Lew,
I think that whereas the opening of the normally operating inlet valve
allows a full swept volume of air to enter the cylinder, then to be
compressed, the cylinder without any valve opening will usually give a
(lesser) pressure because it will have started out prior to the test
with an amount of air in each cylinder dependent upon the position of
the cylinder's piston which cd be anywhere.
Only if the cylinder is at BDC wd the pressure be at a max.
It seems possible that all four cylinders started out with their
cylinders midway between TDC and BDC.
.....Pat
Pat Mullen wrote:
>
> Lew Palmer wrote:
> >
> > OK, folks. I have another mystery.
> >
> >
> >
> > I've been finishing the restoration on a J2 for a fellow club member.
> > Unfortunately, I did not assemble the engine, and the person that did
> > apparently had no clue on how valves are adjusted on triple-M engines.
> > Therefore, when the head was assembled, there was insufficient (read NO)
> > clearance on the intake valve on #4 cylinder and precious little on the
> > exhaust valve. A compression test showed around 95 pounds on each of
> > cylinders 1, 2, and 3, and zero on #4.
> >
> >
> >
> > Hoping to discover it was only the tight valves causing the problem, I
> > then removed the cam shaft so that all valves should have been closed.
> > To my surprise, #4 cylinder now showed about 45 pounds. To my further
> > surprise, #1, 2, and 3 now read between 45 to 50 pounds.
> >
> >
> >
> > What would cause a normally operating cylinder (with valves opening and
> > closing properly) to show 95 pounds pressure and that same cylinder to
> > show 45 pounds with both valves closed?
> >
> >
> >
> > Please help clear up the fog from my brain and give me a hint of what
> > I'm missing.
> >
> >
> >
> > Regards,
> >
> > Lew Palmer
> >
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