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thilo.kind(at)gmx.net Guest
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Posted: Wed Mar 12, 2008 10:31 am Post subject: AW: Re: 912 with low RPM--- new vibration problem |
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Hi Les,
I also had some vibrations on my Zodiac 601 HDS with Rotax 912. Started all
of a sudden. Did the same than you: sync'ed the carbs, checked the ignition,
checked the prop - nothing at all. Turned out, that the choke cable somehow
slipped a tiny little bit and the choke didn't fully close. re-set the choke
cable and - voila - no more vibrations.
Good luck
Thilo
-----Urspr�ngliche Nachricht-----
Von: owner-rotaxengines-list-server(at)matronics.com
[mailto:owner-rotaxengines-list-server(at)matronics.com] Im Auftrag von Les
Goldner
Gesendet: Wednesday, March 12, 2008 6:28 PM
An: rotaxengines-list(at)matronics.com
Betreff: RE: Re: 912 with low RPM--- new vibration
problem
<lgold(at)quantum-associates.com>
Roger, Guy, Bob, and William.
I phones Lockwood and the tech there told me that on new engines they have
seen this vibration when the idle jet gets clogged from installation crud.
So I immediately drove the 50 miles to the Petaluma Airport and cleaned all
the jets... There wasn't any dirt in them (although there were a few specs
in the bowl) and this did not stop the vibration. I also checked the
cylinder pressures (all running 1790-180#)... so I'm back to square one!
To answer your question, there is only a normal (100RPM) drop when doing mag
checks.
I still can't believe the prop is out of balance since it only has 20 hours
on it, was fine up to Saturday, and Warpdrive says they have not seen this
type of problem and I did everything right regarding the adjustment (the
prop tracks within 1/64th of an inch and the pitch of each of the 3-blades
does not vary by more than a 1/5th of a degree). I will call Lockwood again
and may give up and get a local tech to look at the engine... Maybe I'll
sync the carbs again...
Out of ideas,
Les
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Roger Lee
Joined: 10 Jan 2006 Posts: 1464 Location: Tucson, Az.
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Posted: Thu Mar 13, 2008 9:12 pm Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Hi Thilo,
Good advice at rpm's below 3500. The enricher does not play a part though above 3500rpm. Certainly not above 4000. If it ran rough below 3500 then the enricher could be the culprit, but then it should smooth out at cruise rpm.
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_________________ Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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lgold(at)quantum-associat Guest
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Posted: Fri Mar 14, 2008 1:54 pm Post subject: AW: Re: 912 with low RPM--- new vibration problem |
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Checked the choke Roger, good idea but no cigar! The chokes were set
right... So I'm back to square 1.
I have an engine mechanic coming Wednesday.
Les
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Gtblu
Joined: 18 Jul 2006 Posts: 37 Location: Australia
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Posted: Sat Mar 15, 2008 4:33 am Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Hi Les, I had a vibration in 912 uls which turned out to be sprag clutch circlip coming undone (or breaking) and going through the sprag clutch gears. In my search for the vibration also found slipper clutch had been incorrectly installed, which can also be responsible for vibration. There are three disk springs that must oppose each other, mine were installed in the same plane. Eventually with the sprag clutch, the engine would not start.
How bad is the vibration? The effect I was getting was enough to shake my legs on the seat.
Has anyone tried using neoprene mounts instead of rubber mounts? I suspect that they would be too hard for shock absorbtion.
This is a just released report of an accident in Australia with a 912uls installed. http://www.atsb.gov.au/publications/investigation_reports/2007/AAIR/aair200700054.aspx
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lgold(at)quantum-associat Guest
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Posted: Sat Mar 15, 2008 11:31 am Post subject: AW: Re: 912 with low RPM--- new vibration problem |
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Thanks for the info Slepcev,
I'll let the mechanic who is coming on Wednesday know about this but my
vibration is not as bad as yours was. It just doesn't hum like should and
it's a little annoying.
How many hours was on the engine when you discovered the problem? (My engine
has only 20 hours TT).
Les
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Gtblu
Joined: 18 Jul 2006 Posts: 37 Location: Australia
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Posted: Sat Mar 15, 2008 2:18 pm Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Hi Les,
Hours were about 600. However, there has always been a vibration, an annoying feeling its not running sweetly, between 4400 and 5100 revs that has just recently increased to 5300 revs. I have pretty well followed your path trying to track it down, but without a balance have become stuck on that. I suspect my prop, and will try and change it for someone elses soon.
I took three photos from a stationary camera of each blade in the same position then outlined each blade and superimposed them. I don't know if this is a valid way of checking, but it shows one blade is certainly not on track and surprisingly for a lot of its length. Checking the tips for track is not enough perhaps. see attachment.
What is strange, if that is what the problem is, is that at 5400 revs it runs so sweetly. If the prop was the problem is that possible?
The only other clue I have is that checking the mags will give a rough patch very briefly as the revs drop, which I think could be in the float of the bearings of the gearbox. This engine was completely opened up when the sprag clutch broke, 100 hours ago.
Basically, I "share your pain" It is bloody frustrating trying to track this down as there are so many variables, and it is potentially an engine destroyer.
I wait for your summing up on Wednesday with baited breath.
regards
Gtblu
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Last edited by Gtblu on Sat Mar 15, 2008 2:27 pm; edited 1 time in total |
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Gtblu
Joined: 18 Jul 2006 Posts: 37 Location: Australia
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Posted: Sat Mar 15, 2008 2:19 pm Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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deleted duplicate and added photo
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Last edited by Gtblu on Sat Mar 15, 2008 5:38 pm; edited 1 time in total |
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Roger Lee
Joined: 10 Jan 2006 Posts: 1464 Location: Tucson, Az.
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Posted: Sat Mar 15, 2008 3:15 pm Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Hi GTBLU,
Typically the vibration and the range of rpm with that vibration is what you feel if you have a bad pneumatic carb balance. Even if you have done it in the last 25 hrs. do it again. I believe that will help. Don't forget the mechanical balance first and be precise with both.
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_________________ Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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Gtblu
Joined: 18 Jul 2006 Posts: 37 Location: Australia
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Posted: Sat Mar 15, 2008 5:40 pm Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Cheers Roger. I keep doing them, but I take your point. Be precise!
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Thom Riddle
![](images/avatars/1237767069518b8b321e02a.jpg)
Joined: 10 Jan 2006 Posts: 1597 Location: Buffalo, NY, USA (9G0)
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Posted: Sun Mar 16, 2008 10:33 am Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Gtblu,
In answer to your question about vibration smoothing out at 5400 rpm, yes, it is possible. As the centrifugal forces increase with increasing rpm, the apparent out-of-trackness at places other than the tip could disappear. Do you know which blade is running out of track? You might consider removing the blades and comparing them to each other on a true flat surface in several directions. If one of them is measurably out of synch with the others that could be your problem and a blade replacement might resolve the issue.
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_________________ Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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Gtblu
Joined: 18 Jul 2006 Posts: 37 Location: Australia
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Posted: Tue Mar 18, 2008 3:26 am Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Thanks Buffalo Thomas,
I Can't imagine the temperature problems you deal with over winter!
I do know which prop is out, but may get a chance to swap props this weekend.
Is it feasable to get one blade, or are all three nessessary for a match.
Also doing another mechanical and pneumatic carb balance. Suddenly running very roughly at about 2500, however got too dark to follow that up.
regards
Gtblu
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Thom Riddle
![](images/avatars/1237767069518b8b321e02a.jpg)
Joined: 10 Jan 2006 Posts: 1597 Location: Buffalo, NY, USA (9G0)
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Posted: Tue Mar 18, 2008 3:37 am Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Gtblu,
The winters here are not so cold as in Minnesota or northern Maine due to our proximity to Lake Erie and Lake Ontario, but they are long and perpetually overcast with lots of snow. We still have about 8-10" of the white stuff on the ground now.
Woodcomp has a precise weight record of each blade they sell by serial number so if we bang up a blade they can replace it with one of the identical weight. Whether or not the center of mass is in the identical location is another matter, which can affect dynamic balance, but so can other factors as Roger has stated. I don't know if the other prop manufacturers do this or not. I broke both blades on the PowerFin on my Kolb so will be replacing them with a matched pair reusing the hub.
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_________________ Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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Gtblu
Joined: 18 Jul 2006 Posts: 37 Location: Australia
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Posted: Fri May 09, 2008 2:31 am Post subject: Re: AW: Re: 912 with low RPM--- new vibration problem |
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Hi
Bringing up this same old problem again as I have a new piece of info.
Followed all advise on this, to refresh have a 912 uls that always and as advertised had a rough running area between 4000 and 5000 revs. However recently has extended the rough running onto about 5250 revs with a slight change in nature. I can be in a turn with the prop loading up, I presume as G's increase, and engine will lose its rough running at a set throttle setting, similar to bearing float in a car. However the new info is that the vibration is considerably more noticeable if the oil temperature is over 100. The desire is to keep temperatures over 100 to burn off impurities, but not at the expense of the vibe.
With those symptoms, I suspect the gearbox. I have tuned the carbs very carefully, re-adjusted the pitch on the prop (at 200mm in from the tips as the tips are not consistent!)
Has anyone had concerns or experiences about particular oils? Currently using vsx4
Thanks for all the inputs. I tried them all bar a prop balance. Swapped props instead and still had the same issues.
regards
Gtblu
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