Another Old Wives’ Tale (OWT) that I constantly hear in this business concerns the extensive – but necessary – work that has to be accomplished in order to remove any contaminants from the oil system after changing an engine that "made metal" during its failure. Metal particles and slivers circulating through the veins of your expensive replacement engine can easily spoil your whole day! And it can easily be even worse; it sometimes has been the replacement – for the replacement – engine
Things to write:
Obviously, no one wants to go to all the trouble and expense of this work, it very likely will appear to be economically unfeasible. A hundred voices will sing some version of "We don't need to do all that stuff, I know how better/cheaper/quicker", "We never did that at X (pick an operator), "I can flush it out just as good as new!" or other refrains – and all in good faith! But, when the replacement engine fails, ah-hah, then everyone very quickly will start pointing fingers!
If the engine hashes/trashes/craters (whatever you wish to call it), the contaminating metal from that failure is likely to be completely circulated throughout the oil system and the propeller system (unless it's an electrical prop or a propeller with a separate reservoir) by the time the pilot notices it and the engine is either feathered or shut down. This metal can be either (a) ferrous or (b) non-ferrous. Then, it can be further defined as (1) aluminum (2) steel, (3) chrome (4) brass (5) tin (6) silver (7) x Sometimes – as the saying goes – you can almost read the part numbers on the metal pieces that come out when the screens are removed for checking.
potential in the above scenario.
An excerpt from an earlier Warbird Note follows: "When you see it, it's already happened and nothing you can do will undo it. It's bad enough that the engine has reduced itself to hash and a BIG buck overhaul. But, the oil cooler is junk until it's cut completely apart and cleaned. No amount of flushing is going to fix it. The same is true of the oil tank. Unless it is of the very simplest design where every bit of the interior is visible, it needs to be cut apart for cleaning before reuse. The whole system needs to be really cleaned of all the associated metal contamination."
When I’d originally written the above, it was knowledge I'd gained from an engine shop that stood behind its warrantees, they'd furnished a replacement engine when the freshly overhauled one had failed shortly after installation. It didn't take very many instances of seeing the replacement also make metal (fail) in order to realize that there was something totally amiss.
Remember that a typical oil tank on the types of airplanes we use is likely to contain a reservoir or hopper tank, whose interior remains hidden from view of even the most discerning and careful inspector. The feathering system consists of many hoses, lines, valves, and assorted paraphernalia, any of which could harbor contaminants that might be trapped, stubbornly resisting even the most valiant efforts to dislodge them by flushing.
X-rays taken of the oil cooler certainly should show whether the flushing process worked and whether it’s cleaned out, huh?
R. Sohn © 2000
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