240 knocks

[nitrogt1]

My 89 240sx with a ka24 motor just started a very loud knock between 2500-3500 rpms, it's a faint, if any, knock outside of this range. A couple people have said it was the timing chain, but when you get under the hood it's not coming from the front of the engine, but more to the center. Out of timing? I'm not sure where to go from here. Any ideas?

[rogoman]

Most likely it's a rod/main bearing knock. To isolate a rod knock, pull off one spark plug wire at a time to see if the noise is reduced at the RPMs you specified.

[nitrogt1]

Thanks! I treid this and when I got to the 4th(back) cylinder, the knock was almost not there. This is a bearing causing the knock? Is it worth repairing, or is it time for an upgrade?

[rogoman]

Looks you've found a wiped out rod bearing. If the crank journal got damaged, the motor will have to be pulled out and the crankshaft reground. Now's a good time for an upgrade!