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Mags vibration

  • Charles Neels
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1 week 3 days ago #17497 by Charles Neels
Charles Neels created the topic: Mags vibration
Hi there,
I have a problem, couldnt find it under search thru all the previous posts.
I have a rotax 912UL , it was overhauled about a year ago, and i have just under 60 hours on it. The issue is, around 2750-3100 there is a strange vibration noise which is out of the ordinary. when I switch it to one mag whether it is right or left the vibration noise goes away. It only is there when I am running both mags.
Does anyone have any idea what this could be?
The engine runs beautifully makes same power as normal everything else is normal. Just for the odd vibration it has within that range. Ive already put new spark plugs in, and at first I thought that helped but apparently it didn't.
Any help would be appreciated.
Thanks,
Charles

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1 week 2 days ago #17499 by Roger Lee
Roger Lee replied the topic: Mags vibration
Hi Charles,
Need a little more info.
What is the mag drop? Have the carbs been synced recently? Any maint. done on it just before this started?
Out of curiosity what are your plugs gapped at?
Maybe this rpm range for you may just be a harmonic with the prop and engine mounts.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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1 week 2 days ago #17500 by Charles Neels
Charles Neels replied the topic: Mags vibration
Hi Roger,
Mag drop is like 50-100 rpm. it isnt much at all and this is even at 2700 rpm all the way up to 4000 there isnt much difference in rpm drop amount. I can tell its switching mags because it does change a little but all within 100 rpm. We synced the carbs about 50 hours ago. It is a new installation. Do you recommend we check that again?

To be honest I didn't gap the spark plugs just got new ngk ones and put them in.

But the noise is only there when I'm running both mags. like I can be on the left mag (with no noise) and when I am slowly switching it over to the right mag there is a spot in the turn of the key where it runs both mags for a second or less, and I can hear the noise again and when it goes to only right mag it goes away again, and then when on both again the noise comes back. I can hear the noise with my headset on and with it off so it isn't electrical interference.

It just seems odd that it would be a harmonic with prop and engine because it wasn't there for the first 45 almost 50 hours. and then it appeared. Ive been trying to trace what is causing it and I finally tried the mags and that seemed to show me that it was that. Could that eclectric ignition box possibly have issues?

Thanks in advance for your response!

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1 week 2 days ago #17502 by Rob Seaton
Rob Seaton replied the topic: Mags vibration
approx 3000 rpm range is the worst for vibration in a boxer engine. just don't hold the engine in that range.

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1 week 2 days ago #17503 by Charles Neels
Charles Neels replied the topic: Mags vibration
Hi, Rob
The fact that it is something that changed .. i can just hear it as i rev down or up thru that range on shutdown or start up etc. Used to never do it. Just worries me because what if it is something that is a issue. Are you saying I should just not worry about it?

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1 week 2 days ago #17506 by Rob Seaton
Rob Seaton replied the topic: Mags vibration
It may be nothing to worry about but I am just giving some more info.
Boxer engines have a pronounced harmonic at 3000 range, (rocking couple) maybe the engine mount rubbers and not dampening them as much as before. or something else is getting excited (exhaust?)
The mag check is changing it slightly so it is less pronounced?

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1 week 2 days ago #17507 by Roger Lee
Roger Lee replied the topic: Mags vibration
Hi Charles,

I agree with Rob and I absolutely would put a set of gauges on and check the carb sync. It only takes a few minutes. With those low hours anything may have settled in a tad and changed the carb balance. (i.e. throttle cable)
I would also while you're at it regap the plugs. Out of the box they are .030 - .031.
They should be between .023 - .027. Pick .025 it's in the middle.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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1 week 2 days ago #17508 by Charles Neels
Charles Neels replied the topic: Mags vibration
Ok i will do that and see if it fixes it. and will let you guys know! Thanks

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1 week 1 day ago #17510 by Roger Lee
Roger Lee replied the topic: Mags vibration
You have to start your diagnostics somewhere and doing the most common causes and least expensive is the way to help rule systems or specific causes in or out.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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6 days 8 hours ago #17521 by Kevin Stewart
Kevin Stewart replied the topic: Mags vibration
Only a thought, but if the vibration is not purely a function RPM but of having BOTH ignitions on. Could it be a problem with the ignition timing in that both modules are not receiving the same advance from the pick-ups on the back of the engine. Is it worth checking the gaps and their mounting security? You could use a xenon timing light with an inductive pick up to check the timing of each ignition module at the troublesome RPM, in theory they should be the same.

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6 days 7 hours ago #17523 by Charles Neels
Charles Neels replied the topic: Mags vibration
Hi there, I have regapped the plugs and we re synced the carbs because they where not perfect. Now it runs way smoother overall... and it seems that sound went away but i am not a 100 % sure. I will know next flight for sure.

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6 days 3 hours ago #17529 by Roger Lee
Roger Lee replied the topic: Mags vibration
That sound may not even be the engine or prop. It can come from other sources.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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