The hub is supplied engine oil through an oil delivery tube via the prop governor and blade pitch is controlled by changing the oil amount (under pressure) in a piston assembly. The oil delivery tube has paper gaskets that seal its connection to the flange and 2 oil seals work in conjunction with the piston assembly. Allowing for blade rotation are 4 large bearings (2 inner & 2 outer) along with their supporting races; the other 2 seals are in this region (inside the large "toothed" nuts on each side of the hub).
Bearings should be lubricated around every 100 hrs of operation. The seals and gasket(s) will communicate when they are in need of attention.
- If you notice oil dripping from the rear of the hub assembly, you may want to check the oil delivery tube gasket(s). The initial leakage may be stopped by a slight tightening of this tube.
- If you are getting more than a slight "peppering" of oil on your shutters and/or oil is dripping from the prop hub "skull" cap, your piston assembly seals may be in need of attention. Some initial leakage can be stopped by cleaning and reseating the piston assembly (as long as the piston assembly is in good condition) but the seals do harden with time.
- Excessive grease streaking on the prop blades, fuselage and the right wing or excessive "peppering" may be an indication that the bearing seals are worn.
Another area of interest is prop vibration. Most planes experience a bit of vibration, how much is OK or acceptable is subjective. A good indicator is the pitot tube and/or the wing tips. If the wing tips and/or pitot tube are moving around quite a bit, your prop may need attention. Simply said, the propís static and dynamic balancing should be checked along with the tracking and blade angle. Some of this should be left to licensed professionals, but you can easily check and adjust the blade angles. Note the diagrams below. The blade angle should be set at 14.5 degrees at a length equal to 1 meter from the center of the hub when the system is level and the blades are placed in a flattened state. I found it hard to make the measurement from this location due to triangulation and no place to secure the tape measure. I found a tape measure "hook point" by placing the end between the teeth of the opposite side bearing retainer - this lengthens the measurement to 1.10 meters or 43 5/16 inches (note diagrams) or even easier, one can mark of 7 7/8 inches from the end of the prop. I mark the rear of the prop with a grease pencil and then I can make my angle measurement with a digital level or appropriate instrument taking into account the sitting angle of the plane (angle of incidence).
