Prop Balancing

[alaskan99669]

I paid $150 two months ago here in Alaska. Here's the story:
I filed a fairly large rock nick out of my prop and soon after noticed a a substantial vibration at around 2100 RPM's. Not enough to feel it in my seat, but enough that it made it hard to read the GPS that extrudes from the panel on an adjustable mount. I mentioned to my mechanic that I thought a prop balance was in order and he just shrugged his shoulders and said it may be a good place to start and he gave me the number of the guy with the equipment. The day of the appointment I did a few touch and go's and could not reproduce the vibration. So I flew to the guys shop and $150 later (2 hours labor x $75) my prop was balanced. I did not have to remove the cowling. He simply put some reflective tape on the back of the prop (as he mentioned that was actually referred to as the "face" of the prop) and then he secured with duct tape the probe and wires that would measure the vibration. Another probe was secured to near the front of the engine and the wires and computer were ran inside the cabin. He would have me fire it up and asked me to run it up to cruise RPM (2450) which is impossible with a fixed pitch propeller, so we settled for WAO throttle which was about 2350 RPM with my 80x43 prop. He said initial reading were 0.13 which was not very bad and considers anything under 0.05 acceptable. The computer told him were to add weight and if there was not a screw on the spinner at that point he would pull out a chart that told him on which of the nearest screws to add how much weight. Then we would repeat the entire procedure each time removing the just installed weights and putting on weight in the new location the computer suggested. We did this four times and that made the measurement 0.01.

A good portion of the time charged was putting my plane on a trailer since I was on floats at the time and then securing it to said trailer. Flights since then have not shown any noticeable improvements, but like the guy said, it was not that bad to begin with. The earlier vibration could probably be explained by a fouled plug or something similar at the time.