Conrad Posted September 20, 2015 Report Posted September 20, 2015 I've just gone through my first annual and have more or less emerged on the other side, apart from the fact that my bird is hostage to the good people battling the Lake County blaze. Only one squawk is going to be unresolved coming out of annual, but maybe someone here knows how I might go about fixing it. My trim indicator lags significantly behind the trim setting. It takes more than a full turn of the trim wheel before the indicator shows any change at all. Inspection revealed that the problem is with an elongated aluminum block which connects the indicator cable to the trim jackscrew. The block has worn (not possible to see the wear directly) around the threaded portion that the jackscrew passes through, which allows it to torque a bit fore and aft instead of maintaining an entirely perpendicular (downward in this case) orientation. My question is, what part/part number is this, and how hard would it be to replace? Addendum: while I was helping turn wrenches, I happened to have a pretty good view of a strikingly good looking Mooney on approach and final to 1O2. I believe that was bonal's. Hi!
takair Posted September 20, 2015 Report Posted September 20, 2015 Not sure of the part number, I suspect it is a part of the assembly. My gut says you might be best off getting one from a salvage yard. Look for a low time corroded airframe donor.
N201MKTurbo Posted September 21, 2015 Report Posted September 21, 2015 That would be the little aluminum nut that rides on the screw behind the trim gear box. I would think the lubrication state of the indicator cable would be a big part of it.
Conrad Posted September 21, 2015 Author Report Posted September 21, 2015 (edited) Perhaps you are referring to a different type of assembly? What I have riding on the jackscrew is definitely a block not a nut. It's about 2" long, 1" wide, and 1/2" deep, and it could definitely be replaced without replacing the entire assembly. There is a nut-based assembly which attaches to the block though. I guess if they changed it on later models it's going to be harder to find a replacement though. Funny you mention the state of the indicator cable, there was a ton of friction in it. The result of pressure lubing that cable was described to me as an explosion. I assume the excessive friction in the cable is what caused the wear on the block, however the damage is done and even with the cable now relatively frictionless the problem persists. Edited September 21, 2015 by Conrad
N201MKTurbo Posted September 21, 2015 Report Posted September 21, 2015 FWIW I call anything that rides on a screw a nut. I realize it is a custom made aluminum plate that has been threaded. The cable attaches to it with two standard lock nuts and it sets in an anti rotation assembly.
Conrad Posted September 21, 2015 Author Report Posted September 21, 2015 That sounds right. So it's the same on the later models?
N201MKTurbo Posted September 21, 2015 Report Posted September 21, 2015 As far as I know, but I've never worked on a long body.
M20F-1968 Posted September 26, 2015 Report Posted September 26, 2015 The aluminum block I think you are referring to is threaded onto a steel screw (like might be seen on a metal lathe or similar machine) and is a square cross sectioned thread. The aluminum will wear with time. That assembly is a pain to disassemble. It can be done, and you could have your favorite local machinist make you a new aluminum block. If I were to have one made, I would make it from brass as it is a better bearing surface and will last longer. The square threads probably would need to be cut on a lathe with a boring bar and fitted onto the steel screw shaft you have. There could be a second cause of slop, that being in the trim mechanism itself. You meed to determine where the extra play is an eliminate it. The trim cable must be frictionless. You can lubricate it with Tri-flow. The cabin end of the trim cable must be held motionless by the screw that secures it (clamp type arrangement). The newer models did away with the trim cable with the treaded ned and two lock nuts. The later type is just a hole into which the steel cable wire is inserted and secured with a lock screw. This difference should not affect the excessive play you mention. John Breda
ryoder Posted September 29, 2015 Report Posted September 29, 2015 (edited) Mine exhibited this lag after installing carpet that slightly impeded the pointers movement. We looked at it and what is happening is that there is an unshielded portion of a thin wire that is trying to push up on the indicator dial and is bending under the load. This results in a lag in the indicators movement. The wire is too thin for its push pull purpose in life without shielding to keep it from bending. I had to thin out some carpet to help it out but it's still slow when adding nose up trim. Nose down is fine because it can pull fine, it isn't rigid enough to push. Edited September 29, 2015 by ryoder
M20F-1968 Posted September 29, 2015 Report Posted September 29, 2015 The only part of my trim indicator system that is original is the trim wheel assembly and the cable. I am using the J model trim indicator and a new binder block (all with DER approval of course) which holds the outer cable housing more securely. When I got the cable lubricated well, and moving easily, there is vertually no lag. Another critical point I remember is there was about 3/4" of cable travel that was very easy. If I went either side of that, the cable would bind slightly. You can use the 2 locking nuts to position the trim cable at the trim wheel assemble (under the floor) so that the useful cable travel is in that "sweet spot" where the cable moves easily. Triflow is your friend. John Breda
Conrad Posted September 29, 2015 Author Report Posted September 29, 2015 Interesting thought about the unshielded portion Ryan and perhaps that is the answer to someone else's problem, however I have seen the way the block moves with my own eyes and also LASAR kindly ensured that there is now only the most minimal force required to moved indicator and cable assembly. John, your suggestion is what I will look into. I suspect owner produced may indeed be the way to go if I'm to embark on the Cheap Bastard path of aircraft ownership. Seems like the only path to tread since my initials are CB already.
Conrad Posted September 29, 2015 Author Report Posted September 29, 2015 Some more fun post-annual facts. Though it was no 8 second ride a new steering horn was installed and the rudder controls are noticeably more responsive on the ground. My PC system is working for the first time after a faulty pilot control valve was replaced. In the nice smooth air on the way back to KOAK I flipped the handy dandy panel mounted switch, bumped the roll control a smidgen, and the aircraft tracked heading (and altitude) perfectly with no control inputs for 4 or 5 minutes before losing a degree. I think the improved tracking might also have to do with a bit of play they managed to work out of the rudder controls at the rod end going into last bell crank. Finally: 150 knots TAS. Super! 2
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