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Crash, Jr.
09-08-2020, 01:46 PM
The trim on my J3 has been pretty bad off ever since I've owned it. It will go all the way to the lower (nose up) limit but will only go halfway up the jackscrew before binding and the cable slipping on the pulleys. In addition the crank is very stiff compared to other PA-18's I've tried. I've been back in the tail cleaning old grease out of the jackscrew, manually running it up and down by turning the pulley on the bottom of the screw manually, and re-lubing/greasing it but still no luck. On the last flight it was okay (still bound up halfway to nose down) but at the end of the flight the pin for the trim handle pulley fell out and started free spinning. After pulling the panel for inspection I was able to put the pin back in but the pulley groove for the pin is all wallowed out and has probably been that way for a while.

So after some research it looks like there is a company that makes aluminum pulleys that would work better but are pretty spendy at about $150 each and I would re-use the cable but have to cut the fabric and patch it to get the crank handle shaft out and back in to replace the pulley. PA-18 pulleys are much cheaper even for the aluminum versions but to convert to PA-18 trim I would have to cut a larger section of fabric and weld in an idler pulley below the handle and add a spring tensioner at the rear in addition to replacing the cable which would obviously be more $$$.

Is it a big upgrade to go to PA-18 trim over a cleaned up J3 trim system? Would keeping the J3 trim system affect any mods down the road like PA-18 elevator control or an extended baggage? Any ideas how much more it would/should cost over just refurbing the J3 trim to go to PA-18 trim?

behindpropellers
09-08-2020, 01:50 PM
Is your yoke installed correctly?

Your frame is probably wallowed out where the trim pulley is in the cockpit also.

Tim

Crash, Jr.
09-08-2020, 02:15 PM
Yep, the trim handle brackets are wallowed out, bushed, and the bushing is loose and wobbly.

mike mcs repair
09-08-2020, 02:32 PM
New pulleys are main thing. They originally had a V shaped grove. But as it slips it cuts the grove to the shape of cable. I canít speak to changing to 18. Never did a J3. Clean cable with something helps. You can have pulley groves recut on a lathe. Thatís actually on my list of tools to make. As far as getting pin out, go to Stoddards and get a small fabric grommet. It has a 3/4Ē center hole or such and glue that on with fastbond10 as you poke pin against fabric. Then just put a snap cap in it.


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mike mcs repair
09-08-2020, 02:43 PM
Or put a nice big grommet on give yourself room to work and change bushing and pin.

Hereís the steps to convert on a covered pa-12

You will need to weld a pulley mount to a clamp(ms27405-T add correct last number for size of tube trim crank is mounted off of (also known as an741- clamp) (T designates 2 piece clamp) mount needs to be a little crooked so-cables can pass to the new double grove trim pulley

At the back you will use another on of those clamps but leave out the T in part number(one piece clamp)to put on longeron to attach a tab for spring to clip into like an -18.


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mike mcs repair
09-08-2020, 02:44 PM
https://www.gen-aircraft-hardware.com/images/pdf/ms27405.pdf


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mike mcs repair
09-08-2020, 02:47 PM
If you post what size clamps you need I can tell you who has stock since I been on a quest to have a selection on hand and just order many sizes. Hard to find the T versions.


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Crash, Jr.
09-08-2020, 03:07 PM
Thanks for the help, I may just replace the pulleys with new aluminum ones if that can be made to work well. The main concern is just getting it smooth and full travel.

I appreciate the tip with the clamp. I was imagining having to weld in PA-18 pulley brackets. If I can get away with just putting a grommet in for the pulley pin all the better. The plane will get rebuilt in a few years so no need to get too crazy with it now.

mike mcs repair
09-08-2020, 04:17 PM
As far a stiff trim.... you want SLOP on both sides of stabilizers at jack screw. Put you finger on jack screw at yoke and feel for slop in yoke there as you pull up stabilizer and also as you push down. If you only have slop one way adjust flying wires till you have slop both ways. Ignore the rigging instructions that say stabilizers need to be within half inch of level. They donít. But make sure they are in line with each other. Old planes have crooked fuselages and you must match stabilizers to whatever angle the jack screw tower is.


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Philly5G
09-08-2020, 04:26 PM
I really suggest doing the trim winder oilite bearing mod, itís pretty easy to do and makes a MASSIVE difference to the smoothness and joy of cranking the trim [emoji41]

My PA-12 trim slipped like crazy when I first bought it and despite the potential ďbigĒ problems and ďbigĒ costs I diagnosed/tried the easy stuff first and it boiled down to the front pulley slot being u and not v shaped. Ordered one from Univair, yes a bit spendy, but now does the job brilliantly.

Let me know if you need more details/pics [emoji41]


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Crash, Jr.
09-08-2020, 04:59 PM
I really suggest doing the trim winder oilite bearing mod, it’s pretty easy to do and makes a MASSIVE difference to the smoothness and joy of cranking the trim [emoji41]

My PA-12 trim slipped like crazy when I first bought it and despite the potential “big” problems and “big” costs I diagnosed/tried the easy stuff first and it boiled down to the front pulley slot being u and not v shaped. Ordered one from Univair, yes a bit spendy, but now does the job brilliantly.

Let me know if you need more details/pics [emoji41]

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Yes! Details and pics of the bushings please!

I think I'm going to bit the bullet on the aluminum pulleys but I need a detail of how to make the bushings for the crank shaft brackets

Crash, Jr.
09-08-2020, 05:02 PM
As far a stiff trim.... you want SLOP on both sides of stabilizers at jack screw. Put you finger on jack screw at yoke and feel for slop in yoke there as you pull up stabilizer and also as you push down. If you only have slop one way adjust flying wires till you have slop both ways. Ignore the rigging instructions that say stabilizers need to be within half inch of level. They don’t. But make sure they are in line with each other. Old planes have crooked fuselages and you must match stabilizers to whatever angle the jack screw tower is.


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Are you talking about slop if you're pulling up and down on the front of the stabilizers? I do have some slop, just a little.

One thing I'm concerned about is the free movement of the rear stab liner tube. Someone at Birchwood looked at and mentioned that sometimes the liner tubes corrode in place and when you run the trim it's not pivoting, just flexing the stabilizers in the front but not turning in the rear. I squirted some PB blaster in the oil port on the rear stab cross tube bracket but can't tell if it's rotating or not since its such a small amount of rotation.

behindpropellers
09-08-2020, 05:42 PM
Are you talking about slop if you're pulling up and down on the front of the stabilizers? I do have some slop, just a little.

One thing I'm concerned about is the free movement of the rear stab liner tube. Someone at Birchwood looked at and mentioned that sometimes the liner tubes corrode in place and when you run the trim it's not pivoting, just flexing the stabilizers in the front but not turning in the rear. I squirted some PB blaster in the oil port on the rear stab cross tube bracket but can't tell if it's rotating or not since its such a small amount of rotation.

Run it to one end of travel and mark it with a sharpie and then move it to the other side of travel.

mike mcs repair
09-08-2020, 06:08 PM
Are you talking about slop if you're pulling up and down on the front of the stabilizers? I do have some slop, just a little.



Not slop in general. But slop in how the yoke fits against jack screw. You need slop both ways. Not just crooked and bound tight one way and slop other way. Put your finger there at yoke to jack screw point and try it. It will make sense once you try it.


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bob turner
09-08-2020, 06:53 PM
I have owned a J3 for 58 years - and a second for 11 years. The trim system as Piper designed it is bulletproof unless the airframe gets tweaked.
Mike, above, has the answer. That yoke cannot bind anywhere in its travel. If it binds, even ball bearings will not free it, let alone oillite.
Usually the binding is due to tailfeathers tightened up at the wrong angle (or the right angle but the jackscrew is not vertical). Frozen tubes do not help, and used to be a big problem when these things were stored outside.

Amy
09-08-2020, 11:52 PM
I canít speak to a retrofit install with fabric on, but I upgraded to a PA-18 style system with double-groove pulleys and it is a delight. All of my trim system was worn out and I had the airplane apart so I did the Dakota Cub jack screw and double-groove trim system (including new handle) with a new endless cable. No slip (to be fair, it is new on my airplane, but I have a few hundred hours and several years on another identical system Iíve flown and itís been great), the jack screw and yoke have a handy grease zerk too.

+1 to checking the liner tube though, mine had corroded enough to be stuck and it was extremely evident something was amiss. Relatively simple replacement in the grand scheme of things unless it is really stuck in there...

Steve Pierce
09-09-2020, 07:57 AM
ou might look at the aluminum single pulleys for the PA16 and 12. Some pictures of fixing the trim system without major disassembly. Post 27 is my fix.
https://www.supercub.org/forum/showthread.php?53444-Trim-Misery

Crash, Jr.
09-09-2020, 10:15 AM
Steve, that's a good idea adding a second tensioner pulley. Next time I'm up in the tail I'll see if there's room to drill and add another one. If I recall the tension screw is crazy long and sticks out pretty far on the back side of that bracket. There's definitely been some monkey business with previous ownership on this plane screwing with the trim with misguided efforts to fix the slipping. The tension was cranked darn near the max on the cable so I backed it off a few turns and things got better. Still slips in all the same places but at least its easier to turn the handle.

The aluminum pulleys are up next along with loosening/re-rigging the flying wires to see if that relieves the binding. Kind of one of those jobs that I'd rather put off until winter but it's pretty annoying flying along holding the stick forward when the nose tank gets below half full.

It's definitely binding though. Thanks Mike and Bob for the tips there that will be the very next thing I try is to loosen those flying wires and try running the trim through its range (on the ground of course) to see if it stops binding. I never thought about the relationship between the plane of the stabilizers vs the jack screw.