Hello all, Want to share a problem I am having and see if there is any cures or ideas for cures.
I have a RV-4 with a Lycoming O-320 160 hp engine. Prop is a Sensenich fixed pitch metal prop. The prop is a model number 70cm7s9-0-81 and in the paperwork for it, it states to avoid operations above 2600 rpm. My engine mount is a dynafocal type mount and also worth noting is the plan was first flown in 2003 and only has about 240 hours total time BUT.... the engine is a first run engine put in service in 1986 on a Cessna 172 and had 1971 hours total time at the time it was removed from the Cessna and put on the RV-4 in 2003. So it has not been overhauled and now has over 2200 hours since new. Compression checks on cylinders at last oil change was 70#, 75#, 75#, 71#, over 80.
Okay the problem......
When I start the engine and run it at idle it is reasonably smooth, in other words there is some vibration but not enough to bother me. Run the engine up around 900 RPM up to about 1600 RPM and the vibration is quite pronounced. Above that rpm and the vibration is again not too bad, it is there but just not that bad. At RPMs close to 2500-2600 it is reasonably smooth.
I took the plane to a mechanic who put on equipment to do a dynamic balance and after the 1st runup the computer called for weights placed at a certain degree, and the mechanic used washers on the spinner for this, then we ran a 2nd runup and the computer would again call for more weight at a different degree, so more weight added and a 3rd runup with the same results... more weight needed in a new position. During this process as I did the runups, the low rpm vibrations worsened each time more weight was added. In frustrationwe took off all the weights and put the cowling back on and said forget it.
On two occasions people have told me my prop does not appear to be tracking in plane. One of those times was by a aerobatic pilot who was flying extremely close off my right wing, and the other time was a pilot who was standing next to the plane while the engine was at fast idle on the ground. The mechanic tested the prop by putting a dab of paint on the tips of the prop - a different color dab on each blade - and had me run the engine while he stood behind the prop and touched the tips of the blades with a piece of tape on a stick and then looking at the tear in the tape and color transfers. He also did another test where he put a ladder in front of the prop and rotated the blade to a fixed position and measured the distance to the ladder and then turned the prop to the other blade and measured the distance again and in both tests he claimed it was in perfect track.
I did not build the plane, I bought it from the builder with about 150 hours on it. In the planes log book there is notes about these vibrations from as early as the first flight and all it appears he did to resolve it was to remove the prop and reinstall 180 degrees to where it first was.
The engine does not seem to be sagging on the mount and I can not see any cracks in the mounts or any signs of the mount moving on the firewall, but my eyes might not be trained well enough to spot a problem on these areas..... The rubber cushions between the engine and mount look to be in good shape with no obvious rotting or cracking. I have not checked anything with a torque wrench - I don't even own one... - so I can not comment on that.
The mags are slicks and turning one mag or the other off seems to have no effect other than the drop in RPM.
The only other thing I can think of worth mentioning is there is a noise coming from the firewall area when taxiing over bumpy ground or even on smooth ground if I taxi at the rpms the vibration is bad. I had the cowling off a few weeks ago and had someone bounce the plane up and down while I listened and looked at the firewall and there is a noise coming from a aluminum plate that the starters relay is bolted to and the plate is riveted to the firewall, a few of those rivets are loosened up and was making a noise as the plane was bounced. I assume this is what I hear when I taxi, although I believe I have heard the noise on climbout after taking off.....
So.... sorry for the long post, but any ideas or hints or whatever would be appreciated.
I have a RV-4 with a Lycoming O-320 160 hp engine. Prop is a Sensenich fixed pitch metal prop. The prop is a model number 70cm7s9-0-81 and in the paperwork for it, it states to avoid operations above 2600 rpm. My engine mount is a dynafocal type mount and also worth noting is the plan was first flown in 2003 and only has about 240 hours total time BUT.... the engine is a first run engine put in service in 1986 on a Cessna 172 and had 1971 hours total time at the time it was removed from the Cessna and put on the RV-4 in 2003. So it has not been overhauled and now has over 2200 hours since new. Compression checks on cylinders at last oil change was 70#, 75#, 75#, 71#, over 80.
Okay the problem......
When I start the engine and run it at idle it is reasonably smooth, in other words there is some vibration but not enough to bother me. Run the engine up around 900 RPM up to about 1600 RPM and the vibration is quite pronounced. Above that rpm and the vibration is again not too bad, it is there but just not that bad. At RPMs close to 2500-2600 it is reasonably smooth.
I took the plane to a mechanic who put on equipment to do a dynamic balance and after the 1st runup the computer called for weights placed at a certain degree, and the mechanic used washers on the spinner for this, then we ran a 2nd runup and the computer would again call for more weight at a different degree, so more weight added and a 3rd runup with the same results... more weight needed in a new position. During this process as I did the runups, the low rpm vibrations worsened each time more weight was added. In frustrationwe took off all the weights and put the cowling back on and said forget it.
On two occasions people have told me my prop does not appear to be tracking in plane. One of those times was by a aerobatic pilot who was flying extremely close off my right wing, and the other time was a pilot who was standing next to the plane while the engine was at fast idle on the ground. The mechanic tested the prop by putting a dab of paint on the tips of the prop - a different color dab on each blade - and had me run the engine while he stood behind the prop and touched the tips of the blades with a piece of tape on a stick and then looking at the tear in the tape and color transfers. He also did another test where he put a ladder in front of the prop and rotated the blade to a fixed position and measured the distance to the ladder and then turned the prop to the other blade and measured the distance again and in both tests he claimed it was in perfect track.
I did not build the plane, I bought it from the builder with about 150 hours on it. In the planes log book there is notes about these vibrations from as early as the first flight and all it appears he did to resolve it was to remove the prop and reinstall 180 degrees to where it first was.
The engine does not seem to be sagging on the mount and I can not see any cracks in the mounts or any signs of the mount moving on the firewall, but my eyes might not be trained well enough to spot a problem on these areas..... The rubber cushions between the engine and mount look to be in good shape with no obvious rotting or cracking. I have not checked anything with a torque wrench - I don't even own one... - so I can not comment on that.
The mags are slicks and turning one mag or the other off seems to have no effect other than the drop in RPM.
The only other thing I can think of worth mentioning is there is a noise coming from the firewall area when taxiing over bumpy ground or even on smooth ground if I taxi at the rpms the vibration is bad. I had the cowling off a few weeks ago and had someone bounce the plane up and down while I listened and looked at the firewall and there is a noise coming from a aluminum plate that the starters relay is bolted to and the plate is riveted to the firewall, a few of those rivets are loosened up and was making a noise as the plane was bounced. I assume this is what I hear when I taxi, although I believe I have heard the noise on climbout after taking off.....
So.... sorry for the long post, but any ideas or hints or whatever would be appreciated.
