I had some flying to do before we pulled the engine

After I had found the magnetic metal filings in the oil filter I talked with Tim and we both agreed that the problem was either the cam shaft and one or more of the hydraulic tappet bodies.  There are 12 tappet bodies and 9 cam lobes on this engine (Lycoming IO 540 1WA5).  They are made of a ferrous metal that has a hardened (nitrided) surface.  Once the nitrided surface wears away, the softer metal underneath wears at an accelerated rate and comes off in large chunks (spalling). Camshaft wear will result in loss of engine performance due to loss of volumetric efficiency and changes in valve timing.  Cam lobe wear may be most pronounced were two tappet bodies share the same cam lobe (these are the intake valves).

Here is a link to an Airworthiness Bulletin issue by the Australian Government  Civil Aviation Safety Authority issued on November 23, 2012 that discusses this issue in both Lycoming and Continental engines: http://www.casa.gov.au/wcmswr/_assets/main/airworth/awb/85/014.pdf

The tappet bodies run against the camshaft lobes and through the rods cause the valves to open and close.  That controls the intake and exhaust of gases to and from the cylinders which through the pistons turn the crankshaft that rotates the propeller.

We decided the prudent thing to do was pull a couple of valve covers and to check the valve lift to see if any height difference could be detected which would indicate wear on the cam lobes.  Tim found some significant change on the intake valve on one cylinder.  That's not what I was hoping for, but that confirmed what we had expected. The engine has had a history of having a broken piston around 1100 hours, which was before I owned the plane.  At that time during that repair a reconditioned camshaft was placed (in retrospect that was a mistake and is exactly why we are starting with a new one this time).

With all of the available information Tim and I had a long and detailed discussion about the risks of continued flight. This kind of wear would not be a catastrophic failure but a slow degradation of performance.  We decided that given the stage of the process and recommendations from Lycoming, it was safe to fly the plane another 20 hours and I would change the oil again then cut the filter to look at any metal accumulation.  As PIC (pilot in command), this was no different than all of the judgement calls before any and every flight.  One other parameter I was to keep especially close eye on the CHT (cylinder head temperature) readings.  Particularly cylinders 3 and 4 as they share the lobe that appeared to be wearing faster than the rest.  This is why I was very happy to have put in a JPI engine analyzer when we did the rebuild two years ago.  If the wear was progressing, eventually I would start to see a decrease in temperature of those two cylinders as less air would be drawn on the intake cycle thereby enriching the mixture and decreasing the temperature.

As far as the flights until that oil change everything was uneventful.  In fact, the engine seemed to purr and the performance was as good as ever.  Kind of ironic but yet a little disconcerting realizing that ignorance is bliss.  If I hadn't been cutting the oil filter and checking for metal every time I would have never even had a suspicion of anything being awry, especially since the oil analyses were showing everything within normal limits.  For me, it again reinforced that flying safely is not to be taken lightly and requires full attention all of the time.  

As a sidebar, while flying those last 20 hours, I did have one occurrence that turned out with no consequences but could have had a bad outcome and it had to do with the other end of the airplane.  I was landing with a heavy load on Stuart Island where we are building a small cabin that we hope to spend a lot of our autumn years in.  When I landed, I heard a deep pop when the tail wheel settled to the grass and knew immediately that wasn't good.  I had directional control and came to a normal stop at the end of the airstrip.  As I turned off the runway I noticed that the plane did not seem to turn normally.  In retrospect, I should have gotten out of the plane as soon as I had stopped and never even attempted a turn until I ascertained what had caused the pop.  Luckily the turn caused no damage but could have once I realized what had happened.  One of the leafs in the tail spring had broken.

There appeared to be a corrosion pit in the center of the spring right where the failure occurred.  This was an Alaskan Bushwheel Maule Tail Spring that we had installed two years ago and there must have been a slight pit defect in the metal that was painted over because you could not see any evidence during preflight inspections.  After this incident however, I now crawl under and look at the area of this bend much more carefully.

Luckily the second leaf held and the tail wheel did not bend up into the rudder.

This occurred early on a Thursday morning and I called Tim and he was able to get a shipment of a new tail spring out from Alaskan Bushwheels to his shop that arrived the next day.  A little more luck had a friend by the name of Tom Watkins, who happened to be going out flying that Friday afternoon.   Tom flew into Vaughan Ranch airstrip where Tim's shop was located and flew the tail spring up to Stuart.  

The new tail spring arrived.

A few boards and a jack and 30 minutes...

Torqued and good as new by Friday night.

I went on to fly the plane until late August did another oil change and cut the filter looking for the signs that would decide what would happen next.

As I washed through the filter I could see the same amount of metal I had seen before but in a shorter amount of time, so Island Flyer was put in the hangar not to fly again until the overhaul of the engine was done.  Interestingly, the oil analysis from the prior oil change when the metal in the filter was first noticed, still showed everything within normal limits.