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jonboede(at)hotmail.com
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 Posted: Sun Dec 30, 2018 7:46 pm Post subject: Oil blurp on start |
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Anybody ever see an engine that blurps a couple of tablespoons of oil on start that just wouldn’t come out no matter how much you pulled it through by hand??
Jon
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migfighter42(at)gmail.com
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| Posted: Sun Dec 30, 2018 10:20 pm Post subject: Oil blurp on start |
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Yep. It’s up in the intake tubes. Destroyed an engine that way. We had a particularly “wet” engine that was dumping a lot of oil during pull through. I pulled 15 blades and still had hydraulic lock on start. Destroyed the engine. Fortunately I had a “spare” engine on my Yak-55. Wet engines can pull oil up into intake tubes due to camshaft scavenge during pull through. This according to Jill.
Bill Culberson
Red Star Aero Services
251/716/8119
| Quote: | On Dec 30, 2018, at 8:45 PM, Jon Boede <jonboede(at)hotmail.com> wrote:
Anybody ever see an engine that blurps a couple of tablespoons of oil on start that just wouldn’t come out no matter how much you pulled it through by hand??
Jon
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mark.bitterlich(at)navy.m
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| Posted: Mon Jan 07, 2019 11:10 am Post subject: Oil blurp on start |
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With respect, I can't say I agree with Jill's analysis.
The real difference with YAK-50's and 55's and Sukes, is that they are tail draggers, thus the engines do not sit perpendicular to the ground but instead are canted slightly backwards. This allows oil to flow backwards through the intake valve into the intake tubes themselves more so say than on a 52. Another big factor that can add to this is if the engine is pulled through backwards when a hydraulic lock is felt. This will push oil right back out the intake valve again into the tubes. If you are using single weight oil, say SAE 50 or so, and it gets cold, this oil can get so thick it is hard to drain. Of course this is most prevalent in the lower cylinders. This is the whole purpose behind the intake drains, and of course sometimes yanking plugs out to let the oil drain.
That being said, if it gets into the intake tubes and gets thick, you will usually notice it because when you prime the engine, and I mean REALLY REALLY prime it (as in over prime it on purpose), the raw gas will NOT flow out the intake tube(s) drain because it is full of oil. That is your OMG indication to NOT CRANK THE ENGINE. If that happens, you must get that oil out of there, and that means either heating the whole engine, or over priming to thin the oil with gas, opening up the individual intake drains, whatever... to get that oil out of the intake tubes before cranking.
So.....Part of the solution is having an intake drain kit on the lower cylinders, leaving that drain open and KEEPING it open when priming for the next start. If you don't see fuel running out that drain after priming then you have a very bad incident getting ready to happen, and you have to take it seriously. Another big advantage is that it is hard to over-prime with that drain open. Large amounts of excess fuel just runs right out the drain.
Mark
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