My 1991 Bonneville SSE, started this loud knocking sound when its in park idling. When the car is driving there is no knocking sound, when I hit the brake there is the loud knocking sound. Does anyone know what the problem could be?

Thanks!

Possibly the harmonic balancer (crank pulley) has shredded its rubber. If you grab the accessory belt, can you move it so that the pulleys rotate a few degrees? If so, the HB is the problem.

Mechanics stethascope would help you a lot as we can't tell where the noise is coming from online unless you narrow down the area for us. Otherwise we would just be guessing.

Does it sound like this?



Nevermind the fact there is nothing to watch. It'* the sound you are concerned about.

[quote="sandrock"]Does it sound like this?

Yes that is what it sounds like.. I was told todat that the timing chain gears are shot, and that the chain is hitting the side of the timing case.. I can still drive it but I have to put the car in N at stop lights..

Thanks!

Hmm...only does it at idle? Timing gears on these engines rarely, if ever, go bad. Chains tend to stretch, but not bad enough to jump time. Chain tensioner MAY be bad, but either you have rod knock or like stated before, the HB.

Yes it does this while in idle. It does NOT rattle when I'm in drive, when I stop at lights it will rattle loud, I have to put the car in N and give it a bit of RPM'* to stop the rattle.. Then when I start to Drive it will rattle just for a second. It rattles loud when car is in R. I put the car into the 1 & 2 gears and it rattled LOUD! Like I said abive only while in D it will not rattle unless at a stop light..

You think it is the HB?

If you're not moving and have the shifter in 1 or 2, does it rattle? I'm not sure I understand what you wrote.

Based on the way the noise has been described so far, it sounds like the harmonic balancer has separated. The noise is present while idling in gear, but is diminished when driving.
The easy test for this has already been suggested. With the engine off, try to roll the accessory belt one way or the other while watching the crank pulley hub. If the belt moves and the hub doesn't, you need a new pulley. They cost about $100 retail in the lower 48.

dude, its harmonic balancer for sure. It just happened to me last weekend and I got really scared. I started to replace tensioner pulleys and then I saw harmonic balancer rubber separating from crankshaft. Take a closer look and then go get some parts, its easy job.