912 hydraulic lock

[egp8111]

I went to pull the prop through prior to starting yesterday and it turned through three blades and stopped solid. What the ? Went home and researched on the web and learned about hydraulic lock on 912s. I went back to the airport and pulled the plugs and sure enough I got a shot of oil out of one cylinder. buttoned everything up and the engine ran fine. It had been sitting for a couple of weeks without running. Can I expect this to be a normal occurance or is there anything I can do to lessen the chances of this happening. My understanding is it has something to do with the oil tank being positioned higher than the crankshaft. I know I had an Europa for several years with a 912 and it never had this issues even after sitting idle for a prolonged period. It's oil tank was mounted much lower

thanks EG

[DesertFox4]

EG , Yes you can. If you fly a model 1-4 with a 912 series you should always make sure the engine is free by turning the prop in the direction of rotation only to clear the oil before hitting the starter. Since the oil tanks on those models usually sit higher than the crank they can pass oil into the cylinders. Just had to pull all 4 bottom plugs from my 912 S and let the oil escape. Not flying enough. :o You did the right thing by not forcing the prop or trying the starter and doing damage to the engine. Make it part of your pre-flight but make sure first the ignitions are in the off position. Looks like you have a model 3. Should be a blast with that 912.

[Slyfox]

Yes there is something you can do... fly more:D

I always turn the engine over by prop 18compression strokes(not revolutions mind you) slowely before starting, and than when I start I let it crank over at least 3 seconds with the choke on and mags off and watch to make sure the pressure comes up for the oil before I turn the mags back on. In which case it starts right up. I never listen for the burp, 250hrs on this engine and about 1800 or more on the old with this practice. Oh and I also have an oil thermostate that I bought from lockwood and since I put that on slowed the drainback on the oil tank, I have a model 4. with 912uls

hope this helps

[kitfox2009]

Hello Slyfox

Why do you have the choke on when cranking for the oil pressure check? I always crank over until the oil pressure raises, but I never thought about using the choke.
Another thing I have stared to do recently is turning off the fuel as I am taxiing in. My idea there is to lower the fuel level in the carb bowls so just in case I wanted to restart when it is hot, opening the fuel valve would put fresh cooler fuel in the carbs. Seems the work for me.
The "pull through" is part of my preflight.

[Slyfox]

simple, if I don't pull the choke it don't start on first touch of the starter. Kind of hitting two birds with one stone. One to put fuel in the cylenders the other to make sure the oil pressure comes up. Works for me and starts real nice. Also because I have a 100horse 912 the compression is high, I have the idle way low, I pull hard back on the throttle and crank for start, mags on, and it ignites nice and I push in on the throttle slowly and there is absolutely no kick on startup nice and smooth. Same with shutdown I pull back on the throttle and kill the mags, nice smooth shut off no kick. My way I guess. My idle is set at 500. OH no you say, well it never idles there it's just that way for 3 reasons on that. One for nice start up, shutdown, and so I can hang on the prop, you know nose down when I land, nice short landings, that with a flat prop I can land her on a dime on a really short approach, really fun.:D

[kitfox2009]

I am going to try your startup procedure. I have been choking AFTER I turn mags on. Always starts well, but maybe your method is even better. I do use your shut down and with the 80 horse there are no issues with kick back. I also like the slow idle idea. I have mine about 1400 but think I will move it down some more too. Great discussion.

Good evening

Don

[Monocock]

I also use the same method as Slyfox although I manually burp first.

1. Burp by hand
2. Throttle closed and choke on
3. Mags off
4. Crank engine with starter until oil pressure hits 40psi (5 seconds)
5. Choke off
6. Mags on
7. Crank starter.

In over 100 starts with this method I havent had one hard start now. I also have a low idle set (1000) which helps keep inertia down on shut down and a smooth end to your day.

[catz631]

EG,
This is good that this happened to you. This is one of the MAJOR reasons you turn the engine by hand prior to start.(that and oil quantity check) Think of the 912 as a radial.(at least when it has a high oil tank like the Kitfox)
I used to fly a couple of different bi planes that had Warner engines. Turning the prop by hand was a standard procedure prior to starting the engine. We often found hydraulic locks. In fact on a Meyers OTW it locked up so much that we installed a small mechanicalvalve on the lower cylinder intake tube to release the accumulated oil. Just open it,drain the oil after positioning the prop so the intake/exhaust valve was open to allow the oil to drain out of the head,close it,and you were ready to go.(didn't have to plug a spark plug every time that way)
Happy flying !
Dick

[kitfox2009]

G`day Slyfox
I have just tried your "choke ON" during the oil pressure crank and it works very well. Instant start-up every time.
Thanks for the tip. Mine always started well but this method is even better.
Cheers
Don.

[Dorsal]

I have also adopted this method, works nice (thanks Sly).

[Slyfox]

thanks guys.

[109JB]

Old thread, but working on engine installation for my rebuild project. The engine, with mount, oil tank and all was mounted on a stand for the last 10 months or so. I got it on the airplane, and went to turn the crank and it would not budge. Pulled the top plugs and the #4 was full of oil. I mean the top plug came out soaked in oil. Pulled all the bottom plugs and #3 also had some oil in it but not as much. Finding this thread, I understand it now, but is the quantity of oil I found concerning or should I just chalk it up to sitting for 10 months, do a prop pull-through on every preflight and just forget about it? Or, is there possibly a check valve or something like that I need to replace?

Thanks

[Av8r3400]

Always pull it through before starting.
Always use a Rotax oil filter. They have a check valve that *helps* prevent this from happening.

[desertdave]

^^^^^^^^^
This!

[henrysamson]

I have had this happen twice in seven years. Both times when the engine sat for a few months. I ALWAYS pull the engine through before starting. Always the left rear cylinder. Model IV with 912 ULS.