Nasty rattling/knocking noise, 98 LSS

[4boostin]

I know that this is a Grand prix forum, but i figured i'd get some good help here, not too many supercharged oldsmobiles.
My supercharged LSS is making a scary knocking noise at and below 1100 rpms, it gets worse when i put it in gear and just sit there with the brake on. I've removed both belts and tested all the pulleys, they're all solid. But when we try to turn the motor a bit manually by spinning the either belt while attached, the main crank pulley only goes so far in either direction, clockwise or counter, and clanks to a stop, making a similar noise to the one it makes while running. (We took the main belt off and turned the motor a bit with the other attached, and also with did the same removing the supercharger belt.) Note that the noise fades out quick as the rpms raise in gear or not. Could this be my harmonic balancer? And if so, what does that entail to fix it/replace it?

[grandprixgtx00]

Originally Posted by 4boostin

Could this be my harmonic balancer? And if so, what does that entail to fix it/replace it?

that was my thought while reading your description. while removing the balancer, you have to ensure the motor will not turn over. I put a small pry bar in the flywheel to keep it from turning over. you can do so by removing the inspection cover located by the starter. you will also need to purchase a puller to remove the harmonic balancer. they can be purchased fairly cheap at most automotive stores.

[CrazyHorst]

I made up this tool to restrain the crank from the pulley end while the balancer bolt is removed or installed. Advantage is that you can probably work alone but will need access to holesaws/drill presses and a welder and some time to make it up first.

[CrazyHorst]

Oh yes...while you are in there I would strongly recommend changing the crank sensor if you haven't done so yet.

[tblake]

try running it with the belt off and see if the noise changes.

I'm also leaning towards a bad balancer.