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Originally Posted by Jim Burns
We had the props on our Aztec balanced this summer. The man that did it is
a long time friend of mine that runs an aerial application business (crop
dusting). He and his family have been in it all their lives they are all
CFIs A&P/Is. They own many airplanes and many helicopters. Anyway, they
know what they are talking about. They balance props on round engines, flat
engines, turbines, and blades on both shafts of the helicopters.
The biggest problem he told me that he's had balancing props/engines,
including round engines, is when the engine mounts are worn. Nothing you
do, no amount of weight, will balance a prop attached to an engine that has
bad mounts. Even if you don't think they look worn or burned, they can
loose their rigidity and become spongy. I replaced the mounts on our
right IO540 in less than 3 hours. Mounts from AirSuppliers.com cost me
$270.
Another thing to look for is to see if any weight had been added to the back
side of the ring gear/flywheel. You may be adding weight to the prop that
is counter-acting a weight that has already been added.
YMMV
Jim
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Jim,
Thank you.
I did not see any weights on the ring gear, but I also did not make a point of looking closely. We thought it was symmetric and paid no attention to its orientation as we placed it on the engine and in the Bendix teeth. We will look more closely.
Replacing the mounts would insure that they are all the same with regards to stiffness and dampening effects. The current ones have about 600 hours on them. The io540 is a heavy engine cantilevered by 4 mounts. There could be some asymmetrical stiffness between the top and bottom mounts just from supporting that weight for 4 years. One of the mounts may have had difference physical properties when new. Seems like one of the things to do.
Are some mounts better than others? One would not expect the current ones to fail in 4 years and 600 hours. Picking the better quality mounts may be wise.
What about the 1500 rpm resonance vibration? Is any of this crank shaft related? The biggest concern is engine failure in flight. That can make for a bad day.
Allan