Oil Filter Examination - continued

John,
So, being a reformed lab-rat myself, I set up a little scope and had a look at my filter washings. Here's a little show if you have a minute to view and comment. I realize there are services that will do this and I will likely send the next filter to them to see what they say but I thought you might like to see what I came up with...Incidentally, under magnification, most of the tiny reflectivity's I was seeing on the filter in the sun represented light reflecting off of oil dampened flat surfaces of a variety of tiny non-metallic looking debris. My stereo scope:

I washed one half of the total available oil filter, after cutting it out, with solvent into a cup.For reference, the cup's base diameter is about 1.5 inches.Here's all that I got in washing:

Under magnification it looks like this (20-40X)

I threw in a hair (ouch!) for reference:

The vast majority of the material appears to be non-metallic junk (silicates, carbon, or whatever). I was able to see only a couple of very tiny magnetic bits using a magnet. You would never have seen them move with the naked eye. I next did a trial of drano with some aluminum filings so I'd have something as a reference. Bubble and fizz as advertised.I then applied the drano solution to the washings. I was able to locate only 2 or 3 microscopic fizzies out of the whole lot. Not much aluminum in there. What is notable, and you can see it in the photo immediately above, is that there is a scattering of metallic looking particles (red circle).These are mostly the width of a hair and smaller. They are not aluminum and are not magnetic. They have the appearance of microscopic bits of aluminum foil as you can see.Plating of some kind? Any thoughts? Know anyone crazy enough to look at their filters this closely?

I hope your not tiring of this! A little more... Re-reading your metals analysis post, I proceeded to look at the effect of HCL on the debri.I tried 25% HCL first with very little observable effect. I then went to 100% HCL. At this concentration, the tiny shiny bits were clearly seen to bubble and begin to dissolve. No green tinge was seen anywhere so I doubt chrome. There is no blackening seen either. Based on your post, I'm guessing tin. So, I would characterize this as scattered, microscopic platelets consisting of tin. Question is, is this a matter of concern or a normal wear finding? Any opinion? As I said, I will send the next filter out and see what the professional lab has to say.

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I thought this was a professional lab! Your microscope looks familiar - just like mine! A good bench microscope is a handy shop tool. Now that I'm older I use it to read tiny part numbers off of parts.

Your sample looks very clean. If you have blow-by of combustion gas past the rings, the sample will be darker with more flakes of black carbon. On turbocharged engines the filter paper will be almost black and brittle.

What I used to do was to squish all of the debris between two microscope slides. If it squished with no scraping sound - good - no sand or rocks. If it scraped, scratched, and made noise then I had some sand particles - time to check the induction system for leaks; or stop pulling out the alternate air door on run-up if the runway was dirty!

If your tiny bit of shiny metal is brittle then suspect chrome, otherwise tin if it passes the drano test. Either way one microscopic bit is not important.

I would use a stick magnet to collect all of the bits of iron. Usually they were not shiny and looked like iron filings that you collect from dragging a magnet in sand. If they encircled the tip of a stick magnet then there was cam or cam follower problems. If less, then everything was OK.

Bendix D3000 magneto redundancy

John, I purchased and read your magneto book, which I found informative and interesting. After reading the book, I do have two questions I'm wondering if you could answer given your experience with magnetos.

1. Our Cardinal has the dual magneto, although I am considering a conversion to a non-D at the upcoming overhaul. My question regards redundancy: what internal elements are common to the two magnetos within the D housing?

Do they only share a common drive shaft (and gear), or are any other electromechanical components shared - e.g., cam, magnets, etc.? Do you know of any source where I could see internal photos or mechanical or cutaway drawings of the D3000 magneto so I could better understand its design?

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About the only parts that are truly redundant is the coil, points, and capacitor.

The D3000 magneto is a good magneto, easy to work on and reliable. Like any device it has its limitations. The following three areas should be well understood, respected and maintained, as all have caused fatal aircraft accidents:

• Impulse coupling spring (part number 10-51324)
• Hold-down clamps
• Cam retaining screw
  
  
  Impulse Coupling Spring:
  
  Breakage retards timing causing complete loss of engine power. Cessna 172N N738BC ditched at sea with 2 fatalities. On any magneto the impulse area sometimes gets rusty from condensation. The impulse spring gets tiny rust pits that create stress corrosion cracking. There is no warning - it just breaks. With two magnetos you also loose timing but you can turn the bad magneto off. With the D3000 magneto the broken spring retards the timing on both magnetos and you lose power.
  
  Follow TCM's instructions and recommendations to the letter in regards to inspecting and replacing the impulse spring. Personally, if I lived in a corrosive area I would replace it every year.
  
  Hold-down Clamps:
  See my article at http://www.sacskyranch.com/eng410.htm
  
  
  Cam Retaining Screw: "Everything hangs on this connection"
  
  Here is a copy of an email I received some time ago from Germany:
  
  A pilot came to an aircraft workshop with the problem,that the engine did not start well and did not reach more the 2200 RPM. (Cessna 170 N engine Lyc.O-320-H2AD SNR L-8408-76T)

The workshop made -a test run on ground:

the engine rpm drop was 120-130 rpm.-
The different pressure in the cylinders was 1.)80/78; 2.)80/79; 3.)80/78; 4.)80/77.-
The intake tube of the Cylinder No 3 was leaky -it was renewed.-
The timing of the ignitions examined and adjusted.-
The air intake filter was dirty and cleaned -
The following ground check did show no problems: rpm drop 70-80 rpm max rpm 2320 rpm.

After this the aircraft made a take off and crashed immediately in the ground, as the engine lost power. The investigation did show, that the screw (Fig 1-14 D-3000 Magneto manual ) was loose and so the cam breaker could turn on the cone.

The problem here is that the mechanic did not order a new cam screw and re-used the old one. You loosen this screw when you adjust adjust internal timing. Continental says to replace it with a new one.

Continental (Bendix) has addressed each one of these areas in their maintenance manual. Personally, if the mechanic did not have the maintnenance manual for the D3000 in hand I would not let him touch the magneto.

There is an interesting discussion of this screw and the problems associated with installing it that I highly recommend be read by anyone working on this magneto. http://www.aaib.dft.gov.uk/cms_resources/Mooney%20Aircraft%20Corporation%20M20J,%20G-EKMW%2011-06.pdf