Bill McKee wrote:

When the valve breaks off there is not a little hole in the piston.
Normally the piston splits and the rod breaks. And the cylinder can crack
also. Makes a little tapping sound before a single big bang sound. Been
there, done that.


Pistons rarely have a hole burned through them, unless
you are running really hard and lean. Then you see aluminum on the
sparkplug when you pull the plug. And depending on the size of the head
gasket hole, and the speed of the engine turning, you get so little
compression, it will not register on the gauge. Takes a couple of PSI to
move the gauge. You have to overcome the Schrader valve spring in the
tester. Same for a burned valve. And if the rocker for the intake is
broken, you also get a zero to very low reading on the compression gauge.

I've changed Several head gaskets that showed SOME compression on the
gauge. I've never, ever seen a head gasket that would blow a chunk of
it out that it wouldn't read anything, seeing how the valve in the
tester keeps the pressure reading. Same with an burned exhaust valve.
The thing being, in your reply, you acted definitive. You could VERY
EASILY be wrong.

wrote in message
oups.com...


Bill McKee wrote:

When the valve breaks off there is not a little hole in the piston.
Normally the piston splits and the rod breaks. And the cylinder can
crack
also. Makes a little tapping sound before a single big bang sound. Been
there, done that.


Pistons rarely have a hole burned through them, unless
you are running really hard and lean. Then you see aluminum on the
sparkplug when you pull the plug. And depending on the size of the head
gasket hole, and the speed of the engine turning, you get so little
compression, it will not register on the gauge. Takes a couple of PSI to
move the gauge. You have to overcome the Schrader valve spring in the
tester. Same for a burned valve. And if the rocker for the intake is
broken, you also get a zero to very low reading on the compression gauge.

I've changed Several head gaskets that showed SOME compression on the
gauge. I've never, ever seen a head gasket that would blow a chunk of
it out that it wouldn't read anything, seeing how the valve in the
tester keeps the pressure reading. Same with an burned exhaust valve.
The thing being, in your reply, you acted definitive. You could VERY
EASILY be wrong.


I could be wrong about what is wrong, but I have seen several head gaskets
without compression. And my daughters Explorer broke the intake rocker and
zero compression reading.

Bill McKee wrote:
.. And my daughters Explorer broke the intake rocker and
zero compression reading.

How? Intake valve ALWAYS closed that way. So, when the piston comes up
on the compression stroke, both valves would be closed JUST EXACTLY
like they would be if the intake rocker wasn't broke.

Where does it get the air to compress? Pulls a vacuum when the piston goes
down before the compression stroke.

wrote in message
ups.com...


Bill McKee wrote:
. And my daughters Explorer broke the intake rocker and
zero compression reading.

How? Intake valve ALWAYS closed that way. So, when the piston comes up
on the compression stroke, both valves would be closed JUST EXACTLY
like they would be if the intake rocker wasn't broke.