WHAT’S WRONG WITH MY PROP??? (Prop indexing, prop clocking, prop installation)
As I was about to buckle in after doing the outside preflight, one of the group came up to me and said that my prop wasn’t installed properly. Looking at the other 27 (I counted a third time) Baby Beeches, I saw only one other whose prop was at Noon and 6; all the others were at about 1 and 7 (as viewed from the pilot’s seat). So, what’s with what direction my prop points in?
Larry Perry
BOB STEWARD, A&P-IA:
There are 3 possible orientations of the prop (6 bolts, 2 blades), so even though it can go on 6 ways, only 3 installations actually LOOK different. Your prop blades are marked #1 and #2. All prop and cylinder positions in this note are as described from the pilot’s seat. Correct prop positioning is important to minimize the vibrations in the crankshaft and propeller, as engineered by the engine and prop manufacturers.
Here is the way to tell whether the prop is correctly installed:
Make sure the mags are OFF and the mixture is in idle cut off, and then pull the prop through. Feel for the compression indicating TDC and listen for a sharp CLICK when the compression is at its maximum. This should occur at TDC, and with the descending blade at about 7 O’clock as you face the prop. Since the prop could be put on with either blade in he 7 O’clock position, and the engine can be firing any of the 4 cylinders when you hear the “click”, you have to pull the spinner and the spark plug from #1 cylinder so that youc an read the blade markings (either “1” or “2”) and feel for compression on the #1 cylinder as the blade reaches the position where the engine fires.
If the mag fires when the prop is in the 1-and-7 O’clock orientation, with the #1 blade at 7 O’clock, then it is on “right”. If it’s at 3-9 or 11-5, then it’s installed wrong (60 degrees/one bolt hole off one way or the other, plus the possibility of incorrect #1 blade orientation/180 degrees off). If wrong, you’ll need to pull the spinner and clip the safety wire, untorque the prop bolts, and reposition the prop on the crank hub so that the #1 blade is in the 7 O’clock position when the #1 cylinder is at TDC on compression. Then correctly re-torque the prop, safety wire the bolts, and install the spinner. Have the A&P who supervised you, countersign your maintenance log entry, and go test-fly.
If you have previously had the engine and prop dynamically balanced, you need to TAKE OFF ALL THE WASHERS, and let them re-balance it again later. You have just changed the relationship of the parts (prop,spinner, etc.), and the “balance” might now be an imbalance. It would almost certainly be worse with the washers, than without them.
EDITOR’S NOTE:
While you are doing all this, make sure that you check for the index marks on your spinner and backplate, to make certain that they, too, are reinstalled in the correct orientation. If you have a constant-speed prop, follow the instructions and lubricate it properly (with the grease called for on the label that is on the prop), so that it will have the correct grease load when you have the prop-rebalanced. On engines subject to Lycoming AD 98-02-08, verify that the engine log shows compliance with this AD, before the prop gets reinstalled. All our affected aircraft should have long since complied.
Here is an excerpt from this AD that helps define applicability:
98-02-08 Textron Lycoming: Amendment 39-10291. Docket 94-ANE-44.
Applicability: Textron Lycoming 320 series limited to 160 horsepower, and 360 series, four cylinder reciprocating engines with fixed pitch propellers; except for the following installed in helicopters or with solid crankshafts: HO-360 series, HIO-360 series, LHIO-360 series, VO-360 series, and IVO-360 series, and Models O-320-B2C, O-360-J2A, AEIO-360-B4A, O-360-A4A, -A4G, -A4J, -A4K, -A4M, and -C4F. In addition, engines with crankshafts containing “PID” stamped on the outside diameter of the propeller flange are exempt from the inspection requirements of this AD. The affected engines are installed on but not limited to reciprocating engine powered aircraft manufactured by Cessna, Piper, Beech, American Aircraft Corporation, Grumman American Aviation, Mooney, Augustair Inc., Maule Aerospace Technology Corporation, Great Lakes Aircraft Co., and Commander Aircraft Co.