O-200A Timing Confusion

farmrjohn

Pre-takeoff checklist
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farmrjohn
I'm confused on the mag timing for an O-200A engine. AD 96-12-06 restricts timing to 24º btc unless all four cylinders meet a part number requirement, in which case it allows timing to be set at 28º btc. However TCDS E-252 rev 34 calls for 24º btc only. What should the timing be for an engine if all four cylinders meet the 28º requirement?
 
What does the aircraft maintenance manual say?
 
The SB most likely says you are eligible for 28btc but that sure sounds like you aren’t obligated to bump it that far.
Upside of 24btc might be longer cyl life.
Downside might be less power available.
This being unsubstantiated opinion of course.
 
What does the aircraft maintenance manual say?
Doesn't matter the AD must be complied with, and the Link provided by Bell gives the detailed instruction. see note #5
 
Doesn't matter the AD must be complied with, and the Link provided by Bell gives the detailed instruction. see note #5

Might be nice to know what the aircraft manufacturer originally wanted in their aircraft.

The OP sounds confused between what has precedence, the TCDS or the AD. The AD takes precedence and by reference, the SB. The AD is basically amending the TCDS specs in this case.
 
Might be nice to know what the aircraft manufacturer originally wanted in their aircraft.
Doesn't really matter either, it was the Continental cylinders that were cracking, so then they came out with this lame fix, then did a redesign and made replacement cylinders that the AD does not apply to.
And remember if you have after market cylinders none of this applies.
 
Are any of the old cylinders still around?
That was 25? years ago?
Continental got a real black eye over this, just about time superior came out with new after market cylinders. Continental had quit making cylinders prior to this so every one was required to buy after market cylinders.
Kinda sorta like Continental got the idea that they should get back in the game, and started making new cylinders again, but their reputation was crap, and very few bought their cylinders.
about that time ECI started to make cylinders too.
Now all you can buy is Continental and Superior, ECI is gone.
But to answer your question, YES there is probably some on an old hangar queen some place.
To add, some of these cylinders got chromed and may have orange bases, and still be in service.
 
Thanks for the history notes, Tom.
What is your opinion on the statement in the SB, "eligible for" (28deg btc).
If a person has a choice, would you go with 24 or 28? Or maybe it doesn't matter a whole bunch.
 
Thanks for the history notes, Tom.
What is your opinion on the statement in the SB, "eligible for" (28deg btc).
If a person has a choice, would you go with 24 or 28? Or maybe it doesn't matter a whole bunch.
If 28 BTDC is legal for your cylinders, that is the timing required by the AD.
Timing is 28 by design, the AD retarded to 24, If the AD does not apply, you should be at 28.
hope that makes sense.
 
If 28 BTDC is legal for your cylinders, that is the timing required by the AD.
Timing is 28 by design, the AD retarded to 24, If the AD does not apply, you should be at 28.
hope that makes sense.
The wording on the SB is not clear; it does not say "Must be set at 28" or such - it only says "eligible for". My mind wants to take it as 'our discretion' due to the unusual wording.
 
The wording on the SB is not clear; it does not say "Must be set at 28" or such - it only says "eligible for". My mind wants to take it as 'our discretion' due to the unusual wording.
Remember when the AD does not apply, you must be at design. (Unchanged from the original 28) the SB is not mandatory, the type design is.
When you must comply with the AD, you are required to be at 24.
 
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Thanks all, the fog is clearing at least a little bit. I gather that even though the current TCDS is much more recent than the AD the AD is still controlling (and the SB also by reference). The AD states:
"(b) For engines that have all four cylinders with P/N 641917 or higher, the engine timing may be reset to 28o (+ 1o, -1o) BTC on both magnetos in accordance with the magneto engine timing procedure for direct drive engines in TCM SB No. SB94-8, dated September 14, 1994."
In this case is "may" permissive or mandatory for resetting the timing? I gather if the timing is reset to 28 the data plate must be stamped accordingly, and back to 24 if a non-conforming cylinder is subsequently installed.
 
Thanks all, the fog is clearing at least a little bit. I gather that even though the current TCDS is much more recent than the AD the AD is still controlling (and the SB also by reference). The AD states:
"(b) For engines that have all four cylinders with P/N 641917 or higher, the engine timing may be reset to 28o (+ 1o, -1o) BTC on both magnetos in accordance with the magneto engine timing procedure for direct drive engines in TCM SB No. SB94-8, dated September 14, 1994."
In this case is "may" permissive or mandatory for resetting the timing? I gather if the timing is reset to 28 the data plate must be stamped accordingly, and back to 24 if a non-conforming cylinder is subsequently installed.
When all of your cylinders are above 641917 the AD does not apply. when it does not apply, you must comply with type design. which is 28 degrees
 
When all of your cylinders are above 641917 the AD does not apply. when it does not apply, you must comply with type design. which is 28 degrees

Does TCDS E-252 specify the type design? If so it calls for 24o btc for top and bottom.
If the TCDS does not specify the type design, then what does? The fog is rolling back in.
 
The fog is rolling back in.
You're creating some of the fog. The TCDS is a summary of the original Type Design of the engine. Full stop. The only path to get to the 28 deg timing is via the TCM SB which alters the original engine configuration. Stop. If your engine meets the requirements of the SB then the timing and data tag update are permitted/signed off per the SB and not the TCDS. The SB is one method to properly alter the original type design.
 
You're creating some of the fog. The TCDS is a summary of the original Type Design of the engine. Full stop. The only path to get to the 28 deg timing is via the TCM SB which alters the original engine configuration. Stop. If your engine meets the requirements of the SB then the timing and data tag update are permitted/signed off per the SB and not the TCDS. The SB is one method to properly alter the original type design.
Thus the wording in the SB.
 
I'll have to look at the data tags I have to see what they say.
 
The TCDS specifies 24 degrees now. The last revision of it was back in 1982, so it must have been changed either then or before to reflect the 24 degree timing. My Cessna 150 manuals also all call for 24 degrees.

The 1996 AD supercedes two earlier AD's that did the same thing (changed the timing to 24 degrees). How they were worded, who knows now at this time. The main thing is to follow the AD at this point.

http://www.airweb.faa.gov/Regulator...848004b6075?OpenDocument&Highlight=2,96-12-06

Harry Fenton's website has lots of interesting reading on low compression Continentals, including this exact subject.

http://www.bowersflybaby.com/tech/fenton.html
 
The TCDS specifies 24 degrees now. The last revision of it was back in 1982, so it must have been changed either then or before to reflect the 24 degree timing. My Cessna 150 manuals also all call for 24 degrees.

The 1996 AD supercedes two earlier AD's that did the same thing (changed the timing to 24 degrees). How they were worded, who knows now at this time. The main thing is to follow the AD at this point.
What happens when you have after market cylinders, and the AD doesn't apply?
 
I'll have to look at the data tags I have to see what they say.
The best one I have. The others have been changed so many times they have a hole in them. :)
 

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While leafing through my STCs this morning, I realized that my timing had been misadjusted to 24 last annual... argh.
 
...the engine timing may be reset to 28o (+ 1o, -1o) BTC on both magnetos in accordance with the magneto engine timing...
To get the degree sign, hold down the "Alt" key and type 248, then release the Alt key. Looks like so: 45°
 
Thread drift for the experts, why the two degree difference. Between left and right on the c85?
 
I owned a C150F for 16yrs. As purchased, it had 2 Continental cylinders affected by the ad. At 2nd annual, I replaced 3cylinders with Superior Millinium cylinders to give 4matching cylinders. This allowed the 28deg timing, and my IA gave it the +1deg allowed. At 24deg timing, the engine puts out approximately 94hp. A noticeable difference. 28deg timing also allows the engine to better digest a continuous diet of 100ll.

Based on the previous owners experiences, the 24deg timing didn’t help much with the cracking. No cracks with the Millenniums but dreaded annuals due to constant valve issues. Even new millenniums had to be o/h’d at 1,100hrs.
 
Hi all, not to complicate this. I have read all and understand. I have the required cylinders installed to go to 28 degrees. What I am looking for, if exists, is the Cessna 150F publication (S/B, S/I, etc.) that enables the Continental S/B authorizing to go to 28 degrees? From my compiling of S/B's etc., there always seems to be a an enabling Cessna publication to the engine manufacturers S/B's, etc. Any thoughts on this. Appreciate feedback.
 
Hi all, not to complicate this. I have read all and understand. I have the required cylinders installed to go to 28 degrees. What I am looking for, if exists, is the Cessna 150F publication (S/B, S/I, etc.) that enables the Continental S/B authorizing to go to 28 degrees? From my compiling of S/B's etc., there always seems to be a an enabling Cessna publication to the engine manufacturers S/B's, etc. Any thoughts on this. Appreciate feedback.

You may not find it, what cylinders are you running? The AD applied to certain continental cylinders. Outside of those cylinders, superior etc. the TCDS applies.
 
What I am looking for, if exists, is the Cessna 150F publication (S/B, S/I, etc.) that enables the Continental S/B authorizing to go to 28 degrees?
When dealing with products (aircraft, engines, propellers) that have their own TC, they are usually maintained under their respective OEM ICAs. So in this case Cessna does not "enable" the use of a TCM SB as TCM is the controlling entity for the engine work. Where you might find Cessna listing a TCM SB is merely to inform the owner the engine SB exists as most engine OEMs do not track customers but airframe OEMs do.
 
You may not find it, what cylinders are you running? The AD applied to certain continental cylinders. Outside of those cylinders, superior etc. the TCDS applies.
Thanks for your reply. I do have the cylinders required to comply with AD 96-12-06 para (b). They are TCM P/N 653426 from 1993 which is higher than P/N 641917 stated in AD. The AD does, however, reference Cessna 150 in "Applicability" of AD. I'm doing a comprehensive review of all ICA"s in a chart form and find so far there is no Letter of Transmittal from Cessna to raise awareness of TCM S/B 94-8 to the aircraft owner authorizing 28 degrees BTC timing. I may be wrong. Mostly I'm finding these TCM ICA's and components (mags, carbs, etc.) have a Cessna Letter of Transmittal. Maybe I'll find it and pass it on. Cessna will eventually capture it probably.
Thx again.
 
When dealing with products (aircraft, engines, propellers) that have their own TC, they are usually maintained under their respective OEM ICAs. So in this case Cessna does not "enable" the use of a TCM SB as TCM is the controlling entity for the engine work. Where you might find Cessna listing a TCM SB is merely to inform the owner the engine SB exists as most engine OEMs do not track customers but airframe OEMs do.
Thanks for your response....appreciated. Cessna will eventually capture it as they have done with other TCM ICA's.
 
Cessna will eventually capture it as they have done with other TCM ICA's.
Maybe, but that is not my experience. However, unless you have not already done so, Textron offers a free service that allows you to search bulletins, here, and TCM has a bulletin search page, here. And if you are still uncertain, you can also email technical support and see if they can offer you some input.
 
Thx reply. I have these sites already and haven't found corresponding S/B from Cessna. Not there I believe. At least it's noted in AD and TCM S/B about Cessna 150 ... 28 degrees BTC with correct cylinders. . As previously stated in a member's response, at some past revision in the TCM - TCDS - E-252the timing was at 28 degrees. Not going to look for that. Thx for your assistance.. very appreciated.
 
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