Originally printed in the February 2000 issue of the MAPA LOG,
the Mooney Aircraft Pilots Association's monthly magazine.)

If 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 ever built.

The 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!

As 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.

What 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.

• As a general rule regarding compression readings for a M20J, 70/80 is considered good.
• 70/80 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.
• If 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.
• If 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.
• Make 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!
• While 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.
• Most 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.
• On 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 it.
• With 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.
• If 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.
• Inspect 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.
• Speaking 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.
• If 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.
• Check 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.
• Check 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.
• The 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.
• Check the metal engine mount for rust especially in the "wells" that the firewall attach points are located.
• Check to ensure that the flexible fluid hoses have not exceeded their recommended useful life of 7 years.
• Ensure 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.
  
  
• Inspect 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.
  
  If 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!

• With the purchase of any older Mooney comes the possibility of fuel tank leakage. The good news is fuel leaks can�t 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.
• Purchasing 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 M20J�s 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.

• On 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.
• The 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.
• Check 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.

• Approximately 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 associated records.