This month’s Ask a Tech Q&A come from the owner of a Lycoming engine that’s making attention-getting amounts of metal and one from the owner of a Cessna 172 who says neither of his two newer VHF radios will receive unless the airplane is directly over the station. IA Mike Berry addresses the metal in the oil issue, first.
“My Lycoming IO-360 has had high levels of aluminum in oil analysis for some time and we have begun finding some small, tiny, flat nonmagnetic shiny flakes in the oil filter. The metal has a flat, almost foil-like appearance to it.
“There isn’t much of it, but we are concerned. Should we keep sampling or ground the airplane?”
The metal flakes are probably coming from a piston pin plug that is self-destructing. You need to determine which cylinder(s) it’s coming from. The best way to do this is to inspect the cylinder walls with a borescope. (There are so many reasonably priced borescopes now on the market that it makes little sense to pull cylinders as a first reaction anymore.)
Look for marks at 3 or 9 o’clock on the cylinder walls, indicating piston pin problems. Piston pin failure is usually gradual at first and then accelerates rapidly. If you have metal in the filter, you are in the rapid acceleration phase and should therefore ground the airplane. Get a latest copy of Lyc SI 1492. It has a ton of good information on the entire topic and procedures.
The reports seem to crop up from time to time and involve the LW 11775 plugs, as we’ll as the older style P/N 60828 plug. The latter plug is not used much anymore because of its spotty service record. There are three OEM plugs in all that may have been used.
Piston pin plug problems are often symptomatic of other engine problems, such as poor crankshaft/crankcase alignment or excessive connecting rod twist or other geometry problems—all things that can and should (especially as time accumulates) be checked during engine assembly.
If your case is badly warped or poorly machined (with the crank not running to the true geometric centerline of the engine) you can expect other cylinders to show up with the same problems. The best (not the cheapest) solution is to pull all the cylinders and inspect them. If need be, replace all wrist pins with swaged-plug-type wrist pins. If there is any chance of aluminum contamination throughout the engine, check the bearings (the metal contamination will show) and get the oil cooler flushed and checked at at an oil cooler repair service shop.
“My Skyhawk has a Garmin GTN 650 GPS/navcomm and a Garmin GNC 255 VHF navcomm. Neither radio will pick up the VOR station unless the aircraft is within a few miles. Interestingly, I can receive the glideslope without any issues at normal distances. My shop told me this could take a fair amount of troubleshooting. How could that be with newer equipment?”
Larry Anglisano responds: The shop is correct that it could take some effort to fix. That’s because the issue is most likely antenna related. What they’ll likely do is check the signal working from the radios all the way back to the VHF nav antenna, which on your Cessna is installed on top of the vertical tail in the fairing. This dipole antenna is a source of corrosion because water tends to accumulate at the base of the antenna disk and that can gradually deteriorate the signal. There’s also an antenna splitter in the mix, plus a long run of coax cable and some shorter ones behind the panel that might be shorted. Some disassembly of the interior might be required. The glideslope works because there is likely a dedicated glideslope antenna for it.
Got a question for Ask a Tech? Drop us a line with a good description and we’ll help noodle it.
