Replacing over center link bushings to re-establish clearance to main gear trusses

[carusoam]

Now, for fun... measure the bolt and see if it meets the spec.

Its interesting that the spec is that precise.  To 1/64th.

i’m still Thinking the hole should be centered in the castle part.  (Not based on any real experience)

If you have a washer. Put it under the head of the nut to see if that thickness gives the clearance you need.  This will be helpful for your conversation with Lasar... just don’t leave it in there until some level of approval is given...  

Best regards,

-a-

[Vance Harral]

The advice this morning is to go with a washer behind the head of the bolt, so I'll be giving that a try as soon as I can get out to the hangar.  I'll measure the bolt at that time just for grins.

[Vance Harral]

Update: one AN960-616L washer on the bolt head plus an ever so slight grinding of the bolt tail - taking care to leave plenty of "meat" for the cotter pin hole - gave me the clearance shown below.  I'm going to call it good.

[Vance Harral]

Some important details for those still reading...  First, while all the pros thought it fine to put one thin washer on the head side of the bolt, I'd caution against anything more than that.  The grip of the bolt (i.e. the length of the non-threaded portion of the shaft) is clearly supposed to extend all the way through both forks of the forked retract truss.  The 0.750" grip of an AN26-17 bolt does just that.  A single AN960-616L washer draws the bolt head back 0.032", leaving 0.718" of grip, which I was comfortable with based on a visual look - I could still just barely see the edge of the grip shoulder at the surface of the retract link indention.  I also tried a standard AN960-616 washer, which has a thickness of 0.063".  That results in a grip distance of 0.687".  I was uncomfortable with this visually - the thicker washer drew the bolt back far enough that I could no longer see the grip shoulder on the nut side.  Based on this observation, swapping the AN26-17 bolt for an AN26-16 would not have been a good solution either, as the grip on the -16 bolt is only 0.688".

Second, I double-checked with DMax on this (actually got to talk to Don himself, which was an honor).  Don was OK with the washer solution, but said he would probably have just installed a thinner shim behind the "baby shoe" bracket.  He also said some airplanes have no shim at all there, just like in my "experiment" video above.  In fact, I walked out and looked at another Mooney on the ramp, and it was entirely shim-free - the baby shoe bracket was installed directly against the wing spar strap.  I'm still not sure this is a great idea, but I'm really in no position to question Don's expertise.  The main reason I didn't go that route is I didn't want to order or machine a thinner shim, and going with no shim at all seemed like it would place too much side load on the bearings during operation.

Finally, one mechanic asked why I didn't just install the bolt in the other direction, despite what the parts manual says.  We looked into it as a thought experiment, and there are a couple of reasons not to do this.  The more important one is there are clearance issues on the other side of the retract truss too, and the consequences of interference on that side would be more severe.  The less important one is we came to the conclusion you might be able to remove this bolt and nut without removing the entire landing gear leg, with the parts installed as shown.  If you flip the bolt around, it would be absolutely impossible to do so.

I still have to re-install the rods and swing arms, then check the gear rigging, so too early to declare victory yet.  But good progress today.

[Vance Harral]

On a somewhat different note... I'd mentioned the missing grease fittings on our forward trunion bearings earlier in this thread.  Turns out the bearings in our airplane are indeed tapped for a threaded grease fitting, not a pound-in barbed fitting.  The parts manual specs an Alemite 3018, which is a 6-40 threaded fitting, and I'm able to thread a common 6-32 screw into the hole (close enough when the hole is only a couple of threads deep).

On one side the grease fitting was simply missing.  On the other, it had been broken off, but I was able to extract the broken shank with a left-hand-cut screw extractor.  I now have two empty 6-40 holes awaiting a solution.  I packed grease in the bearings before re-installing the landing gear, so I'm not particularly concerned about lubrication in the short term, but I'd like a clean finish.  Nothing turns up for Alemite 3018 or 6-40 grease fittings at Aircraft Spruce, and this older Mooneyspace thread on the same topic has no resolution.  But there do appear to be suppliers, e.g. https://www.huyett.com/Products/Grease-Fittings-Lubrication/Fittings/Grease-Fittings/A3018.  I suspect hangar fairies might also find something suitable at the local aircraft parts and hardware store (which is suspiciously full of car parts...)

In the short term, I'm trying to decide whether to cut down a common 6-32 screw short enough to screw it in without interfering with the rotation of the trunion, or just to leave the hole open.  The latter actually seems less of a risk.

[N201MKTurbo]

4 minutes ago, Vance Harral said:

On a somewhat different note... I'd mentioned the missing grease fittings on our forward trunion bearings earlier in this thread.  Turns out the bearings in our airplane are indeed tapped for a threaded grease fitting, not a pound-in barbed fitting.  The parts manual specs an Alemite 3018, which is a 6-40 threaded fitting, and I'm able to thread a common 6-32 screw into the hole (close enough when the hole is only a couple of threads deep).

On one side the grease fitting was simply missing.  On the other, it had been broken off, but I was able to extract the broken shank with a left-hand-cut screw extractor.  I now have two empty 6-40 holes awaiting a solution.  I packed grease in the bearings before re-installing the landing gear, so I'm not particularly concerned about lubrication in the short term, but I'd like a clean finish.  Nothing turns up for Alemite 3018 or 6-40 grease fittings at Aircraft Spruce, and this older Mooneyspace thread on the same topic has no resolution.  But there do appear to be suppliers, e.g. https://www.huyett.com/Products/Grease-Fittings-Lubrication/Fittings/Grease-Fittings/A3018.  I suspect hangar fairies might also find something suitable at the local aircraft parts and hardware store (which is suspiciously full of car parts...)

In the short term, I'm trying to decide whether to cut down a common 6-32 screw short enough to screw it in without interfering with the rotation of the trunion, or just to leave the hole open.  The latter actually seems less of a risk.

Here is one for half the price:

www.partdeal.com/alemite-special-thread-straight-fitting-6-40-unf-2a-3018.html?zmam=74973193&zmas=1&zmac=4&zmap=77211866&gclid=EAIaIQobChMIzbnSwauz2QIVkKDsCh3dDwUKEAYYASABEgLPLvD_BwE

 

 

[MB65E]

Awesome detailed report!! 

A Little jealous!

-Matt

[carusoam]

Refreshed link that Rich posted above...

http://www.partdeal.com/alemite-special-thread-straight-fitting-6-40-unf-2a-3018.html?zmam=74973193&zmas=1&zmac=4&zmap=77211866&gclid=EAIaIQobChMIzbnSwauz2QIVkKDsCh3dDwUKEAYYASABEgLPLvD_BwE

Click and go....

-a-

[Vance Harral]

The price at partdeal.com is definitely great.  But I'd have to order 28 of the little suckers to reach the $10 minimum order.  Anyone up for a group buy?

Surely there's other cool stuff at partdeal.com I "need".  Anyone have suggestions?

[lamont337]

48 minutes ago, Vance Harral said:

The price at partdeal.com is definitely great.  But I'd have to order 28 of the little suckers to reach the $10 minimum order.  Anyone up for a group buy?

Surely there's other cool stuff at partdeal.com I "need".  Anyone have suggestions?

Grease gun?

[Vance Harral]

36 minutes ago, lamont337 said:

Grease gun?

Great idea, but looking more closely, the shipping charges at partdeal.com kill any bargain element.  Same at huyett.com.  Think I'll look around locally a bit first.

[N201MKTurbo]

Get a Lock N Lube so you don't break the new fittings.

https://locknlube.com/

 

[Vance Harral]

I'd already obtained a Lock N Lube based on previous comments here on MooneySpace.  So far it's fantastic, truly a great gizmo.  I haven't hit every zerk in the airframe just yet and I'm wondering if there will be places where there's not enough space to get the tip locked.  But I'm willing to try hard, because once it's locked on, it's flawless.

[lamont337]

Searched "Alemite Special Thread Straight Fitting 6-40 UNF-2A - 3018" on Amazon, $0.60 each so I bought 4 plus a Lock N Lube. Free shipping 

[N201MKTurbo]

7 hours ago, Vance Harral said:

I'd already obtained a Lock N Lube based on previous comments here on MooneySpace.  So far it's fantastic, truly a great gizmo.  I haven't hit every zerk in the airframe just yet and I'm wondering if there will be places where there's not enough space to get the tip locked.  But I'm willing to try hard, because once it's locked on, it's flawless.

You won't be able to use it on the top fittings on the nose gear. I was able to use it everywhere else. I have two grease guns. One with the Lock N Lube and one without.

[flyer7324]

Is the bolt on backwards?


Sent from my iPhone using Tapatalk

[Vance Harral]

1 hour ago, lamont337 said:

Searched "Alemite Special Thread Straight Fitting 6-40 UNF-2A - 3018" on Amazon, $0.60 each so I bought 4 plus a Lock N Lube. Free shipping 

Great find!  I looked on Amazon twice, but must not have found the magic search phrase.

[Vance Harral]

17 minutes ago, flyer7324 said:

Is the bolt on backwards?

No, see my post above about which side the head goes on.

Edited February 21, 2018 by Vance Harral

[Vance Harral]

Coming back together.  As usual, more blood, sweat and tears (and cursing) trying to get all the bolts and nuts back on vs. getting them off.  Particularly frustrating today trying to reinstall the bolts and nuts for the rod ends inside the belly.  There just isn't any room in there to work with.  I must've dropped and fished out nuts and bolts a dozen times over the course of several hours...  It's also essentially impossible to get everything reinstalled without scuffing up the new paint a bit, but it still looks 10x better than before.

 

 

[flyer7324]

Then it’s gotta be the wrong size bolt.


Sent from my iPhone using Tapatalk

[Vance Harral]

1 hour ago, flyer7324 said:

Then it’s gotta be the wrong size bolt.

Nah, you need to read the rest of the thread.  The bolt is the one spec'd in the parts manual, and matches the measurement tolerances for said bolt.  The whole design is an "as required" arrangement that varies from hand-build airplane to hand-built airplane.  A longer bolt obviously wouldn't work, and a shorter one wouldn't have the required shoulder length.  There's a reason the shims behind the baby shoe bracket are spec'd "as required" rather than a specific size.

[flyer7324]

So you’ve figured out the issue then.


Sent from my iPhone using Tapatalk

[helitim]

13 hours ago, N201MKTurbo said:

Get a Lock N Lube so you don't break the new fittings.

https://locknlube.com/

 

I just ordered two of them. Thanks for the link.

Tim

[carusoam]

+1 on the lock ‘n lube site... all you ever wanted to know about zerk fittings and their options....

+1 on Vance’s level of patience and understanding, and ability to teach a dozen ‘students’ learning along the way! 

Nice work, Vance!

thanks for sharing,

-a-

[Vance Harral]

Finished the basic reassembly this morning, next up was rigging.  I was unsurprised to find the rigging way out of spec.  When we checked last year, the preload torque in the down-and-locked position was right at the minimum of 240 in-lbs.  With the new bushings and everything tightened up, I measured the torque at 360 in-lbs - way above the max spec of 280 in-lbs.  This makes sense.  Taking the slop out of the links effectively lengthens the mechanism, resulting in more force on the springs.  I wound up turning the main retract rods in (i.e. shortening them) one full turn.

As others have observed here on Mooneyspace, measuring gear preload isn't exactly the most precise of procedures, particularly for electric gear.  It's not that the instructions in the manual aren't clear, but in practice there are several challenges.  The first is the instruction to take a torque reading "the instant the joint begins to move".  This is pretty subjective.  You can eyeball it, or try to do something scientific like catching a sheet of paper in the interface and watching for it to fall.  But both of those methods seem to have a lot of variation in repeated experiments.  The second is the torque reading itself.  I have access to both beam-type and click torque wrenches.  With the beam type, it's difficult to look at the gauge and the motion of the links at the same time.  The clicker is a little better, but the "click" itself tends to nudge the links into motion.  Next, as the manual mentions, preload varies depending on whether the gear is extended manually until "the moment the gear down light illuminates", vs. being extended electrically.  The manual says to check after manual extension, but even that varies from iteration to iteration.  Finally, there is the issue of the rod ends only being adjustable in atomic increments (half turn or full turn, depending on whether you're willing to reset the stops).

In the end, I found that with full turn increments, one turn in resulted in an average torque right at (a little over if I'm being honest) the max limit, while two turns had an average torque below the lower limit, so I left it at the higher setting.  I'm comfortable with this because the bungee springs are nowhere near "bottomed out", and the collective wisdom in the shop was that it's better to be a little on the high side vs. the low side.

Cycled the gear up and down several times and pleased to say everything seems normal.  Still need to install the mud guards, clamp/zip tie the hoses and squat switch wiring, and reinstall the wheels (new tires are on order).  But I can finally see light at the end of the tunnel.