> I have a 1988 Buick Park Avenue with 65K miles on the 3.8 L (balance shaft)
> engine that is(well was) in perfect condition.
>
> I have a rapping/knocking sound when the car is placed in gear, brake
> applied, and reved to approximately 1200 rpms. The rapping is so loud that
> is sounds like the rods are going to come through the block. The sound
> radiates across the complete engine. Doesn't matter if the engine is cold > or hot.
>
> Now the strange part. If I remove the serpentine belt the noise disappears,
> the engine runs perfect, smooth and no noise at any rpms, in gear or out. >
> The power steering pulley, water pump, and alternator pulley are all very
> smooth. Checked the damper pulley and bolt tightness...all OK!
>
> I have replaced the idler pulley and the tensioner spring assembly and also
> replaced the A/C compressor pulley bearing in hopes of eliminating the
> noise....no luck!
>
> I have rotated the belt, put a new one on....no help.
>
> Again the strange thing is the rapping noise is defening with the belt on
> and gone with the belt off.
>
> What kind of load is the serpentine belt applying to the the crankshaft to
> cause such a noise? How could this cause the crankshaft to move, if any, to
> make noise?
>
> Any help as to what to look at next would be appreciated?
>
With the engine running and the rapping noise present, get a long screwdriver and place the handle against your ear or other part of your head so that sound will conduct through the screwdriver, then start placing the screwdriver against various accessories until you hear the one making the most noise. It will be evident right away what the source is.
JazzMan