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06-06-2018, 07:35 AM
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Join Date: Jun 2012
Location: Madison, AL
Posts: 67
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Can?t get oil gurgle after 10 months idle
My RV-12 Rotax 912 has not been started for 10 months while doing ACI, brake job, satisfying SB?s, etc. l recently thought it would be a good idea to turn the prop by hand to pump the oil back into the oil canister. (A fresh oil change was done just before my final flight 10 months ago). Well, the first thing I noticed when I started turning the prop was that the engine compression seemed low. I kept turning the prop - about 100 revs - and I never could get the ?gurgle?. Can someone explain what is going on an tell me what to do. I don?t intend to try starting the engine until I?m sure everything is back to normal.
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Jim McCarter
Madison, AL
RV-12 N864RV 90 hrs TT
Donation Made for 2019
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06-06-2018, 08:41 AM
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Join Date: Sep 2006
Location: Windsor, California
Posts: 924
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First off, be sure that there is oil in the engine.
Second, be sure you are pulling the prop through relatively slowly with a 2-3 second pause at the point of each cylinder's maximum compression -- quickly rotating the prop delays the gurgling process.
You could perform an oil system purge (the process is described in the ROTAX service manuals) to ensure that there is no unwanted air in the system and that the oil is properly flowing.
After the purge, you could remove the top spark plugs and quickly turn the prop by hand -- you should see oil pressure registering on the oil pressure gauge.
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David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 940+ hours (as of September 2020)! 
V AF donation through June 2021.
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06-06-2018, 08:46 AM
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Join Date: Jul 2009
Location: Coeur d'Alene, ID/Casa Grande, AZ
Posts: 654
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As David has suggested...do an oil purge per Rotax service buliten (your valves are probably not sealing...hence, no compression. Which is needed to return oil to tank.
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Ric Dickison
307 (CAB) Phantom
Search and Destroy (Can Tho RVN)
Distinguished Flying Cross Society Member
CH-47 & UH-1H "Driver"
Rotax 9 Series Service IRMT
RV-12 Kit#729 "N312RD" is now a full functioning fun machine!! Thanks Van for fulfilling my dream😎
2018 Dues Paid
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06-06-2018, 08:48 AM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,070
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Do not turn the prop fast. Turn it slowly until at the top of a compression stroke, then pause for a few seconds, then repeat, pausing at the top of each compression stroke. The pause gives time for air to leak past the piston rings and pressurize the crankcase. The pressure in the crankcase will push oil out and into the tank. Does any oil show on the dipstick?
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Joe Gores
RV-12 Flying
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06-06-2018, 10:19 AM
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Join Date: Sep 2006
Location: Windsor, California
Posts: 924
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Jim --
I trust that you know NOT to turn the ROTAX 912's propeller backwards any significant amount. Doing so has the potential to introduce air into the oil system -- not a good thing.
BTW, the ROTAX Service Instruction for oil system purging can be found at:
https://legacy.rotaxowner.com/si_tb_...-912-018r2.pdf
-- David
__________________
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 940+ hours (as of September 2020)! 
V AF donation through June 2021.
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06-06-2018, 10:52 AM
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Join Date: Oct 2010
Location: La Feria Texas
Posts: 3,822
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Even following all the previous tips, it took FOREVER for mine to gurgle after sitting for some months. I think that the valves don't seal quite as good after sitting, and therefore the crankcase pressure is less than normal getting by the rings..
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06-06-2018, 04:23 PM
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Join Date: Jun 2012
Location: Madison, AL
Posts: 67
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Thanks for the tips guys. I’ll try again and follow your suggestions. Yes, I do know not to turn the prop backwards. And I’m sure there is a full load of oil in the engine. I made only 1 short flight right after an oil change and there have been no oil leaks, so it has to still be in there. I think I WAS turning the prop too fast. I’ll slow down next time.
I’m not sure what the oil purge is suppose to do for this problem.
— Jim McCarter
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Jim McCarter
Madison, AL
RV-12 N864RV 90 hrs TT
Donation Made for 2019
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06-06-2018, 05:58 PM
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Join Date: Jan 2011
Location: Clearwater, Florida
Posts: 398
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Quote:
Originally Posted by JimMac
Thanks for the tips guys. I?ll try again and follow your suggestions. Yes, I do know not to turn the prop backwards. And I?m sure there is a full load of oil in the engine. I made only 1 short flight right after an oil change and there have been no oil leaks, so it has to still be in there. I think I WAS turning the prop too fast. I?ll slow down next time.
I?m not sure what the oil purge is suppose to do for this problem.
? Jim McCarter
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Jim,
Please follow up with us and let us know how this turns out.
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06-07-2018, 09:24 AM
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Join Date: Jan 2016
Location: Chiloquin OR
Posts: 94
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Quote:
Originally Posted by DonFromTX
Even following all the previous tips, it took FOREVER for mine to gurgle after sitting for some months. I think that the valves don't seal quite as good after sitting, and therefore the crankcase pressure is less than normal getting by the rings..
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Why would the valves not seat? Have never seen that on any auto engines that I have worked on.
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06-07-2018, 01:43 PM
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Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,065
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Quote:
Originally Posted by EXflyer
Why would the valves not seat? Have never seen that on any auto engines that I have worked on.
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I think the reference was to lifter bodies pumping up with air if oil not purged correctly. You'd have to draw air into oil pump/pressure galleries.
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 622 
LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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