AD 76-07-12 Ignition Switch

[treebobboy]

I admit. I'm a low time pilot, but doing a ground idle check prior to shutdown, saved my bacon this last winter.  I always turn the prop thru three revs during preflight.  I actually had a P Lead break during a flight, and if I had not caught it on shutdown, who knows what might happened, two days later when I went flying again. The ground idle check is one of those things that should be on every checklist.  All you Mooney pilots USE your checklist-----RIGHT?

[ArtVandelay]

I was never taught to do this, and POH doesn't say to do it, it gets tested every annual, and I never turn the prop by hand except to get it horizontal to allow me to use the tow bar.

[Shadrach]

I always turn the prop thru three revs during preflight.  

Wow, this conjurs up a very nostalgic scene for me! Pulling the prop through was pretty common back in the '70s. I recall seeing pilots do this (including my father) when I was child. I don't recall anyone who preheated, but turning the prop through to "redistribute the oil and prime the oil pump" was the thing to do whether it was 90df or 19df. I think it was a left over from the days of radials. So what's the modern reasoning behind doing this?

Unless one is flying behind a Radial engine, I can think of no logical reason to do it other than wanting to indulge in some minuscule risk (starting an unprimed engine with the starter is challenging, I doubt it could be done by hand).  The real risk with a broken P-lead is after shutdown when the fuel in the lines is percolating fuel into the intake manifold. An SOS engine would likely not start, but the kick back could break bone.

[Mooneymite]

 

I'm not advocating turning a prop by hand.

A low, or no compression cylinder can be felt pretty easily when turning a prop by hand.  There's a guy in our neighborhood who can predict with fair accuracy an engine's compression readings by turning the prop through.  It may be the early indication that you need to do a full compression check due to a broken ring, or a valve problem.

I am not advocating turning a prop by hand.

[Shadrach]

 

I'm not advocating turning a prop by hand.

A low, or no compression cylinder can be felt pretty easily when turning a prop by hand.  There's a guy in our neighborhood who can predict with fair accuracy an engine's compression readings by turning the prop through.  It may be the early indication that you need to do a full compression check due to a broken ring, or a valve problem.

I am not advocating turning a prop by hand.

Couldn't the same thing could be done with the starter. Just crank for a sec or 2 without priming. I'm pretty sure a compression issue would reveal itself just as easily.

[kortopates]

Another reason I know of too pull the prop through by hand is to get the excess fuel out of flooded engine.

However, one of the things they teach you in A&P school is always pull the prop through backwards as a safety precaution. Such as to re-position the prop to attach the tow bar. Plus that old wives tale about breaking the vacuum pump turning the prop backwards is a myth.