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We have an M-20 Oil Separator installed on our 0290-D2 and it's been working well for several years. However, we just started having an issue with oil going overboard. Starting with the easiest solution/issue first, I disconnected the hoses to the oil separator. The drain line appeared to be possibly clogged as it still had oil in it. I blew the line out and then also flushed out the M-20 as well. Haven't put it all back together and flight tested yet but I'm hoping that was the issue and not something more catastrophic within the engine. I.e. something that's causing more oil to go overboard and overwhelming the separator. We've certainly not noticed any decrease in performance though.
Just wondering if the M-20 oil separator needs to be periodically maintained/cleaned based on others experience? If so, how often?
I think I remember Steve saying he's taken one of these apart before. Any chance you have some pictures? Curious as to what the insides of one of these looks like. Doing some google searches I saw this image and figured it's probably pretty close:
The inside as I remember it are two concentric tubes of very fine brass wire mesh that the causes the oil vapor to condense.
The condensed droplets flow to the bottom of the container and the resultant oil collected at the bottom is returned to the crankcase.
The bottom vapor outlet is actually a standpipe that forces the remaining water vapor and exhaust blowby out up to the top of the container and out.
This is consistent with commonly used oil vapor or water recovery systems used in machining operations.
I have an excellent article on oil vapor separation I will try and find it.
If that's the case with the mesh material, I can certainly see that flushing it out periodically would make sense. We've had our installed for maybe 5 years or so.
“Seek advice but use your own common sense.”
― Yiddish Proverb
I have suspect mine was stopped up on several occasions. Found out after removal it wasn't. The problem was piston rings rotate, occasionally the gaps in on cylinder will line up and the blow-by increases. After an hour or so it clears up. How do I know this?
When I rebuilt my engine I made especially sure the ring gaps were spaced 120 degrees apart. I had to remove a cylinder for stuck valve, the ring gaps were lined up. Ring rotation really does happen and has been documented by various means.
My M20 has been installed for about 18 years. I have a clean belly except the couple of times I believe the ring gaps lined up.
Last edited by Gilbert Pierce; 01-14-2019 at 02:03 PM.
The following article on oil mist separation was copied from Kit Planes Magazine. I highly recommend this magazine even if you are not building an airplane. It has excellent hands on articles like Sport Aviation use to have.
Figure 1 is basically the M20. Steve took one apart and me the pieces to analyze.
Last edited by Gilbert Pierce; 01-14-2019 at 02:19 PM.
I suspect our engine has some blow-by issues in general. One clue is that the oil changes color pretty quickly after an oil change. We installed the oil separator and it solved the issue of oil on the belly at least. However, in the last 3-4 hours we've suddenly had a bunch of oil on the belly so that's why I suspected a clogged return line. Not sure how much oil flow an M-20 can handle but it sounds like in your case when the rings aligned just right it overloaded yours. Maybe that's part of our issue as well.
Never done a borescope on the engine since we don't have one but that might be worth looking at as well.
“Seek advice but use your own common sense.”
― Yiddish Proverb