AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Engine Balancing and Resonance Vibration Problem          AirTalk.org Forum Index -> Owning Airplanes View previous topic :: View next topic   Author Message AllanFuller Guest Posted: Sun Sep 04, 2005 9:12 pm    Post subject: Engine Balancing and Resonance Vibration Problem Plane: Commander 114 - 1976 SN: 14007 Engine: Factor re manufactured - IO-540-T4A5D, tested 12/19/2000, SN L-22326-48A, shipped end of 2000 Propeller: 3 bladed McCauley - just overhauled and balanced - July 200 The current engine was put into service in March 2001 with the existin prop. There were engine vibrations and 13 washers were required t balance the prop as best as could be. I never felt it was as good an smooth as it should be considering it was a new engine. This July 2005 (at the time of my annual) we had the prop overhauled a Memphis Prop at Memphis, Mississippi. They said they balanced the prop It was installed and there was engine/prop vibration. There was also resonance vibration that has a maximum at 1500 rpm and a second lowe magnitude harmonic vibration at 750 rpm. I brought it to a nearb airport for dynamic engine/prop balance. The vibration at 2000 rpm wa close to 1 without weights and they thought there was a problem with bulkhead crack. We dye tested the bulkhead and there was no crack. W flipped the prop 180 degrees to see if that reduced the vibration. I did. This was actually the orientation of the prop when the prop wa removed for the prop overhaul. I brought the plane to another airport for engine balancing. They foun that the vibration was about 0.9 without weights and they were able t bring the vibration down to about 0.12. Probably could have eve improved on that, but the concern was that they needed about 1 washers. We flipped the prop 180 degrees and found that the vibratio without weights was 1.4. Again the vibration could be lowered with th use of about 17 washers in the same direction on the bulkhead (sam direction as the balancing of the new engine in 2001 with 13 washers). There still is this noticeable resonance vibration at 1500 and les intense resonance vibration at 750 rpm. The difference in vibration with the two prop orientations is abou 0.5. That probably suggests that the major vibration is in the engin and not static prop balance. People have suggested that the vibration could be caused by a number o things. The Insight – GEM gauge show even CHT/EGT readings for al cylinders. The engine mounts were new at the time of the engin installation in 2001. The governor was overhauled in 2001 and yello tagged. One observed problem is that prop cycling at 2000 rpm onl produces a 250 rpm drop and one would expect least 300. Before the ne engine and overhauled governor the engine rpm drop during prop cyclin easily went to 300 and lower if I did not stop it by bring the pro forward. Currently, At 2300 rpm the prop cycling drop will go to 50 rpm. Is this an oil pump pressure or governor problem? Could this b the source of the vibration or the resonance vibration at 1500/750? My problem is that I am not sure what to do. It is being suggested tha I could replace the motor mounts at about $360 plus labor (They were ne in 2001 and look good/new.). I could have the governor overhauled fo $500 plus labor. I could have the prop sent back to the prop shop t check their work and re-balance. I will throw money at the problem but I want to make smart choices on where to spend the time and money. The other fear is that the vibrations are in the engine and related t the crank shaft recall. I certainly do not want the engine to fail whe I am IMC or at night even if VFR. The resonance vibration coupled wit the recall has me concerned. Having a doctorate in physics probably ha me overly sensitized to the potential problem. Thanks go to any and all who have comments and suggestions. Allan Fulle -- AllanFuller Back to top Jim Burns Guest Posted: Mon Sep 05, 2005 12:49 am    Post subject: Re: Engine Balancing and Resonance Vibration Problem 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 Back to top nrp Guest Posted: Mon Sep 05, 2005 8:26 pm    Post subject: Re: 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. Back to top toecutter1962@yahoo.com Guest Posted: Mon Sep 05, 2005 11:39 pm    Post subject: Re: Engine Balancing and Resonance Vibration Problem On Sun, 4 Sep 2005 22:12:12 +0100, AllanFuller <AllanFuller.1uuull (AT) news (DOT) aviationbanter.com> wrote: Below snip Quote: The current engine was put into service in March 2001 with the existing prop. There were engine vibrations and 13 washers were required to balance the prop as best as could be. I never felt it was as good and smooth as it should be considering it was a new engine. This would be your first clue. Was the propeller inspected at all at this time? Flush and re-seal? If I needed "13 washers" to balance a prop on a "new" engine, I would verify the propeller static balance at a bare minimum. I'm betting that the prop was balanced, it was the engine with an issue/issues. Quote: This July 2005 (at the time of my annual) we had the prop overhauled at Memphis Prop at Memphis, Mississippi. They said they balanced the prop. It was installed and there was engine/prop vibration. There was also a resonance vibration that has a maximum at 1500 rpm and a second lower magnitude harmonic vibration at 750 rpm. I brought it to a nearby airport for dynamic engine/prop balance. The vibration at 2000 rpm was close to 1 without weights and they thought there was a problem with a bulkhead crack. We dye tested the bulkhead and there was no crack. We flipped the prop 180 degrees to see if that reduced the vibration. It did. This was actually the orientation of the prop when the prop was removed for the prop overhaul. What was the IPS before and after the 180 degree "flip"? Again, if I had overhauled the propeller, I would have removed it, re-verified the static balance and blade angles. Still sounding like an engine problem to me. Quote: I brought the plane to another airport for engine balancing. They found that the vibration was about 0.9 without weights and they were able to bring the vibration down to about 0.12. Probably could have even improved on that, but the concern was that they needed about 13 washers. We flipped the prop 180 degrees and found that the vibration without weights was 1.4. Again the vibration could be lowered with the use of about 17 washers in the same direction on the bulkhead (same direction as the balancing of the new engine in 2001 with 13 washers). There still is this noticeable resonance vibration at 1500 and less intense resonance vibration at 750 rpm. Third time, same story. Again, have the static balance and blade angles on the propeller been verified? Are you aware that manufacturers of prop dy-bal equipment forbid, repeat FORBID adding weight/balancing an engine/prop combo that is over 1.0 IPS? Again, I would guess that the prop is OK, but has it been verified? Quote: The difference in vibration with the two prop orientations is about 0.5. That probably suggests that the major vibration is in the engine and not static prop balance. You've pretty much summed it up in one sentence. Quote: People have suggested that the vibration could be caused by a number of things. The Insight – GEM gauge show even CHT/EGT readings for all cylinders. The engine mounts were new at the time of the engine installation in 2001. The governor was overhauled in 2001 and yellow tagged. One observed problem is that prop cycling at 2000 rpm only produces a 250 rpm drop and one would expect least 300. Before the new engine and overhauled governor the engine rpm drop during prop cycling easily went to 300 and lower if I did not stop it by bring the prop forward. Currently, At 2300 rpm the prop cycling drop will go to 500 rpm. Is this an oil pump pressure or governor problem? Could this be the source of the vibration or the resonance vibration at 1500/750? Find a picture, or do a little digging on the web/in the groups. I know I've described the engine/governor/prop system at least a couple of times over the years. On a single, the governor steps up the oil pressure to "fatten" the pitch to control/reduce RPM. Low/no oil pressure makes the prop go "flat". If the engine/governor was not producing sufficient pressure, you could not reduce engine RPM in flight using the prop control. (emphasis on the period) Cycling the prop on the ground is a feel-good crude ops check, not necessarily anything to be used for diagnosis. Quote: My problem is that I am not sure what to do. It is being suggested that I could replace the motor mounts at about $360 plus labor (They were new in 2001 and look good/new.). I could have the governor overhauled for $500 plus labor. I could have the prop sent back to the prop shop to check their work and re-balance. I will throw money at the problem, but I want to make smart choices on where to spend the time and money. It sure sounds to me like you had the exact same problem when the engine was initially hung/prop installed and the engine mounts replaced w/new-unless I'm not reading things right. Getting the prop condition verified is a no-brainer, it should have been done immediately following the first dy-bal attempt after propeller o-haul. If the governor is working at TO/cruise, I wouldn't worry about it. Quote: The other fear is that the vibrations are in the engine and related to the crank shaft recall. I certainly do not want the engine to fail when I am IMC or at night even if VFR. The resonance vibration coupled with the recall has me concerned. Having a doctorate in physics probably has me overly sensitized to the potential problem. I seriously doubt that the "crank shaft recall" is related to your particular problem, but I do strongly suspect that your engine is the source of your vibration. Using your knowledge in physics (mine is strictly practical, sorry) and my alleged experience in dy-bals, did any of the by-bal dudes mount two transducers on your engine? Standard practice when faced with a shaky weird engine/prop is to mount one 'ducer on the front of the engine and one on the rear of the accessory case. If the propeller imbalance is "making" the vibration, the rear 'ducer should be picking up the vibration 180 degrees out of phase with the front. The way a dynafocal engine mounting system is designed, in theory (in a perfect world), the amplitude of the rear should be close to the amplitude in the front. Reducing the measured IPS on the front, should also reduce the IPS on the back-are you following me? It was very, very, very rare, but I did have a couple of engine/prop combos that I had to play with (trial and error, coupled with experience) that I used an intentional imbalance on the propeller/front (by adding too much weight in the "wrong" spot) to reduce the IPS measured at the rear. Again-strictly an assumption based on limited data and past experience-I'm assuming that with the prop/front zero'ed out via dy-bal you still have measurable vibration present at the engine/rear. The only other concern that I have is that in another post, you mentioned that you thought the ring gear support was uni-directional. It should have no real bearing on what you are experiencing (unless it has a stack of washers bolted to it), but it can only be installed properly in one position. regards; TC snip Back to top John_F Guest Posted: Tue Sep 06, 2005 5:53 am    Post subject: Re: Engine Balancing and Resonance Vibration Problem There is ONE nut plate hole in the crankshaft flange that has a larger diameter nut than the other bolt nut plates. If you index the prop incorrectly the prop tip will NOT track correctly in a single plane since the prop will not sit flush against the crankshaft flange. If the prop does not track in a single plane then it will shake and it will require a lot of weight to correct. A dial caliper will show which crankshaft flange nut is the larger one and it should match up with the larger hole in the prop. If someone has installed the prop so that the larger nut is in the wrong prop hole then torqued the bolts down it may look ok as the nut swages out the prop or the extender spacer but is will not correctly seat and will wobble. On Sun, 4 Sep 2005 22:12:12 +0100, AllanFuller <AllanFuller.1uuull (AT) news (DOT) aviationbanter.com> wrote: Quote: Plane: Commander 114 - 1976 SN: 14007 Engine: Factor re manufactured - IO-540-T4A5D, tested 12/19/2000, SN: L-22326-48A, shipped end of 2000 Propeller: 3 bladed McCauley - just overhauled and balanced - July 2005 The current engine was put into service in March 2001 with the existing prop. There were engine vibrations and 13 washers were required to balance the prop as best as could be. I never felt it was as good and smooth as it should be considering it was a new engine. This July 2005 (at the time of my annual) we had the prop overhauled at Memphis Prop at Memphis, Mississippi. They said they balanced the prop. It was installed and there was engine/prop vibration. There was also a resonance vibration that has a maximum at 1500 rpm and a second lower magnitude harmonic vibration at 750 rpm. I brought it to a nearby airport for dynamic engine/prop balance. The vibration at 2000 rpm was close to 1 without weights and they thought there was a problem with a bulkhead crack. We dye tested the bulkhead and there was no crack. We flipped the prop 180 degrees to see if that reduced the vibration. It did. This was actually the orientation of the prop when the prop was removed for the prop overhaul. I brought the plane to another airport for engine balancing. They found that the vibration was about 0.9 without weights and they were able to bring the vibration down to about 0.12. Probably could have even improved on that, but the concern was that they needed about 13 washers. We flipped the prop 180 degrees and found that the vibration without weights was 1.4. Again the vibration could be lowered with the use of about 17 washers in the same direction on the bulkhead (same direction as the balancing of the new engine in 2001 with 13 washers). There still is this noticeable resonance vibration at 1500 and less intense resonance vibration at 750 rpm. The difference in vibration with the two prop orientations is about 0.5. That probably suggests that the major vibration is in the engine and not static prop balance. People have suggested that the vibration could be caused by a number of things. The Insight – GEM gauge show even CHT/EGT readings for all cylinders. The engine mounts were new at the time of the engine installation in 2001. The governor was overhauled in 2001 and yellow tagged. One observed problem is that prop cycling at 2000 rpm only produces a 250 rpm drop and one would expect least 300. Before the new engine and overhauled governor the engine rpm drop during prop cycling easily went to 300 and lower if I did not stop it by bring the prop forward. Currently, At 2300 rpm the prop cycling drop will go to 500 rpm. Is this an oil pump pressure or governor problem? Could this be the source of the vibration or the resonance vibration at 1500/750? My problem is that I am not sure what to do. It is being suggested that I could replace the motor mounts at about $360 plus labor (They were new in 2001 and look good/new.). I could have the governor overhauled for $500 plus labor. I could have the prop sent back to the prop shop to check their work and re-balance. I will throw money at the problem, but I want to make smart choices on where to spend the time and money. The other fear is that the vibrations are in the engine and related to the crank shaft recall. I certainly do not want the engine to fail when I am IMC or at night even if VFR. The resonance vibration coupled with the recall has me concerned. Having a doctorate in physics probably has me overly sensitized to the potential problem. Thanks go to any and all who have comments and suggestions. Allan Fuller Back to top Fly Guest Posted: Tue Sep 06, 2005 2:14 pm    Post subject: Re: Engine Balancing and Resonance Vibration Problem I concur with ToeCutter. Especially in your case, you need two vibration sensors, fore and aft, to gather info on the engine and prop. You can surmise what the crankshaft balnce quality is. You cannot do it with one sensor alone unless you move the sensor to different locations during subsequent runs.. Your post stroungly suggests you need to get find someone of experience to give you good advice. I wonder where are you located? Wish I could help with a good answer but internet makes it difficult. Answer is only a good as the information provided. couple of other things: Sounds as if the operator has a Micorvibe DSS prop balancing rig. Their manual suggest checking the balnce at 2000 rpm. Usually I find higher amplitudes of imbalnce and sometimes different phase at higher rpms. The previous balance of 13 washers was beyond the FAA approved maximum correction. After 600 hours, the isolation mounts can take a set, maybe even have metal-to metal contact between the bolt and engine mount. I recall Toecutter suggesting at least a rotation every 500 hours. Doublecheck the ring gear installation. It will only go on in one position. And verify the crankshaft index bushing is in the correct location for your engine. How are you percieving the resonance at 1500? How did you measure the freq? have you consider that it might be an idle mixture problem? good luck Kent Felkins Tulsa Ok. Back to top Don Hammer Guest Posted: Tue Sep 06, 2005 9:15 pm    Post subject: Re: Engine Balancing and Resonance Vibration Problem On Tue, 06 Sep 2005 05:53:08 GMT, [email]John (AT) no_where (DOT) com[/email] (John_F) wrote: Quote: There is ONE nut plate hole in the crankshaft flange that has a larger diameter nut than the other bolt nut plates. If you index the prop incorrectly the prop tip will NOT track correctly in a single plane since the prop will not sit flush against the crankshaft flange. If the prop does not track in a single plane then it will shake and it will require a lot of weight to correct. A dial caliper will show which crankshaft flange nut is the larger one and it should match up with the larger hole in the prop. If someone has installed the prop so that the larger nut is in the wrong prop hole then torqued the bolts down it may look ok as the nut swages out the prop or the extender spacer but is will not correctly seat and will wobble. Don't know about this partucular prop/engine combo, but I agree with John. There is usually only one way a prop can be mounted and is keyed as such. Not unusal to see one put on worng though. 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