Landing gear over-center linkage

[takair]

I have to replace my main gear over-center links.  SB20-155 indicates that on some aircraft it can be done without removing the entire gear.  My serial number apparently falls under the category that requires removing the gear.  The problem is that one bolt holding the link to the gear cannot be removed easily.  Has anybody replaced the link on an older aircraft without fully removing the gear? My shortcuts usually end up taking twice as long as doing things right, so I figured I'd ask.

[Sabremech]

I had both of my main gear out this past Summer and if memory is right, they'll need to come back far enough to get the bolt out that goes front to back. I stripped my gear, primed and rebushed them before reinstalling. It wasn't a hard job. You could do it fairly quickly if you don't find any issues after you get it loose and moved back. Hope this helps.

David

[N201MKTurbo]

Remove the retraction rod so the grear swings freely. Loosen all the hardware. Have the new parts handy. Have a buddy help you. Remove the four bolts at the rear of the landing gear at the pivot plate. Pull the gear leg out of the front pivot, change the link and put it back together.

[takair]

5 minutes ago, N201MKTurbo said:

Remove the retraction rod so the grear swings freely. Loosen all the hardware. Have the new parts handy. Have a buddy help you. Remove the four bolts at the rear of the landing gear at the pivot plate. Pull the gear leg out of the front pivot, change the link and put it back together.

Thanks.  Sounds reasonable.   I assume you need to remove the retraction spring too.  Any idea why they distinguish early serial numbers (remove gear entirely) vs slightly newer ones (apparently you can do it with spring attached and only removing rear pivot)?  I suppose what you described is technically removing the gear and is not much more difficult.  I think I got myself carried away and was picturing removing brake lines and such.  Just need to get some clearance.  

 

[Andy95W]

Not sure why the change, but it really isn't that bad as David and 201MK said.

Yes, you will want to remove the spring.  Using the factory spring removal tool isn't necessary- it is easier and safer to use a bunch of quarters in between the spring coils to hold the spring extension.  I used big, cheap washers instead of quarters.  N201MKTurbo posted this idea a while back, it works great.

[N201MKTurbo]

You are right about the spring I forgot about that part. You have to give Piloto credit for the quarter idea. 

[geoffb]

Blocking the spring is a great idea.  Wish I'd heard about that trick before I did mine.  Other than fighting the spring, it's an easy job and there's lots of things that you can tidy up, clean and lube while it's apart.  The retract link bungees were all stiff and gunked up on mine.  Might not be a bad idea while your in there to replace the retract springs, link bungee springs, rod ends while you're in there.  You're going to need to rerig anyway so it's a good time to freshen up things you don't want to have to touch again.

Edited October 11, 2016 by geoffb

[takair]

2 hours ago, geoffb said:

Blocking the spring is a great idea.  Wish I'd heard about that trick before I did mine.  Other than fighting the spring, it's an easy job and there's lots of things that you can tidy up, clean and lube while it's apart.  The retract link bungees were all stiff and gunked up on mine.  Might not be a bad idea while your in there to replace the retract springs, link bungee springs, rod ends while you're in there.  You're going to need to rerig anyway so it's a good time to freshen up things you don't want to have to touch again.

it is always tempting, but I am afraid it would never end.  I'm not sure the new parts are available anyway, and if they are they may go out of my budget quick.  I'm on more of a long term resto...started 20 years ago and figure it could take another 20...wouldn't want to get too far ahead of schedule...lol.  Good idea about the bungees though.  I'm just hoping I don't end up finding something that requires long downtime, major issue is that I will be blocking my hangar mate in.  His plane hasn't moved in a while, but it would be my luck that he needs to move mid project.

[jetdriven]

Lasar sells a 60$ kit with oversize bushings and you can borrow their reamer to do the repair.  Real the holes oversize and insert the new bushing and reassemble.  It takes all the slop out of the gear  linkage l. We just did all 3 when we rebuilt the gear 

[takair]

22 minutes ago, jetdriven said:

Lasar sells a 60$ kit with oversize bushings and you can borrow their reamer to do the repair.  Real the holes oversize and insert the new bushing and reassemble.  It takes all the slop out of the gear  linkage l. We just did all 3 when we rebuilt the gear 

Are you talking about the drag links (over center) bushings?  I talked to LASAR, but I'm not sure that the bushings alone are the problem.  They didn't mention the kit.  One gear is going pretty far over center and I'm out of travel to get more preload.  I'm right at the low end limit.  Gear actually ends up not going in the well enough.  I have a couple sets of newer links on the way.  

[jetdriven]

If the gear is down and locked on jacks, and you can wiggle the main gear inboard and outboard if you feel slop in it and it's probably the bushings in that retract link

[cliffy]

When you do your rerig of the gear (and you WILL have to rerig the gear) do start at the beginning and rerig according to the complete procedure. Don't short cut it and thing you can just do a couple of rod ends to make the preload come out. It sounds like some of your push rods are maladjusted.

If you have electric gear make sure you have starting point 1 correct by having the correct amount of actuator extension showing (measure it) before it is connected to the major bellcrank. You can measure the bellcrank position buy putting a bolt in the bellcrank hole (as shown in the MM), and measure it from the datum (with a sheet metal gauge cut to the correct size minus 1/2 the bolt diameter), as the distance required is measured to the center of the bolt hole (refer to the MM for this). 

Then you can work forward to the nose gear and back to the main gear getting the push rods and bellcranks lined up where they belong. 

It's not hard, it's just detailed work

[takair]

3 hours ago, cliffy said:

When you do your rerig of the gear (and you WILL have to rerig the gear) do start at the beginning and rerig according to the complete procedure. Don't short cut it and thing you can just do a couple of rod ends to make the preload come out. It sounds like some of your push rods are maladjusted.

If you have electric gear make sure you have starting point 1 correct by having the correct amount of actuator extension showing (measure it) before it is connected to the major bellcrank. You can measure the bellcrank position buy putting a bolt in the bellcrank hole (as shown in the MM), and measure it from the datum (with a sheet metal gauge cut to the correct size minus 1/2 the bolt diameter), as the distance required is measured to the center of the bolt hole (refer to the MM for this). 

Then you can work forward to the nose gear and back to the main gear getting the push rods and bellcranks lined up where they belong. 

It's not hard, it's just detailed work

This is a Johnson bar aircraft and it has been a gradual thing over many years.  I think Byron is right about the bushings, but I also suspect that one link is worn where it goes over center.  I agree it will require full re-rig.  Nose gear is the worst, in my mind since it has the cams that are difficult to get in place and matching the two rods.  Depending on what the used links look like, I may re-bush as Byron suggested and limit my down time.  

[takair]

On October 11, 2016 at 7:51 PM, jetdriven said:

Lasar sells a 60$ kit with oversize bushings and you can borrow their reamer to do the repair.  Real the holes oversize and insert the new bushing and reassemble.  It takes all the slop out of the gear  linkage l. We just did all 3 when we rebuilt the gear 

Got the replacement links and other than cosmetics, they are in good shape with good bushings.  They came off of a "K". Then I noticed that the main bolts are one diameter larger than those in my E.  Have gone through the service letters and bulletins and there have been various changes to the hardware, but they don't appear to include larger diameter.  Looks like the 201manual may be larger.  I can't go with the large hardware in the E.  Has anybody come across this?  Are the links the same, with different bushings to accommodate the hardware?  Will call LASAR to see if they know.  Worst case I will order the kit Byron referenced and see if I can salvage my links.

[takair]

Figured it out.  The "K" link is not compatible with the "E".  Will have a pair of cleaned up "K" links going up for sale soon. 

Byron

Thanks for the heads up.  I ordered the bushings from LASAR today and Dan and Dave were very helpful, as always.  

 

[takair]

I want to thank everybody for their input, I'm usually shy about asking for help, but this forum is great.  Thought I would document a couple of things while it is fresh in my mind.  So, for 1964 vintage you DO have to remove the gear, but this does not mean all the way.  First remove the main spring.  I took the "quarter trick" and used it in the reverse as well.  With the gear unlatched, and the gear slightly retracted, I added washers in between the spring coils...top and bottom.  Then, retract the gear the rest of the way and the spring is essentially unloaded.  It is than rather easy to remove, although I still needed the tool.  Quarters may be a hair thicker, so perhaps no tool needed at all.  Put gear down and disconnect the links.  Remove the 6 rear bearing bolts.  Slide the rear spacer inboard while holding the gear.  Now the gear can be maneuvered to drop out of the front bearing.  I dropped the gear out of the well enough to remove the link bolt and then let it rest on the ground on the tire.  Thanks to Byron on the oversize bushings.  LASAR had a TSOd set.  Ended up getting my own .503 chuck reamer. After clean up it was a simple job to ream the links.  Take your time, use lube and look up reaming tips on the web.  Easy to ruin the reamer if you don't use proper technique.  Also, disassemble and clean the pushrod bungee.  One of mine was frozen, not helping my basic situation. It is a little difficult to reassemble, so be prepared to use some muscle.  Installation is the reverse.  Sure enough, just the new bushings took care of all the slop.  As Cliffy mentioned, rigging of the gear is required.  Followed the book and needed a a couple of iterations to get the main gear preloads even.  One thing that may not be obvious is that the gear will go deeper in the well (cheap speed mod?).  You must re-rig the gear doors as well, otherwise they will deflect.  I believe my right gear may have gone at least 1/2" deeper based on the amount I needed to adjust that door.  These tips are not in place of the MM and SB 20-155, but hopefully supplement it.  Overall, the job went faster than I expected, but it is fairly involved.  Because I share my hangar, I could not take full advantage and clean up the entire gear, but I am back to airworthy..another annual inspection done.

[MB65E]

Nice explanation for those that have not done it yet. One day I'll pull mine and re-finish everything!

 

Thanks!

-Matt