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Why My Engine Failed

By Max Grogan

Columnist

 

 

In July, 2006, I experienced a catastrophic airplane engine failure while in flight.  I was flying my Beechcraft Bonanza V35B, a single engine plane.  I wrote a story about it at the time entitled “ These Things Always Happen to Other People”. 

 

In this report I will give the details of the later events that transpired afterwards including my purchase of a new engine and resumption of flying.  Also, I will explain the exact cause of the engine failure. 

 

It was not discovered until later why the engine failed.  It was visibly obvious, through the hole in the engine case, the connecting rod of the number four cylinder had seized on the crankshaft, but not why.  When the rod seized, welding itself and its bearings to the crank, it was under power.  As the crank rotated, the rod, unable to rotate around its bearings, was broken in half.  When it broke it allowed the crank to turn a bit more.  The broken rod then impacted the engine case and broke a four inch hole in it.  This resulted in loose parts wedging into other parts of the engine which caused it to completely stop.  Elapsed time from the breakage to the stoppage was for all practical purposes immediate.

 

After I landed the airplane at Powell, TN (airport 9A2), with no damage, I had to determine my next steps towards moving the plane to my home field and hangar.  I contacted the man who does the maintenance and inspections of my plane, Barry Sanders for assistance.  I checked to find the availability of a new engine and discovered it would be eight weeks before I could expect shipment as they are built on order and not for stock.

 

Barry had an engine available he could loan me.  This would allow the plane to be flown back to DKX, Knoxville Downtown Island Airport, and secure it in my hangar.  I would also be able to continue to fly while waiting for an engine to be built for me.  The airport where I landed sits right beside I-75 and a very busy cross street.  It has no fences or gates and is all but abandoned.  My airplane, although in a shade port, was in plain view.  I was told I should be concerned about theft.  So, the day after the engine failure, I had Barry’s assistant mechanic, Quentin Elkins, go to the plane for me to remove all avionics to prevent possible theft.  I removed all personal items from the plane and left it unlocked to avoid door damage by someone who might want to break in.

 

 

I contacted Teledyne Continental Motors (TCM), the maker of my engine, and told a customer service representative what had happened.  He expressed little interest and said he would make a note for the technical support department and someone “might” want to talk to me.  I directed him to Fatboyzaviation.com where the story with photos was already posted for all the world to see.  He looked the story up on his computer as we talked and immediately asked me to hold.  He was soon back on the phone and said: “We just happen to have a technical representative coming to the Knoxville area the day after tomorrow.”.  What a coincidence!

 

Joe Barton, of TCM, visited the plane.  Barry and I were there to observe.  Joe bore scoped the engine, drained and captured the two quarts of remaining oil and took photos.  Before he started he promised TCM would grant me the $11,000 core credit for the engine even though it was damaged. (TCM does this routinely, I found out, as they want to know the causes of engine failure.  They do a tear down at their laboratory in Mobile, Alabama.)  He put it in writing on a TCM form.  He said TCM would give consideration to possible warranty coverage even though the engine was just beyond the warranty period.

 

I then ordered a re-manufactured engine (good as new) from Air Power, of Dallas, Texas, TCM’s largest engine distributor.  The cost was $27,811, including one way shipping, as TCM was paying the freight to have the core (the old engine) shipped to them.  Paying this bill, and Barry’s bills, seriously damaged my flying budget!

 

A week later Barry, Quentin and I, with a little help from a couple of other folks, removed the damaged engine and replaced it with Barry’s loaner engine.  This took about six hours.  Barry flew the plane to his private airfield where he does his maintenance work and put the finishing touches on the installation of the engine.  He flew my Bonanza to DKX the next day and it was home again!

 

TCM shipped me an empty engine crate with pre-paid return shipping.  The crate was marked “Warranty Department”.  We secured the damaged engine in the crate and turned it over to the trucking company for shipment to Mobile.

 

Prior to shipment of the engine Barry diagnosed the cause of the failure.  It was so simple and avoidable.  It was due to the installation of the engine oil temperature probe using an improper method for the location in which it was installed.  This particular probe provides oil temperature to a JPI brand, model EDM-700, engine monitor. 

 

Allow me to explain:  The oil temperature probe is a basic thermocouple.  It is sealed inside a metal tube brazed to a threaded shank.  The length of the probe, from the end to the beginning of the threads, is one inch.  Two attached wires transmit the temperature reading to an instrument inside the airplane for the pilot’s information.  The probe is screwed into the engine at a place where it will be in contact with oil.  The protruding wires are then attached to the wires going inside the cabin to the engine monitor.  There is more than one location at which the probe can be installed on this model of engine.

 

 

My plane’s engine had slightly more than 200 hours of running time when I bought it.  This engine model is expected to give approximately 1700 hours of service before overhaul should have to be considered.  Whenever this engine was installed the installer would have had a choice of locations for the oil temperature probe.  He chose the location at the bottom of the oil cooler even though the JPI literature recommends the top front of the engine.  Oil coolers on this engine model are  attached to the engine at the left rear. This is actually not a part of the engine itself as the cooler is a heat radiator for cooling of engine oil.  This location is OK for installation of a probe IF IT IS DONE CORRECTLY.  On my engine it was done wrong.  The male threads on the probe are 3/8 inch outside diameter.  The female threads in the hole on the oil cooler are 5/8 inch diameter.  To use this hole for a probe one must use a reducer bushing.  Techno-speak: The bushing used was an NPT 1/8 to NPT 1/4.  The bushing just was not long enough as Barry discovered.  He measured the length of the probe while attached to the bushing and the space available through the threaded hole.  The space available was not enough for this particular installation.

 

As received from the factory, there is a threaded stud at  the bottom of the oil cooler.  This is adjacent to the internal verni-therm valve.  This valve works much the same way as a coolant  thermostat on a car engine.  Engines perform best with warm oil.  Warm oil circulates much more easily than cold oil which is thick.  When the temperature warms up on initial engine operation the valve opens allowing oil to flow through the cooler.  This cooler will maintain oil at an optimum temperature of approximately 190 to 200 degrees F. 

 

When the verni-therm valve opens it grows in size due to expansion of a spring as it heats up.  On this particular installation its spring was contacting the probe slightly each time it expanded .  This would have flexed the probe each time the valve opened and closed, i.e. one cycle each flight.  Eventually the probe broke after 480 hours of engine running time.  When it broke it allowed the oil, which is under great pressure, to exit alongside the probe’s wires.  The diameter of the probe tube is approximately 1/16 inch. Enough oil was ejected through this very small hole in less than six minutes.  There was not enough oil remaining in circulation to lubricate the connecting rod bearings (and probably other things as well by the time it seized).  This oil would have come out in a fine stream exiting the engine compartment near the left side exhaust pipe.

 

Simply put: The engine failed due to a lack of lubrication.  The loss of oil was due to a broken probe.  The probe was improperly installed.  The engine did not fail due to a manufacturing defect.

 

As promised, in about eight weeks, my new engine was received.  Barry took out his loaner engine and installed the new one.  He DID NOT use the hole on the oil cooler.  Instead, as he says is proper to do, he removed the 3/8 inch stud at the top front of the engine and installed the probe directly into it.  I hope that others flying with a probe installed at the oil cooler location have it installed with a correct, longer, adapter bushing.  If they don’t they may also experience an engine failure if the probe should break.  Let’s hope this does not happen to anyone else.

 

TCM declined to give me warranty credit.  They said it was not under warranty and that was all.  I’m glad I at least got the core credit.  They do not disclose their results when they do an engine tear down and laboratory analysis (for liability reasons?).  The grand total cost of my engine failure was about $33,000 including the costs associated with two engine removals and two installations.  As of late January, 2007, I have operated the new engine 78 hours and it runs very well.

 

Flying is not cheap!  I learned that in 1969, the year I became a pilot.  However, I have found no other endeavor which is as thrilling, satisfying and enjoyable so far in my life.  My belief is life should be enjoyed as much as possible while living up to one’s responsibilities.  Flying my plane provides a tremendous amount of enjoyment. 

 

 

The engine failure was traumatic.  I handled it successfully and did not allow it to stop me from doing what I love most.  I will admit some nervousness on my first few flights afterwards.  May this be the only engine failure I will experience. I hope to be able to fly myself, and my wife and our friends, to many more wonderful places and to have the speed and convenience of my Bonanza for many more years.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Want to read more from Max Grogan?  Check out of his other columns.

Got a comment, question or suggestion for future article? eMail Max.

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