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Notchy trim diagnosis


Marek7

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Howdy guys,

I want to get the board's opinion on something my mechanic is having a little bit of trouble with. Flying back from the coast to a balmy - 40 degrees Celsius Saskatoon my trim started to lock up. First I noticed the electric trim was not working, then I noticed that the wheel was very stiff. I managed to land it without further incident.

I let the aircraft sit for a while in a warm hanger. AME thought it was just frozen up and did all the simple things like regreasing stuff. I took the aircraft on another cross country, in the cold. And the trim was better after thawing out in the hanger however I still noticed it was notchy  while warm.  The autopilot failed to work and the breaker popped a couple of times. Electric trim seemed better but even that quit.

 

Anybody have anything similar happened to them? What could it be?

Thanks from the great white North,

 

Mark

 

 

 

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My first reaction is old, hard grease in the trim jack screw. It's at the rear of the belly. There are several threads here describing how to remove, clean, re-grease and reinstall them. The painful part is removing and replacing the belly . . . .

New grease is thinner, less viscous, flows easily, has no chunks and may resist clumping in cold temps better.

Good luck!

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pull the belly panels use a brush and cleaner/lubricant of choice and clean all old hard grease and lube. there are about 3/4 ujoints. The chain and Jackscrew are places to focus on.   The Jackscrew can be lubed by removing that strip of alum. wiping and lubing and running the trim is the way to do it without removing the whole unit.

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I got a little bit of feedback from the Mooney Center and this was there thoughts on the trim getting stiff.

 

" I have been looking at the trim system for your Mooney. I do have a couple of questions with regard to the trim. The M/M talks about the Trim ControlActuator rigging in the centre of the Aircraft. Do you know if anyone has looked in that area ref. Fig 27-10 Trim Control Actuator Rigging in the M/M. I ask the question because if your AME’s are not seeing anything significant in the rear of the Aircraft with the trim jack perhaps the settings in the Trim Control Actuator require some lubrication and/or adjustment.

As well in Fig 27-9 the M/M talks about the Variable Down spring. I am wondering if this cable tension has been looked at? These are my initial thoughts to look seeing as your AME has been into the trim jack."

 

For searching knowledge in the future. 

Edited by Marek7
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I know some here don't believe in WD-40 but before you start any disassembly spray WD-40 right into the jackscrew and nut and allow 30 minutes for it to penetrate the threads. Rotate the trim wheel back and forth to loosen the jackscrew.

https://www.bing.com/videos/search?q=WD-40+on+screws&&view=detail&mid=C21F67AE5999CD8385CEC21F67AE5999CD8385CE&&FORM=VRDGAR

José 

Edited by Piloto
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53 minutes ago, jetdriven said:

Show me the approved procedure for that...why not use water. Or bacon grease. Or 3-in1 oil.  This is a secondary flight control. Follow the SMM, not an internet expert. 

Someone mentioned a few months ago there was a crackling noise in their headsets. Maybe it was bacon frying which led to the bacon grease gumming up the trim wheel. :)

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10 hours ago, Andy95W said:

Wait a second, are we NOT supposed to use bacon grease on the trim anymore?!?  

And people wonder why we always save bacon grease! It has so many uses, even beyond gravy . . . .

Edited by Hank
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Ancient history of grease... can often be studied by looking at the jack screw of the trim system of a Mooney...

For a real interesting insight, one has to think inside the box, the gear screw operates in.

Old grease and cold grease, can be hard as rocks and refuse to flow... there is no old, cold grease (that works).

Expect a good cleaning and regreasing to be the order of the day... get as much of the old grease out.

Much of the jack screw is available to eyes and fingers of a PP...  see what you have back there first...

Then there is the gear box up front at the trim wheel...

PP thoughts only, not a mechanic...

Best regards,

-a-

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Thanks for the replies. After various situations. Trim working then not. Disassembly and relubing of the trim screw. I am just replacing the assembly.   It's pricy and a bit annoying but sometimes fixing stuff over and over again leads to more problems. 

A point that I caught was the screw boot can fray and make things much worse.

 

Ill let you know how she goes. 

Cheers, 

 

Mark 

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On 2/16/2018 at 11:12 PM, Piloto said:

Not going to follow the recommendation of someone using the wrong tools for the job.   The flat jaws of the vice would have never held a stuck pipe.  That is what chain vices are for.  And the adjustable wrench was wrong.  

image.png.8985a580d4a8a2fc32a4b93ad9f7f783.png

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3 hours ago, Marek7 said:

Thanks for the replies. After various situations. Trim working then not. Disassembly and relubing of the trim screw. I am just replacing the assembly.   It's pricy and a bit annoying but sometimes fixing stuff over and over again leads to more problems. 

A point that I caught was the screw boot can fray and make things much worse.

 

Ill let you know how she goes. 

Cheers, 

 

Mark 

Can you tell us the price for the assembly?

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On 2/17/2018 at 12:12 AM, Piloto said:

I have replayed the video like 5 times and swear he is pulling (clockwise) the first time to make it tighter.  After the WD40 he pushes (counterclockwise) to loosen it. 

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5 hours ago, Yetti said:

Not going to follow the recommendation of someone using the wrong tools for the job.   The flat jaws of the vice would have never held a stuck pipe.  That is what chain vices are for.  And the adjustable wrench was wrong.  

image.png.8985a580d4a8a2fc32a4b93ad9f7f783.png

There is a square section at the trim jack screw.  I would not want to put a pipe wrench on a torque tube.  Even one as built as our Mooney ones are. 

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Well... Looks like we finally solved it.    The bearing where the autopilot trim servo attaches was inadvertently sprayed with a corrosion inhibitor and it turned into cement, in particular when cold.    I doubt my adventures in this will help anyone but it's good to have this thing fixed.   

Mark 

 

 

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Great pirep/follow-up, Mark!

The MS community detailed what happens when the lubrication turns to sand...

Of course, if you accidently put sand in there, you will get the same result.  :)

It takes some strength of character to come back and explain those details!

Nice work!

Best regards,

-a-

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