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  #1  
Old 05-07-2020, 01:38 AM
dinowal dinowal is offline
 
Join Date: Dec 2011
Location: TWIN WATERS, Queensland, AUSTRALIA
Posts: 89
Default Prop Problems ?

After a flight recent flight, I returned to join the circuit (pattern), and as I reduced power to 4000 - 4500 rpm I noticed some unusual & significant new vibration. All had seemed normal on cruise at 5200 -5500 ish rpm while the prop was pulling. On inspection of the prop I found a 5/8 by 5/8 inch flake of paint had departed from the back of the metal strip on the leading edge, approx. 4 inches from the tip. I realise that our props are hollow & made from Carbon Fibre & are very light, but I am surprised that such a small amount of missing weight could affect things so much. Has anyone had a similar situation,or have experience & knowledge to share? Thanks, DEAN
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  #2  
Old 05-07-2020, 02:40 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,066
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Your vibration may not be prop related. Small flake of paint missing, even at tip, shouldn't be noticeable. Sounds to me more like carburetor. Could be heavy float causing rich mixture and imbalance L-R. Floats work great until they don't...
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  #3  
Old 05-07-2020, 08:32 AM
John-G John-G is offline
 
Join Date: Jan 2012
Location: Northeast Ohio
Posts: 685
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I remember reading a thread last year pertaining to vibrations at reduced throttle settings. If memory serves me correctly, I believe the vibrations were determined to be coming from the gear reduction unit ... so keep that in mind as a possibility after the carbs are eliminated as a problem.
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Last edited by John-G : 05-07-2020 at 08:34 AM.
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  #4  
Old 05-07-2020, 08:52 AM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
Posts: 820
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Rotax has made some recommendations to decrease clutch and dog wear, as well as sometimes needing the belleville washers which provide tension, being replaced in the gearbox. at low hours

Rotax now recommends warm up at 2500 rpms, not 2000, to save wear and tear on the gearbox dogs. There have been failures at 300 to 400 hours on the dogs on RV-12 SLSA planes.

Speculation about brands of oil is another issue, as those that run only Mogas, no 100LL, have gone to a full synthetic Mobil 1 Full Synthetic 10w-40 T4 motorcycle oil with additives for shared gearbox/engine lubrication, to reduce gearbox wear. The jury is still out on that one, but if almost all you run is Mogas, it might be a better solution.


See cammiepatch posts on this in a search. They have replaced dogs, and belleville washers to keep their school rental plane up and running on the line, until parts arrived. The Rotax gearbox parts are a pretty penny, best to address it shortly it that is the cause.
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  #5  
Old 05-07-2020, 09:19 PM
dinowal dinowal is offline
 
Join Date: Dec 2011
Location: TWIN WATERS, Queensland, AUSTRALIA
Posts: 89
Exclamation

Thanks to you 3 gentlemen for your replies.. I have contacted Sensenich & the more I read & think, my Prop is probably not the problem.- I can assure you that I will be seriously p'd off if it's sinking carby floats, - I am on my 4th set, with only 52 hours on the Hobbs meter. I will of course be even more unhappy if gearbox is involved, - my friend, (who services Rotax engines for a living) & I will continue to investigate & report back in a few weeks.. Cheers, DEAN
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  #6  
Old 05-07-2020, 09:40 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,820
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Just a thought and may not be helpful in this case, but is your engine in the serial number range that needs to have the crankshaft journal checked for cracking? If so might want to do the check since it is quick and easy. As I said, not sure the symptoms match the failure mode, but at least you could eliminate one more thing.
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  #7  
Old 05-17-2020, 12:28 AM
dinowal dinowal is offline
 
Join Date: Dec 2011
Location: TWIN WATERS, Queensland, AUSTRALIA
Posts: 89
Default Aaah, yes it was!!

Yes, thanks Jim ! On restarting the engine with top cowl off, the RH carby was spewing fuel from the little overflow tube!. Guess what ? The floats were way overweight, & the ones in the LH carby were right at the upper limit. Now, I know you folks are really polite & you don't swear much, so I am sparing you a lot of what's in my head! However I will ask: what the bloody **** is going on? This is really unacceptable - this is my 4th set after 52 hours of flying , - I'm not sure if the problem lies with Mr. Bing, Mr Rotax, or even Mr Van's, but would love to hear from someone with a permanent fix. My dream of having an RV12 ready to fly anytime after a quick preflight seems to be disappearing..
The only good thing about this saga is that the Australian Rotax agent has paid for all these floats, -thanks to them, - hopefully they can give Bing/Rotax a poke? Cheers, (not happy), DEAN
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  #8  
Old 05-17-2020, 08:16 AM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 189
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One thing I always do at the same time as I change my engine oil is clean the pistons on the carbs and put a small amount of 3in1 oil on them. I do this because I have noticed that the pistons can start to feel rough in their bores possibly due to combustion / fuel etc deposits.

I find that doing this creates very smooth transitions in power.
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  #9  
Old 05-17-2020, 06:35 PM
dinowal dinowal is offline
 
Join Date: Dec 2011
Location: TWIN WATERS, Queensland, AUSTRALIA
Posts: 89
Default Thanks

Thanks Azjulian, - yes, we found the piston in the RH carby was a little sticky & had some black deposits on & around it.. Possibly was another part of the problem, but floats were definitely overweight. Cheers, Dean
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