www.mcfarlaneaviation.com Items on this page: WARNING: Cancer and/or Reproductive Harm - www.P65Warnings.ca.gov
FAA-PMA Approved
McFarlane Aviation Products
132
Landing Gear and Nose Wheel
Steering Parts
McFarlane's Australian Seal Kit Solves the Problem!
Don't waste your time with substandard seals, nothing compares!!
FAA-PMA and manufactured by McFarlane.
• Double edge (“X” style) O-ring seal that will not twist and leak!
• Solves the continuous leak and re-service problems with the Cessna nose strut.
• Go years without servicing!
P/Ns MCSK172-1F
• FAA-PMA direct replacement for Cessna P/N SK172-1F.
• Also includes AN901-5A gasket.
• Improved lock rings are made of 304 stainless steel for better corrosion resistance.
• Components also available separately.
New
Improved
Kit!
Aircraft MCSK172-1F Contains
All 150, 152, 172, 175, 177RG series Qty P/N Description
Landing Gear and
Nose Wheel Steering Parts
Qty P/N Description
Note: P/N NSS-KT-2 doesn't
contain the improved square
(“X” style) O-ring. Adding
this improved part is pending
FAA-PMA approval.
Aircraft
182, 182A,B,C,D
210-5 (205)
210, 210A
310, 310B,C,D,F,G,H,I,J,J-1,K,L,N,P,Q
320, 320-1, 320A,B,C,D,E,F
336
Maintenance Tip:
Wipe the chrome strut down with
Stoddard solvent (mineral spirits)
periodically to soften and remove
any dried oil lm, dirt, dust and
bugs.
By Dave McFarlane
Cessna Nose strut “leak down” has plagued
Cessna owners for the last 65 years. Why
is it that a month after you reseal the nose
strut you nd the strut down again or just
low and showing signs of a little MIL-5606
on the pretty chrome? It always happens on
Sunday when no one is around to help you
service it. You service it up the next week
only to have it do it again next month. After
several strut reseals most people just resign
to servicing it often and consider it part of
owning a Cessna. Piper and Beech struts do
not leak down or need to be resealed often
and they are high pressure!
With a strong belief that everything that
goes wrong on an airplane has a reason that
can be explained by physics, we did some
research. It was observed that the low time
leaking O-ring that was removed always
showed signs of being slightly twisted and
otherwise like new. Further experiments
and close evaluations proved that the O-ring
would twist from friction caused by an
oxidized hydraulic uid lm on the chrome
strut. You probably have noticed how
MIL-5606 hydraulic uid tends to dry and get
sticky after it is exposed to air. Add a little
runway dust to the back side of the strut and
it really gets sticky. The low operating
pressures of the Cessna strut does not put
a lot of holding pressure to stabilize the
sealing O-ring. It was observed that the
sticky lm on the chrome strut can grab and
adhere to the O-ring during a normal strut
action cycle. If the sticky lm is not evenly
dispersed on the strut, the O-ring is rolled a
little on the lmy side only. This uneven
rolling action puts a slight twist in the
O-ring. This slight twist can break the
normal seal between the strut and the
O-ring allowing a slow unpredictable leak.
It seemed logical that if you lowered the
friction on the O-ring surface you could
eliminate the problem. A hunt was on for a
low friction O-ring that would resist being
rolled and would have good durability. After
many experiments with Teon® coated and
other specialty O-rings only partial success
was achieved. They either were not as
durable or the sealing characteristics were
not as good as the standard rubber O-ring.
A break nally came at Airventure Oshkosh
when Tony Brand of Horsham Aviation
Services located in Horsham, Victoria, Aus-
tralia came by and explained how they solved
the problem. They had observed the same
twisting of the strut O-ring and went on to
explain how they replaced the round O-ring
with a square (“X” style) O-ring that can not
rotate. The standard backup rings were
simply reversed to match the square sides of
the new style O-ring. The “X” O-rings have
the same material as the standard ones.
Brilliant! Why didn’t we think of that!? We
rushed home and changed all the O-ring seals
in ve of the airplanes on the eld. One of
them was our 152 trainer that takes a lot of
abuse. We were going to nd out if those
innovative Aussies knew what they were
talking about. Sure enough, that was almost
ve years ago and we have never had to
service the nose strut (not even with air) on
any of the aircraft with the square O-rings! My
hat goes off to the boys from Down Under for
saving the industry thousands of man hours
every year and making the Cessna eet more
reliable! Thank you!
Our FAA-PMA seal kit, P/N MCSK172-1F now
includes the square (“X” style) O-ring and
instructions for reversing the back up rings.
Why Does My Cessna Nose Strut Keep Leaking Down?
Old style
O-ring
New Style
O-ring
