This article from Mike Busch has just turned up in email. It contains an interesting snippet on metal potentially getting past the oil filter and ending up blocking the galleries feeding the crankshaft bearings.
However, how the hell can metal get through the oil filter, I have no idea. Perhaps gross negligence in running the same oil filter for years? Who does that?
is it not going to happen quite soon after the bearing becomes oil-less
Not if the blockage is partial, which is very likely because what blocks these passages is dirt.
Don’t ask me how the dirt gets in, but one TB21 owner managed to get a non-functioning prop pitch control, purely by getting enough dirt inside the front of the crankshaft to completely block the oil feed to the prop. He never posted any details… – here.
As a Group/solo owner, there are big variations in engine usage.i suspect this would make oil analysis unreliable. I change oil at 25 hours, spin-on oil filter at 50. And do not fill to max, or allow down to minimum. O200 engine.
Peter wrote:
you could be chewing up some bearing (due to an oil gallery offshoot being blocked) really nicely and will never notice it on performance, not until the bearing is red hot, and there won’t be any metal in the filters because it is way too fine.
But if that happens, is it not going to happen quite soon after the bearing becomes oil-less? Thus unlikely to be caught by periodic oil analysis….. unless the period is every 15 minutes in the cruise.
High aluminium is probably one of the less important things. You can get elevated “soft” metals just by having a hole in the air filter, or by the alternate air door not closing fully.
BlackstoneLabs wrote:
I think operational factors are going to have more of an effect on how much metal shows up in analysis. But even more than that, you might be seeing aluminum from the case itself. Any time the engine sits idle you can get moisture that collects on the case, and that causes oxidation. The oxidized aluminum washes into the oil when you start the engine, and voila! Extra aluminum. It might be worth looking at your aluminum values vs. hours on the oil and the time it took to accrue those hours. We consider anything less than 5 hours a month to be inactive, though of course that will vary depending on climate.
I didn’t write that quote.
easy to get into false positives
Can you give an example? I have not seen one. Short of really way out numbers, there are few “positives” in oil analysis. It’s a trend thing.
Peter wrote:
zero renters, and zero schools … who remain as clueless on operations as ever and continue to spread scare stories about leaning.
You know that’s not true.
The thread of eight years ago was interesting. As suggested, easy to get into false positives. The engineers I know are ex heavy iron and with a strong practical and engineering knowledge, including turbine analysis.
Am not suggesting this is a cost issue, just that the ‘science’ seems to be somewhat soft and the practical benefits do not seem to be quantified, scientifically.
Votive candles are quite cheap I believe:)
no operator that I have come across does oil analysis on their piston fleet.
That’s probably true, but for the wrong reasons. The “business” of GA generally knows little about “mechanical things”. It was only Deakin who dragged GA kicking and screaming into the late 20th century, and this got through to only those who actually “read stuff” and “think about stuff” – maybe a few % of owners, and zero renters, and zero schools, and definitely zero maintenance companies who remain as clueless on operations as ever and continue to spread scare stories about leaning. In the US, a bit more generally, due to a bigger population of “analytical” owners compared to Europe which basically struggles, with the one-eyed man being the king in the land of the blind 
Is this oil analysis a statistically proven preventive maintenance practice for low utilization piston operators?
Not sure about “low” specifically but one example is here.
Another is here.
These are easy actions based on oil analysis.
If it runs ok and feels/sounds/looks ok, then it’s probably ok
Generally that is true, but it’s a matter of risk management. Not all major failure mechanisms make big particles. With the massive torque in use, you could be chewing up some bearing (due to an oil gallery offshoot being blocked) really nicely and will never notice it on performance, not until the bearing is red hot, and there won’t be any metal in the filters because it is way too fine. The engine won’t sound any different until a conrod pops out through the crankcase Oil analysis costs practically nothing (~25 quid per 50hr check) and it gives you a level of reassurance that there is nothing horrible going on inside the engine.
If you just fly locally, then “who cares” but I fly over the Alps and over lots of water and I like to not worry too much. Look at the GA scene, and look at how many won’t do any of that. Look at how many people fly to Le Touquet all the way along the coast to Dover so they cross the shortest over-water distance.
I’ve just bought a new high pressure fuel pump, £250, based on the 1.5% fuel in the last oil analysis, because that’s exactly what I had a few years ago. 250 quid is peanuts, especially as my TB20 maintenance costs are so low.
It is like flying at night. I have almost 3k hrs TT but only ~30hrs at night, and it is partly because it is bad risk management. The other reasons of course are the well rehearsed ones: airports shut etc. Or not going to unknown grass; just because everybody tells you “it is perfect” they may all be flying Maules with tundra tyres.
will anyone actually pull the engine apart based solely on what the oil analysis shows?
If no metal was found in either oil filter? If I had lots of tin I would open it up ASAP.
Or one might get an engine, making way too much metal in the oil, done at say 1800hrs rather than wait a bit longer, especially if it convenient for some other reason…
Remember that the Lyco guidance on how much metal in the filters is “ok” is quite scary. They measure it in spoons… Conti, I believe, gives no guidance.
The other oil analysis threads are well worth reading.
