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A very expensive polished nut
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| Sorry for the fuzzy pictures below...someone else took the pictures | |||
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Making Metal in Oil Screen |
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click image for larger view |
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Is anyone on the list using an oil screen with their radial? I have an oil screen made by Aviation Development Corporation, link below, which is great in so far as one can change the screen without having to change the oil. I posted two images of the oil screen at 111 - S/M Engines.
Link to Aviation Development Corporation and their oil screen products |
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Follow up Questions & Information |
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A couple of questions:
------------ Info from Pitts list regarding M14's making metal: ------------ I don't have any operating experience with the Vedeneyev engines yet. But i do have with some other radial engines and a whole lot of operation and overhaul experience with aircraft engines in general. The radial engines I am familiar with, Jacobs, small P & W, small Wrights have a tendency to thrust the master rod axially, usually forward. This is not to be confused with the thrust load applied to the front thrust bearing but is a result of natural twisting that occurrs because of the different torsional loads applied to the mainshafts of the cranks. The result of this is wear to one piston pin plug more than the other, depending on which way the master rod gets displaced and a small amount of aluminum in the screen would be acceptable, the amouont decreasing in time. A spectographic oil analysis is not likely to show this because the pieces are too large ( even though they are small to the eye ), but the aluminum content in the oil sample would be elevated slightly. After a period of " bedding in " the visible particles should decrease, almost down to nothing. Then as the engine approaches its service life, the particle count would increase. At some point, usually around 75 Hrs time in service or 75 hours after major overhaul, the engine should become stable as far as particles in the oil are concerned. I am going to make a judgement call here and say that if the particles are no more than 1/4 a thimble. and are not increasing, everything is most likely operating safely. This assumes nothing is magnetic. Any " flakes " or small pieces of non-ferrous material showing up in a screen or in a paint filter as when changing the oil, would be cause for investigation as there are very few points in an engine where aluminum would be abraided but the most likely is a piston pin plug. That is why some mechanics suggest close observation and they are reasonably comfortable with a resample after another short operational period on clean oil and clean screens. The screens do not keep these events from happening, they only trap some of the stuff so that routine maintenance will allow discovery of an impending failure. Also residual " trash " from a previous failure is likely to show up for a while no matter how thoroughly the oil system, particularly the cooler is cleaned. Any " new " magnetic particles showing up after the initial 75 hrs or so is reason to call off all bets. these require immediate attention and no further airborn operation should,. in my opinion, be done until the cause is positively identifed and corrected. Most experienced engine people can look at the contamination with a high powered jewelers loop, a microscope, and with the aid of a magnet, can identify ball bearing material which becomes oil borne when a bearing race is spalling and / brinnelling. Most bearing races, even foreign ones will be made from 52100 steel or a similar composition. If subjected to a metals lab for identification it will be high in chrome. Iron from piston rings, tappets, that sort of part will have a different crystal structure which is visibly different from high alloy steel, sometimes even to the un-aided eye. |
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The rest of the story... |
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Some time ago, I reported that my M-14P was showing metal in the Aviation Development Corporation (ADC) oil screen. As I reported, some folks told me it wasn't any big deal, as these engines are legendary tough. Another guy told me he wouldn't even taxi it. I talked to folks all over the country about this, including the ADC folks. This was supposedly a brand new engine with, at the time, about 120 hours. Finally I decided that I'd check the compression and have the engine bore-scoped, at least in the lower cylinders. Wanting a knowledgeable opinion, I flew the plane to Allen Tinnes and his folks at Lamar, Colorado. They looked at the metal in the screen with the roughly 5 hours I had on it since last cleaning and said there was definitely something going on that needed to be traced down. Compression was low in two cylinders (#5 & #8), with an obvious exhaust valve leak on both during the compression check. With their comment, "We need to get to the bottom of this," I decided to have them tear things apart (ouch!). All nine cylinders off only showed 4 broken rings. Why would there be 4 broken rings after only 120 hours on a new engine? Still no sign of what was causing the metal though. Took off the front accessory case. Metal in there. Drained the oil tank; more metal in the bottom of that. Finally, took off the oil pump and found a loose nut in the pump! Where did that nut come from? A "Friday afternoon special" from the Romanian factory? That mystery will probably never be answered. Sooner or later the pump would have failed. How the nut didn't lodge between the housing and the drive (?) gear is a mystery (minor miracle perhaps). I have about 14 hours on the engine now since replacing the oil pump. Virtually zero metal is showing now. Allen Tinnes, at Lamar, Colorado, and his folks did an outstanding job! I highly recommend them (contact me off list if you want their contact information). These folks really know the M-14 inside and out (my engine in particular |
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Romanian M-14P Engine Break-in Process as reported by George Coy |
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For your information the following is the testing sequence for EVERY engine at the Romanian factory:
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Contact: webmaster |
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