O-200A Timing Confusion

Discussion in 'Maintenance Bay' started by farmrjohn, May 24, 2018.

  1. farmrjohn

    farmrjohn Pre-takeoff checklist

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    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?
     
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  2. Bell206

    Bell206 En-Route

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    This bulletin should help:
    www.tcmlink.com/pdf2/MSB94-8D.pdf
     
  3. JAWS

    JAWS Cleared for Takeoff

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    What does the aircraft maintenance manual say?
     
  4. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    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.
     
  5. Tom-D

    Tom-D Taxi to Parking

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    Doesn't matter the AD must be complied with, and the Link provided by Bell gives the detailed instruction. see note #5
     
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  6. JAWS

    JAWS Cleared for Takeoff

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    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.
     
  7. Tom-D

    Tom-D Taxi to Parking

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    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.
     
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  8. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    Are any of the old cylinders still around?
    That was 25? years ago?
     
  9. Tom-D

    Tom-D Taxi to Parking

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    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.
     
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  10. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    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.
     
  11. Tom-D

    Tom-D Taxi to Parking

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    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.
     
  12. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    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.
     
  13. Tom-D

    Tom-D Taxi to Parking

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    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.
     
    Last edited: May 25, 2018
  14. farmrjohn

    farmrjohn Pre-takeoff checklist

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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.
     
  15. Tom-D

    Tom-D Taxi to Parking

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    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
     
  16. farmrjohn

    farmrjohn Pre-takeoff checklist

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    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.
     
  17. Bell206

    Bell206 En-Route

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    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.
     
  18. Tom-D

    Tom-D Taxi to Parking

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    Thus the wording in the SB.
     
  19. Tom-D

    Tom-D Taxi to Parking

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    I'll have to look at the data tags I have to see what they say.
     
  20. JAWS

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    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
     
  21. Tom-D

    Tom-D Taxi to Parking

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    What happens when you have after market cylinders, and the AD doesn't apply?
     
  22. Tom-D

    Tom-D Taxi to Parking

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    The best one I have. The others have been changed so many times they have a hole in them. :)
     

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  23. JAWS

    JAWS Cleared for Takeoff

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  24. Tom-D

    Tom-D Taxi to Parking

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    Last edited: May 25, 2018
  25. GeorgeC

    GeorgeC Administrator Management Council Member PoA Supporter

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    While leafing through my STCs this morning, I realized that my timing had been misadjusted to 24 last annual... argh.
     
  26. Dan Thomas

    Dan Thomas Final Approach

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    To get the degree sign, hold down the "Alt" key and type 248, then release the Alt key. Looks like so: 45°
     
  27. unsafervguy

    unsafervguy Pattern Altitude

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    Thread drift for the experts, why the two degree difference. Between left and right on the c85?
     
  28. AeroLudite

    AeroLudite Pre-Flight

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    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.