Who's that knocking..?

[johnholt@halhinet.on.ca (John Holt)]

bbell@csn.net wrote ...

< Other suggestions are reasonable; but one possibility for the knocking (
< assuming you have the 5cyl.) is the vacuum pump attached to the head (near
< the upper radiator hose manifold). this generates a fairly loud knocking
< that has a rather hollow sound. I thought connecting rods when I first heard
< it. Lifters will be higher pitched  and more of a chatter.the Vacuum.
pump has < a steel rod that is actuated by a camshaft eccentric.
< When it gets dirty it tends to stick then release with impact against the
< cam. Solution? Try a can of engine cleaner in the oil at idle for about
< 10-15 min then replace the oil and filter. don't rev the engine with the
< cleaner. It does not have great lubricating properties. You may have to do
< this over a couple of oil changes. Audi's like clean oil.

Over the last two years, the clanking sound was erratic and tended to occur
on cool mornings or after a long drive. I too thought it was a connecting
rod but I tried to justify it as a very bad lifter based on my time and
finances. Before your message, I was contemplating  a re-build because I
didn't know that the vacuum pump rod existed. The vacuum pump or rod
doesn't show in Haynes or Bentley. Before your post, I tried an engine
cleaner, two slippery additives and finally synthetic oil. There was no
change in the knocking but the lifter noise was quieter. Seeing your post,
I instantly knew that you had solved my problem. Having already
experimented with your solutions, I tried to remove the vacuum pump but the
2 nuts were under extreme pressure. I wasn't sure what I was going to lose
if the pump sailed off into the wild blue yonder. After removing the valve
train cover, I could see that the cam eccentric was putting the rod/pump
under pressure. After moving the crankshaft 180 degrees, the pressure on
the rod  was released which allowed removal of the rod/pump. After sanding
the rod with steel wool, removing the particles of steel wool from the rod
and coating the rod with oil, I re-assembled the pump/rod. Now I hear only
the sound of chattering valves. I guess it's possible that this will
re-occur but the rod, after releasing the pressure, is accessible from the
outside of the block - a 10 minute maintenance item.

This item should be in the archives because I couldn't find it. I suppose
this could have been posted before my subscribing to the list but ..... I
thank you for cluing me into the problem and saving me a bundle in time,
aggravation and money.

John Holt, (1988 90Q)
Highland Grove, Ontario, Canada


"The Major difference between a thing that might go wrong and a thing that
can not possibly go wrong is that when a thing that can not possibly go
wrong goes wrong it turns out to be impossible to get at or repair.

>From the novel "Mostly Harmless" by Douglas Adams