Engines are the focus this month as Mike, Paul, and Colleen talk about valve failures, valve springs, burned valves, and more. And of course we had to have a leaning question. Send your questions to podcasts@aopa.org for a chance to be on the show.
Full notes below:
Marius owns a Cessna 172XP that routinely has a rough mag check on run-up. His mechanic is recommending fine-wire spark plugs after finding oil on the plugs. He has since bought them, which set him back more than $1,500. Colleen recently purchased some as well, and thinks they definitely work better.
Nigel wants to get deeper into condition monitoring on his turbonormalized Bonanza, specifically with the turbo system. Mike said that the turbo controllers almost never fail. Waste gates are fairly problematic. Eventually they’ll start to stick, which you can tell by an inability to properly hold manifold pressure. The turbocharger itself is inspected at each annual. The shaft is checked as part of the inspection, and there should be a little wiggle in the radial direction, but none in the axial direction. Also look for blade scrape and cracks in the flange. Paul also recommends checking turbo system oil inlet and outlet check valves.
Michael had a rough-running engine when he reduced power. They pulled the exhaust valve and found the keeper groove of the valve was much smaller than it should have been, and he’s trying to figure out what caused the problem. He’s now finding that the third cylinder is also behaving the same way. Mike thinks it almost looks like it’s been ground down. He suspects an installation problem. The hosts recommend pulling the valve covers and springs to check the rest of the cylinders.
Viatcheslav is wondering about rotator spring failures and how they cause exhaust valve hot spots. He owns two airplanes, one with a Continental O-300 and one with a Continental E-225, neither of which have rotator springs. He's curious how and if his valves rotate without it. The hosts break the news that he does, in fact, own two of the few engines without them. He can continue to watch for hot spots on borescope inspections, and also occasionally lap the valves as a preventative measure.
Reid is concerned about a burned valve on his 172. He leans aggressively, but doesn’t have an engine monitor, and wondered if his leaning led to the burned valve. His only source of information is the stock EGT gauge. Mike did some research on the Alcor gauge. Most of the Alcor gauges aren’t calibrated, and many don’t have temperature references. Some have an adjustable pointer that the pilot can set. Others have a calibration screw. On those, the manual tells you to lean to peak EGT at an altitude where you can get 65 percent power at wide open throttle, and then set the needle to match. Mike thinks the changes Reid is seeing could just be changes in the mechanism of the gauge. It’s not meant to measure absolute EGT. Furthermore, leaning doesn't burn valves. That's most often caused by a bad set.