Refinishing Spring Gear legs

[GAHorn]

I have no problem with glass-bead-blasting gear legs then priming/painting them with polyurethane. Soda-blasting would also be fine with me.

I only post the following links because I found them interesting:

http://www.ibdaweb.com/members/knowledg ... r_legs.htm

http://www.seaplanesnorth.com/gear.html

[T. C. Downey]

I have no problem with glass-bead-blasting gear legs then priming/painting them with polyurethane. Soda-blasting would also be fine with me.

I only post the following links because I found them interesting:

http://www.ibdaweb.com/members/knowledg ... r_legs.htm

http://www.seaplanesnorth.com/gear.html

If you need to find the cracks in any parts, do not bead blast. It will actually peen the crack closed. Very few strippers contain any acids that will cause hydrogen embrittlement, most are now jellied acetone or naphtha. Gone are the days of carbontetracloride (sp) and hydrochloric acid strippers.

[ghostflyer]

One method of stripping off paint and cleaning is using walnut shells or plastic pellets in a bead blaster . Another method used is dry ice at very high velocity.

[Bruce Fenstermacher]

I've contemplated this for some time now as I'd like to remove, clean and repaint my gear. Would have used a chemical stripper long ago except I heard about the chemical embrittlement issue.

I just can't imagine using a belt sander or any kind of powered sander for fear of removing metal.

And so far I've just settled for cleaning off rust and feathering out paint chips best I can with scotch brite and then repaint over old paint.

[T. C. Downey]

I've contemplated this for some time now as I'd like to remove, clean and repaint my gear. Would have used a chemical stripper long ago except I heard about the chemical embrittlement issue.

I just can't imagine using a belt sander or any kind of powered sander for fear of removing metal.

And so far I've just settled for cleaning off rust and feathering out paint chips best I can with scotch brite and then repaint over old paint.

Using a palm type dual action sander and 320 grit, you will not remove any significant amount of steel.
When you bead blast them you will find they are really rough, and will require about three coats of primer filler to get them smooth enough to paint. Simply sand until you start seeing bare steel, then stop and paint.

[bagarre]

I've contemplated this for some time now as I'd like to remove, clean and repaint my gear. Would have used a chemical stripper long ago except I heard about the chemical embrittlement issue.

I just can't imagine using a belt sander or any kind of powered sander for fear of removing metal.

And so far I've just settled for cleaning off rust and feathering out paint chips best I can with scotch brite and then repaint over old paint.

Using a palm type dual action sander and 320 grit, you will not remove any significant amount of steel.
When you bead blast them you will find they are really rough, and will require about three coats of primer filler to get them smooth enough to paint. Simply sand until you start seeing bare steel, then stop and paint.

+1

Unless you're using 80 grit on a wheel, you'd have to really really try hard to remove any significant amount of metal from the gear legs.

[GAHorn]

I don't wish to start any personal-arguments on this subject so I will refrain from "quoting" any previous posts herein.....
But CESSNA specifically warns DO NOT USE CHEMICAL PAINT STRIPPERS and DO NOT USE POWER-SANDERS on spring gear!

Here IS a quote directly from Cessna (https://support.cessna.com/docs/custsup ... 2ndQtr.pdf ) :
"Chemical strippers and rust removers are not to be used on high-strength steel components. These chemicals can cause
hydrogen embrittlement. This is an undetectable condition that may lead to micro-cracking of the steel. Failure of the part may occur without warning when this condition is present. The only reliable way to prevent hydrogen embrittlement is not to use chemical rust removers or paint strippers on landing gear springs."
AND
"There are few considerations to keep in mind when taking on this task. Power sanders are not approved for use on high strength steel because of the potential for heat to build up on the surface. This heat is detrimental to the temper of the metal and can significantly reduce the life of the landing gear."

Questions, please contact:
Cessna Customer Care
316-517-5800
1-800-423-7762
Customercare@cessna.textron.com

See the link above for the full procedure.

[bagarre]

Power sander can describe a pretty wide range of tools tho.

I can't imagine a DA sander with 320 or 220 grit paper generating any heat. if you were really concerned, you could stop and feel if it's warm to the touch. I'd use one to cosmetically improve the gear but if you wanted to remove all the paint for inspection - it would take a month of sundays.

A heavy belt sander or wheel could certainly over heat and ruin the part.

[mike roe]

One other thought on any sanding. The underside of the legs are shot peened to a specific dimension. If you were sanding to remove paint you would reduce the shot peened surface or remove it. Cessna has a spec on passable depth. Just a thought.
Mike Roe

[T. C. Downey]

One other thought on any sanding. The underside of the legs are shot peened to a specific dimension. If you were sanding to remove paint you would reduce the shot peened surface or remove it. Cessna has a spec on passable depth. Just a thought.
Mike Roe

What's your reference on the shot peening?

[mike roe]

George posted this in 07. (sorry George)

Landing Gear Corrosion Inspection (Svc Man revision 7/1/07)

Postby gahorn » Mon Sep 24, 2007 3:55 pm

The following temporary revision should be added to your 100 series service manual (official Cessna revision fwd'd from FAA):
5-4. MAIN LANDING GEAR.
5-5. REMOVAL.
NOTE: Shims and wedges are used to attach the main landing gear spring at the fuselage
outboard structure. The spring is attached to the fuselage inboard structure with a bolt
which passes through a hole in the end of the spring.
a. Remove floorboard access cover over spring to be removed.
b. Remove screws and slide external fairing and seal down around spring.
c. Hoist or jack aircraft in accordance with instructions outlined in Section 2.
d. Disconnect brake line at wheel and drain hydraulic fluid.
e. Disconnect brake line at fuselage fitting and cap or plug all open lines and fittings.
f. Remove attaching bolts and pry shims and wedges out of fuselage.
g. Remove nut, washer and bolt attaching inboard end of landing gear spring and pull entire gear
out of fuselage.
NOTE: Note shims placed under inboard end of spring strut. Mark shims to be sure they are
replaced correctly at installation.
5-5A CORROSION CONTROL ON LANDING GEAR SPRINGS.
a. General
(1) The main landing gear springs are made from high strength steel that is shot peened on
the lower surface to increase the fatigue life of the part.
(2) The shot peened layer is between 0.010 and 0.020 inch thick.
(3) If the protective layer of paint is chipped, scratched, or worn away, the steel may corrode
(rust).
NOTE: Corrosion pits that extend past the shot peen layer of the gear spring will cause a
significant decrease in the fatigue life of the spring.
(4) Operation from unimproved surfaces increases the possibility of damage.
b. Corrosion removal and repair.
WARNING: Do not use chemical rust removers or paint strippers on
landing gear springs. High-strength steel parts are very
susceptible to hydrogen embrittlement. Acidic
solutions, such as rust removers and paint strippers,
can cause hydrogen embrittlement. Hydrogen
embrittlement is an undetectable, time-delayed process.
Since the process is time delayed, failure can occur
after the part is returned to service.(1) Examine for signs of corrosion (red rust) if damage to the paint finish of the landing gear
spring is found.
(2) Carefully remove any rust by light sanding.
(a) The sanding must blend the damage into the adjacent area in an approximate 20:1
ratio.
EXAMPLE: An 0.005-inch deep pit. The pit must be blended to a 0.10-inch radius
or 0.20-inch diameter.
(b) Make sure the last sanding marks are along an inboard-to-outboard direction, or
along the long dimension of the spring.
(3) After the sanding is complete, measure the depth of the removed material from the
damaged area.
NOTE: The maximum combined depth of removed material to the top and bottom or
leading and trailing edge is not to be more than 0.063 inch at any two opposite
points on the gear spring. This measurement limitation includes areas that have
previously been damaged and repaired.
(a) Make sure the depth of the damage area on the bottom of the gear spring is not more
than 0.012 inch deep.
1 If the damage is deeper than 0.012 inch deep and less than 0.063 inch deep,
replace or shot peen the gear spring. The gear spring must be removed and sent
to an approved facility to be shot peened.
a The shot peen specification is to be Almen intensity of 0.012 to 0.016 with
330 steel shot.
(b) Make sure the depth of any damage on the leading edge, trailing edge, or top of the
gear spring is not more than 0.063 inch deep.
1 If the damage is deeper than 0.063 inch deep, replace the gear spring.
(4) Touch-up paint as required.
NOTE: Additional information regarding corrosion control can be found in FAA document
AC-43-4, Chapter 6, or AC43.13-1B Chapter 6.
c. Axle bolt hole corrosion.
(1) Operation of an airplane on skis increases the loads on the lower part of the gear spring
because of the unsymmetrical and twisting loads.
(a) The increased loads have produced spring fractures that originate from pits in the
axle attach holes.
1 Catastrophic failures can occur from fatigue cracks as small as 0.003 to 0.010-
inch long that originated at pits.
NOTE: Although operation on skis causes more loads, the criteria apply to all airplanes.
(2) There is no maximum damage depth for pits that develop in the axle bolt holes. If pits or
corrosion is found, ream to remove it, subject to the following limitations:
(a) Remove the minimum material necessary to repair the damage.








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[GAHorn]

No need to apologize Mike! Glad you found it!

By the way, the shot-peen process is specific: The shot peen specification is to be Almen intensity of 0.012 to 0.016 with 330 steel shot.

[c170b53]

Flap peening likely would be the easiest for the DIY 170 owner if the surface needs to be repaired. http://multimedia.3m.com/mws/mediawebse ... SeSSSSSS--
Gives a bit of info for flap peening.
I'm guessing the initial peening goes to a depth of .005"- .0075 again just a guess, so unless your removing a lot of material I don't thing it's a concern or need (unless there's damage) for those blasting and re-painting.

[T. C. Downey]

1 If the damage is deeper than 0.012 inch deep and less than 0.063 inch deep,
replace or shot peen the gear spring. The gear spring must be removed and sent
to an approved facility to be shot peened.
a The shot peen specification is to be Almen intensity of 0.012 to 0.016 with
330 steel shot.

Note that this is a repair procedure, and not done on all gear legs.

[GAHorn]

It was done on all gear legs when they were new, and should be inspected/maintained. (Few owners of 60+ year old airplanes have given consideration of the numbers of times theirs have been stripped and repainted....and may have never been properly and closely inspected.)