Valve lash - MM or engine plaque?

Adjusting valves, do you go by the manual or the plaque

  • The maintenance manual.

    Votes: 6 54.5%
  • The engine plaque.

    Votes: 1 9.1%
  • Whichever one is looser.

    Votes: 0 0.0%
  • Whichever one is tighter.

    Votes: 0 0.0%
  • Either one, it ain't rocket science.

    Votes: 0 0.0%
  • Wait, I have adjustable valves?

    Votes: 4 36.4%

  • Total voters
    11

alfadog

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alfadog
So in the classified forum, the subject of adjusting valves came up. Last week, I did the better part of a 100-hour on an American Yankee AA-1 with Lycoming O-235 engine. I noticed a discrepancy between the maintenance manual and the engine plaque. Manual said .007-.009 but plaque said .010.

Which would you go by?

What about mag timing if there were a discrepancy there?
 
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use which ever has the best results.....start with the MM. Most of us have non-adjustable hydraulic valves and the clearance/lash is around 0.0028"
 
Have the manuals been updated more recently than the engine plaque? I wonder if there are any service bulletins or letters that explain the change.
 
Whichever is the latest info... I'm used to working with maintenance books that have by s/n effectivities, so latest data is the bible.
 
IAW the updated Service Instruction which discusses the this exact question.

What do I win?
 

Attachments

  • Valve Lash Service Instruction No. 1068A.pdf
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use which ever has the best results.....start with the MM. Most of us have non-adjustable hydraulic valves and the clearance/lash is around 0.0028"
IIRC the hydraulic lifter lash is .028-.080". That's the dry lash, and the lifter has to be taken apart and all the oil drained from it to get that measurement. In operation, there is no lash at all. That's the idea behind hydraulic lifters. They adjust to the expansion and contraction caused by thermal variations, and are quiet.
 
Brings up the question "Which maintenance manual? The airframe or engine?".
 
Brings up the question "Which maintenance manual? The airframe or engine?".

I was going to ask the same thing...

The other thing I wondered about was what the pushrod material was. I haven’t had to maintain an o-235 but it is my understanding that there were both aluminum and steel pushrods. I’d think the clearances for one would be different than the other.
 
if a 41 year old SI was still valid
I believe it is unless it has been incorporated into the MM which is possible. A quick check in the Front Matter of the manual will tell you if it has been incorporated. But there are a number of SIs from as early as the 50s that are still "valid." The copy I posted above for the SI was off the shortwingpiper website which indicated the SI was still the go to reference. But I could be wrong on that.
 
Go read the SI linked above.

"When setting the tappet clearance on the 0-235 Series or 0-290-D Series Engines, it has been
customary to set the clearance at .010 inch as stamped on the engine nameplate. If this is done
indiscriminately, the desired running clearance will not be obtained.".

My old 152 manual says to follow the SI in the special inspection. I went online and found an old Lynx maintenance manual and it mentions the SI. No other information on setting valves in the aircraft maintenance manual. Just this below.

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what date is required for the Maintenance Manuals? Cert date?
Depends. The guidance pushes you in several ways if you're using the manuals for maintenance per Part 43.13 or for an inspection program per 91.409. It seems "current" has several meanings in the FARs. But there is FAA guidance to use the older manuals that were "current" at the time of manufacture or at the time you "adopted" them when it comes to inspections. Unless the Feds can show an older manual version is unacceptable then its okay to use it under the latter half of 43.13(a)--"other methods, techniques, and practices acceptable to the Administrator,"

While it's usually easier to use the latest and greatest manual revision, sometimes on older aircraft the newer revision manual does not address an older configuration. So in some cases you either find an older manual or other acceptable reference, or upgrade the aircraft to the latest configuration. I've had "fun" with this on mainly older helicopters, but it usually worked out in the end.
 
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What part of the valvetrain in piston planes is adjustable to set lash?
 
Depends. The guidance pushes you in several ways if you're using the manuals for maintenance per Part 43.13 or for an inspection program per 91.409. It seems "current" has several meanings in the FARs. But there is FAA guidance to use the older manuals that were "current" at the time of manufacture or at the time you "adopted" them when it comes to inspections. Unless the Feds can show an older manual version is unacceptable then its okay to use it under the latter half of 43.13(a)--"other methods, techniques, and practices acceptable to the Administrator,"

While it's usually easier to use the latest and greatest manual revision, sometimes on older aircraft the newer revision manual does not address an older configuration. So in some cases you either find an older manual or other acceptable reference, or upgrade the aircraft to the latest configuration. I've had "fun" with this on mainly older helicopters, but it usually worked out in the end.
for part 91 use.....current means the date of the certification.

So....maintenance for my 1972 Cessna C-172M needs to be dated 1972 or newer.
 
Lycoming Direct Drive Overhaul Manual: https://www.expaircraft.com/PDF/Lycoming-OH-Manual.pdf

Page 115 of the pdf has the tappet clearance. For the O-235 it's .006-.012". If someone has a more recent amendment to the manual it might say something a little different. This one is 1993.

The "dry tappet clearance" is for hydraulic lifters.

There's also a prodedure for adjusting that needs to be followed. That camshaft moves back and forth a little and you can get false readings unless the crank is in the right place for each pair of valves.
 
for part 91 use.....current means the date of the certification.
Date of manufacture--which can be different than cert date. This is the only reference used from what I've seen.
So....maintenance for my 1972 Cessna C-172M needs to be dated 1972 or newer.
Provided your mechanic will accept using an old manual. Part 43.13(a) calls for using current (latest/greatest) OEM documentation in performing maintenance. Several FAA LOIs redefined that 43.13 statement to include older manuals (non-current) but as a secondary definition to 43,13(a) via an "other method acceptable." Here's one LOI:
https://www.faa.gov/about/office_or...r documents - (2010) legal interpretation.pdf

With Part 43 maintenance it's the mechanics call which reference he uses. However, if you had selected (adopted) an OEM inspection program under Part 91 from your 1972 MM then the mechanic is required to follow that old inspection program. And there is a LOI for that too. It gets a little complex especially when you throw a Repair Station into the mix.
 
In the engine in question, the rocker arms.

So same as automotive. I set to zero lash and use the thread pitch of the rocker nut/stud to calculate how much to turn the nut to get the lash I need. This is how I set hydraulic lifter preload.
 
So same as automotive. I set to zero lash and use the thread pitch of the rocker nut/stud to calculate how much to turn the nut to get the lash I need. This is how I set hydraulic lifter preload.

These are not hydraulic.
 
Same thing, just loosen 1/8 turn (or whatever) to open lash, instead of tighten to set preload. No?

I really am not sure what you’re trying to get at. There are specific instructions on how to do the valve adjustment on the engine in question, and they have been linked in this thread. It would be in a mechanic’s best interest to follow them rather than just doing it however they feel like.
 
Same thing, just loosen 1/8 turn (or whatever) to open lash, instead of tighten to set preload. No?
Depending on the thread pitch, it would be easy to calculate the fraction of a turn required to achieve .006 to .012" lash. But a feeler gauge is better.
 
I really am not sure what you’re trying to get at. There are specific instructions on how to do the valve adjustment on the engine in question, and they have been linked in this thread. It would be in a mechanic’s best interest to follow them rather than just doing it however they feel like.
Actually, using the thread pitch of the adjuster can be quite accurate, and comparable to the numbers using feeler gauges. In some cases, such as when the end of the valve is dished due to wear, you'll bet better results.
 
Actually, using the thread pitch of the adjuster can be quite accurate, and comparable to the numbers using feeler gauges. In some cases, such as when the end of the valve is dished due to wear, you'll bet better results.

I never said it couldn’t be.
 
I really am not sure what you’re trying to get at. There are specific instructions on how to do the valve adjustment on the engine in question, and they have been linked in this thread. It would be in a mechanic’s best interest to follow them rather than just doing it however they feel like.

I agree. I was just wondering if another way was possible on aircraft engines. I wouldn’t advocate straying from written procedure for an airplane power plant.
 
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