Sterba Prop Installation Instructions

NOTE: During Installation, please treat the Urethane Leading Edge carefully, it takes a few weeks to fully cure!

Because of the slight differences in prop hubs and spinner bulkheads, it may be necessary to lightly file out one or more bolt holes in the propeller. It may also be necessary to radius the large prop hub hole to get a proper fit on the engine. This can be accomplished with a small round file and abrasive paper. Some spinner bulkheads are designed to "crush" against the rear of the propeller upon the first installation of the prop, bulkhead and hub. At this time it is also imperative to make sure that your bolt drive bushings are not able to "climb" into the propeller because the bushings are loose and the holes in the prop for the bushings are too deep. This has caused a problem in the past. It may be necessary to have spacers in the bushings holes so that this can't happen. This is important!

Propeller bolts should always be tightened evenly in a cross pattern gradually tightening all to an even torque. The standard value on 5/16 nuts is 10 to 12 ft/lbs., and the standard value on 3/8 is 15 to 18 ft/lbs. Even if torqued to an even value with a torque wrench, the actual value will change through the year as the wood continues to change thickness according to the weather and the season. It should be checked several times a year for tightness, especially if the aircraft sits for any length of time. That's how wood is!

The propeller should always be "tracked" upon each installation and whenever unusual vibration is noticed. This can be accomplished with a tape measure held to a fixed part of the aircraft and measurements made to each blade tip, or by positioning an object near the sweep of the blades. Track should be within 1/8" between the two blades. If not, try loosening all the prop bolts then re-torquing again giving first preference to one side of the other in order to correct to 1/8".

All screws and washers used on the spinner should be the same length to maintain the balance of the spinner and the prop. Any repair made to one side of the spinner must be matched by a similar patch on the other side. Front spinner bulkheads tend to crack so it may be necessary to reinforce them during initial assembly. The spinner itself must not wobble too much and can be tracked with the use of a grease pencil and a yardstick while the engine is at idle. Be careful! Elongating the front bulkhead boltholes and shifting the bulkhead will put the spinner into correct alignment. Aerodynamically, it doesn't seem necessary to have a real close fit between the prop and the spinner so it is better to have a little too much room than not enough to avoid damage to the prop finish.