Re: Annoying Engine Tapping

[Dan Simoes <dans@ans.net>]

>      My 88 90Q has the vaccum assist unit.  The tapping has become 
>      progressively worse over the two years I've owned the car.  

Heidi (and fellow tap-tap victims),

In my experience, there are at least 4 possible causes of 
engine 'tapping':

a) worn hydraulic lifters.  Initially these will be noisy when cold
and then quiet down a bit when warm,  but on my 90 they were 
loud all the time (sounded like a diesel).  After I replaced them,
the car was quiet ALL the time, even at startup.
New lifters cost around $8 each and there are 2 per cylinder, so
$80 plus labor (an hour or two I'd guess) involving the removal of
the valve cover, camshaft and cam sprocket.

b) distributor.  This is pretty uncommon but does happen according
to my mechanic

c) leaky exhaust manifold or broken studs.  This is pretty common
too, but easier to detect since when the manifold warms up it
expands and plugs the leak, so no more noise.  I'm not sure what this
will cost but it's labor intensive.

d) vacuum pump 'plunger'.  The pump itself is expensive, but in 
the archives you'll find a note from Ned Bennett with part numbers
for the rod and seals, supposedly only around $20.  Chris Ice wrote
up how to remove the pump (it's pretty simple) so if you or anyone
wants to, you can try removing the rod to see if it cures the noise.
I would also test whether or not is is needed.  I would worry a bit,
since it's obviously there for a reason...

I found that a stethoscope is the best way to confirm where the noise
is coming from.  Or, you can hold a large screwdriver to the
engine (blade down) with the handle against your ear.  Does about
the same thing, and you will be able to 'feel' where the tapping
is coming from.

If you haven't had new lifters installed on the 80, I would bet
that is the problem.

| Dan |
-- 
Dan Simoes			          dans@ans.net
Heidi,
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