Re: COMPRESSION? WHAT COMPRESSION?

["David R Johnson" <johnsnd@domain.elided>]

On Apr 6, 11:55pm, John Hammer wrote:

> My 2.5 Milano is very sick...my neighbor came over & did a rudementary
> compression test after the car started misfiring VERY BADLY the other
> day...there's almost NO compression in #5...Obviously I have a major
> problem here.  I have a good(and unfortunately, expensive) mechanic who
> can do anything I need, but how bad is this & do you know of options?
> No, I haven't taken it apart yet, so I don't know the extent of the
> damage.

Well, before you do something like pull the head, take a quick look under the
cam cover to make sure you don't have a broken spring.  If the valve is not
closing properly, this could be the cause of your minimal compression.  If you
are lucky, you may have gotten away with no bottom end damage.  If you are
outrageously lucky, the valve is still OK and you can replace the spring
without pulling the head.  I'm not sure if this is possible on the V6, but I
have done on an OHV engine.  The trick is to make sure the valve does not drop
when you remove the retainers.  This can be done by pressurizing the cylinder
with air (assuming you can get the valve to close at all), or by making sure
that the piston in that cylinder is at TDC so the valve will sit on the piston
crown instead of falling into the cylinder.  At worst it falls in and you pull
the head anyway.

Other possibilities include a holed piston (had any detonation problems
recently?), bent valve (if on 1 cylinder only then most likely due to broken
spring), dropped valve (ouch), or badly damaged rings (unlikely to result in
sudden total loss of compression I would think).  A blown head gasket is also
possible, but again I would think zero compression on 1 cylinder an improbable
result.  If the gasket is blown, you should see symptoms like white exhaust
smoke and/or froth in the oil or coolant.  Without some dissassembly it is
impossible to tell if the damage is as minor as a new valvespring or as major
as new piston and liner, plus bottom-end rebuild due to metal particles in the
oil (you could drain the oil and cut open the filter to look for this).  A
holed piston or bad rings may result in puffing blue smoke from the oil filler
(or other valve cover orifice) if the cap is removed when the motor is running.

Last piece of advice - I wouldn't run the motor again until the problem is
found.  A broken valve spring could be relatively minor, but if the valve later
drops start looking for a new motor :(.

Good luck,

Dave J.
1982 GTV6

- -- 

------------------------------