Re: Annoying Engine Tapping

[Jeremy R King <kingjer@eng.auburn.edu>]

After sealing my exhaust manifold leak, sealing the leak in the downpipe 
gasket, replacing 10 lifters, and attempting to quiet the knock of the 
plunger in the vaccuum pump, I'd consider myself at least knowledgeable 
in the area of tapping noises.  For all of you who keep recommending 
checking lifters when those of us ask for suggestions to quiet the rod 
in the vaccuum pump, I'd like to make a comment (this will probably 
finally get me kicked off the list).  While it IS possible to confuse the 
manifold leak noise with lifters TAPPING (one can definitely tell the 
difference), there's no mistaking the VERY PERCUSSIVE KNOCKING sound that 
the vaccuum pump plunger produces.  You don't have to go around bending 
your ear up against a screwdriver to tell where this knocking is coming 
from.  Even my dad - who knows nothing about Audis - (not to mention just 
about everybody else I asked) said that the noise didn't sound like 
lifters.  These people all described the sound (very accurately I think) 
as a lot heavier than lifters.  Plus the VW/Audi dealer I consulted about 
this said that they have NEVER replaced lifters in an Audi I5 because 
they've NEVER run accross a bad one.

Sorry.  It just seems impossible to mistake the vaccum pump knocking with 
lifter or exhaust leak tapping.  The knock is a $0 fix, the lifters are a 
$300 dollar fix.  If someone says the vaccuum pump rod is knocking, it's 
NOT lifters.

I guess now I should voluntarily refrain from contributing to the list.  
I do enjoy all of y'all's discussion.  And it's truly a joy to find 
others who appreciate the genius of Audi.

Jeremy R. King
1986 VW Quantum GL5
Audi at Heart

On Fri, 3 Nov 1995, Dan Simoes wrote:

> >      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,
> ANS 				http://coimbra.ans.net/dans.html
> 100 Clearbrook Road  			(914) 789-5378 (voice)
> Elmsford, NY 10523			(914) 789-5310 (fax)
>