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SB M20-289A aileron center link clearance before and after videos


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For those of you not familiar with SB M20-289A, or those who just haven't gotten around to performing it, here are before/after videos on our 1976 M20F.  We've been aware of the issue for a while now, but it was only within the last year that our original installation actually began to have the clearance problem described in the S.B.  Ordered the kit from Mooney, and installing the new spacers does make a significant difference.

Before:

 

After:

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The especially eagle-eyed will note that at some point in the history of our airplane, the bolt and nut in the "before" video were installed backward.  The bolt head is supposed to be aft, and the nut forward.  There is a slight downward tilt of the mechanism from aft to forward, so with the bolt head aft, the bolt would theoretically stay in place if the nut were to fall off.  In the backward installation, if the nut were to come off, the bolt would be more likely to work completely loose.  That's the aviation "standard", though I don't put much faith in it - I'd rather be sure nuts don't come off!

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Vance,

Great videos and details... thanks for sharing them...

When copying links for videos...  there is a button question that asks if you would prefer the link in place of the video...

There may be an undo for the choice?

Best regards,

-a-

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7 hours ago, RobertGary1 said:

What does the kit run? My ailerons have always made a banging noise because of this. 

We paid $220 for the kit at our local Mooney MSC (Arapahoe Aero) a few months ago - just now getting around to installing it.  LASAR also has the kit listed for $236: https://lasar.com/service-bulletin-kits/service-bulletin-kit-289-m20-289-000

Not very expensive in aviation dollars, I guess, but a little frustrating.  The kit contains an AN bolt, castle nut, and cotter pin that you can get from Spruce for about two bucks.  The "magic" is the three specially-sized washers that exactly fill the gap where the rod ends are captured by the U-bracket.

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On 4/8/2021 at 7:58 PM, N201MKTurbo said:

You might want to put a washer under the bolt and nut to get the cotter pin in a better place.

I see what you're saying, only one of the two cotter pin shanks is actually locking the nut.  But the SB doesn't mention additional washers, so it's unclear to me if that's "authorized" (maybe it's kosher under generic 43-13 principles).

In any case, I'm not particularly concerned about it.  There is no meaningful torquing load on the nut that would cause it to break a castle point or to pop the cotter pin, even with only one shank holding against the nut.

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25 minutes ago, Vance Harral said:

I see what you're saying, only one of the two cotter pin shanks is actually locking the nut.  But the SB doesn't mention additional washers, so it's unclear to me if that's "authorized" (maybe it's kosher under generic 43-13 principles).

In any case, I'm not particularly concerned about it.  There is no meaningful torquing load on the nut that would cause it to break a castle point or to pop the cotter pin, even with only one shank holding against the nut.

I put a washer under all nuts and bolts. You add washers to get the nut to the right place and to protect the expensive airplane parts. I’m pretty sure if you looked in the parts manual, it would show washers. 
 

All that being said, I wouldn’t take it apart to put them in.

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26 minutes ago, Vance Harral said:

I see what you're saying, only one of the two cotter pin shanks is actually locking the nut.  But the SB doesn't mention additional washers, so it's unclear to me if that's "authorized" (maybe it's kosher under generic 43-13 principles).

AN bolts come in lengths of 1/8" increments, so it is standard practice to adjust within 1/8" using washers.  Washers will spread the load and also take up any abrasion due to rotation of the fasteners.  Also, I figured somebody would point out that the cotter pin is not done quite right per 43.13, and there's a description in AC 43.13 Par 7-127 (p.7-26) showing the two accepted methods for safetying with a cotter pin.   The short tail is not supposed to touch the washer or surface below it, and the tail over the bolt should not extend past the bolt.   There's an alternate method to wrap the tails around both sides of the nut.    One of the reasons for this is to keep the tails clear of anything else so that they can't snag or be snagged by other stuff in the vicinity.

26 minutes ago, Vance Harral said:

In any case, I'm not particularly concerned about it.  There is no meaningful torquing load on the nut that would cause it to break a castle point or to pop the cotter pin, even with only one shank holding against the nut.

There's been far worse done to airplanes that flew without trouble.

 

 

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Thanks to N201MKTurbo and EricJ for the pointers.  The A&P who looked it over said it was kosher, but I'm always learning.

With regard to what's in the manual, the original parts manual shows one washer under the self-locking nut, but no washer under the bolt head.  The diagram in SB M20-289A shows no washers at all.  I can see how the bolt head and nut could wear on the U-bracket.  But again, there's basically no torque or fore/aft load on the bolt and nut, all the forces are in shear.

 

image.png.11e4f1aa0231bc3f7469ec3fb736f630.png  image.png.6a93c4334b45418ad9252181eb289ec0.png

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6 hours ago, ArtVandelay said:


I will check this visually at next annual but is the banging noise consistent and pronounced? I don’t recall hearing any noise when I preflight ailerons manually moving them by hand.

I check it every year. Been doing it for the 20 years I’ve owned it. Used to annoy me. 

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I never heard any banging or clicking noises operating the ailerons by hand or via the yoke during a normal preflight.  The only way I could get them to click was by manually twisting the linkages back and forth in the belly at annual, as seen in the video.  For most of the time we've owned the airplane, doing this would only get the aileron links "very close" to the gear retraction torque tube.  I could still slide a sheet of paper in there, and I didn't observe any wear marks, so we didn't bother with the SB.  It only started actually touching a couple of years ago.  We would have done the work at the 2020 annual, but could not get the spacer kit at the time.

In summary, I don't think this is an OMG-we're-going-to-die maintenance item, just something to keep an eye on from year to year.

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  • 1 year later...
On 4/11/2021 at 3:27 PM, Vance Harral said:

I never heard any banging or clicking noises operating the ailerons by hand or via the yoke during a normal preflight.  The only way I could get them to click was by manually twisting the linkages back and forth in the belly at annual, as seen in the video.  For most of the time we've owned the airplane, doing this would only get the aileron links "very close" to the gear retraction torque tube.  I could still slide a sheet of paper in there, and I didn't observe any wear marks, so we didn't bother with the SB.  It only started actually touching a couple of years ago.  We would have done the work at the 2020 annual, but could not get the spacer kit at the time.

In summary, I don't think this is an OMG-we're-going-to-die maintenance item, just something to keep an eye on from year to year.

Vance, just wondering if the airplane trimmed different after you did this?  

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@tony, we didn't notice any difference in trim or other flight characteristics after adding the spacer kit.  The axis of slop that gets cleaned up by installing the spacers is perpendicular to that which actually moves the ailerons, so the slop that gets cleaned up doesn't really change the position of the ailerons at all.

@AlexF, as mentioned above, I couldn't really tell what material the spacers are made of.  I just know it didn't seem like nylon/plastic (not light enough), or conventional cad-plated steel MS washers (not heavy enough).  Almost seems like they were painted aluminum, but I seriously doubt that's what they actually are.

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