New Aero Shell Sport Plus 4

[MrMorden]

Andy, while I may not always burp the engine I will pull it through at least 4-5 compressions or more to make sure I don't have hydraulic lock.

I have never heard of hydro-lock being a problem in the 912 series...has anyone had issues with this happening?

I do usually pull my prop through at least one turn, because I'm too lazy to bend over to inspect the prop blades...

[FastEddieB]

I pull my prop though one turn to check each of my 3 prop blades, necessary with my high mounted engine.

I think any more than that is excessive. I've been led to believe a lot of engine wear occurs on startup, before oil pressure can "float" the rings and plain bearings. Metal-to-metal sliding contact is to be avoided as much as possible, not prolonged. I've been taught that its best for the engine to just go ahead and start it - excessive "pulling it through" just causes more wear. Even in winter the concept of "limbering up the oil" seems to be an Old Wive's Tale.

But I'm not an engineer and will yield to anyone who knows different!

[designrs]

Most interesting Eddie. Thank you.

[3Dreaming]

Andy, while I may not always burp the engine I will pull it through at least 4-5 compressions or more to make sure I don't have hydraulic lock.

I have never heard of hydro-lock being a problem in the 912 series...has anyone had issues with this happening?

I do usually pull my prop through at least one turn, because I'm too lazy to bend over to inspect the prop blades...

Hydraulic lock is something they cautioned us about in school for the Rotax, and they had parts examples to show what happens.
I think the biggest area of concern is from fuel. With the top side intake manifold and a leaky float valve you can fill the intake with fuel.

[FastEddieB]

Hydraulic lock is something they cautioned us about in school for the Rotax, and they had parts examples to show what happens.
I think the biggest area of concern is from fuel. With the top side intake manifold and a leaky float valve you can fill the intake with fuel.

I'd think it would be mainly an issue with gravity-fed systems.

Otherwise no way the fuel would travel uphill to then flow downhill to get in the cylinders.

Right?

[sandpiper]

I have heard it is because some installations placed the oil tank too high. But, I don't know for certain.

I pull through a couple of times, mostly because that is what I have been doing for 50 years now.

[FastEddieB]

I have heard it is because some installations placed the oil tank too high. But, I don't know for certain.

Oh, I was thinking fuel, not oil.

Having trouble visualizing it, but I suppose it could happen.

My one encounter was with oil. My BMW airhead had fallen over while I was away. Good thing it was kickstart only - when I went to start it it was totally frozen. Oil had apparently seeped past the rings and filled the combustion chamber. That'll lock it up tight and do some real damage if an electric starter has enough oomph!

[MrMorden]

I have heard it is because some installations placed the oil tank too high. But, I don't know for certain.

I did some more reading, and that indeed seems to be part of the issue. The factory Kitfox location for the tank is above the cylinders, and a lot of owners moved it lower after a few had hydro-lock problems, it appears.

[roger lee]

The Kitfox was in fact the major offender in the beginning, but there have been others. In the Installation manual there is a spec on how high and low to mount the oil tank. Some have ignored that. Now back years ago with the old oil filter and pre-check valve and new anti drain back membrane this was a problem. If a tank was too high the oil could (not always) drain from the tank and seep into the cylinder. If you tried to start the engine without checking for oil in the cylinder the piston would slam to a stop on start because the oil would not compress in the cylinder. This will bend parts. The second issue was if people mounted the tank too low and that could syphon oil out of the tank back into the engine case. Ideally you want the oil in the oil tank to be at the same level as the oil pump. Approximately 12-14 inches below the prop shaft. With the introduction of the new oil filter from Rotax a few years back they installed an internal check valve, a new and better anti drain back membrane and increased the by pass pressure from 14-16 psi to 18-22 psi. The car and aftermarket oil filters some use have none of this. Most aftermarket oil filter by-pass pressures are at 13-15 psi. On start up the unfiltered oil flows into the engine. The check valve prevents oil from syphoning in either direction along with the new anti drain back membrane so most all the hydra lock is gone.
If you use aftermarket oil filters that lack these new features you are right back where the old Rotax filter problems were.

[Wm.Ince]

Good information Roger, thank you.
Dean Vogel (Lockwood) touched upon this when going through school with him.

In your opinion, would you say that the CTSW has a good vertical tank position?

[roger lee]

The oil tank position for the FD fleet is fine.

[drseti]

I did an oil change on a Sting Sport TL-2000 recently, and was surprised at how high on the fire wall the oil tank was mounted. The owner reported difficulty burping the engine. I wonder if the two are related?

[MrMorden]

Andy,
I'm going to go out on a limb and bet you case you got last week is red.

You should have laid money on it...you were right!