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This list of operational tips is gathered from personal experiences and from various Airmaster folks including the former owner of N25485, and Gar Williams, an Airmaster guru who restored N25485 in the early 70s.
Airmasters have tight cowlings. The C-165 cowl closes around a ring that's attached the engine rocker box covers, and the cowl is secured by bolts along the bottom. Do not overtighten the cowling bolts, because the engine expands as it heats up during flight. If the bolts are overtightened then the cowl will probably crack and rub when in flight. When cold, you should be able to rotate the cowling back and forth several degrees.
Airmasters should be upholstered with Bedford cord. My plane had blue seats with gray sidewalls and headliner. Bedford cord is available from dealers of antique car interior fabric such as LeBaron Bonney in Massachusetts. Check out Hemmings Motor News for ads.
The Airmaster interior sidewalls are supposed to be covered with tightened aircraft fabric stretching from the window frames over wooden stringers on the inside of the cabin, and tacked down at the floorboards. My airplane is lacking this interior "cover", and consequently the top layer of Bedford cloth tends to flap in the breeze and provide little resistance to knees, elbows, and cargo accidentally punching out and damaging the exterior fabric.
The brakes take some abuse on the Airmaster because they're the only way to steer on the ground. The brakes are not compatible with the red MIL-5606 brake fluid commonly used in many general aviation aircraft. 5606 will melt the brake seals. Instead use the straw colored automotive DOT3 fluid. Newer style automotive silicon brake fluid is also compatible.
Gar Williams says to avoid completely cleaning the brakes because they need a little bit of lubrication, and the dust provides a small amount of lube. Brakes have been known to lockup after they've been completely cleaned.
Additionally, set up the brakes so that they a little loose. This will keep them from become too sensitive and make it harder to accidentally overheat the brakes and lock them up.
Engine oil is something of a religious subject. A number of people I've talked to have recommended flying Warners engines with straight-weight mineral oil all the time.
Engine oil temperature is a good measure of when a Warner is in need of an overhaul. If the temperature goes above 190, it is likely that too much oil is being blown past sloppy clearances and consequently is picking up lots of engine heat. A bad front thrust bearing will also generate a high oil temperature.
Gar Williams says that with regular use, a fresh engine will go about 14 hours on a quart of oil. If you're not flying regularly then these measurements are somewhat meaningless because so much oil leaks out of Warner engines. When the engine is run out the oil is used at about 4 hours per quart.
Here's some tips on Warner 145 HP engines, which the early Airmasters used. Most of the tips are applicable to the Warner 165 HP.
Pay particular attention to lubricating the magnetos! The bearings must be regularly lubricated. See the 145 HP tips for info.
The Fairchild club publishes a CD-ROM set that includes information on Warner engines. Here's some tips for the 165 engine:
Airmaster blueprints are available from Cessna Aircraft Company for individual parts and assemblies, but Cessna will not provide a full set of drawings. Individual Airmaster owners are also known to have drawings on microfilm, but in most cases the film is bad enough already that it won't yield readable copies.