bmcconnaha Posted September 19, 2021 Report Share Posted September 19, 2021 I installed a new engine in my J. Ever since the install, the vibration of the left panel has become more evident. I don’t feel like the plane has an excessive amount of vibration, but the panel shakes more now than it did before. I had the shock mounts replaced, made a little difference, but it still has some vibration at certain RPMs. Prop has been dynamically balanced. Made it slightly better, but still there. Anything else I can check? Or do? I believe he balanced it at 2300, I’m leaning with having it rebalanced to 2450-2600. I fly high and that’s where I spend the most time. The panel still has the original 6 pack, including the century AI and slaved HSI. I assume the weight on the panel isn’t helping things? thanks! Bryan Quote Link to comment Share on other sites More sharing options...
carusoam Posted September 19, 2021 Report Share Posted September 19, 2021 New vibration sources can be found coming from anywhere… Where they get noticed… might not be the cause… Making them go away using fancy techniques may be trying to hide the more important issue… Note for BMc… I’m not implying You have gone about this in the wrong direction…. But I know a guy… Example: My 65C was showing bubbles appearing in the compass mounted on the center post…. And they were shaking around a lot…. Normally, there aren’t any bubbles in the compass… Turns out…. Something was going wrong with the engine mount. So… be on the look out for other signs of the different vibration appearing… compass, and the other side of the instrument panel… Then be on the look out for things that are allowing the vibrations to get there… Some people have reported engine mounts that had failed allowing metal to metal contact… they looked OK until much closer inspection… My C’s challenge was some broken welds on the engine mount that led to three bolts holding the engine in place, in stead of four… The rubber mounts are often called isolators… if a rubber mount fails to isolate, vibrations can be transmitted through it… Probably easiest enough to check on the rubber isolators on that section of the panel… to see what is keeping one of them from working properly… There might be a proper torque on those things to keep from over or under tightening…. Then check to see if the prop is somehow in contact with the lower cowling, a serious sign of a broken engine mount weld…. PP thoughts only, not a mechanic… Good luck with the hunt… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
bmcconnaha Posted September 19, 2021 Author Report Share Posted September 19, 2021 5 minutes ago, carusoam said: New vibration sources can be found coming from anywhere… Where they get noticed… might not be the cause… Making them go away using fancy techniques may be trying to hide the more important issue… Note for BMc… I’m not implying You have gone about this in the wrong direction…. But I know a guy… Example: My 65C was showing bubbles appearing in the compass mounted on the center post…. And they were shaking around a lot…. Normally, there aren’t any bubbles in the compass… Turns out…. Something was going wrong with the engine mount. So… be on the look out for other signs of the different vibration appearing… compass, and the other side of the instrument panel… Then be on the look out for things that are allowing the vibrations to get there… Some people have reported engine mounts that had failed allowing metal to metal contact… they looked OK until much closer inspection… My C’s challenge was some broken welds on the engine mount that led to three bolts holding the engine in place, in stead of four… The rubber mounts are often called isolators… if a rubber mount fails to isolate, vibrations can be transmitted through it… Probably easiest enough to check on the rubber isolators on that section of the panel… to see what is keeping one of them from working properly… There might be a proper torque on those things to keep from over or under tightening…. Then check to see if the prop is somehow in contact with the lower cowling, a serious sign of a broken engine mount weld…. PP thoughts only, not a mechanic… Good luck with the hunt… Best regards, -a- Well, engine mount was OH 75 hours ago, new engine mounts as well…. prop def is not in contact with the cowl….. good point on the rubber isolators torque tho… maybe someone can chime in with the correct torque, and I can check that. thanks! 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted September 19, 2021 Report Share Posted September 19, 2021 Oddly… The Lord company supplies rubber donuts for three parts of the Mooney… 1) Engine mounts 2) Gear donuts 3) Instrument panel mounts… See if the lord company has any installation instructions to go with their panel mounts… they may have a torque value clearly mentioned somewhere… PP thoughts only, -a- 1 Quote Link to comment Share on other sites More sharing options...
OR75 Posted September 19, 2021 Report Share Posted September 19, 2021 How many hours on the engine ? The counterweights may need a bit of time to sit then dynamic balancing Quote Link to comment Share on other sites More sharing options...
bmcconnaha Posted September 19, 2021 Author Report Share Posted September 19, 2021 12 minutes ago, OR75 said: How many hours on the engine ? The counterweights may need a bit of time to sit then dynamic balancing The 390 has about 80 now Quote Link to comment Share on other sites More sharing options...
OR75 Posted September 19, 2021 Report Share Posted September 19, 2021 80 hours should be more than sufficient 1 Quote Link to comment Share on other sites More sharing options...
PT20J Posted September 19, 2021 Report Share Posted September 19, 2021 How is the vibration at 2300? If you’re happy with it there, I’d rebalance at the rpm you fly. I assume it was a new prop for the 390 STC so it should have been statically balanced. I know an A&P who claims that removing and remounting the prop 180 deg sometimes makes it smoother. Skip 1 Quote Link to comment Share on other sites More sharing options...
Raymond J1 Posted September 19, 2021 Report Share Posted September 19, 2021 When a two-bladed propeller is mounted on a flat four, it is known that the explosions of the cylinders are never coordinated with the horizontal position of the propeller. It is one of the sources of vibration and sometimes we forget this detail. Quote Link to comment Share on other sites More sharing options...
bmcconnaha Posted September 19, 2021 Author Report Share Posted September 19, 2021 2 hours ago, Raymond J said: When a two-bladed propeller is mounted on a flat four, it is known that the explosions of the cylinders are never coordinated with the horizontal position of the propeller. It is one of the sources of vibration and sometimes we forget this detail. That seems to go against the common theme that three blades mounted to a 4 cylinder vibrate more than a two blade. In fact, of the two propellers allowed with the 390 stc, the two blade has no rpm restriction. If I could have gone MT tho, I would have. Quote Link to comment Share on other sites More sharing options...
Guest Posted September 20, 2021 Report Share Posted September 20, 2021 Way back there was an SB M20-206 which allowed conversion of the A1B6D to an A3B6D by relocation of the crankshaft drive bushings. I wonder if the same issue exists in the 390? https://www.mooney.com/wp-content/uploads/2020/12/SBM20-206.pdf Quote Link to comment Share on other sites More sharing options...
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