<VV> Did it go from bad to worse?
N. Joseph Potts
Tue, 11 May 2004 11:53:07 -0400
In my experience with methods like yours, I've found that air at 100psi WILL
find a way out of the cylinder, typically around the rings. An engine's
cylinders do NOT provide a true hermetic seal. The whole question turns on
the RATE at which air is passing your rings/piston, something you can judge
by the sound, but something a real leakdown tester might help you judge with
Before you disassemble, I think you should evaluate valve lift at the
cylinder. You've got your rocker arms loose already, so measure the lift at
the pushrods. In fact, before you do this, rotate your rocker arms out of
the way and remove both pushrods to make sure they aren't broken or bent.
Then you have to evaluate the possibility that you have a
stuck/collapsed lifter (which CAN be dealt with without removing the head).
Here, my experience runs out - I've never had a stuck or collapsed lifter.
But I DO know that either of these CAN produce a deficiency of compression
such as you're measuring.
So, perhaps someone else on the list will chime in with guidance
concerning the lifters.
Going on to an even simpler possibility, be aware that the
distorted-thread nuts that hold the rockers down CAN lose tension and back
out, producing compression loss. When this gets to a certain point (always
with the engine running), you hear the rocker arm clanking and clattering.
But perhaps yours didn't get that far. This happens when rocker nuts are
re-used too many times (thread tension wears down - they SHOULD be replaced
after one or two valve adjustments).
You've already upset your rocker nuts' initial positions, so you can't
look for the result I describe, but you CAN still evaluate the ability of
the nuts to "stick" to their studs. With the rockers turned off their
pushrods and valves, just crank the nuts down on their studs through the
point where the other nuts appear to be on their studs. You should
experience good, stiff resistance (don't know what the minimum torque would
be - 20ftlb?). To truly ELIMINATE this possibility, you should get two new
nuts, adjust the valves on #4, and check compression (engine hot on
I don't think you're ready to tear that head off, yet.
Miami, Florida USA
1966 Corsa coupe 140hp 4-speed with A/C
[mailto:firstname.lastname@example.org]On Behalf Of ChiefTAM@aol.com
Sent: Monday, May 10, 2004 9:48 PM
Subject: <VV> Did it go from bad to worse?
OK all you experts, here is where I am:
I have gone through all the basics. Moving my car from Iowa to my new home
in Texas. The car developed a miss about 700 miles out in Kansas, not after
fueling, while running, (69 Monza Convertible, 110hp, 4-speed, just under
50,000 miles). They drive it another 100 miles or so and park for the
get a trailer and go up and get it, don't notice any smoke or miss when I
start it up, but notice a bit of an off miss when I idle it after I drive it
around the block to the garage. Run a compression check, 150-160 in five
cylinders, #4 is at 60lbs.
Tonight, after borrowing an air compressor, I put a fitting in #4 and hook
up to the tank. Air comes RUSHING out of the carburator. I thought that
cylinder was at TDC, but when I wiggled the rockers, one was a little
than the other. SO, I proceeded to loosen both of the rocker arm nuts, so
that both springs had no pressure on them and should be at the top, with
I put it back on the compressor tank, heard no air from the exhaust system,
no air from the carburator now, but when I take off the oil filler cap, I
air coming from that.
SO, what does that mean. I assume from previous posts that air from the
carburator is a dropped valve seat, and that air from the exhaust is a burnt
valve. Is that right? So, air from the oil filler means what? Hole in
broken piston rings? Could it be anything else? Head gasket?
What say you experts? Am I really up the creek now?
I guess it is time to take the head off now.....