Please Mr, we’d like our bung back …

Sometimes not everything is as it seems or should be!

We’ve recently been working on a newly rebuilt aircraft imported from the USA early in 2022. Logbook entries had been run past CAA prior to purchase, in particular the engine overhaul which did not include an FAA 8130-3 and just a very basic 337. I’d thought this might be a problem, but our authorities were happy to accept it.

The aircraft was duly shipped and put through its NZ C of A process. Beautifully restored, it was expected that there would be no real issues with the aeroplane even though it had only flown once after its rebuild. The backstory on the sale was that the owner, the proprietor of a busy restoration shop, had built the aeroplane for himself but on finishing it, was unable to get insurance due to his advanced years. A single proving flight was carried out – and that seemed to fit with this story.

During regular contact with the restorer during the reassembly, he asked us to check the condition of the old stock military primer fitted, as it had been noted that there was quite a bit of black smoke from the RH exhaust during engine runs and that first flight. He told us he’d seen this before and that it was a sign that the primer was leaking. We were a bit puzzled as to why this would only effect the RH exhaust.

Engine runs went smoothly and the C of A was granted. All seemed well and the owner was duly rated.

As time went by it was noted the RH exhaust was much sootier than the LH exhaust, and gradually the engine seemed to not be as happy as it once had been. Oil consumption started increasing and we thought that we had somehow glazed the bores on the overhauled engine.

The decision was taken to remove the three cylinders associated with the sooty exhaust. Number 2 cylinder came off and we were a bit alarmed to see that the rocker boxes on the cylinder appeared to be completely dry with no sign of lubrication. Hm… Number 3 cylinder came off and it had a bent pushrod and dry rocker boxes. Number 4 came off and it had a broken valve spring. Being down the bottom of the engine, it had oil in the rocker boxes. Hmm… Guess we had better remove the other cylinders for a look. Sure enough, they all exhibited similar faults, including one with an extremely worn rocker arm bearing.

By this stage we had concluded there was no oil getting to the rocker boxes, but why? After talking to an overhaul shop in the USA we conducted some checks on an time-expired engine and eventually found that the person who had overhauled the engine in the USA had left a 1/8 NPT bung out of an oil gallery in the crankcase. Oil from the pump goes off to the bottom end and also through another gallery, which has a relief valve that lowers the oil pressure from around 65psi to 15psi for the rocker boxes. The missing bung was downstream from the relief valve and all oil meant to be going to the rockers was going straight back into the crankcase. Because it was downstream from the take-off for the oil pressure gauge, we had no idea that oil was not getting to the rockers.

Hindsight is, of course, a wonderful thing as, given the engine had been overhauled, we had not carried out valve clearance checks at the C of A. We’d intended to do these as part of the first oil change to let everything bed in.

With oversight and help from Southair Ltd, we were able to put the bottom end of the engine back together in preparation for a new set of pistons and cylinders from the USA. A big job in the end due to a moment’s inattention

The engine has since flown around ten hours and is going well except for a pesky leak from the oil pump. Removal and inspection of the pump showed this also to be in less than ideal condition, and an overhauled pump is currently on its way to NZ.

Unfortunately, the previous owner’s response to the situation has been to just shrug his shoulders and tell us that he won’t use that engine guy again! Some of you may not be aware that in the USA, an A&P can overhaul an engine and sign it off, unlike here where a standard category engine must be signed off by a Part 145 shop.

I guess the moral of the story is that sometimes the paperwork (or lack of) does tell the true story!

This article first appeared in the Autumn 2023 edition of Approach Magazine, the dedicated magazine of AOPA NZ, which is published quarterly.