I uploaded a video of my 2000 GMC Jimmy 2WD making a knocking sound. I’m not sure whether the noise is coming from a bad connecting rod, crankshaft, or possibly the torque converter. I’m hoping someone with experience on the GM 4.3L can help identify it.

It has been about 6 months since I removed the transmission and engine mount. One of the engine mounts was completely destroyed the rubber layer was totally gone and I believe this may have caused or at least worsened the knocking sound.

The situation is very difficult where I live. In my country, it is almost impossible to find a clean 4.3L GM engine. Most engines available are already in very bad condition, and rebuilding or importing parts is extremely expensive. Sadly, most GMC Jimmys and Chevy Blazers here are now being sold as scrap metal, so good parts and donor vehicles are nearly nonexistent.

At this point, I honestly don’t know what to do whether to rebuild this engine, try to find another one, or give up on the project entirely. This truck means a lot to me, and I don’t want to make the wrong decision.

Please take a look at the video and let me know what you think the sound could be. Any advice or guidance would be greatly appreciated.

Video link:

 

First take the drive belt off and see if it stops. Then check torque converter bolts if still makes noise. on a 4WD Blazer the torque converter bolts are accessed by removing the starter and working through the hole where the starter sits (not fun).

 

wow, looking forward to this one !

 

I second removing the drive belt to see if the noise stops. Years ago I had a car (not a GM) with an alternator that developed some kind of bearing issue, and it made quite the racket

 

Unfortunately, I have already removed the drive belt but it was still have same sound and it becomes much louder when I rev up engine. Regarding torque converter bolts yes I have notice one bolt was very hard to tighten and it was sit uneven with flexplate surface.

 

Will the torque converter bolts move back and forth laterally in the holes of the flywheel? Could also be a broken flex plate (flywheel for automatic transmission) around the 6 bolts that attach it to crankshaft. It does not sound like an internal bearing knock to me.

There is a hole in the transmission bell housing directly at the bottom near the front. Can you stick a screwdriver in there and pry around to see if anything with the flex plate or converter seems loose?

 

I have removed flex plate but I didn't notice any cracks. I only found one bolt was very hard to tighten and it was sit uneven with flex plate surface so I make a new thread using same size tap and now it is tighten normally and and straight and the new replaced rear main seal before few months was twisted and leaking so I replace it. Transmission already taken off and flex plate replaced with new one.

Now which is left is to install transmission again and run car to see if still this sound remain or gone.

 

good luck and best wishes!