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OS 25 vibration issue on FF Taco

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Old 08-03-2004, 06:00 PM
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basmntdweller
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Default OS 25 vibration issue on FF Taco

I have an OS25 FX on a profile 3D plane. When the plane was new I had a vibration problem. I tried many props to eliminate the problem. It caused serious fuel foaming issues and would get lots of air bubbles in the line from the needle to the carb. One day the problem went away on its own and I started having a great time with the plane. I have dorked the plane many times but rarely any damage. Yesterday I dorked it again and stripped gears in one of the servos. While I had the plane in the shop to repair the servo, I did a little preventative maintenance. I tightened up the motor mounting bolts they were not loose but not "firm tight" in the 1/4" ply motor mount. I went out today and my vibration problem is back! Could the tightened motor mount bolts have altered the vibration absorbsion level to the point that I have a harmonic that wasn't coming into play when they were slightly looser? If you think this might be the problem, can you give me ideas on how to correct it? Other ideas on correcting if you think it's something else. The key here is that it did it new then went away for 60-100 flights and now it's back! Tightening the bolts is the only thing I did while working on it that could have affected the motor.
Ideas???
Thanks,,,Matt
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Old 08-04-2004, 02:25 AM
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Default RE: OS 25 vibration issue on FF Taco

Matt could we perhaps start right from the start and eliminate everything one by one? I know you are a very experienced flyer and do not doubt that you've already tackled more than half of the possible problems. But yes why not check on everything? I'm by no means an expert on high frequency vibrations and all that funny jazz. But can we perhaps start by checking the usual stuff first? I'll put together a little list quickly of where I would start but i'm sure you've checked everything i'm going to mention.

1) Prop? No nicks etc from the last dork? You have used a magnetic prop balancer?
2) The hole of the prop? Is it a nice tight fit onto the engine? All centered?
3) I gather you are not using a spinner. Well I haven't really seen spinners on these little profiles so i'm guessing.
4) The washer etc that you use to tighten the prop is a good tight fit over the shaft so it is all nicely centered? The bolt etc?
5) Have you tried loosening the tank a wee bit? You've obviously checked the foam between the tank and the fuz so the tank has a little bit of play on the fuz.
6) The air bubbles are not coming from a hole in any of the tank tubes? Air leaks are none existent?
7) Ok now I would have a look into the crank shaft!
8) And next the bearings of the engine. They could be a little shot causing the shaft to be loose and not always centered?

I know i'm not being of much help but I have mixed thoughts on these type of things. If everything above is right then I would definitely look into the tank and the fuel route to the engine. Its not very often that i get a motor that doesn't vibrate at all.
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Old 08-04-2004, 05:38 AM
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Default RE: OS 25 vibration issue on FF Taco

This vibration isn't a little bit. It's to the point to whole front end of the plane is a blur. I have tried several props some intentionally unbalanced and mounted at various "clockings" on the shaft. No amount of padding or isolation would keep the fuel from getting bubbles at this level of vibration. It is hitting a harmonic, I just need to do something that moves the harmonic to a higher RPM that the engine can't reach.
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Old 08-04-2004, 08:58 AM
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Default RE: OS 25 vibration issue on FF Taco

Could it be possible that the front end of the plane got knocked loose and that's causing your vibration? Maybe a little thin CA wicked into the mount might help. You might also have induced some twisting to the case of the motor if there is something uneven about the mount....

I had a 4 banger on my EF Edge 540 that vibrated like crazy..... I used two pieces of hard rubber under the mount that seemed to help a bunch...
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Old 08-04-2004, 09:12 AM
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Default RE: OS 25 vibration issue on FF Taco

IMO all profiles are escentially a vibration source on a tuning fork. can you drill thru the fork (fuselage) top to bottom anywhere and glue in a wood dowel from top to bottom. I had to do that on my sledge some time ago when the irvine 53 I had on it vibrated it badly. You may be able to reinforce the fork and "move the tune" to a different spot. My saito 72 shakes pretty bad on my omp edge but It has never caused fuel delivery problems. As paul said check the front of the fuse for cracks
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