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25 or 20 TDC?

LettersFromFlyoverCountry

LettersFromFlyoverCountry

Well Known Member
I just finished with Mike Busch's excellent advanced leaning webinar from EAA (I'll write up notes and share them on the blog later), but this one section caught my attention.

Here's what he said:

Lycoming originally specified that all of their IO-360 engines be timed at 25 degrees before dead center and they had lots of problems with high CHT. It?s a company that traditionally has said ?don?t worry about CHT? but eventually these high CHT were manifesting themselves in detonation damage so Lycoming respecified all timings to be 20 before TDC instead of 25.​

That surprises me because I think I bought my engine in 2008 from Mattituck and I'm pretty sure (I'm not out at the hangar) that it still has a data plate for 25. I've heard nothing about this before that.

Can anyone enlighten me on this assertion?
 
Caught that too, but he did not address it as related to 540s.

I have wondered if my high CHT issue could be due to timing.....

Sent Busch an email, hope he answers.
 
Timing

My IO-360M1A by Lycon with one Slick mag and one Lightspeed III was set for 20deg BTDC for the EI. This was, I thought, for the 10:1 compression. You engine experts out there - should it be even less? Thanks in advance for any input!
 
Timing at 20DBTDC will move Theta PP to the right or to higher numbers of DATDC, and in doing so will lower the peak pressure. This is the reason CHT will lower.

With the Lightspeed and other EI's they will keep firing off at anywhere up to the max available. You can work out ways to reduce the spark timing of these EI's.

The HP output will most likely not vary much if anything at all and the observations should be a higher EGT value and lower CHT values.

The downside might be less effective LOP ops, so if you are going to make a change do so in small amounts or be prepared to settle somewhere in-between.
 
My IO-360

from Superior, a parrallel valve model, has Compression of 8.5, right on the lightspeed instructions borderline. I have dual Lightspeed ignition. I set it up at 25 advance and the CHTs were a little high. I changed the timing to 21 before and the CHTs came down from 380 in cruise to 360. Similar improvement in climb. No loss in cruise speed. Re your question on timing Lightspeed, I believe it is more important than the timing of the mag. If your CHTs are on the high side it is worth the time to change to about 20 advance and check the results. My timing change was done be removing prop and moving trigger plate, not fun but worth it to me.
 
LettersFromFlyoverCountry said:
I gotta go out to the hangar. I could swear the dataplate on my engine date 25 degrees. New engine.

Update: I've written up my notes from the webinar here.
Click to expand...

This is in the 2000 revision of the O-360 operator manual and seems to be serial number dependent -

On the following model engines, the magneto spark occurs at 20 BTC. Consult nameplate before timing magnetos.
Models Serial No.
IO-360-A Series (Except -A1BGD) L14436-51 and up
IO-360-C,-D Series (Except -C1C,-C1F,-C1CG,-C1D6) L14436-51 and up
IO-360-C1C,-C1F L13150-51 and up
IO-360-C106 L14446-51 and up
LIO-360-C1E6 G1064-67 and up
AIO-360-A1A,-A1B,-B1B G220-63 and up
HIO-360-C1A,-C1B G14436-51 and up
IO-360-C1C6 All Engines
IO-360-J1AD, -K2A All Engines
 
Spark Advance

Am I correct in thinking that, generally speaking, parallel valve engines, with or without fuel injection, are good for 25 degrees?
 
This had put some doubt in my mind so I consulted my manual that came with the engine from Lycoming (HIO-360-M1B) and sure enough it says 25 TDC.
I also remember that I had checked the data plate on the engine during my last condition inspection just to be sure.
 
My IO-360 MiA is a parallel valve with 10:1 compression. Ken Tunnel @ Lycon and Klaus both recommended 20 BTDC for the Lightspeed 3, and it came set up that way from Lycon. YMMV!
 
az_gila said:
This is in the 2000 revision of the O-360 operator manual and seems to be serial number dependent -

On the following model engines, the magneto spark occurs at 20 BTC. Consult nameplate before timing magnetos.
Models Serial No.
IO-360-A Series (Except -A1BGD) L14436-51 and up
IO-360-C,-D Series (Except -C1C,-C1F,-C1CG,-C1D6) L14436-51 and up
IO-360-C1C,-C1F L13150-51 and up
IO-360-C106 L14446-51 and up
LIO-360-C1E6 G1064-67 and up
AIO-360-A1A,-A1B,-B1B G220-63 and up
HIO-360-C1A,-C1B G14436-51 and up
IO-360-C1C6 All Engines
IO-360-J1AD, -K2A All Engines
Click to expand...

IF I am not mistaken, all the 20 degrees BTC engines listed above are 200 HP Angle Valve Engines. I remember some of the Angle Valve Engines having 20 BTC and some were 25 BTC.
 
Does this also apply to carbed 160-hp O-320's where the data plate says 25 degrees? Can something closer to 20 degrees be used without losing much power in order to get CHT's down a bit?
 
If you have a standard O-320, with 8.5:1 CR, and high CHTs, I would recommend finding the problem instead of "masking" it with other alternatives.
 
Mel said:
If you have a standard O-320, with 8.5:1 CR, and high CHTs, I would recommend finding the problem instead of "masking" it with other alternatives.
Click to expand...
Thanks, though I was asking theoretically, still trying to learn. Just curious how significant the difference b/w 20 and 25 is, given Lycoming's apparent change of heart on the io-360s. Since lower CHT is generally better than high, knowing how much one must or should adhere to the exact number on the engine data plate would be good to know.
 
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Just as another point of data, I have over 850 hrs on my O-320 overhaul with 9.5:1 CR. I'm still running at 25? and my chts are all in the good range.
 
Mel said:
Just as another point of data, I have over 850 hrs on my O-320 overhaul with 9.5:1 CR. I'm still running at 25° and my chts are all in the good range.
Click to expand...

I agree with Mel, cht's are primarily a result of good cooling airflow, proper baffle construction etc., not timing.

I run duel LSI with 25 degree timing, I very rarely see my cht over 350 even on 100 OAT with a good climb, avg cruise temp is around 325 when its 100 deg.
 
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I should point out that all of Mike's talk revolved around the main point of contention that 400 is a bad bad thing in a cylinder, which threatens to become the primer war of this generation. ;)
 
400 Deg CHT & Yield strength

The point of the 400 deg CHT "limit" is that the yield strength of the cylinder materials starts to dramatically drop when over 400 deg. Thats when you run much greater risk of blowing a head off the cylinder. It seems to me that folks aren't getting the connection that greater than 400 Deg is a strength of materials issue that simply ups the risk ante.
 
Yep ... Mel hits it on the head ...

Mel said:
Just as another point of data, I have over 850 hrs on my O-320 overhaul with 9.5:1 CR. I'm still running at 25? and my chts are all in the good range.
Click to expand...
My IO-320 with 8.5:1, 25 degrees BTDC, Slick/Lightspeed combo (and SJ plenum) has always exhibited acceptable or better CHT's and peak EGTs in the mid 1400s.
 
To close the loop on my prior post, Mike Busch did reply to me, and said he absolutely does recommend I use 20* as my timing with my engine.
 
The lycoming data sheet along with the comments from Mike Busch are enough for me to give it a whirl. IO-360B1B
 
Sorry the ignorance but it is important the fuel type? y have TMXIO-360 with 25? 9 to 1 and runing 100/130 fuel, we dont have 100LL
 
RV6_flyer said:
IF I am not mistaken, all the 20 degrees BTC engines listed above are 200 HP Angle Valve Engines. I remember some of the Angle Valve Engines having 20 BTC and some were 25 BTC.
Click to expand...

That link was to the operator manual -

The Type Certificate says "optional" with this description -

* All models except IO-360-A1B6D and -A3B6D have optional timing of 20?BTC

Are those two IO models the only 180 HP ones?
 
az_gila said:
The Type Certificate says "optional" with this description -
* All models except IO-360-A1B6D and -A3B6D have optional timing of 20?BTC
Are those two IO models the only 180 HP ones?
Click to expand...

The above models are rated at 200HP. FWIW the larger bore IO390 is also 20 degrees.

As for engines like Mike's parallel valve 540, heck, you can't damage anything by trying 20 degree timing. It's a nice safe experiment. Report back please.
 
Those two versions both have the 2 in 1 dual mag and counter weighted cranks.
The dual mag may have something to do with the timing.
Dave
 
I'm kind of stupid so please excuse me but if I change my mag timing to 20; what is the process for changing the timing on the Lightspeed plugs? Seems to me it's done with a timing light and an existing mark to check current timing but I don't recall instructions on how to adjust that.

Like I said, now, no laughing.
 
rv9av8tr said:
The point of the 400 deg CHT "limit" is that the yield strength of the cylinder materials starts to dramatically drop when over 400 deg. Thats when you run much greater risk of blowing a head off the cylinder. It seems to me that folks aren't getting the connection that greater than 400 Deg is a strength of materials issue that simply ups the risk ante.
Click to expand...

Does anyone read the Lycoming manual?

Operator's Manual Lycoming O-360 said:
Page 3-6 - General Rules
Never exceed the maximum red line cylinder head temperature limit.

For maximum service life, cylinder head temperatures should be maintained below 435*F (224*C) during high performance cruise operation and below 400*F (205*C) for economy cruise powers.
.
.
.
1. LEANING TO EXHAUST GAS TEMPERATURE GAGE.
a. Normally aspirated engines with fuel injectors or uncompensated carburetors.
(1) Maximum Power Cruise (approximately 75% power) - Never lean beyond 150*F on rich side of peak EGT unless aircraft operator's manual shoes otherwise. Monitor cylinder head temperatures.

(2) Best Economy Cruise (approximately 75% power and below) - Operate at peak EGT.
Click to expand...


There is a lot more and based on a number of the posts in this thread, there are many pilots out there who either have never seen the manual or haven't taken the time to read it.

Don't believe everything you read on the internet.
 
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This is all good info, on the dyno I have seen CHT rise does affect HP/TORQ. out-put @ specific settings with out change. Mid 300 hundreds I recall best power temp, every 10f degrees above that showed an average of 1.5 ? 2 hp loss. So reducing timing to lower CHTs is a wash in power loss/gain in the perfect cooling world.

I?ll be in KOSH this year with my ride, over @ IAC head quarters, continuing the power/economy R&D conversations.

http://www.g3ignition.com/images/AirVenture.jpg
 
"There is a lot more and based on a number of the posts in this thread, there are many pilots out there who either have never seen the manual or haven't taken the time to read it."
Click to expand...

I'm "sure" Lycomings numbers could not possibly be influenced by the operational realities of most airframe manufacture's. Not to mention the lost opportunty to sell you a new top end a bit sooner than you may like.
 
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N941WR said:
Does anyone read the Lycoming manual?



There is a lot more and based on a number of the posts in this thread, there are many pilots out there who either have never seen the manual or haven't taken the time to read it.

Don't believe everything you read on the internet.
Click to expand...


And DON'T believe everything printed in a Lycoming manual either.

Do your own research on CHT's and the strength of Al at those temps Vs what the rest of VAF land think is ideal. Then think abut the pressures involved....

In fact use some critical thinking when reading all their stuff. Some is good, some is just simply bizarre.

:cool:

Walt's comment is rather appropriate ;)
 
N941WR said:
Does anyone read the Lycoming manual?



There is a lot more and based on a number of the posts in this thread, there are many pilots out there who either have never seen the manual or haven't taken the time to read it.

Don't believe everything you read on the internet.
Click to expand...

The criticism is a little unfair inasmuch as Mike addresses the differences between the manual and present day experience and knowledge, especially considering the testing done in Ada.

The fact we may have these questions may not indicate a reluctance to read, but a passionate proclivity to. It's not a flaw.
 
LettersFromFlyoverCountry said:
I'm kind of stupid so please excuse me but if I change my mag timing to 20; what is the process for changing the timing on the Lightspeed plugs? Seems to me it's done with a timing light and an existing mark to check current timing but I don't recall instructions on how to adjust that.
Click to expand...

If you have a Hall Effect (mag hole) trigger simply time it like a mag with the green LED on the cover. If you have a direct crank trigger you'll need to remove the prop, flywheel/ring gear and retard the circuit board 5*. If you have the new mini sensor better call Klaus after reading the manual.:D
 
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One bit of data

I just checked the timing on my engine today, and it was in fact set at 25* btdc.

Got it changed to 20*------but still have to finish up a few thing on the annual before I test fly it.

Hoping this will slay the high CHT dragon.....

Will report back with flight report.
 
Mike S said:
I just checked the timing on my engine today, and it was in fact set at 25* btdc.

Got it changed to 20*------but still have to finish up a few thing on the annual before I test fly it.

Hoping this will slay the high CHT dragon.....

Will report back with flight report.
Click to expand...
Much different engine, Mike, but, in the process of chasing down my higher than desired CHT's found that both my mags were exactly at 27* when they should have been 25*. Not sure if they came from Aerosport that way or both drifted exactly the same over the past 90 hours. Unfortunately, setting it to 25* did not change my CHTs or OT at all. Again, though, I've never seen anything that said my engine would benefit temp wise from retarding the timing, so your experience may be much different. Only offered my experience so that you don't get depressed like I did if retiming doesn't help. Hope it does though!
 
The 20 BTDC timing change for the IO-360 only applied to 200HP slant valve engines. It was not applicable to the parallel valve engines. To me the 8.5:1 and 9:1 parallel valve engines with mags should be timed to 25BTDC. If you have modified compression ratio higher then that or run Mogas continually then you could go to 20 BTDC. Timing with electronic ignition was generally set to 20 BTDC to limit the max advance the timing would go to during cruise power. You can experiment with timing and will get varying power and temp output but besides those items, you change the fuel requirements and detonation margin for the engine. So be careful when you experiment, keep good data, evaluate it well and change the timing in small amounts, gradually, to be safe. BTW, I am a firm believer that Lycoming cylinders running chts in the 425 or slightly more area will last just as long as one running at 300- 350 CHT. Years in the engine overhaul business bears that belief out.
Good Luck,
Mahlon
 
Mike S said:
I just checked the timing on my engine today, and it was in fact set at 25* btdc.

Got it changed to 20*------but still have to finish up a few thing on the annual before I test fly it.

Hoping this will slay the high CHT dragon.....

Will report back with flight report.
Click to expand...

Dragon pretty much dead:D

In apx 5 hours of flight to the weekends Homecoming, I saw the climb CHT down apx 20* and the cruise CHT down at least 25.

I suspect the reason for the difference (climb vs. cruise reduction) is that the Lasar brain box dials in a bit of retard while in the high load conditions of climb, and puts in max advance in cruise.

But, this was not without a downside unfortunately:( the engine which has always had an occasional stutter in LOP is now much rougher LOP----to the point I had to richen it up a bit.

Guess it is time to go through the injector balancing act.
 
Mike, not sure what you have in the ignition department, but on an IO540D4A5 you should not be doing anything more than fixing the Air flow through the engine.

I will go as far as to say most of the EI's I am not a fan of, in fact none o them float my boat a great deal as they all chase higher advance and none have either a pressure reactive closed loop or a knock sensor like the auto's.

So that being said, of course your LOP ops will suffer, theta PP is much later and the combustion event is not what the maker intended.

What is your GAMI spread? If it is 0.5 or better move to the next step, if not fix it.

Next step is keep your timing up closer to 25 degrees, maybe 23-24 if that helps, but fix your exit air.

Hear is a link from another thread, see Bill Prendergasts photo http://www.vansairforce.com/community/showthread.php?t=36695&page=7

Last of all, this is my engine at high power LOP, stock engine, stock baffles (better seals) and GAMI's with an upper deck reference system like a Turbo engine.

Get the heat in correct (balanced F/A) and get the heat out right =>good CHT's. And yes I live in a warm climate. ;)

80LOP_zps6e22f7f3.jpg


If you want some help let me know, PM or email me a full detailed description of the engine and setup and some photos.

Cheers.
 
RV10inOz said:
Mike, not sure what you have in the ignition department,
Click to expand...

Slick Lasar.

RV10inOz said:
but on an IO540D4A5
Click to expand...

Mine is a IO 540C4B5-----rebuilt before I got it, I was told it has higher compression pistons-----I do not remember if 9:1 or 9.5:1. Googling the piston and cylinder part numbers from the invoice doesn't reveal any specifics.

Cylinder TIST 10.1 CA on one piece of paper, AEL 65102 ST 10.1 on another.

Piston AEL 15357.

The repeated "10.1" in the cyl numbers would lead me to think it is actually a 10:1 compression----------but I thought the compression was a function of the piston?

RV10inOz said:
So that being said, of course your LOP ops will suffer, theta PP is much later and the combustion event is not what the maker intended.
Click to expand...

Correct, less time for flame front to spread, and LOP doesn't want to burn well anyway, and also less ICP too.

RV10inOz said:
What is your GAMI spread? If it is 0.5 or better move to the next step, if not fix it.
Click to expand...

Absolutely no idea. As I said above, that is a project I still need to tackle.

RV10inOz said:
Next step is keep your timing up closer to 25 degrees, maybe 23-24 if that helps, but fix your exit air.
Click to expand...

I have already added a couple of louvers to the cowl sides, and that did very little to help the CHT issue. I did open up the right cowl intake area by re-sculpturing the upper ramp, and that made a much larger improvement than the exit louvers.

plane%2520paint%2520trim%2520layout%2520015.JPG


RV10inOz said:
If you want some help let me know, PM or email me a full detailed description of the engine and setup and some photos.

Cheers.
Click to expand...

Will send a PM.
 
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