Radial motors - hydraulically locked

[johnm]

hope the terminology is right ?

 

been wondering when a radial motor has hydraulic lock (oil bottom cylinders) I imagine you either pull the prop through or take the spark plugs out

 

a) how is that achieved when a radial powered flying boat is moored in water ?

 

thanks 

[facthunter]

You turn  the motors over with the starter a number of blades before you start it / them watching that they turn evenly.  Nev

[Student Pilot]

That's what I was told as a sprog pilot in the olden days Nev 👍 

[facthunter]

Yeah, I never had any hydraulic, but you did that for every start.   Nev

[old man emu]

So when you see videos of ground crew pulling through the prop of a big radial engined WWII fighter, are they priming or clearing a possible oil pooling problem?

 

Why do you have to burp Rotax's?

[Blueadventures]

34 minutes ago, old man emu said:

So when you see videos of ground crew pulling through the prop of a big radial engined WWII fighter, are they priming or clearing a possible oil pooling problem?

 

Why do you have to burp Rotax's?

Rotax done to check oil level in system.

[facthunter]

No they aren't priming it. Even if it  turns over you could still have a plug oiled up. AN 2's get pulled over by hand. They have a 4 blade prop which makes it easier.  Often when starting some of the ground crew  have a fire extinguisher handy. The engine is run on the primer initially before the fuel cut off  lever is moved to idle rich.   Nev

Edited March 23, 2023 by facthunter

[Area-51]

Rotax 9XX are rolled over at the beginning of each new day for two reasons; 1. To allow compression pressure to push past the rings and push oil out of the crankcase back into the reservoir for correct level assessment, 2. Primary function though is to ensure hydraulic lifters are fully primed with oil prior to startup, expelling any air that may of somehow settled after last shut down.

 

Engines started without a daily roll over have been known to suffer early valve train failure.

[rodgerc]

Rotax installation manual is very specific about the height of the oil tank in relation to prop shaft.
 

When I queried the detail with Flood Imports I was advised it was to avoid hydraulic lock from the tank being mounted too high. 

[Roundsounds]

A few things to remember about radials and hydraulic locks…

- never force the prop through a hydraulic lock when pulling through. Big radials have a clutch on the starter that’ll slip rather than force rotation through a lock. Big radials turn the engine over with mags off for a set number of blades (revolutions)
- if you force an engine to turn over through a hyd lock you’ll bend or break a link rod. A bent one will likely fail at a later time. 
- do not pull the engine backwards. This can force the oil into the intake manifold and suck it back in during engine start and break / bend a rod.