Ron:
I have never encountered a broken crankshaft, so I don't know
first hand what its syptoms are. However, I would think that if
you have compression in all four cylinders, and its uniform at
about 135 lbs/sq. in. then I would think its something else.
If the crank were broken, then the starter would only be turning
those throws still connected to the flywheel. Additonally as the
cam runs from the front of the crank, if the front of the crank
was broken off, you wouldn't get any valve action. To check, I
would remove just the valve cover, and see if all the valves are
opening and closing when the engine is turned by the starter.
That would verify that the compression is from the cylinders be
fed fresh air through the carbs, and its not just compressing the
static air within the cylinder.
Since you lost the drive, and if the engine checks out okay, I
would look at the clutch or transmission. Was the noise the same
whether the clutch was in or out? If the noise is always there,
then I would check the clutch. If the noise goes away when the
clutch is depressed, then I wouls check the transmission.
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