe the Mooney TCDS merely states that the engine is an IO-360A1A.... I guess I'm still confused

[Justin Schmidt]

2 minutes ago, MikeOH said:

So, if I call up Lycoming and order a brand new IO-360A1A for my M20F will I get one with a 20 or 25 degree data plate?

Does it depend on what plane I'm installing it in?

Do I have to prove what plane I'm going to install it in before they will sell to me?

I believe the Mooney TCDS merely states that the engine is an IO-360A1A.... I guess I'm still confused

I would imagine all IO-360A1A will have a 20 data plate as well as any listed from the factory. If not, it would give less credibility to their reason of going to 20 degrees in the first place. Spoiler, there wasn't a good reason. I will admit I did not research other applications nor ask about other applications as that would be a waste of my time. Disclaimer...I have not read the SI as I cannot find it, it is listed in their SI list but doesn't seem to be available on their site. What I do know is on a certified airplane that data plate dictates your timing. There is mental gymnastics of how certifications actually happen and (loosely) work. Submarines are far worse

[Justin Schmidt]

15 minutes ago, MikeOH said:

I guess I'm still confused

For some reason I thought you were an A&P

[MikeOH]

And, my mind wanders to yet another question:

If I send my IO-360A1A with its 25 degree data plate to Lycoming for OH, will it come back with a 20 degree data plate?

[Justin Schmidt]

Just now, MikeOH said:

And, my mind wanders to yet another question:

If I send my IO-360A1A with its 25 degree data plate to Lycoming for OH, will it come back with a 20 degree data plate?

That I do not know...It's not an AD, just an SI, so I would guess they would have a conversation. Or they may just do it, Or if the owner doesn't want it done they may reject the work and send it back. You maybe waiting years though, I had a quote at 2 years. I never said any of this makes sense, only what they said and willing to do. My main point was that data plate is legal and if they won't allow it to change then the timing cannot be changed. The data plate must agree with the TCDS. It is my position to keep everything legal to the best of my knowledge and if the FSDO said ask the manufacture and the manufacture said no, then it is what it is.

Well I must go sleep, taking the bird out for her first break in if the weather cooperates

[Shadrach]

9 hours ago, MikeOH said:

@Justin Schmidt

So, if I understand you correctly, some engines, when overhauled, had their data plates changed to 20 degrees?

Further, are you saying Lycoming now ships new engines with 20 degree data plates??!?

All factory new, overhauled and rebuilt IO 360s are delivered with 20° except for the dual mag engines (A1B6D and A3B6D), which are still delivered at 25°. Apparently those “Lycoming engineers” have determined that 25° is only acceptable if you have a dual mag?  All kidding aside, the TCDS is the final authority on the engine’s configuration. Several members of this forum have advanced their factory engines to 25° with the blessing of Lycoming. A cursory search will turn up multiple threads that include folks that have had direct conversations with the factory. After looking at some previous threads, it looks like Lycoming does not ship out new data plates and the correct procedure is to enter the change in the logs and re-stamp the data plate. 
 

the next question is. Does the change make a difference? Some say yea and some say nay. I noticed it when a mechanic inadvertently set mine to 20° but without hard dyno data there is no way to really know. There could have been other factors that affected my perception of the engine’s performance, but the change was enough to have me review the maintenance entry. 

[Pinecone]

8 hours ago, dzeleski said:

I completely understand and I appreciate the conversation. There are unfortunately endless old wives tales that continue to be circulated around in aviation. So I’m always very hesitant to believe anything without seeing specific data or proof.

Except Walt, along with George and John, are the SLAYERS of OWT.

It any of them told someone they did the test and that results were X, I would bank on that being the REAL STORY.

What is hilarious is those making up NEW OWTs.  Like 380 CHT is too hot.

[Shadrach]

10 hours ago, dzeleski said:

I completely understand and I appreciate the conversation. There are unfortunately endless old wives tales that continue to be circulated around in aviation. So I’m always very hesitant to believe anything without seeing specific data or proof.

GAMI has the most sophisticated general aviation engine test cell in the states. Those close to that facility typically deal in hard data over anecdotes. I would be careful when drawing parallels between the Lycoming and the low power, low compression, vw engine with its ducted fan and shroud set up. There may be differences for which you’re not accounting.

[jlunseth]

12 hours ago, Shadrach said:

I don’t think anyone is GAMI ever said that peak EGT is a bad place to run an engine. Especially given that 100° ROP is closer to peak ICP. That being said if you’re running a turbo, Peak TIT is not an option in most cases. 
your other points are all very well taken. I would just add that the 5606 in your brake lines has a pour point of <-76°F. It’s not going to be phased by 20° temps. 

You are correct, you can run at peak at 65% or lower. But I wasn’t thinking about low power settings. If you are trying to keep a cold engine warm in challenging low temps, depowering the engine to 65% just makes matters worse. The point I am making is that you want to run it hot, up around 75-80%. If you run at that HP and at peak (a “best power” setting per my POH) you are well into GAMI’s red box. Your point about not running at peak TIT is well taken. If you try to do that at 75% or better and at peak EGT, you will exceed TIT redline. I should say I have not tried that in the dead of winter. There is a definite cooling effect on the turbo and the TIT especially in the low altitudes. 

These settings are obviously different than what the OP would do in an E, or even what a pilot might do in the “big bore” Bravos and Acclaims. I don’t fly those and don’t have enough experience. My point though, is that you can choose to deliberately run the engine a little hot and bend some rules if you want to keep the CHTs and OT up in cold weather. 

In my engine the critical temp as I mentioned is the OT because it directly impacts the health of the turbine. So it is a matter of making some not-so-perfect choices. Run the engine colder than you should, or dip into the red box just a little to keep it warm. I dip into the red box a little, but not very far. Better than to damage the turbo. In an NA you might make a different choice.

As far as the brake fluid is concerned, up here in MN we face a doubly whammy, icy runways and taxiways and very cold brakes. The brakes get very stiff in below zero temps, better to warm the fluid. Critical, however, to warm the air/oil separator.

[A64Pilot]

Lycoming reduced the timing from 25 to 20 to reduce cyl head temps at high power. The “average” engine will still make spec power at 20 degrees, of course it will make more power at 25, how much who knows? I bet Lycoming does but I guess they aren’t telling. Average engine has to meet or exceed spec power. I’ve never Certified an engine so I don’t know specifics.

Max power and usually max efficiency with timing is achieved just prior to detonation, that is run as much timing advance as engine can tolerate, that’s why for decades modern automobiles have detonation or “knock” sensors as they run as much timing as the engine will tolerate, it’s one of the reasons modern auto engines are so powerful now, many others of course but variable timing is one.

Ideal in my opinion would be a timing retard above some set manifold pressure so that would retard to 20 then but run 25 or higher at lower manifold pressures, I believe that exists but I don’t know how much timing difference there is.

However talking to Hartzell design Engineers they are greatly concerned about timing as it can in some instances set up vibrations that can damage their props, mostly cause hub cracking I think, when they certify a prop on an engine / airframe combination they conduct a vibe survey at engine manufacturers settings but not others, of course an engine ‘ prop combo that was previously certified for 25 is good for 25 and the new setting of 20, but maybe not 30 or higher or even less than 20. The lack of a vibe survey is one reason you can’t use a prop that a different airplane with the same engine does.

Having said that one guy who happened to be a Pax river graduate did some testing on significantly advanced and in cockpit adjustable timing on his Lycoming powered RV and came to the conclusion that the differences weren’t worth it, for those that don’t know Pax river is the Naval Test Pilot school, most accept it as the best test pilot course there is, so you can be sure that a Pax river grad knows how to conduct engine performance testing.

I didn’t keep that link, but should have I guess. It’s out there for anyone to find.

The reason why variable timing doesn’t make the difference it does in automobiles is because we tend to cruise in a very narrow RPM band, where an automobiles RPM varies tremendously. It’s also because we cruise at relatively high power, but it’s primarily RPM

Not every airplane out there has good engine cooling and my assumption is two fold, one that there were problems with overheating in some of those and the reduction in timing was a life issue, that is reduced timing meets specs and increases how long an engine will last due to reduction in heat.

For example Pratt & Whitney on the PT-6 engine have continuous limits, but Pratt strongly cautions owners that if the engines are operated continuously near those limits it will significantly reduce engine life. Cessna Caravans with the original smaller engine were having serious problems years ago from running too hot, but within limits for example.

See limits including heat aren’t a set point, one where just slightly below redline is fine with no additional stress, but bang the second you exceed redline something breaks, it’s a sliding scale but a non linear one, stay in the middle of the green arcs is pretty much everything as much as possible and you will get the greatest life out of your engine.

That’s where people like me come up with things like 380 is too hot to me, as there is no reason to run that hot, climb at a higher airspeed, open cowl flaps and or enrichen mixture and you won’t run that hot.

By the way I’m pretty sure Mike Busch also says 380 is too hot I believe.

You can pull the guts out of one, it shouldn’t blow up and I do understand that many didn’t buy a Mooney to go slow and frankly buying an overhaul isn’t that big a deal for them, and for them running it hard is what they want, but for those of us that buying an overhaul is a big deal, if you run one in the middle of the green arcs the majority of the time in cruise for example it will last longer. I have about 1500 left on my engine to TBO, I turn 65 next month, if I fly 100 hours a year then I should have at least 15 years of engine life left, that takes me to 80. IF I even live that long I surely won’t be flying the Mooney then, so if I take care of mine the hope is that I won’t be buying an overhaul in my life. 

 

[EricJ]

4 hours ago, Shadrach said:

All factory new, overhauled and rebuilt IO 360s are delivered with 20° except for the dual mag engines (A1B6D and A3B6D), which are still delivered at 25°. Apparently those “Lycoming engineers” have determined that 25° is only acceptable if you have a dual mag?  All kidding aside, the TCDS is the final authority on the engine’s configuration. Several members of this forum have advanced their factory engines to 25° with the blessing of Lycoming. A cursory search will turn up multiple threads that include folks that have had direct conversations with the factory. After looking at some previous threads, it looks like Lycoming does not ship out new data plates and the correct procedure is to enter the change in the logs and re-stamp the data plate. 

Yet another reason to have the dual mag! 

The SI in question is Lycoming SI 1325, which details how to properly change an engine from 25 degree advance timing to 20 degree advance timing, including replace or remarking the data plates on both the engine and the magnetos.      It is dated 3 October, 1975, so it is nothing new. 

As mentioned, the TCDS for most (non-helicopter) O-360 and IO-360 Lycoming engines show 25 degrees ignition timing.   The only authority to change to 20 degrees is the service instruction.    If an engine is delivered with an engine data plate that says 20 degrees, that might get a little tricky since the TCDS says it can be 25, but there isn't an SI that says the data plate can be remarked to 20 from 25.

I wouldn't blame anybody for setting 25 degrees when the TCDS says you can, but you're really also supposed to set whatever the engine data plate says.

[PT20J]

20 vs 25 deg Timimg:

I've attached the original Lycoming Service Instruction. (This SI is old and not on the Lycoming website. Lycoming only puts the most common service literature on it's website. You may request documents that are not on the website from Lycoming support). @Shadrach provided the TCDS. This is ALL of the official documentation that is available or necessary.

Lycoming would prefer that you leave the timing at 20 deg. It is arduous to get a new data plate and requires FAA approval before Lycoming can issue one. The reason is that the data plate is what defines an engine (or an airplane for that matter). If you have a data plate, you can start adding parts and create an engine. So, data plates are carefully controlled. But there is no legal reason why you need a new data plate to change the timing, and Lycoming and the FSDO need not be involved. Your A&P can use the TCDS as approved data and make the change with a logbook entry and a restrike of the timing entry on the current data pate. Note that you also have to change the starting magneto to have a lower lag angle. The reason that the dual mag version was never set to 20 degrees is that there was no dual mag available with the reduced lag angle.

Skip

SI 1325 Timing Change for IO-360 Series Engines.pdf

 

 

[PT20J]

Warm up with cowl flaps closed:

I have never seen this as an approved procedure anywhere. The POH BEFORE STARTING/STARTING checklists invariably include setting the cowl flaps open.

With airflow blocked by closed cowl flaps there is insufficient cooling air flowing and no way to know what is getting too hot as you only know the oil temp and CHTs. It's not just the engine but other items like the ignition harness and the accessories that need to be considered. Lycoming recommends warming by idling at 1000-1200 rpm with the cowl flaps open until you get 75 deg F on the oil temperature. This is to prevent possible oil starvation due to very cold oil. If it is so cold that this takes too long, it would really be best to preheat the engine. All the Pratt and Whitney radials had a limitation of 100 deg C CHT and 40 deg C oil temperature before applying takeoff power and that's not a bad idea for any engine.

Skip

[Shadrach]

1 hour ago, EricJ said:

Yet another reason to have the dual mag! 

The SI in question is Lycoming SI 1325, which details how to properly change an engine from 25 degree advance timing to 20 degree advance timing, including replace or remarking the data plates on both the engine and the magnetos.      It is dated 3 October, 1975, so it is nothing new. 

As mentioned, the TCDS for most (non-helicopter) O-360 and IO-360 Lycoming engines show 25 degrees ignition timing.   The only authority to change to 20 degrees is the service instruction.    If an engine is delivered with an engine data plate that says 20 degrees, that might get a little tricky since the TCDS says it can be 25, but there isn't an SI that says the data plate can be remarked to 20 from 25.

I wouldn't blame anybody for setting 25 degrees when the TCDS says you can, but you're really also supposed to set whatever the engine data plate says.

The TCDS clearly states 20° as optional per the asterisk at the bottom of page 2 of the TCDS. Words have meaning. It hardly qualifies as optional if there is no means to change it back to the original certified setting from the type certificate.

[Shadrach]

3 hours ago, A64Pilot said:

Lycoming reduced the timing from 25 to 20 to reduce cyl head temps at high power. 

Yes a power reduction will tend to have that effect on CHT‘s.

Since you seem to have some insight into why Lycoming does things, perhaps you could help make clear why the timing was never reduced on the O360? 
Anyone who has spent time in a C or G model would likely tell you that the parallel valve 180hp is much more of a challenge when it comes to temperature management. Yet the “engineers” did not have the foresight to make the change to their hottest running 4 cylinder? I wonder why? Some might be inclined to believe that the decision was driven by something/someone other than engineering data.

[A64Pilot]

21 minutes ago, Shadrach said:

The TCDS clearly states 20° as optional per the asterisk at the bottom of page 2 of the TCDS. Words have meaning. It hardly qualifies as optional if there is no means to change it back to the original certified setting from the type certificate.

That’s not uncommon.

‘When I had my Maule the feds discovered in their opinion that back in the day BD Maule didn’t adequately test the cargo compt load wise. Maule didn’t have the money to test something that plainly wasn’t an issue as there had been zero failures and any bush plane is often overloaded, so they and the FAA came to an agreement, Maule issued a service bulletin that came with a new page for the POH and new placards for the baggage compt reducing the weight.

Well SB’s aren’t mandatory, but the POH and placards are, so if you complied with the SB you significantly reduced the utility of the aircraft with no way back.

I looked at the SB and filed it in the circular file.

One assumes those that complied with it likely reduced the value of their aircraft?

[A64Pilot]

2 minutes ago, Shadrach said:

Yes a power reduction will tend to have that effect on CHT‘s.

Since you seem to have some insight into why Lycoming does things, perhaps you could help make clear why the timing was never reduced on the O360? 
Anyone who has spent time in a C or G model would likely tell you that the parallel valve 180hp is much more of a challenge when it comes to temperature management. Yet the “engineers” did not have the foresight to make the change to their hottest running 4 cylinder? I wonder why? Some might be inclined to believe that the decision was driven by something/someone other than engineering data.

As I said I don’t think Mooney’s were the issue, but think somebody’s aircraft that used the angle valve motor was having temp issues, like for instance older Bonanza’s have temp issues in a climb, but Cessna’s with the same motor don’t.

Why do your think they did it? To decrease their engines performance? 

However as was pointed out, if your going to “bump” your timing back to 25 degrees, be sure to modify the mag, because if you don’t your bumping the starting timing by 5 degrees too, and that could break starters and other bad things.

5 degrees isn’t a whole lot though I’m sure it’s within real world tolerances, only thing I think really could be an issue is if someone lets their timing get out much more than the 25, but that’s an opinion. 

[Shadrach]

Just now, A64Pilot said:

As I said I don’t think Mooney’s were the issue, but think somebody’s aircraft that used the angle valve motor was having temp issues, like for instance older Bonanza’s have temp issues in a climb, but Cessna’s with the same motor don’t.

Why do your think they did it? To decrease their engines performance? 

However as was pointed out, if your going to “bump” your timing back to 25 degrees, be sure to modify the mag, because if you don’t your bumping the starting timing by 5 degrees too, and that could break starters and other bad things.

5 degrees isn’t a whole lot though I’m sure it’s within real world tolerances, only thing I think really could be an issue is if someone lets their timing get out much more than the 25, but that’s an opinion. 

 What I’ve heard and what seems to make sense to me is that a new OEM installation was failing to meet temperature specifications. The path of least resistance to bring temps down was to retard the timing. No significant loss in cruise and <10% hit to climb are easy to swallow to keep approval and production on track. It’s just business…

[A64Pilot]

21 minutes ago, Shadrach said:

 What I’ve heard and what seems to make sense to me is that a new OEM installation was failing to meet temperature specifications. The path of least resistance to bring temps down was to retard the timing. No significant loss in cruise and <10% hit to climb are easy to swallow to keep approval and production on track. It’s just business…

That jives with what I’m saying, except that I would be astonished in a reduction in climb that would require a change in the POH, but there would be a power reduction, how much I could only guess, but think it would be hard to measure. As with everything with timing there is a point of diminishing returns, you do reach a point where not much is gained. Like Octane, my little C-85 makes no more power on 100LL than it does on car gas.

If there was much difference, then (D) motors with their advanced timing would be thought of as hot rods, and I don’t think that’s the case. I don’t think there is a measurable performance difference is there?

Actually the fact that there was no change in the charts sort of proves any loss in power was marginal.

[Shadrach]

16 minutes ago, A64Pilot said:

That jives with what I’m saying, except that I would be astonished in a reduction in climb that would require a change in the POH, but there would be a power reduction, how much I could only guess, but think it would be hard to measure. As with everything with timing there is a point of diminishing returns, you do reach a point where not much is gained. Like Octane, my little C-85 makes no more power on 100LL than it does on car gas.

If there was much difference, then (D) motors with their advanced timing would be thought of as hot rods, and I don’t think that’s the case. I don’t think there is a measurable performance difference is there?

Actually the fact that there was no change in the charts sort of proves any loss in power was marginal.

I don’t think it required a change to the POH. Especially given how much the industry was fudging the numbers in the 70s. A 5% reduction in power makes almost no difference in cruise but yields a 5% decrease in climb.

[Shadrach]

13 hours ago, MikeOH said:

And, my mind wanders to yet another question:

If I send my IO-360A1A with its 25 degree data plate to Lycoming for OH, will it come back with a 20 degree data plate?

It will come back at 20 though you may be able to special request 25 since you have an existing data plate.

[EricJ]

1 hour ago, Shadrach said:

The TCDS clearly states 20° as optional per the asterisk at the bottom of page 2 of the TCDS. Words have meaning. It hardly qualifies as optional if there is no means to change it back to the original certified setting from the type certificate.

Ah, yes, so that's an additional authorization means beyond the SI to set it to 20 degrees.    I'm all for exercising useful options, especially when there's a clear regulatory path to do so.   Sometimes there's a counter-concern that somebody might get excited about, and the engine name plate is one of them.   There are regs about the name plates that some take very seriously, so I was wondering what sort of trouble somebody might try to get one in regarding the details with the name plate.    For reciprocating engines generally the ignition timing is marked on the name plate.   SI 1325 says to get a new one from Lycoming if you change the timing, but that's probably a long lead time, an expense, and somebody said they maybe don't even do it any more.   There's been wisdom to just restamp it, which is what the SI says to do with the magnetos if you make the change.

So I looked a little further and FAR 45.11 allows name plates to be changed during work performed under Part 43 (maintenance) with the usual caveat that it must be done "in accordance with methods, techniques, and practices acceptable to the FAA..."   45.11 doesn't even require the timing to be on the name plate, and I don't know if there's a requirement other than general practice to set timing to what the name plate says.   That's what they told us in A&P school, but I don't know of a reg requiring it.

So from my reading of 45.11 and the TCDSs there's nothing preventing someone from changing appropriate Lycoming (I)O-360 from 25 to 20 or back if they so desire.

[PT20J]

Power loss with timing change from 25 BTDC to 20 BTDC

Several people have claimed that they noticed and measured performance differences when changing timing. I have no basis to doubt their claims related to their specific airplanes and engines. But, there are reasons to be suspect that it makes little difference across a large sample of engines.

1. The Lycoming TCDS specifies an allowable variation of +5%/-2% of rated power regardless of which timing is used. So if the change reduced power, it couldn't be more that a percent or two without eating into the design margin significantly.

2. There is an optimum timing advance. It is called MBT and results in the maximum brake torque for a given operating point. According to Heywood, Internal Combustion Engine Fundamentals, it is not uncommon for engine manufacturers to back off slightly from MBT timing in order to improve detonation margin. But all the textbooks, and a graph provided in the APS course, show torque vs timing curve is broad in the vicinity of the peak and a few degrees either way only causes a small power drop off (on the order of 1-2%). The APS graph includes the note: "Notice that HP (BMEP) remains nearly constant across a broad range of spark timing settings."