Preignition

[A64Pilot]

59 minutes ago, PT20J said:

I actually did contact lycoming when I purchased my IO-360-A3B6 and this is precisely what they told me I should do if I wanted to change the timing.

Skip

Skip, 

‘My concern was it seemed some didn’t know there was a procedure to be followed and especially parts to be changed in order to prevent damage to their engine to say nothing of not being airworthy, invalidating their insurence etc..

‘I have a (D) engine, so I don’t have a dog in this “fight” really, it’s not an option for me. 

‘From an efficiency / performance perspective an engine needs to run as much timing as it will tolerate, and what it will tolerate changes of course based on load and RPM and of course Octane, temperature etc.

‘Way back I guess before I was even born automobile engine manufacturers recognized this and equipped distributors with flywheel weights and springs to advance timing with RPM, then later added vacuum advance so that under light loads the distributor advanced timing.

‘Then I’d guess about 30 years ago knock sensors were added so that the engine can be operated right at the edge of detonation, which is exactly where you want to be for performance and efficiency., but without a knock sensor thst can retard timing, it’s a dangerous place to be.

However of course we don’t have any of that, we rarely operate at low loads and then for only short periods so we don’t really need vacuum advance, and as we operate in relatively narrow RPM bands, our need for mechanical advance is less too, but we don’t have knock sensors, so we should have a cushion.

Which brings us to why do you think Lycoming chose to go to the trouble and expense of turning the timing down from 25 degrees to 20?

The SIL seems to allude to that it was done to improve longevity, so if you decide to undo the SIL understand why it was done to start with.

There are gains to be achieve with more advance, but there are trade offs too, there is no free lunch

Edited March 21, 2021 by A64Pilot

[N201MKTurbo]

I’m pretty sure they retarded the timing to reduce CHTs. You can do the same thing by reducing MP and have a slightly more efficient engine.

lf you run LOP you are better off with 25. If you run ROP, go for 20.

[A64Pilot]

9 minutes ago, N201MKTurbo said:

I’m pretty sure they retarded the timing to reduce CHTs. You can do the same thing by reducing MP and have a slightly more efficient engine.

lf you run LOP you are better off with 25. If you run ROP, go for 20.

Agreed, but with both you will lose some power, if that’s acceptable then sure.

 

[jaylw314]

1 hour ago, A64Pilot said:

‘My concern was it seemed some didn’t know there was a procedure to be followed and especially parts to be changed in order to prevent damage to their engine to say nothing of not being airworthy, invalidating their insurence etc..

I disagree.  I reviewed every post in this thread, and found no instance where anyone appeared to be advocating for changing the timing arbitrarily, and a perfunctory MS search about "IO 360 mag timing" turned up previous posts from some of these members describing the procedure outlined above.  I'm not an A&P, and I've never bothered changing the mag timing on my IO-360, yet I still recall the procedure to do so because it's been discussed ad nauseum on MS by a lot of knowledgeable people who've either had it done or done it themselves as mechanics.

Edited March 21, 2021 by jaylw314

[N201MKTurbo]

45 minutes ago, A64Pilot said:

Agreed, but with both you will lose some power, if that’s acceptable then sure.

 

I don’t lose any power LOP. I can make more power LOP. But I have a turbo.

[A64Pilot]

Turbo’ s are really a cool thing, they make little motors, big, but without the weight.

‘It’s amazing how long ago that forced induction was developed, been over a Century I think.

I lusted for one, but as I live on the East coast and only rarely climb over 10,000, I didn’t need one, plus probably a little out of my budget.

You don’t run into any ITT issues running LOP? 

[Shadrach]

20 hours ago, A64Pilot said:

Had a whole response typed up, then downloaded and read the SIL

‘It said pretty much exactly what I have been saying, that is that reducing the timing by 5 degrees will make the engine run cooler, last longer and give you more margin on detonation.

‘It didn’t say the decreased timing advance will decrease HP, but it will trust me. The reduced power is largely why it will run cooler, and last longer.

‘Now some of you will think this is it picking and that’s what aviation is, but it does require parts to be changed, and doesn’t say that you can take an engine that the SB has been complied with and return it to the pre SB configuration, and if your just cranking it up to 25 degrees leaving the SB parts in, that’s incorrect too and may cause damage if the engine kicks back during starting.

 

Question for those that are bumping the timing to 25 degrees, have you replaced the magneto parts and engine ID plate?

 

 

IIRC any IO360 manufactured before  1972 came from the factory with 25° timing. My data plate says 25° and that’s how my engine is timed. I do not have any problems with cooling. If anything, there was a time when I worried about lead scavenging in the winter because it ran so cool. That’s proven to be a non-issue but I am careful not to let any cylinder’sCHTs spend an appreciable amount of time below 270° during cruise power settings.

[PT20J]

11 minutes ago, Shadrach said:

IIRC any IO360 manufactured before  1972 came from the factory with 25° timing. My data plate says 25° and that’s how my engine is timed. I do not have any problems with cooling. If anything, there was a time when I worried about lead scavenging in the winter because it ran so cool. That’s proven to be a non-issue but I am careful not to let any cylinder’sCHTs spend an appreciable amount of time below 270° during cruise power settings.

Ross, here’s the page in the operator’s manual that gives the changeover point by serial number. FWIW I had a ‘78 J with 25 deg and never had a CHT issue and my ‘’94 J with 20 deg is about the same. We’ll probably never know exactly what drove Lycoming’s decision 45 years ago. 

[Shadrach]

19 minutes ago, PT20J said:

Ross, here’s the page in the operator’s manual that gives the changeover point by serial number. FWIW I had a ‘78 J with 25 deg and never had a CHT issue and my ‘’94 J with 20 deg is about the same. We’ll probably never know exactly what drove Lycoming’s decision 45 years ago. 

Thanks for the clarification on the time frame for the switch. My guess is that it was driven by expediency. The angle valve IO360 Enjoyed widespread popularity with a number of airframe manufactures. Some of those applications had cooling deficiencies, especially on cylinder #3. Mooneys are not exempt from some of those problems. I have addressed this in other threads. The aforementioned George Brawly devised a simple way to lower the number #3CHT in the C177. 
I think that there is a good chance Lycoming introduced that SB as an easy solution to Band-Aid cooling deficiencies in some applications. No question it works, but having flown my engine at both settings, I don’t think it’s optimal.

Edited March 21, 2021 by Shadrach

[jetdriven]

I heard that they did this to reduce warranty claims for rear cylinder cooling on Grumman‘s with the 200 hp engine.  Lycoming actually does not have a brake dynamometer, they simply look at airflow and fuel flow and say well it’s making rated power...well you know you can run it full rich at  20° or 25° and the fuel flow doesn’t change much but the power at the crank does. 

[Shadrach]

7 hours ago, A64Pilot said:

You can believe what you want, it’s more convenient that way. I’m not trying to make friends. When I see information that is incomplete and has people believing things are acceptable and legal when they aren’t. I speak up. They should hear the other side to make a decision.

‘But the FAR’s are pretty clear, the timing has to be set according to the data plate. 

I wish you were here to make friends.  It's a pretty friendly and welcoming community most of the time. This thread is my first memorable interaction with you and it's my hope that your online persona is a misfire and not deliberate.  I would say you're pedantic (not in short supply around here) but it's not the right word because that word is by definition reserved for people well versed in a subject who are annoying in the delivery of their expertise. You've got the first part down...the second part, not so much.  Many of your statements are either untrue or not really pertinent to the discussion. You are lecturing people who clearly have a stronger grasp of the subject matter than do you.  It's cringe worthy to read some of things you've written with regard to combustion science. Add to that you acting the part of wise man cautioning members of this forum against doing things that no one has advocated. You don't know what you don't know and it's seems from this thread you have little interested in finding out.  Think about the time wasted in writing and deleting a post showcasing what you don't know when you could simply do a little research.  It is telling that it never occurred to you that you might not be informed on the subject.  I truly hope you stick around.  Members define themselves overtime.  A misfire here and there does not make a reputation. I speak from experience.

BTW, If the Mooney Chronology is to be believed, there were over 2700 four cylinder Mooneys delivered from the factory with 25° timing. There are far more aircraft flying that were delivered that way than have been converted back.

Edited March 21, 2021 by Shadrach

[carusoam]

A64,

I get it..

You are good with machines...

Just terrible with people...  

 

Yes, I’m only a PP, Private Pilot...

I am not a mechanic...

 

Now you can tell me... I’m not as smart as you, and my thoughts don’t matter...

I’m Ok with that too...

We have an ignore button...

You probably won’t use it yourself...

But other people will be pushing that button for you...

 

MS is on the internet... but it is not the usual internet...

For a site to work... it has to be enjoyable to visit.

 

After awhile the fun wears off, people stop visiting...

 

When people stop visiting, they miss the opportunity to discuss simple safety of flight issues...

 

Sorry you are missing the big picture...

It is tough being a tech person in a low tech world...

Take some time off, think about...

 

Best regards,

-a-

[PT20J]

13 minutes ago, jetdriven said:

I heard that they did this to reduce warranty claims for rear cylinder cooling on Grumman‘s with the 200 hp engine.  Lycoming actually does not have a brake dynamometer, they simply look at airflow and fuel flow and say well it’s making rated power...well you know you can run it full rich at  20° or 25° and the fuel flow doesn’t change much but the power at the crank does. 

Yeah and I heard it was the Cardinal  That's the problem with trying to track this down -- it's just too far back. 

I'm sure you are correct that the production test cell doesn't have a dynamometer -- standard practice is to run it in with a test club and make sure that all the parameters are within specs. But, I'd be surprised if the engineering department doesn't have one.

The whole power/timing thing is somewhat of a mystery to me. A number of people have sworn that they get noticeably more power (shorter takeoff roll, higher TAS) with 25 deg timing, and I don't doubt them. Noticeably more power would have to be a lot though since airspeed varies as the cube root of power. Also, various textbooks which include actual measurement of real engines all show that the max power doesn't vary significantly with +/- 5 deg timing changes around MBT timing. One possibility is that MBT timing for the IO-360 is more like 30 deg so the 25 was off optimum (sometimes engine manufacturers back off timing from MBT to increase detonation margin). This would put the difference between 20 and 25 on a steeper part of the curve of power vs timing. 

Skip

[Shadrach]

9 minutes ago, PT20J said:

Yeah and I heard it was the Cardinal  That's the problem with trying to track this down -- it's just too far back. 

I'm sure you are correct that the production test cell doesn't have a dynamometer -- standard practice is to run it in with a test club and make sure that all the parameters are within specs. But, I'd be surprised if the engineering department doesn't have one.

The whole power/timing thing is somewhat of a mystery to me. A number of people have sworn that they get noticeably more power (shorter takeoff roll, higher TAS) with 25 deg timing, and I don't doubt them. Noticeably more power would have to be a lot though since airspeed varies as the cube root of power. Also, various textbooks which include actual measurement of real engines all show that the max power doesn't vary significantly with +/- 5 deg timing changes around MBT timing. One possibility is that MBT timing for the IO-360 is more like 30 deg so the 25 was off optimum (sometimes engine manufacturers back off timing from MBT to increase detonation margin). This would put the difference between 20 and 25 on a steeper part of the curve of power vs timing. 

Skip

I don't have any data on TAS but I doubt it makes a lot of difference.  I think it would probably give a slight edge above 10K in level flight. The difference in take off and climb was obvious enough to me that I corrected the mechanic's mistake within 24 hours.  However, that does not mean it would look like a lot on paper.  It just felt a bit tired...obvious enough for me to put two and two together when I saw the retarded timing in the logs.  

Edited March 21, 2021 by Shadrach

[carusoam]

Small amounts of HP increase show up when excess HP is available and gets used...

Acceleration and T/O run...

Climb rate...

 

The cool part of increased timing... is the more complete conversion of fuel to power...

 

With the stronger spark delivered by electronic mags... a similar affect occurs... the flame front is initiated in a larger way... as If an ordinary spark was started sooner...

 

Measurable performance or not...

Use an app like CloudAhoy connected with a WAAS source...

10% more hp is a seat of the pants noticeable difference...

1% more hp would be very mild in comparison... but still measurable via WAAS.

Timing difference between 20 and 25°BTDC is measurable and shows up on the engine monitor as well...

 

All of this data has so many outside influences  affecting it... like OAT... take good notes.

PP thoughts only, not a mechanic...

Best regards,

-a-

[Shadrach]

4 hours ago, N201MKTurbo said:

I’m pretty sure they retarded the timing to reduce CHTs. You can do the same thing by reducing MP and have a slightly more efficient engine.

lf you run LOP you are better off with 25. If you run ROP, go for 20.

Why?  25 yields perfectly acceptable CHTs on either side of the spectrum and likely better high altitude performance on both sides. There are really two logical reasons I can think of to run an IO360 at 20 degrees:

1) despite best effort with regard to baffle seals and cowling, the cylinders are not operating within the desired range. 

                                                                  -and-

2) My plane came from the factory this setting and I don't feel like messing with it.

 

[N201MKTurbo]

11 minutes ago, Shadrach said:

Why?  25 yields perfectly acceptable CHTs on either side of the spectrum and likely better high altitude performance on both sides. There are really two logical reasons I can think of to run an IO360 at 20 degrees:

1) despite best effort with regard to baffle seals and cowling, the cylinders are not operating within the desired range. 

                                                                  -and-

2) My plane came from the factory this setting and I don't feel like messing with it.

 

I have mine at 25, that’s what it says on the data plate. I tried it at 20, it didn’t run quite as good.

[Shadrach]

Just now, N201MKTurbo said:

I have mine at 25, that’s what it says on the data plate. I tried it at 20, it didn’t run quite as good.

My experience as well.

[jetdriven]

Especially LOP.  The 25 degree spec, the airplane loses 3 KIAS at 25 LOP.  The 20 degree spec, it slows down quite a bit more than that.  It slows down more than the fuel flow decreases, yielding a lower NMPG