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
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
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
Any help as to what to look at next would be appreciated?