the port. If I’m cleaning a guide, I normally push the valve into the cylinder and pull it out of the bottom spark plug hole to clean the valve stem too.” Kuti said he does not deploy the rope trick any longer, opt- ing to pressurize the cylinder with air while the piston is at the bottom dead center (BDC). Reamer Action Time Sampson removed the spark plugs and fed the rope into place. Driving out the rocker shaft with a brass drift, he re- moved keepers and springs. It was then time to drop the valve. Taking the brass drift, he gently tapped the exhaust valve into the cylinder head. Special reamers like these are just the ticket to clean up the valve guides. Slowly slipping the reamer into the number 6 exhaust guide, the tool moved smoothly for approximately one-half inch, then began to drag. The reaming process is not difficult, but it is imperative to keep the tool aligned so as not to damage the valve guide. Where Kuti held the valve with a thin line, Sampson used mechanical fingers in the top spark plug hole to maneuver the exhaust valve back into place. With a flashlight in the bottom spark plug hole; the valve was visible and could be manipulated toward the guide.
Once in place, a magnet was inserted into the exhaust guide, contacting the tip of the valve stem, and the valve was slowly pulled back into place. Next, the valve springs and keepers were replaced, topped off with a rotocoil or up- per retainer, depending on your setup. In aircraft maintenance, the line between preventative and unscheduled maintenance can often blur. While he had the time and the tooling available, Sampson opted to apply the reamer to all of the remaining cylinders’ exhaust valve guides as a precaution. What causes exhaust valves to stick? “Heat is the primary cause of valve sticking,” according to AVweb. “High temperatures in the exhaust valve guide oxidize oil and form carbon deposits on the valve guide, and these deposits can cause the valve to stick. The most frequent reason for elevated valve temperatures is valve leakage.” Richard Scarbrough is a US Navy Veteran, A&P Mechanic, and Embry-Riddle Aeronautical University alumni. His experience ranges from general and corporate aviation to helicopters, business jets, and commercial airliners. Former owner of a 145 repair station, he currently has an aerospace product management role and is a member of the T-C-Alliance. Follow him on X (Twitter) at @RScarCo.
“High temperatures in the exhaust valve guide oxidize oil and form carbon deposits on the valve guide, and these deposits can cause the valve to stick.
One by one, the temperature readout for each cylinder measured 150 to 160 degrees Fahrenheit.
(bottom) Sampson removed the spark plugs and fed the rope into place.
11 Aircraft For Sale | July 2024 12 Aircraft For Sale | July 2024
Made with FlippingBook interactive PDF creator