Powerplant
Spark plug torque
The value of proper torque can be understood by reference to an engine spark plug. Lycoming and Continental, as well as other engine manufacturers, specify spark plug installation torque using a new or annealed (made soft) spark plug gasket and antiseize compound applied sparingly to the plug threads. Champion spark plug gaskets are soft copper and can be annealed for reuse by heating to red-hot and immediately submerging in cold water. If the gaskets cannot be annealed, new ones should be installed prior to installation.
If the torque is soft, or below the specifications, combustion gases may escape between the spark plug gasket-to-head seal. Since these gases are extremely hot, very corrosive, and can attain pressures of up to 800 psi, erosion of the aluminum cylinder head or the copper seal gasket quickly occurs. This further softens the torque. Under extreme cases the spark plug threads or the steel Heli-Coil thread insert installed in the aluminum cylinder head are weakened and the spark plug may blow completely out of the cylinder.
If the torque applied to the spark plug is above the specifications (excessive preload), then the load imposed on the threads in the cylinder head or the threads of the spark plug may damage the cylinder head.
The fouled-plug test
You say you don't know how to determine which spark plug is fouled? Simple. After taxiing back from the run-up area with a rough or out-of-limits mag drop, find a safe place to park and shut down the engine. Remove enough cowling (it's allowed under PM), or open the cowling to the extent that the exhaust pipes are accessible.
After the engine has cooled off for 15 minutes, run the engine at 1,000 to 1,200 rpm on the bad magneto (the one with the excessive drop) for one and a half minutes. Then shut down the engine with the mixture and determine which exhaust pipe is cold. Most mechanics I know just dip their finger in water and then quickly touch each exhaust pipe in succession. It will be obvious which cylinder isn't firing.
By following the spark plug wires from the cold cylinder back to the magneto that was providing ignition to the engine (remember that when the mag switch is on L, you're testing [using] the left mag, and vice versa) you'll be able to determine whether the fouled plug is the top or bottom plug. Change the plug, install the plug lead, reinstall the cowl, perform a preflight test, and if the mag drop is gone, you're on your way.
This is all perfectly legal as long as you create an entry for the maintenance records detailing your efforts before you take off. No, you don't need to have the maintenance logbooks to do this. If you create a record of the PM task you did in accordance with FAR 43.9, you may enter it into the logbook at a later date.
WARM AIR, CARB ICE
AOPA epilot training tip: http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2006.pdf
As the snows of winter vanish from airport landscapes, pilots cheer the disappearance of snowdrift hazards, icy patches on runways, and morning frost on aircraft. But another ice hazard becomes more likely when temperatures climb.
Think of it as the ice of summer, but whatever you do, don't ignore carburetor icing as a warm-weather flying hazard. Every year, carb ice foils some unwary pilots, even when temperatures soar toward 100 degrees Fahrenheit! The problem, explains Chapter 6 of the "Pilot's Handbook of Aeronautical Knowledge" (6-7) ( http://www.aopa.org/epilot/redir.cfm?adid=18795 ), is "the effect of fuel vaporization and the decrease in air pressure in the venturi, which causes a sharp temperature drop in the carburetor. If water vapor in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the throttle valve." Scrutinize the chart accompanying the chapter; it depicts temperature-humidity combinations that pose the highest carb icing risks.
"Obviously, awareness of carb icing is especially important in the training environment, in which much time is spent practicing low-throttle exercises such as flight at minimum controllable airspeed, landing approaches, and simulated engine failure emergencies," noted the Aug. 22, 2003, Training Tip ( http://www.aopa.org/members/files/pilot/epilot/ft/2002/020823epilot.html?WT.mc_id=100326eflight&WT.mc_sect=tips ) that also discussed proper technique for applying carb heat.
Pilots must also understand a drawback of carb heat use: It robs the engine of power. So remove carb heat fully and promptly when adding throttle, for instance when commencing a go-around. How much power does carb heat sap from the engine? Next time you operate the carb heat during an engine run-up, or when reducing power to begin a practice maneuver, note the specific rpm drop. It can be considerable.
What else can you do in flight to improve your carb-ice risk awareness? Apply carb heat on occasion during cruise flight. Note if your power setting is higher after you remove it.
Another tip: "Develop the habit of keeping an eye on the outside air temperature along with rpm or manifold pressure gauges, while tuning the ear to engine smoothness," wrote Dan Namowitz in the October 2009 Flight Training "Accident Analysis" column ( http://flighttraining.aopa.org/magazine/2009/October/200910_Departments_Accident_Analysis.html?WT.mc_id=100326eflight&WT.mc_sect=tips ). Every detail matters because "carb heat may not save the day if added too late or too low."
Oil line and connector fabrication