My blazer has a bottom end noise at around 1700-2200 rpm and it sounds like a knock but im not sure. I was wondering if anyone else has had this problem and is there any way to queit it down. I have done quite a bit of driving and its not getting worse but it is annoying. Any ideas.

 

This may be caused by the balance shaft. GM has a technical service bulletin detailing the problem.

Here's another thread on the subject: Noise

I can post the procedure for installing the tensioner if you like, but it isn't the easiest thing to do.

 

If i leave it alone will it hurt anything?

 

The TSB doesn't detail the possible affects of leaving it alone...

To give you some idea of what is necessary to repair it, the whole front end of the motor needs to be disassembled. Right down to the timing set and crank gear. A bracket needs to be affixed to the front of the block and held in place by a set of dowel pins. The tensioner is then placed onto the bracket and the crank gear and timing set can then be reinstalled and the front of the motor put back together.

*EDIT* - whoops, for any '99+ you don't have to remove the crank gear. For the '96-'98, the TSB recommends the installation of a roller timing set which will require a different crank gear.

 

I had the same noise you are describing and got rid of most of it by switching to a better quality synthetic oil. I can still hear a little something, but I doubt anyone else would if they didn't know what to listen for.

I'm not positive on what was causing it and would still be very interested to find out.

If you replace the parts suggested in the TSB, I'd like to know if it fixed the problem and how much it set you back... $ wise. I'm guessing it's going to be an expensive proposition.