On Tue, 14 Oct 2003 15:30:32 -0400, "Ron Natalie"
wrote:


"Corky Scott" wrote in message ...

Pete, I'm assuming it's hydraulic lock because the starter cranked the
prop around half a turn and then jerked abruptly to a stop.

When you get hydraulic lock in a radial, it's not that the prop starts turning,
it's that the incompressable fluid tries (and succeeds) to expand the cylinder.
You can break a cylinder even pushing the prop through bu hand when oil is present.


I just called the mechanic on duty for the FBO that maintains the
airplane and described the situation to him. He too thought that it
was probably not hydraulic lock. The time I experienced hydraulic
lock as an auto mechanic was when I pulled a dead Subaru out of a
snowbank where it had been abandoned for a while and dragged it back
to the shop. I was a mechanic and needed a car and thought I could
get the thing running so I pulled it inside and let it warm up. The
starter spun a tiny bit and stopped like the pistons had hit a rock.
I removed the four spark plugs and tried again. This time, geysers of
water shot out of the spark plug holes. One squirt must have traveled
15 feet before it hit the shop wall ten feet up.

I put the spark plugs back in and tried starting it. It did actually
start, but ran so rough, with water spraying out of the radiator that
I immediately shut it off. Busted head gasket, pretty common with the
73 through 76 Subaru's: They had floating cylinder liners.

Anyway, the guy I was talking with claimed no one else had mentioned
this. I ventured that perhaps they just hadn't written it up, since
they always seem to get it running, as I did.

I've never studied the Lycoming starters, but it's possible the
bendix, if it has one, may be popping out prematurely, stopping the
crank sequence. Engine compression would stop the prop spinning very
quickly, since it's a 180 hp model.

But that doesn't adaquately explain why, when I tried to re-engage the
starter, it appeared to have trouble turning the prop. I had to
repeatedly turn the key to "start", again and again and the prop would
turn just a bit and stop. Sometimes it appeared to get over a hump
and turn for one complete revolution, but would then stop again.

I doubt that it's the battery, because when the starter finally
managed to get going, it spun the prop as fast as I've ever seen it
go.

This happened the very first time I tried starting it, when the
airplane had only around 38 hours on it.

The older (but same model 172) has never done this.

Corky Scott