Engine Balancing and Resonance Vibration Problem

Possibly you might have both a small crankshaft flange runnout, and a
prop out-of-balance situation.

Your measurements are probably in inches per second (ips). If so.
reversing the prop should not give that much change in the optimum
vibration compensation vector. That makes the prop balance as rebuilt
suspicious.

Nevertheless, there is probably an inherent engine imbalance too, which
could come from a number of things besides just flange runnout.

You mentioned both a 750 RPM and a 1500 RPM rough spot. Is the
airframe responding at 12.5 Hz and 25 Hz - or is the response always at
the same frequency? I realize it may be hard to tell the difference.

It isn't the governor, and if the vibration came on suddenly on prop
rebuild - not related to the crankshaft recall.

Originally Posted by nrp

Possibly you might have both a small crankshaft flange runnout, and a
prop out-of-balance situation.

Your measurements are probably in inches per second (ips). If so.
reversing the prop should not give that much change in the optimum
vibration compensation vector. That makes the prop balance as rebuilt
suspicious.

Nevertheless, there is probably an inherent engine imbalance too, which
could come from a number of things besides just flange runnout.

You mentioned both a 750 RPM and a 1500 RPM rough spot. Is the
airframe responding at 12.5 Hz and 25 Hz - or is the response always at
the same frequency? I realize it may be hard to tell the difference.

It isn't the governor, and if the vibration came on suddenly on prop
rebuild - not related to the crankshaft recall.

nrp,

Thank you.

What is the significant of the 25 Hz and 12.5 Hz? There is a vibration that occurs when I reduce engine RPM's. When I approach 1500 RPM's there is a noticeable vibration that peaks at 1500 RPM’s and fall off. The vibration re-accrues at a much lower amplitude as the engine RPM pass through 750. I really do not know the frequency of this resonance vibration.

I talked to Memphis Propeller and I will be sending the prop with the bulk head to them to check static balance and if one of the blades is out of track or angled.

It is nice to rule out the governor.

I am going to try to address this is a logical way and try to through the possibilities quickly so that I can get the bird back in the air. I use it for business and flying is faster and more productive than driving to customer sites.

Allan