98 Mercury Grand Marquis 4.6 v8 130,000mi. On a cold start the engine makes a loud hammer/tapping or slapping noise. It is not constant but intermittent. The noise stops when the serpentine is removed. I replaced the idler pulley and the tensioning pulley, and had a good shop check a/c compressor and it is ok. Also the power steering pump and alt. seems ok. Is it possible that the harmonic pulley could make that kind of noise? What could it be? Also, when the noise happens, I can see that something is locking up as the tensioning pulley arm hunts. Thanks, John

 

A Bad water pump bearing can sound like it's full of rocks & it comes & goes like you're describing. Spin it by hand with the belt off & see if you feel any binding.

 

mecka nick,
Thank you very much for your reply. I am inclined to agree with the w/p bearing diagnosis. However, when I take off the belt and spin and shake the w/p sheeve it seems to be OK. Also, the serpentine runs one grove off, on the harmonic balance pulley on the crankshaft exposing the outside groove of the h/b pulley. I guess maybe
I'll just drive it 'till it gets bad enough to tell that that is really it.
Thanks again,
John

 

Sounds like a broken spring in the tensioner. You stated you changed the tensioner pulley but did you change the whole tensioner? Something is not right if your belt is not alligned right. The tensioner spring could be broken making the tensioner pulley smack against the front timing cover. The spring gets hot,expands & keeps the tensioner away just enough so as not to hit the cover. You'll see rub marks right behind the pulley. If that's a no go then eyeball along each pulley & compare to a corresponding pulley & make sure all is square & ligned up.