At 11:27 PM 9/7/2000 -0400, Steve Morris wrote:
>....
>Cylinder #1 165#
>Cylinder #2 90#
>Cylinder #3 95#
>Cylinder #4 150#
>....
>Then I did a blow-down test ....
>....
>Cylinders #2 and #3 on the other hand, lead me almost inescapably to the
conclusion that I have blown a bit of the head gasket between the two.
Putting the air hose to #2 (with it at TDC) blows right back out #3, with
nothing coming from the tailpipe, carbs, or filler. Same with #3 (comes out
#2.) ....
Note: Since the #2 and #3 pressure readings are so close together, I would
also place a fairly high probability on a blown head gasket. However,
there is the possibility that you do not have a blown head gasket, but that
you have two slightly burnt exhaust valves. When #2 is on compression #3
has the exhaust valve open, and since these cylinders share a common
exhaust port anything blowing past #2 exhaust valve will readily blow
through the open #3 exhaust valve and hiss out through the #3 spark plug
hole. Unfortunatly, pluging #3 and listening at the tailpipe won't tell
you which problem you have, because either a blown gasket or a leaky #2 or
#3 exhaust valve will hiss out the tail pipe.
Because of the high oil consumption it sounds like you are at least in for
pulling the head to install new valve guides. When the head comes off you
will be better able to assess the condition of the valves and gasket.
>....
>.... I'd like to run it until the weather gets cold, but I don't want to
ruin anything by putting it off. ....
I'll stick my neck out here and make a few subjective comments based on
prior experience. If the compression problem is bad valves the damage is
already done, and there isn't much risk in running it a little longer. A
blown head gasket is a little more iffy, but also not immediately terminal.
With the compression numbers you have it should still start okay, just may
idle a little rough. You might want to repeat the compression check on the
two center cylinders every few hundred miles, and as long as it doesn't get
worse you will likely not be causing (much) additional harm by driving it a
little more. When the head does finally come off for valve work it can be
resurfaced to assure flatness before reassembly. The block is usually not
damaged by a leaky head gasket, and can generally be cleaned up by rubbing
with a wet stone and oil.
There is of course some limit the amount of this kind of abuse that the
engine will tollerate. If you continue to run it indefinitely, at some
point the valves will be totally fried, or the head gasket will let loose
all together. Continueing to run it with lots of exhaust gas blowing
through the gasket area can erode the head in the center, and possibly the
top of the block as well. Required repairs to valves and seats is probably
the same regardless.
$.02,
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
|