Trim Jackscrew Binding

[kortopates]

Hi Skip, I replaced the bearings on mine due to roughness. I have 7600 hours on my bird and thought if I’m taking this apart, might as well put new bearings in. I tried to remove them myself but ultimately took it to my machine shop and had the old ones pressed off and new ones pressed on. 
The shiming is just as N201MKTurbo stated with just taking up enough clearance between the housing as to have the bearings roll freely without them moving fore and aft in the housing. 
Thanks,
David

After you replaced the bearings, did you find you had to get different sized shims to get it snug - and thus order them?


Sent from my iPhone using Tapatalk

[Sabremech]

34 minutes ago, kortopates said:

After you replaced the bearings, did you find you had to get different sized shims to get it snug - and thus order them?


Sent from my iPhone using Tapatalk

I lucked out as I had another jack screw that was unserviceable and used a shim from that one. Just needed one that was .003 thicker. New shims were $40-$70 each depending on thickness.

David

 

[BiplaneKim]

I have an intermittent electric trim problem with my 1980 Mooney M20K (231) which is equipped with a Bendix/King KFC-200 autopilot/flight director. Before asking some questions, I'll give you some background info.

Through the course of troubleshooting this problem, I ran across this MooneySpace thread which really explained a lot about Trim Jack Screw Binding. I've always thought I had an electrical problem but after reading through this thread, it could very well be a trim jack screw binding problem. At least I'm convinced that my Jack Screw system needs some attention (including removal, inspection, cleaning, lubrication, and reinstallation) before continuing to troubleshoot an electrical problem. I may find that this solves the problem.

I usually use the electric trim and the intermittent problem has become more frequent. Often when using the split trim switch on the yoke, it trips the breaker, sounds an alarm and the electric trim is inoperable. Sometimes I reset the breaker but that generally does not work and I use the manual trim wheel. This problem usually does not occur on the ground and often may not occur on the next flight.

I thought I’d start by making sure it is being maintained correctly, such as lubrication, so I looked through my aircraft service manual which does not provide a lot of information. After talking to the shop that has done my avionics work, I found out that the electric trim system service & maintenance is covered more thoroughly in some later Mooney manuals for the M20R and Bendix/King manuals including Honeywell Service Bulletin 292. They were kind enough to copy the related pages.

From the pages they gave me, I discovered that there was an STC for the addition of a carrier bearing located on the trim shaft directly below the trim servo. From inspection, I can see that bearing has been installed on my Mooney. The pages also say there is a maintenance decal that is supposed to be installed at the same time to provide Annual inspection and lubrication instructions but my plane does not have that decal. I do not believe that this bearing has been inspected and possibly not serviced or lubricated in the 18 years that I have owned the aircraft. For about the first 10 years I owned the plane, I had a highly qualified Mooney specific IA doing my annuals and I worked with him and I do not recall ever doing anything with this bearing. He has passed away, and I do not think my current IA is aware of this bearing inspection or maintenance either.

A few days ago, my friend (A&P) and I spent the day troubleshooting and planned to inspect the bearing (below the trim servo). I started by asking him to operate the trim wheel to see how it felt to him and he immediately thought that it operated too stiff. He noticed that there are smooth areas and stiff areas. As I worked the trim wheel, as he instructed, while he observed and felt the trim shaft from the avionics bay opening to the Jack Screw, he concluded that everything worked freely until it got to the Jack Screw system. At that point we stopped for the day and I did some on-line investigation and found this thread. He and I have gone through all the comments and photos and, as I said, we are convinced that my Jack Screw system is not operating as freely as it should and needs some attention and could be causing the problem with the electric trim.

There is a number of weeks before we plan to remove the jack screw system so we decided to throw out some questions to get any help or ideas any of you have.

1. Do you think Trim Jack Screw Binding is a possible cause of my electric trim problem?

2. I saw some comments that their trim got so stiff that it "jammed" the electric trim.  Has anyone's trim failure been like mine (where it trips the circuit breaker) or does it just not operate.

3. Do any of you with a KFC-200 system have any specific thoughts on trim problems that I should investigate? Have you been inspecting and lubricating the Carrier Bearing below the Trim Servo as I mentioned? It appears to be a difficult job due to access and the screws being behind the servo chain sprocket. Any thoughts?

4. Through all these comments, we didn't see anyone talk about replacing the jack screw boot. My boot looks just like all the photos of yours. It seems well worn and disintegrating on the ends such that tiny threads and pieces come loose and are in the jack screw threads and grease which could be causing binding. We plan to replace mine and wondered if you all have replaced yours when doing this work? Where is a good place to purchase the boot?

Any thoughts and ideas would be appreciated!

Thanks for your help!

 

[N201MKTurbo]

2 minutes ago, BiplaneKim said:

I have an intermittent electric trim problem with my 1980 Mooney M20K (231) which is equipped with a Bendix/King KFC-200 autopilot/flight director. Before asking some questions, I'll give you some background info.

Through the course of troubleshooting this problem, I ran across this MooneySpace thread which really explained a lot about Trim Jack Screw Binding. I've always thought I had an electrical problem but after reading through this thread, it could very well be a trim jack screw binding problem. At least I'm convinced that my Jack Screw system needs some attention (including removal, inspection, cleaning, lubrication, and reinstallation) before continuing to troubleshoot an electrical problem. I may find that this solves the problem.

I usually use the electric trim and the intermittent problem has become more frequent. Often when using the split trim switch on the yoke, it trips the breaker, sounds an alarm and the electric trim is inoperable. Sometimes I reset the breaker but that generally does not work and I use the manual trim wheel. This problem usually does not occur on the ground and often may not occur on the next flight.

I thought I’d start by making sure it is being maintained correctly, such as lubrication, so I looked through my aircraft service manual which does not provide a lot of information. After talking to the shop that has done my avionics work, I found out that the electric trim system service & maintenance is covered more thoroughly in some later Mooney manuals for the M20R and Bendix/King manuals including Honeywell Service Bulletin 292. They were kind enough to copy the related pages.

From the pages they gave me, I discovered that there was an STC for the addition of a carrier bearing located on the trim shaft directly below the trim servo. From inspection, I can see that bearing has been installed on my Mooney. The pages also say there is a maintenance decal that is supposed to be installed at the same time to provide Annual inspection and lubrication instructions but my plane does not have that decal. I do not believe that this bearing has been inspected and possibly not serviced or lubricated in the 18 years that I have owned the aircraft. For about the first 10 years I owned the plane, I had a highly qualified Mooney specific IA doing my annuals and I worked with him and I do not recall ever doing anything with this bearing. He has passed away, and I do not think my current IA is aware of this bearing inspection or maintenance either.

A few days ago, my friend (A&P) and I spent the day troubleshooting and planned to inspect the bearing (below the trim servo). I started by asking him to operate the trim wheel to see how it felt to him and he immediately thought that it operated too stiff. He noticed that there are smooth areas and stiff areas. As I worked the trim wheel, as he instructed, while he observed and felt the trim shaft from the avionics bay opening to the Jack Screw, he concluded that everything worked freely until it got to the Jack Screw system. At that point we stopped for the day and I did some on-line investigation and found this thread. He and I have gone through all the comments and photos and, as I said, we are convinced that my Jack Screw system is not operating as freely as it should and needs some attention and could be causing the problem with the electric trim.

There is a number of weeks before we plan to remove the jack screw system so we decided to throw out some questions to get any help or ideas any of you have.

1. Do you think Trim Jack Screw Binding is a possible cause of my electric trim problem?

2. I saw some comments that their trim got so stiff that it "jammed" the electric trim.  Has anyone's trim failure been like mine (where it trips the circuit breaker) or does it just not operate.

3. Do any of you with a KFC-200 system have any specific thoughts on trim problems that I should investigate? Have you been inspecting and lubricating the Carrier Bearing below the Trim Servo as I mentioned? It appears to be a difficult job due to access and the screws being behind the servo chain sprocket. Any thoughts?

4. Through all these comments, we didn't see anyone talk about replacing the jack screw boot. My boot looks just like all the photos of yours. It seems well worn and disintegrating on the ends such that tiny threads and pieces come loose and are in the jack screw threads and grease which could be causing binding. We plan to replace mine and wondered if you all have replaced yours when doing this work? Where is a good place to purchase the boot?

Any thoughts and ideas would be appreciated!

Thanks for your help!

 

Well, it is possible. The harder the trim is to turn, the more torque the motor needs to generate. The more torque, the more current and it could trip the breaker.

The trim is loaded on the ground by the weight of the tail, in flight it is loaded much more by aerodynamic forces, so any binding would be amplified in the air.

Without feeling your trim, it is hard to make the call. 

I have seen trim motors fail where they would draw a lot of current to generate a small amount of torque. 

If you are an electronics guy I would suggest measuring the running current with the chain removed. It should be less than 1/2 amp and impossible to stop with your hand.

[carusoam]

Search for all the people talking about cleaning the grease out of the gear boxes... grease turns to rocks, rocks are bad for gear boxes...

Motors aren’t any better at turning the trim than humans... it should be smooth and easy... not stiff, ever...

Best regards,

-a-

[Yetti]

For those readers who are reading and saying wow that is a lot of work to do either end of the trim drive line.   You can do alot for your trim system just by cleaning and lubing the chain and all the little u joints front to rear.   the rock hard grease in those is not helping either.   Just takes some time and cleaning brushes.

[PT20J]

13 hours ago, Yetti said:

For those readers who are reading and saying wow that is a lot of work to do either end of the trim drive line.   You can do alot for your trim system just by cleaning and lubing the chain and all the little u joints front to rear.   the rock hard grease in those is not helping either.   Just takes some time and cleaning brushes.

The entire trim system should be lubricated during the annual inspection (with the exception of the front gearbox and the jackscrew thrust bearings which are not accessible without significant disassembly and are generally dealt with on condition). The Maintenance Manual calls out low temperature oil for the U-joints (there shouldn't be grease on these). The jackscrew is heavily loaded and needs to greased with the proper grease. One of the few times I diverge from the manual is in the choice of lubricant for the trim wheel and trim servo chains: the manual calls out grease which makes no sense for a chain since it won't easily get into the rollers -- I use the same oil I use for the U-joints. Also, don't forget to put some oil on the trim wheel shaft and bushing and check the tension on the chain. This bushing is a common wear point leading to a wobbly trim wheel. I generally use electric trim, but I always manually reset the trim to takeoff position after landing so I can feel how the mechanism is working.

Skip

[PT20J]

22 hours ago, carusoam said:

grease turns to rocks, rocks are bad for gear boxes...

Anthony's comment got me thinking about how grease wears out. Does it really turn to rocks? I found interesting information about bearings and lubrication on Tinken's website. https://www.timken.com/pdf/5892_Bearing Damage Analysis Brochure.pdf. Always fun to learn new stuff!

Skip

[Yetti]

9 hours ago, PT20J said:

The entire trim system should be lubricated during the annual inspection (with the exception of the front gearbox and the jackscrew thrust bearings which are not accessible without significant disassembly and are generally dealt with on condition). The Maintenance Manual calls out low temperature oil for the U-joints (there shouldn't be grease on these). The jackscrew is heavily loaded and needs to greased with the proper grease. One of the few times I diverge from the manual is in the choice of lubricant for the trim wheel and trim servo chains: the manual calls out grease which makes no sense for a chain since it won't easily get into the rollers -- I use the same oil I use for the U-joints. Also, don't forget to put some oil on the trim wheel shaft and bushing and check the tension on the chain. This bushing is a common wear point leading to a wobbly trim wheel. I generally use electric trim, but I always manually reset the trim to takeoff position after landing so I can feel how the mechanism is working.

Skip

Interesting that the manual calls for oil as my U joints had hardened grease from I would have to guess the factory.   It matched what was on the chain.   Like the gear, I would have to guess these are the most ignored line items in the Annual/100 hour where the wheel bearings are the most over maintained parts.    Tri flow is a pretty happy lube and it seems to be able to rejuvenate 30 year old grease.

[carusoam]

Whatever the whitish grease is, turns yellow over time... by the time it turns brown... it is hard and crusty in spots... as if it dries out over years...

grease is typically oil mixed with a thickener... the oil is running away over time and leaving nothing but the thickener behind...

Oil companies put a fair amount of engineering into what goes into each lube... so the lube can be selected by number for the job it needs to do...

Over decades, unattended... it can really be like rocks getting in the way of parts that are trying to move...

PP thoughts only, not a mechanic...

Best regards,

-a-

[EricJ]

2 hours ago, Hyett6420 said:

ask the Russians, they saw one up close and personal after they shot it down. 

 

There's a museum where you can go look at the pieces.

[N201MKTurbo]

7 hours ago, EricJ said:

There's a museum where you can go look at the pieces.

See page 113.

unlimited-horizons.pdf

[EricJ]

1 hour ago, N201MKTurbo said:

See page 113.

unlimited-horizons.pdf

Actually, this is what I meant (at the Central Armed Forces Museum in Moscow):

https://en.wikipedia.org/wiki/File:Francis_Gary_Powers_U2_at_Moscow.jpg

https://www.tripadvisor.com/LocationPhotoDirectLink-g298484-d549927-i40480236-Central_Armed_Forces_Museum_of_Russian_Federation-Moscow_Central_Russia.html

The empennage may not be there, or maybe not enough to figure out how the trim worked. 

Edited March 4, 2019 by EricJ

[N201MKTurbo]

11 minutes ago, EricJ said:

Actually, this is what I meant (at the Central Armed Forces Museum in Moscow):

https://en.wikipedia.org/wiki/File:Francis_Gary_Powers_U2_at_Moscow.jpg

https://www.tripadvisor.com/LocationPhotoDirectLink-g298484-d549927-i40480236-Central_Armed_Forces_Museum_of_Russian_Federation-Moscow_Central_Russia.html

The empennage may not be there, or maybe not enough to figure out how the trim worked. 

Sure,

but the documentation above clearly shows it doesn't have a tail like the Mooney. It would whack the tail pipe when you trimmed it. Considering it states it originally had a zero angle of incidence and later a 1.5 deg. angle of incidence leads me to believe the horizontal stabilizer is fixed.

I don't think I've ever seen one in a museum, except the wreckage above. I have been to a couple of airshows where they landed and did flybys, but they never went on display so you could check them out.

[N201MKTurbo]

There are a few. This one is hanging from the roof at the national museum. You can see it has a fixed horizontal stabilizer and a trim tab.

[cliffy]

Early models did NOT have the jackscrew system but a change was made in later production that went to the jackscrew system.

[47U]

19 hours ago, cliffy said:

Early models did NOT have the jackscrew system but a change was made in later production that went to the jackscrew system.

I'm not familiar with the 'C' and previous models, but beginning with the 'R' in '68, the vertical fin is attached to, and moves with, the horizontal stabilizer.  An electrically controlled, hydraulically driven jackscrew and scissors mechanism runs the stab trim.  As Rich previously mentioned, the aft fuselage doesn't move with the stab trim.  You can see the vertical stab white 'slick slide' Teflon sheet where the vertical stab rotates into the fuselage fairing.

Tom

[DEGWS]

Hey,

I want to check the jackscrew at me Mooney tomorrow.

Plan is to remove bearings, disassemble, clean, grease and reassemble. Really good post here. Only question is... where I have to disconnect the trim rod that I can remove the bearing block? Is there enough free play to disconnect in the rear or is it necessary to disconnect the U-joint below trim wheel?

thanks! 

[N201MKTurbo]

9 minutes ago, DEGWS said:

Hey,

I want to check the jackscrew at me Mooney tomorrow.

Plan is to remove bearings, disassemble, clean, grease and reassemble. Really good post here. Only question is... where I have to disconnect the trim rod that I can remove the bearing block? Is there enough free play to disconnect in the rear or is it necessary to disconnect the U-joint below trim wheel?

thanks! 

I have always disconnected it at the trim wheel. With the belly off, it has the easiest access. You can probably do it all in the tail cone. You have to take the pins out of the u joint, slide the square towards the back to get the u joint out of the tube then slide it foreword to get it off the jackscrew. Don’t forget to take the pin out of your electric trim sprocket.

Make sure you measure the trim gap before you start.

[Ibra]

On 3/4/2019 at 2:29 PM, EricJ said:

There's a museum where you can go look at the pieces.

The U2C on display at the Duxford museum has a snapshot of SAM & U2, it does have a traditional trim tab

The SR71 Blackbird sitting nearby had a Mooney like tail (should take better pictures next time) 

Edited April 5, 2020 by Ibra

[Sabremech]

12 hours ago, DEGWS said:

Hey,

I want to check the jackscrew at me Mooney tomorrow.

Plan is to remove bearings, disassemble, clean, grease and reassemble. Really good post here. Only question is... where I have to disconnect the trim rod that I can remove the bearing block? Is there enough free play to disconnect in the rear or is it necessary to disconnect the U-joint below trim wheel?

thanks! 

You won’t be able to remove the bearings from the shaft without a press and a bearing plate to hold the inner race. I took mine to a machine shop to have them removed and the new bearings pressed back on. The bearings are sealed so you won’t be able to disassemble them to clean and grease. 
David

[N201MKTurbo]

22 minutes ago, Sabremech said:

You won’t be able to remove the bearings from the shaft without a press and a bearing plate to hold the inner race. I took mine to a machine shop to have them removed and the new bearings pressed back on. The bearings are sealed so you won’t be able to disassemble them to clean and grease. 
David

All the sealed bearings in the ones I’ve worked on were easily disassembled. There is large circlip holding the shield on the side of the bearings. It can be removed with a very sharp poker. The races actually have a cutout that allows the balls to be removed. You can do this without pressing the the inner races off the shaft.

[Sabremech]

6 minutes ago, N201MKTurbo said:

All the sealed bearings in the ones I’ve worked on were easily disassembled. There is large circlip holding the shield on the side of the bearings. It can be removed with a very sharp poker. The races actually have a cutout that allows the balls to be removed. You can do this without pressing the the inner races off the shaft.

I suspected that was the case as I had one blow up in the press and then saw the cutout. I typically don’t disassemble a sealed bearing and decided it was much better to go new as my airplane has 7600 hours on it. Bearings were $200 for a pair. No worries now for a long time. 

[DEGWS]

Did the trim screw today. Bearings were completly dry! Cleaned everything and trim is working good as before.

Its possible to disconnect trim in the rear. You have to disconnect the U Joint on both sides and slide it into the tube to remove the square. Then put out the nach screw.

[skykrawler]

Here is a picture of the jack screw assembly removed from a 1982 J model.  After reading on this forum we removed mine for service.  The grease on the screw was cleaned and serviced and that made a difference.  The unit was opened by removing the plate on the left to service the interior grease.  But....no grease in here only light machine oil - MIL-L-7870. The shaft exited the housing moving to the left.  It could have been done the other direction by removing the link on the screw but that is massive safety wire.  The bearings are tapered roller bearings as depicted in the parts diagram (VII effectivities) and there are no shims.  The preload on the bearings seems to be function of a spacer between the bearings, which are pressed on, and the thickness of the paper gasket.  The assembly is cone, bearing, spacer, bearing cone.  The blue plug on top is where oil is introduced after assembly, there is another on the side presumably for determining fill level.  Only the top plug is accessible when the assembly is installed.   Only a few cc's of oil is needed.  You will likely find a piece of tape wrapped around the tube that holds the 'nut.'  I removed the tape to slide the shaft through the seal and discovered holes on the top and bottom.  The jackscrew retreats into this tube so potentially one could fully retract or extend the screw and inject some grease into the hole to get a more complete lube with the unit mounted in the tail.  Replace the tape since it presumably was put there to keep dirt and moisture out.