I always pull the prop through at least two revolutions - just to make
sure there is compression on all six cylinders.

As for there being no need to do so with opposed engines, I vividly recall
a pilot telling the story about what happened to him. It seems he had just
bought a new (to him) airplane, and was trying it out. It was an early
model Cessna 210, with fuel injection. He decided to find out how fast it
was, and laid out a course between two points along the Southern California
coastline. Then he flew the course with the throttle and prop firewalled.
To cancel the efect of wind, he planned to fly it in both directions. The
outbound pass went well, but on the way back there was suddenly a loud bang,
and the view out the windshield went black (covered with oil). Down he went,
sighting out the side windows as best he could. He ditched it in the ocean,
and managed to get out before it sank.

It gets worse. As there were no boats within sight, he swam to the beach.
There was no one there either. Then a boat came along, so he swam out to
it. About that time, some rescuers showed up on the beach, so he swam
back again. Later, the plane was recovered. They found that a cylinder
had blown off the engine, right through the cowling. The analysis was
hydraulic lock, caused by a leaky injector. The theory was that the
cylinder had filled with gasoline, and was overstressed when the engine
was started. It could have happened long before the final flight.

Worst of all, he had neglected to obtain insurance for his new toy. The
only good news in this event is that he walked (or rather swam) away
with only a minor injury.


David Johnson