I think what corrodes things is high humidity (temperature and dewpoint being too close) combined with a lack of surface protection.
You see this with machine tools. Lots of hobbyists have a drill, a lathe or even a milling machine, in a shed in the garden. And all that stuff has large precision ground surfaces, which go rusty fast unless covered with oil all the time. Garden sheds are death to all tools, even things like pliers, unless heated to provide a decent separation between temp and DP.
You may be right Vic but engine shops also report camshaft damage due to rust and presumably they can see where the rust was.
One pilot on here, a syndicate, got a “disintegrated” engine, rust assumed due to a long “hangar queen” time before they got the plane (the usual scenario), and they got the metal lab-analysed and found it perfectly to spec. I have seen the report. I tried to get him to consent to publishing it but it seems his syndicate would not agree. Hence I don’t believe the “Lycoming using crap metal” theory, even when it is definitely true on other occassions e.g. the crankshaft saga some 15 years ago (that one was a complex story, with missing heat treatment stages (probably annealing) being the main culprit, but those cranks snapped within hours, IIRC).
Here’s a couple of cam followers with 700hrs on them, my IO540. They came out when the crank was done, in 2008. Whether there was rust there at some point, nobody can tell, but it is known that Socata stored a load of engines for years and some rusted badly before being installed in planes. My engine had rust in the bores below the piston travel – article here.
Very true about sweaty fingers on machine tools
This might sound like a silly question but why can’t you just replace the oil with fresh and put enough in to cover the cam?
You would have to completely fill the crankcases. Yes that would work. I read somewhere that Spitfire engines were stored like that at one point. A lot of oil though – maybe 50-100 litres?
Lyco engines have the camshaft at the top of the crankcase.
Would you even need to use expensive aviation oil? Wouldn’t some first cheap supermarket car oil do the trick?
Yes, but something really wrong might damage oil seals, especially the front crankshaft seal. Straight aviation oil is also cheaper than any decent car oil.
What was your idea for the pre-oiler Vic? I know it is not allowed, but I’m interested!
There is the Centri-Lube camshaft STC. I don’t know if there is an EASA version of the STC but probably yes. In fact that thread is worth a read as directly applicable.
A couple of observations here:
I read in this thread that the engine oil has been drained out. You should not leave an engine for long periods without the correct amount of oil in the crankcase because it’s possible to cause air-locking in the oil pump which will stop the flow of oil when you refill and come to start up the engine. Occasionally, the air lock is very difficult to move. Suggest you at least keep the engine filled with fresh oil and watch the oil pressure when you start up first time.
There are many types of corrosion at work in our engines. As in this thread, the main one talked about is an engine left idle for long periods in a damp atmosphere causing rusting and pitting. There is chemical corrosion going on, galvanic corrosion and electrolytic corrosion all playing their part. Some years ago I was in dispute with an aircraft manufacturer who supplied me a new aircraft with a heavily corroded engine straight out of the factory. I had parts of the engine analysed at Newcastle Universities corrosion analysis department and they were very scathing about the mixture of materials used in Lyc and Conti engines. Mating dissimilar metals were definitely contributing to electrolytic corrosion within the engine causing pitting, for example between a cam lobe and a follower. The best defence we all know is to run these engines often, use as many oil additives as you can get to help such as Camguard and keep the aircraft in as dry an environment as possible.
A common misunderstanding is to think the hangar has to be warm. I doesn’t. What it needed is to minimise the rate of change of temperature. That’s when condensation occurs which becomes the electrolyte for further corrosion. Condensation is the killer. Problem is very few hangars have any heat sink so the rate of change of temperatures is huge so you get condensation.
In this specific situation in this thread, if I was facing another couple of months (in the depths of winter) before one can fly the aircraft, I’d definitely follow the storage/inhibiting guidance from Lycoming. Buy the correct storage oil (forgotten what it’s called) and follow the inhibiting procedure. Disconnect the battery completely (not just by the master switch). Then you know you’ve done the best you can and you can sleep at night.