O. Sami Saydjari wrote:
First, I must say that I am not a mechanic by any stretch. I am just
learning this stuff, so I might have misunderstood what the shop was
telling me. Hopefully, an expert will chime in here soon and explain
this a bit better.

That said, I am not sure I understand what is you did not understand. It
seems to me that if the crank shaft breaks, you end up with essentially
two engines: a set of cylinders running one side of the shaft break and
the rest running the other side of the shaft break. So, it would seem
that some cylinders are running the engine parts (oil pump, magnetos,
etc) and the others are running the prop. Of course, if the break
occurs right next to the prop, then the prop would stop. If it breaks
behind the main rear bearing, then all of the engine accessories stop
(and thus the engine stops soon after). Also, I should point out that
the shop speculated that even though the shaft broke, that in might have
been partially connected through friction (since the break was not a 90
degree shear break).

Seems likely to me that the front and rear parts were fairly strongly connected
if you were able to get enough power out of the engine to keep flying for a few
minutes, as I think you said you did. The rear part of the crank would have the
drive gear that turns the cam (and in turn, the magnetos) and the front part of
the engine is not going to make much power unless the cam and magnetos are
pretty well synchronized with it.

It doesn't bother me that part of the shear looks like fatigue cracking and the
rest looks like a catastrophic failure. The fatigue crack weakened the shaft to
the point where it could finally fail catastrophically, no?


Now, I will hasten to add that my understanding of crank shaft operation
may be overly simplistic, so again, I will defer to expert opinion as it
comes in. I am sharing all of this to get as much out of it as a
learning experience as I can.

-Sami
N2057M, Piper Turbo Arrow III

Bill Hale wrote:

"O. Sami Saydjari" wrote in message
...

Updated update: I was just down at the overhaul shop today )Poplar
Grove). The crank broke just in front of the rear main bearing. So
the front 5 cyclinders were running the prop and the rear-most
cylinder was running the gearing to the rest of the engine. They
said the whole shop stopped to come take a look at the engine! They
were astounded that it ran 10 minutes after the crank broke (which is
exactly the time I needed to get to the nearest airport and land
safely).



How can this be?? The crank drives the camshaft then the mags run from
gears that mesh with the cam gear... at least it's like that on every
other continental I've seen.

So the cam and maqs and oil pump quit working if the crank breaks.

It would windmill, however. Until it locks due to lack of oil.

What don't I understand? If there was metal in the oil filter, the
oil pump must have been running.

Bill Hale




--
Dave Butler, software engineer 919-392-4367