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posted May 28, 2007

Mooney awaiting engine replacement

What’s wrong with this picture?

Read on to find out why the propeller is not on the airplane.

You haven’t seen any flying stories here for a while because we’ve been dealing with some maintenance issues with the Mooney. Here’s a quick update for those who have been wondering what we’ve been up to.

New Cylinder

We first noticed an issue with cylinder number 2 during our Angel Flight to Driggs in the summer of 2006. The spark plugs kept getting fouled with excess oil, so we had our mechanics pull the cylinder and check it out. They discovered a stuck oil control ring which explained the oil fouling, but they also discovered a small crack in the cylinder. Due to the crack, we had no choice but to replace that cylinder.

After the new cylinder was installed, we had to follow the break-in procedure. This involved flying for 50 hours at between 65% and 75% power in order to properly seat the piston rings. Normally aspirated engines lose power at higher altitudes since the air is less dense the higher you go. In order to maintain at least 65% power we were limited to a maximum altitude of 8,500 feet. Above that altitude, the power dropped off to less than 65%. One of the great things about living in Boise is the beautiful mountains all around us, but some of those mountains are close to or above 8,500 feet so this put some limits on our destinations during the engine break-in period.

I couldn’t find any Angel Flight missions we could safely do without exceeding the 8,500 altitude limit. We did manage to make a few smaller cross-country trips, but nothing exciting enough to post here.

The Other Shoe Dropped

We got the 50 hours of new cylinder break-in done just in time for the airplane’s annual inspection this month. One of the things we asked our mechanics to look at was the higher oil consumption we were seeing with the new cylinder (about 3 hours per quart compared to 8-10 hours per quart previously). They pulled off the new cylinder to investigate the situation and found a hairline crack in the engine case. The crack was so small, it’s quite possible it had been there for a while but they just found it while investigating the oil consumption issue.

It’s not economically feasible to repair a cracked engine case. So even though we had good compressions on all the cylinders it was time to replace the engine. Ouch. Our engine is rated for 2,000 hours of flight time between overhauls and we had just passed about 1,600 hours so we were hoping to have another 400 hours of use out of that engine.

Engine Replacement Decisions

There are basically four choices when it’s time to replace an engine: buy a brand new engine, buy a factory remanufactured engine, buy a factory overhauled engine, or have your current engine overhauled. Most people choose the overhaul option since it’s the most cost-effective and there are many good overhaul shops around the country with excellent warranties (some are even better than the factory warranty).

Might As Well…

I think I read this on an aviation forum somewhere: the three most expensive words in maintenance are “might as well.” While we’re looking at engine options, we might as well address the design flaw of the Lycoming IO-360-A3B6D engine (the engine currently on our Mooney). The -A3B6D has dual magnetos to power the spark plugs (just like most piston aircraft engines), however the design flaw is the two magnetos are in a single housing and driven by a single drive shaft. The whole purpose of having dual magnetos is to have two completely independent ignition systems, which the -A3B6D does not really have. Fortunately the Mooney M20J is also certified to use the Lycoming IO-360-A3B6 (without the D) which has two truly independent magnetos.

A quick search of the NTSB database turned up this accident report of a 1977 Mooney M20J just like ours that had a total engine failure due to problems with the magnetos.

It didn’t take long to come to the decision to go with the -A3B6 engine. Just the added safety of truly independent magnetos was really enough information for me. There were a few other factors favoring the -A3B6 over the -A3B6D.

  • Aircraft dealer Jimmy Garrison writes regular articles for the Mooney Aircraft Pilot’s Association magazine where he shows how he values Mooneys based on several factors. According to his article, Mooneys with the -A3B6 engine are worth $3,000 more than those with the -A3B6D.
  • Lycoming charges a $3,500 “unlike core difference charge” to trade in a -A3B6D core for an -A3B6, but the -A3B6 costs $3,000 less than the -A3B6D. So the net cost difference is only $500 more.

Factory Overhaul or Factory Remanufactured?

Changing the engine from the IO-360-A3B6D to the -A3B6 eliminates the option to overhaul the engine. Overhaul shops work on the engine you send them, and it’s not feasible to convert an -A3B6D to an -A3B6. That’s unfortunate because overhauling the engine is less expensive than the remaining three options for a replacement engine: factory new, factory remanufactured and factory overhauled.

Buying a factory new engine is just too damn expensive, and not really worth the price premium in my opinion. So the decision comes down to factory remanufactured engine or factory overhauled engine. According to Lycoming the factory remanufactured engine is overhauled to tighter tolerances than the factory overhauled engine, and therefore costs $3,000 more. The factory engine has “zero” time on the engine, which does give a higher resale value according to Jimmy Garrison’s valuation article.

Primarily based on the increased resale value, I decided to go with the factory remanufactured engine. The increased value doesn’t quite cover the $3,000 premium for the remanufactured engine, but it’s close.

I worked with Air Power who were very helpful in walking me through the steps for changing out the -A3B6D for the -A3B6. They also had the best prices I could find for the replacement engine.

So the new engine is on order, hopefully it will arrive by the end of June and then we’ll start the break-in process all over again. While the engine is coming off, we might as well have the propeller and prop governor overhauled too.

In Other News

We were planning to attend the EAA AirVenture in Oshkosh, WI again this year, after we had such a great time during our first trip there last year. The new engine should be installed prior to Oshkosh 2007, however it doesn’t seem like good idea to fly halfway across the country on a brand new engine. Also we’d have a hard time crossing the Rocky Mountains at less than 8,500 feet in order to keep at least 65% power during the engine break-in period. So we’ll have to try again in 2008 to make it back to Oshkosh.

In the mean time, I’m keeping pretty busy juggling my jobs as a full-time software architect and a part-time flight instructor. I’ve got a few articles queued up that I want to post, including an Angel Flight from last summer that I still need to finish up.

Add your comment     Comments: 5

#1 Anonymous - 07/14/2007 05:32 AM

#2 Phil Verghese - 07/14/2007 05:41 AM

#3 Bill Cox - 10/01/2007 06:03 AM

#4 Joe - 10/12/2011 07:27 AM

#5 Woody - 06/17/2012 06:26 PM

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