printed in the February 2000 issue of the MAPA LOG,
the Mooney Aircraft Pilots Association's monthly magazine.}
you are an Aviator and a Mooney fanatic one of the most enjoyable ways to spend
time is to get into a debate with a group of mechanics and pilots about which
Mooney model is the best ever built. You can argue that nothing beats the
sheer muscle and speed of the TLS/Bravo. Or, maybe you prefer the graceful
and refined ride of the Ovation. And, by the time you read this article, the
Ovation 2. Yes, the rumors you are hearing are true. The Ovation 2 does cruise
at 192 kts. TAS! Many have argued the Mooney 252 is the best Mooney ever built.
However, if judged by units sold, the venerable Mooney M20J is the best Mooney
first Mooney Model M20J was introduced in 1977 as the Mooney 201. Production
continued for 21 years culminating with the Mooney Allegro. During
those years the M20J was marketed with different names. As stated, it started
out as the 201, for a period time you could also purchase a new 201 Lean Machine,
then the MSE, for a couple of years the Mooney 205 and finally In 1998 the
Mooney Allegro. Regardless of its assigned trade name, from 1977 to 1998,
the Mooney Model M20J was the most popular model Mooney built. The natural
combination of the Lycoming 10--360-A3B6D and the refined M20F airframe combined
for a phenomenally economical 162-175 kts. TAS. Many believe the M20J solidified
Mooney Aircraft Corporation in the General Aviation market place along side
the big three. Cessna, Piper and Beechcraft. Who can argue? Over the 21 years
of production, 2,130 Mooney model M20J's were built, with a huge majority
still flying now and for several years to come. Many pilots and perspective
Mooney owners have asked me why Mooney Aircraft
Corporation ceased production of the most popular model Mooney ever built?
The answer is simply evolution. In order to remain competitive in the marketplace,
Mooney Aircraft Corporation needed to streamline its production planning and
hours. In 1998, the last year the M20J was built, Mooney was
producing four different aircraft comprised of two different fuselage
lengths. The Bravo and Ovation were the extended fuselage bodies and the Encore
and Allegro were the classic fuselage bodies. The desire to build the perceived
market demand was exceeded by the enormous costs associated with constantly
"changing gears" from one fuselage length to the other as aircraft
came down the assembly line. In the end, the insightful management team at
Mooney Aircraft decided that production of one type/length of fuselage was
important to the companies overall fiscal health and future prosperity However,
they did not leave us hanging, in 1999 the Mooney Eagle was introduced as
the replacement for the beloved Mooney M20J. And, for the cost of new airplane
dollars these days, the Eagle offers tremendous value and a solid 10 knot
improvement over the M20J!
you read this article you are probably thinking, "OK, Joe, thanks for
the background info, now tell me what to look for 'cause I want one of these
M20J's". All right, let's start with the engine nacelle. As I stated
in a previous article, I like to fly the aircraft initially to test the operation
of the avionics and other systems that just do not test properly on the ground.
Also, I then have an engine that is as close to normal operating temperature
as possible when performing a differential compression test. After the test
flight, perform a differential compression test and record the readings. You
can reference Textron Lycoming Service Bulletin #1191A or subsequent revision
for pertinent information relating to differential compression checks performed
on their engines.
are acceptable or good compression readings? That will depend on a few different
factors. The total time of the cylinders, the relationship of all cylinder
compression readings compared to each other and what the compression readings
were the last time a differential compression check was performed. Also, when
comparing the differential compression readings subsequent to the current
readings, the amount of flight time that has elapsed has relevance.
a general rule regarding compression readings for a M20J, 70/80 is considered
would not be great numbers if the cylinders were only 100 hours since new
but would be great readings if the cylinders have 1500 hours since new.
five of the cylinders varied from 70/80 to 74/80 and one was 58/80, I would
investigate the cylinder that was 58/80. When one cylinder compression reading
varies that much from the others, suspect a problem.
the compression readings varied from 70/80 to 74/80 at 500 hours since new
and then another differential compression test was performed at 600 hours
since new and one cylinder changed to 62/80 while the others were around
68/80 to 76/80, suspect a problem with the cylinder that is 62/80. Where I have mentioned suspect a problem, I mean just that. There
are usually significant reasons why compression readings are low or change
rapidly, however I have also experienced cylinders that "repair themselves"
50 hours later. My point is to consult with your maintenance professional
before passing judgment.
sure all of the cylinders are current with Textron Lycoming Service Bulletin
388B, procedure to determine exhaust valve guide and condition. In the field
we call this, "Valve Wobble test." Recently, Textron Lycoming
revised the time interval for certain cylinders to every 1000 hours of operation
instead of every 400 hours of operation. I recommend all engines should
be compliant with the 400-hour interval! What happens if the exhaust valve
guide has wear beyond the tolerances specified in Service Bulletin 388B?---potentially
catastrophic failure of an exhaust valve. Enough said!
performing the pre-purchase inspection, insist that an oil and filter
change be accomplished. Make sure the oil filter cartridge is examined
for metal contamination. One of the biggest surprises you do not want to
happen to you is unexpected engine overhaul. Your pre-purchase inspection
maintenance personnel must be vigilant in determining the condition of the
camshaft. Having said this, there is not much they can do other than to
examine the contents of the oil filter cartridge and previous oil analysis
provided by the seller.
M20J top cowlings will have hairline cracks on either side of the "bulge".
This is typically just cracking of the fiberglass Gel Coat. However, it
will eventually require repair because cracking of the Gel Coat is structural
weakening of the fiberglass the cowling is made of. There is an STC to add
a reinforcing rib to the top cowl which will eliminate this problem. Most
aircraft I have worked on do not have this rib.
the lower cowling the cowl flaps and associated attaching structure require
attention. The cowl flap reinforcing doubler is made of metal that is riveted
to a fiberglass cowling. Over time, the rivets start to pull through the
fiberglass. Also, the metal doubler and cowl flap hinge pieces will crack
with age and use. Finally, the electrically actuated cowl flaps have minor
service issues as well. Check to make sure the four small screws that secure
the cowl flap motor are tight, over time these will loosen. Also make sure
the motor wiring is properly secured and the two micro switches are clean
and not gummed up. If the micro witches or wiring fails, you will need to
purchase a new motor or have yours repaired, either way you won't enjoy
the cowlings removed examine the flange of the fuselage that both cowls
are secured to. This flange should have anti-chafe tape attached to it.
Typically, the anti-chafe tape is deteriorated and requires replacement.
It is not expensive to keep this tape in good condition and it plays an
important role in preventing the cowling fiberglass from wearing out on
the metal fuselage flange.
the magneto has more than 500 hours since new or last overhaul, make sure
it has received the special inspection which is required every 500 hours.
Except for the Allegros and some modified aircraft in the field, most M20J's
have a Dual Magneto. While this is a reliable component, it is very important
that the magneto is removed every 500 hours and the detailed inspection
called for in the Magneto Overhaul Manual is employed. Also, make sure AD97-12-07
is complied with on the Magneto Impulse Coupling, this AD is due every 500
hours of operation.
the inter cylinder baffle wires and springs. There are four of these
components per engine. Two on either side. They run fore and aft
from the forward metal cooling air baffle to the aft metal cooling air baffle.
If the springs lose tension
or the wires move out of position or they were not installed correctly to
begin with, the wire can "saw" through the cylinder oil
return lines causing a safety of flight issue.
of the metal cooling air baffles, by and large these are trouble free
components. However, the forward left baffle where the engine induction
air baffle is attached is prone to cracking.
you are contemplating the purchase of a M20J with a high time engine and
with the intent of flying beyond the TBO, be aware that in most cases
you will need to
comply with AD96-09-10 before you can exceed TBO. This air worthiness directive
requires the removal and replacement of the engine oil pump. Carefully evaluate
the cost of performing the AD against the amount of hours you expect to
exceed TBO before proceeding.
the thermostatic by-pass valvefor compliance with Textron Lycoming Service
Bulletin 518C. If the engine has the "old style" by-pass valve
replace it. Replacement
is more cost effective, than the periodic inspection called for in the Service Bulletin.
the rubber hangar that is used to secure the aft end of the exhaust system
tail pipe, Often times this part is overlooked at Annual Inspections and
allows the tail pipe to sag. Regarding the remaining components of the exhaust
system, basically they are trouble free other than the usual wear and tear
any exhaust system suffers from.
Propeller and Governor requires overhaul every 5 years or 2000 hours, since
new or overhaul, whichever comes first. Also, and very important, ensure
that the Governor has received the "T" modification. You can tell
this by the serial number designation, it should contain the letter "T"
near the end of the serial number. McCauley Propeller issued a Service Bulletin
#202A which requires substantialGovernor maintenance.
the metal engine mount for rust especially in the "wells" that
the firewall attach points are located.
to ensure that the flexible fluid hoses have not exceeded their recommended
useful life of 7 years.
AD95-26-16 RI has been complied with on the alternate air door. Furthermore,
ensure the rubber gasket that seals the alternate air door has not loosened.
I have seen these gaskets loosen up. If it breaks free the next stop is
the inlet to the engine fuel servo - not a good thing.
the engine controls rod ends. If they are the old style rod ends, replace
them with the new style rod ends, Mooney Kit #660051-005. It is
difficult to describe how to differentiate between the two, but I
will give it my
best shot. The old style rod ends are secured to their respective engine
control via a threaded stud which is then fastened with a nut. The new style
rod end requires a bolt and castellated nut/cotter pin to secure it to the
engine control. Bottom line, if the rod ends utilize a separate bolt and
nut/cotter pin to secure to the engine controls then they are the latest
and vastly superior rod end.
the engine was recently overhauled/installed there are several other events
that should coincide. Depending on the time since last overhaul, the Propeller
& Governor should be overhauled at the same time. At the very least,
the Propeller should be sent out for a flush of the hydraulic actuating
system and the Governor will require an overhaul. A Propeller Governor does
not have an approved flushing procedure. Most engine overhaul facilities
will void the warranty if they become aware of an engine warranty issue
involving the oil system if the Propeller has not at least been flushed
and the Governor overhauled. While the engine is out for overhaul, the metal
engine mount should be removed for inspection and re-certification. Also,
before reinstallation it should be repainted. The oil cooler should be sent
out for overhaul. The
metal cooling air flexible baffle seals should be replaced. When
the engine is reinstalled it should be attached to the metal engine mount
using new shock mounts and attaching bolts, and nuts. Depending on the times
in service, the alternator should be overhauled and consideration given
to vacuum pump replacement. The flexible fluid carrying hoses (air/fuel/oil)
should be replaced. Also, a minor detail but while we are discussing proper
etiquette the alternator belt should also be replaced. The reason for highlighting
these items is because aircraft are often advertised as, "Fresh Overhaul."
Well, what does that really mean and what value does it add to the aircraft
you are considering? If the items mentioned above were accomplished then
chances are good that a quality job was performed and you are receiving
good value. If not, then most likely an overhauled engine was installed
on an aircraft sale. Translation, overhaul the engine and install for as
little bucks as possible!
to the airframe:
the purchase of any older Mooney comes the possibility of fuel tank leakage.
The good news is fuel leaks cant hide. You have visual reference as
well as fuel odor in the cabin for solid indicators. The bad news is that
leaks can be costly to repair. If you are considering an older M20J
(15 years or more)
and the tanks have never been resealed, budget for it because it will
probably happen on your watch. In most cases on older aircraft, the
tanks have been "patched" at one time or another. Do not have
inexperienced maintenance personnel repairing or resealing your Mooney fuel
tanks. I cannot stress this enough! At East Coast Aviation we have heard
a zillion times, customers who have spent thousands of dollars repairing
fuel tank leaks that still leak. Go to someone who knows what they are doing.
a M20J model that was manufactured prior to 1986 presents different challenges
than aircraft manufactured post 1986. The reason for this is the type of
primer that was applied/painted on the tubular structure. The tubular structure
is made of steel and any steel material is prone to rust if not properly
treated. For the earlier M20Js, Mooney Aircraft used a primer common to
the industry known as Zinc Chromate Primer. Zinc Chromate Primer is typically
green and sometimes yellow in color. Post 1986 M20Js and today's currently
manufactured aircraft utilize an epoxy primer. Typically the epoxy primer
is off white in color. The significance is this: Zinc Chromate Primer begins
to deteriorate after approximately 10 years; earlier if the aircraft is
in a corrosive climate. In order to alleviate this problem, Mooney Aircraft
Corporation issued Service Bulletin 208B. Basically, this Service Bulletin
requires the removal of all "old style" insulation, ensuring all
windows are properly sealed and the cleaning of the tubular structure to
remove rust and the repainting with epoxy primer. If 20B is completely complied
with it is very expensive. Tubular structures that are treated with epoxy
primer, whether at manufacture or post manufacture are much less prone to
rusting. This is not to be construed as though epoxy primer applied to the
tubular structure will not rust
because after many years in a corrosive climate, they too, will rust. But
the rate and progression of rust is much less than those aircraft that have
tubular structures treated with Zinc Chromate Primer. My emphasis is this,
if you are considering the purchase of a M20J that still has Zinc Chromate
Primer as the primary corrosion inhibitor, ensure the tubular structure
receives a thorough visual examination. This requires removal of the interior
side panels and if necessary the cabin overhead panel. The extent and detail
of the visual inspection should be dictated by the amount of rust found
in the easy to see areas of the tubular structure. If the aircraft has the
epoxy primer applied to the tubular structure, chances are good that the
tubular structure is in good shape and free of rust.
I have used 1986 as the timeline for the transition from Zinc Chromate to
Epoxy Primers. While I believe this to be about the right timeline, I am told
by Mooney Aircraft that there was not an exact time that anyone can remember.
Therefore, please examine the tubular structure of the aircraft you are considering
for the color of the primer mentioned above in order to determine the type
of primer utilized.
any older Mooneys inclusive of the M20J model, inspect the tail and tail
trim attach points for excess play. These areas are not prone to wear, however,
after several hundred hours they do have bolts, bushings, etc., that will
wear out from repeated usage. The tail is basically attached in four places:
Two main pivot bolts, a large MS type hinge and the tail trim link mechanism.
These are the areas
that need to be checked for excess play.
two elevators and rudder utilize several rivets called, "Cherry Max"
rivets. Inspect these rivets for signs of loosening. Occasionally, we have
seen these rivets start to loosen or "work as technicians call
it in the field. You can identify this by a trail of black soot aft of the
rivets. Technicians in the field call this "smoking rivets.
the top sides of the wing flaps for excess chaffing. All Mooney wing
flaps will chafe to a certain degree. However, if the flap attaching
and actuating hardware are not maintained to near new tolerances, excess
wing flap chaffing will occur.
Mooney landing gear system is a brilliant design. However, like any component comprised of several moving parts,
it is prone to wear and tear, requiring periodic replacement of parts. Before
the aircraft is jacked up, check
the shock discs for excess compression. The maximum allowable dimension
is defined in Chapter
32 of the M20J Service Manual. Once the aircraft is jacked, see if the shock
disc's can be rotated by hand; if so they require replacement. Visually examine
the push pull tube rod ends and attaching bolts for excess play. Check the
landing gear actuator for compliance with Service Instruction M20-92, replacement
of the no back clutch spring. This is an important Service Instruction issued
by Mooney Aircraft that is required every 1000 hours of operation.
three quarters of the way out each wing is wing station 147.5. Right at
this location there are a row of rivets that attach two adjoining skins
to a wing rib. Inspect these rivets for looseness or "working."
Working rivets can be identified by a trail of black "smoke"(stains)
aft of the rivets. Typically, there will be some working rivets in this
location. It can be repaired by removal of the affected rivets and installing
new solid rivets. By the time
you read this article, I will have covered the performance of Pre-purchase
inspections for the Bravo/TLS, Ovation and Eagle, 231/252/Encore and M20J.
Each and every time I write the closing paragraph, I worry if there is something
important that I might have inadvertently omitted. Most likely there is;
this is why you should protect yourself when considering the purchase of
a previously owned M20J by hiring experienced Mooney maintenance personnel.
Ensure all air-worthiness directives and pertinent manufacturers service
bulletins are researched. Discuss the items I have mentioned here as well
as any other important items they feel should be checked. In the end, nothing
can take the place of diligence and careful evaluation of the aircraft and
Once the pre-purchase
inspection has been accomplished, the transaction has taken place and you
are the proud owner of a Mooney M20J model, celebrate. You have proven to
yourself and the aviation community that you are smarter and more sophisticated
than the average pilot/owner. You now fly an aircraft that is at least 20
knots faster than a Piper Arrow, Cessna Cutlass RG, Socata Trinadad or Commander
114. It burns less fuel, is vastly superior in construction and has unparalleled
"ramp appeal". Congratulations!