Hard Trim issues on my M20K

[CMMPilot]

I have developed an unusual amount of resistance in my trim travel around the takeoff position (middle of travel).  So much so, that my electric trim just stops and gives up. I am able to move it manually, but can definitely feel it.  
has anyone experienced anything similar and what was the cause?

We have removed all the covers and lubricated the entire linkage assembly. Removed a lot of overspray paint from the last paint job and confirmed it still hits the resistance. We cannot figure out  why. Any advice is appreciated. 

[PeteMc]

Something binding it up in the Trim Wheel housing? 

I had the pax seatbelt get it there once.  It was buckled, but still loose enough that the slack just happened to slide into the housing along side the wheel and got pulled tight.

 

[Utah20Gflyer]

When you say you cleaned and lubricated the whole assembly did that include the jack screw in the tail as well as the tail hinges and bolts and all the connections between there and the trim wheel?    Have you checked the sheet metal fairings between the fuselage and the tail for binding?  I see a difference on my plane between them being installed or not. 
 

If you disconnect the trim wheel assembly with the linkage going back to the jack screw you can verify on which side the problem is occurring.  If it’s on the trim wheel assembly side it could be a bad bushing/bearing/gear internal to that assembly.  I’ve never torn one apart so I don’t know exactly what’s in there but if everything else is clean and lubricated it would have to be that.  

[N201MKTurbo]

Be careful disconnecting the trim wheel from the trim drive shaft. You can get the trim wheel out of sync with the tail. When it comes to rigging the trim that is all there is.

[PT20J]

No one ever seems to lube the trim wheel shaft or chain. If it’s a BK autopilot, there is a needle bearing at the trim servo that is supposed to be lubed and since it requires some disassembly, it is often overlooked. The jackscrew in the tail should be cleaned and lubricated each annual. 

[jkgyr52]

I have had a trim wheel lock on a 1984 K model that had about 4500 hours on the airframe. Turns out the grease on the jackscrew was like paste. No mention in the logbooks about it ever being serviced. My AI had me clean it up and apply a turboprop type of grease which he said has the benefit of tolerating lower temperatures when I fly in the flight levels. Not sure which grease rating it was.

Jeff

[geoffb]

20 hours ago, PT20J said:

No one ever seems to lube the trim wheel shaft or chain. If it’s a BK autopilot, there is a needle bearing at the trim servo that is supposed to be lubed and since it requires some disassembly, it is often overlooked. The jackscrew in the tail should be cleaned and lubricated each annual. 

I've tried to figure out how I'd get to that.  You can't even see the bearing.  Is there anything that documents servicing that bearing?  Looks like a nightmare.

[CMMPilot]

We have isolated it to the linkage between the trim wheel / servo motor and the worm gear actuator at the tail. We have eliminated any kind of drag at the wheel. There was some slack in the chain and we made a small adjustment to take it out. We disconnected the entire tail section and removed a lot of paint and debris from the hinges and pivot points. All of that is clean and lubricated, and the tail moves freely when not connected to the linkage.

we cleaned the jackscrew and lubricated it, so that seems to be working properly. The rod moves freely through the two passes through points with proper bushings intact and plenty of play. I’m down to the century 41. auto pilot. 
 

my next step is to disconnect the AP and go from there…

[PT20J]

3 hours ago, geoffb said:

I've tried to figure out how I'd get to that.  You can't even see the bearing.  Is there anything that documents servicing that bearing?  Looks like a nightmare.

First I ran the trim all the way down to the stop so I’d have a reference point when putting it back together. Then I loosened the servo and took the chain off the servo sprocket. Next I disconnected the trim torque tube from the trim wheel gearbox and was able to slide the tube forward enough to get access to the bearing. I used a grease needle to grease the bearing around the tube. Then I put it all back together making sure the shaft was on the down stop.

[CMMPilot]

5 hours ago, PT20J said:

First I ran the trim all the way down to the stop so I’d have a reference point when putting it back together. Then I loosened the servo and took the chain off the servo sprocket. Next I disconnected the trim torque tube from the trim wheel gearbox and was able to slide the tube forward enough to get access to the bearing. I used a grease needle to grease the bearing around the tube. Then I put it all back together making sure the shaft was on the down stop.

I’ll give that a try as well. Thanks to everyone for the advice and helpful information. 

[geoffb]

5 hours ago, PT20J said:

First I ran the trim all the way down to the stop so I’d have a reference point when putting it back together. Then I loosened the servo and took the chain off the servo sprocket. Next I disconnected the trim torque tube from the trim wheel gearbox and was able to slide the tube forward enough to get access to the bearing. I used a grease needle to grease the bearing around the tube. Then I put it all back together making sure the shaft was on the down stop.

So it was designed for easy maintenance

[PT20J]

6 hours ago, PT20J said:

First I ran the trim all the way down to the stop so I’d have a reference point when putting it back together. Then I loosened the servo and took the chain off the servo sprocket. Next I disconnected the trim torque tube from the trim wheel gearbox and was able to slide the tube forward enough to get access to the bearing. I used a grease needle to grease the bearing around the tube. Then I put it all back together making sure the shaft was on the down stop.

Now, I'm questioning this. While I was waiting for a new engine to arrive, I was trying to fix a problem with the KAP 150 trim and I removed the servo to send it to Autopilots Central for overhaul. While I had it out, I removed the front trim gearbox to replace the worn bushing for the trim wheel shaft and I cleaned and regreased it. At the same time I lubed the carrier bearing for the trim servo. So, I had a bunch of stuff apart. It might not be necessary to disconnect the trim torque tube to service the carrier bearing. For sure you have to loosen the servo and slip the chain off the servo sprocket, but it may be possible to then unfasten the bearing housing from it's mount under the servo and slip it aft along the torque tube to get access to the needle bearings. I just don't remember. 

[CMMPilot]

21 hours ago, PT20J said:

Now, I'm questioning this. While I was waiting for a new engine to arrive, I was trying to fix a problem with the KAP 150 trim and I removed the servo to send it to Autopilots Central for overhaul. While I had it out, I removed the front trim gearbox to replace the worn bushing for the trim wheel shaft and I cleaned and regreased it. At the same time I lubed the carrier bearing for the trim servo. So, I had a bunch of stuff apart. It might not be necessary to disconnect the trim torque tube to service the carrier bearing. For sure you have to loosen the servo and slip the chain off the servo sprocket, but it may be possible to then unfasten the bearing housing from it's mount under the servo and slip it aft along the torque tube to get access to the needle bearings. I just don't remember. 

Hmmmm, Interesting and worth a Saturday to check out.  Thanks!

[larryb]

I had a similar problem and the fix was a shot of tri flow to the pillow bearing for the trim tube in the tail avionics bay.