Dennis, The Continental Engine Overhaul Manual for the C87, 85, 90 & O-200 Dated February 1980 gives the tightening torque for the 3/8-24 Propeller Hub Bolts as 200 - 220 in-lbs or 16.7 to 18.3 ft-lbs. The Alon Service Manual gives tightening torque for the Prop Hub Bolts as 300 - 360 in-lbs or 25 - 30 ft-lbs. Obviously, there is a conflict there. I don't know why the numbers aren't the same. I torque my prop bolts to 28 ft-lbs which is in the middle of the range given in the Alon manual. I too have noticed that the washers under the bolt heads get deformed slightly. I believe that this is due to the fact that the bolt holes in the prop hub have somewhat of a curved radius on them (like they are slightly countersunk). I think that when you torque the prop bolts, the washers deform slightly to fill this void. I don't think that the washers are getting deformed after the bolts are torqued. Given the way that the prop hub bolt holes are shaped, and given the fact that the washers are very thin steel (they are standard thickness AN washers, but they are still relatively thin), I think that it is a good thing that the washers deform to take up the space. If you don't tighten the bolts enough to deform the washers, then all the pressure that would be exerted to clamp the prop hub to the engine flange would be the amount of pressure that that those relatively thin washers can exert without deforming. I don't think that that amount of pressure is enough to load the bolts properly. I check the torque on my prop bolts at every annual, and have never found the bolts to be loose such that they tighten further when I apply 28 ft-lbs. If the washers were deforming in use, and not when the bolts are initially torqued, then I think that the torque on the bolts would "relax" as the washers deformed over time, and that when I rechecked them, they would need more tightening to bring them back up to 28 ft-lbs. I do install new washers any time I remove the bolts, and I install new bolts every third time I that I remove the prop. Changing the bolts is not required, but I do it anyhow. As a side note - If you are using a break-away type torque wrench to tighten these bolts, make sure that has been properly calibrated. When I was in the USAF one of our jobs in the instrument shop was to calibrate torque wrenches. I would say that about half of the break away torque wrenches that we checked were out of spec, and about 25% of those could not be calibrated and were junked. For my money, on critical applications, I'll take a bending beam type torque wrench any day. Harder to use, but doesn't lose it's calibration. As always, I may not know what I'm talking about, so don't take any of this to the bank. Or to the hangar, as the case may be. Best Regards,
Wayne DelRossi Alon Aircoupe N5618F "Life begins at 50...... knots." **************Looking for a car that's sporty, fun and fits in your budget? Read reviews on AOL Autos. (http://autos.aol.com/cars-Volkswagen-Jetta-2009/expert-review?ncid=aolaut00030000000007 )
