by Kristin Winter » Wed Feb 20, 2013 4:34 am
Mike Busch is an interesting cat. I like a lot of what he says, but some you have to take with a grain of salt. Mike is a Cessna, Cirrus, and Continential guy. I take his recommendations and apply them to Lycomings rather carefully. He on the other hand, has no problem extending his wisdom to all things aeronautical.
I agree with him on TBO, with a caveat. We don't have a sure fire way to detect when the lower end is about to give out. About 25 years ago, a Comanche 250 owner brought his plane in for an annual inspection into the shop. I was director of ops over the shop and the charter operation. We had done the last oil change, about 40-50 hours before. The filter and analysis were clean at that time. At the annual, the suction screen was full of bearing metal. One of the main bearings had apparently slipped just enough to shut off some of the oil to the bearing. Eventually, with enough hours, that will happen to any engine. Will you catch it in time? This owner barely did as the crank was able to be saved by going .010 undersized on the journals. A few more hours, and he may have had a mailbox post instead of a crankshaft. A few hours beyond that, and the engine might have seized over Lake Michigan.
I will probably run Maggie's engines over TBO if everything seems happy. I do the 400 hour valve inspections. I do oil analysis and cut the filter and pull the suction screen at every oil change. I borescope the cylinders at annual. How far over will I go, I am not sure. If they were new, first run engines, I wouldn't hesitate to go over 3,000 hours. With new I might go as high as 3,500, as I know that it has been done successfully before. I am less interested in being the test pilot that sets a new record.
Kristin