Paul,

Normally this work is done by Lancair and that is their strong preference.  We wanted to do it ourselves for its educational value.  After some deliberations, Lancair agreed and required us signing a liability waiver and they would provide absolutely no instructions but would sell us the seals.  We were brave enough to risk doing it ourselves because a maintenance shop at our airport routinely reseals shock struts and we had them as consultants to rescue us if needed. 

Fortunately, we didn’t need any rescuing and we handled it with just one call for help where we determined we had to build some special tools to get the nose gear internals disassembled.  We had the cylinders powder coated, and the shock piston wheel fork attachment flanges re-plated with cadmium.  The replacement seals were fairly expensive.  We didn’t look into getting them directly from Esco in Australia.

A quick outline of how to change out the oleo-pneumatic shock strut seals is to be sure to let the pressure out of the shock strut before disassembly.  Remove the fasteners.  Take photos of how it all comes out of the cylinder.  Change out seals.  Reassemble.  Compress the strut completely and fill with oil.  Pressurize with nitrogen to a level that results in about a 25% compression of the strut under the static weight of the airplane.

Hope that helps,

Valin Thorn

Legacy Project

Boulder, Colorado

Paul,

 

We recently refurbished and re-sealed our Legacy’s gear struts to get them ready for flight after years of waiting to fly...  Ours were made by ESCO in Australia where later versions are made by Lancair owner Bob Wolstenholme’s machining company.  I don’t know if the designs are exactly the same.

 

On the ESCO strut, the mains are much simpler than the nose gear which has more complicated internals to allow for nose wheel pivoting on the ground but straight when fully extended for landings.

 

Here are a few photos of the internals of the ESCO built Legacy main gear shock strut:

 

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So, from my new familiarity with the strut design and what you described, here’s what I think.  The lower cap screws you tightened are for the part closing the cylinder and holding the main and scraper seals and don’t affect wheel alignment.  The screws running up the side of the strut hold bars in place inside the cylinder that keep the strut from turning (left and right).  See the long bars on the table in the third photo.  The large aluminum piece, with the longitudinal slots in it, attaches to the top of the shock strut piston and slides up and down the cylinder -- with the bars in its wide slots preventing any rotation of the strut piston about its long axis (left right alignment/toe).  If they’re a little lose they may allow some very small left/right free play in the wheel alignment.  When you tightened them up it may have change the alignment slightly.  They need to be tight to keep oil from leaking out underneath them and there are little seals under the screws to help with that.  With the “bar screws” lose you may have been getting a tiny bit of castoring motion where the wheel was self-aligning when moving.  With this bit of free play it was probably also more vulnerable to shimmying.

 

With all that said, I think you just need to now realign your main wheels at the strut flange interface (gold dyed cadmium plating end section) to wheel fork and you’ll get this problem corrected.  From the tire wear pattern and turning tendency, I think it is “toed in” too far to the right.  Hope this is helpful.

 

Valin Thorn

Legacy Project

Boulder, Colorado

 

 

 

-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Paul Miller
Sent: Monday, September 23, 2013 6:04 AM
To: lml@lancaironline.net
Subject: [LML] Question on Legacy MG Strut

 

For those with strut knowledge:  My main gear was tracking well and tires were wearing evenly.  Recently, I noticed the 4 cap screws on the bottom of the strut were not tight and up along the body were smaller screws were also loose so I tightened them.  Now, the Left Main tire is wearing dramatically on the outside and the plane turns constantly left during taxiing.   

 

My question is: What would that indicate inside the strut?   I hesitate to pull off the strut.   If it is just normal play, I will try to re-align but I'm not sure I want to loosen anything up on the strut at this point until I understand what happened.  Thanks.

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