Loud Engine Noise

[nex916]

Hello everyone.
Quick Details: 1990 non-turbo Z 180,000 miles (previous owner claims rebuild at about 100K).

Instead of trying to describe the noise, I made a short video
https://www.youtube.com/watch?v=mKp592Eopx0

The engine went from sounding fine to making the loud noise driving down a gravel road (it wasn't something that started as quite noise and gradually increased). At first I thought is was a problem with the one of the guides for the timing belt. So I replaced the belt and guides/rollers. No change. I have all the other belts off to eliminate water pump or anything else (yes I only let it run for a few seconds that way). I have changed the oil on a regular bases.

I'm looking for advice on where to start looking for the source of the noise, any advice will be appreciated.

[ThisIsSparTTa]

Oh man, that sounds terrible. Might be good to go ahead and check for compression. Maybe your t-belt slipped and your valves all rammed into each other?

[nex916]

I still had a good 5-8 miles I had to drive home after the noise started, aside from the noise it drove normal, no temp or oil pressure problems. I do have a compression tester though, certainly wouldn't hurt to check. Thank you for replying.

[nissanfreak12]

I think your car is mad at you for putting those huge speaker whatever they are in the doors.

Try running it again, unplug the coils one at a time to see if noise changes. If it does or stops, that cylinder may be the culprit. The cylinder will not knock if its not getting combustion. Because the the car runs means your valves are not all bent, so no worries there, but that doesn;t mean something is not bouncing around in a cylinder or a piston is slapping the wall or the skirt it broken off.

Double check to make sure the starter is completely disengaging, flywheel doesn't have odd marks, all the pulleys for the t-belt or not making that noise. Check the tensioner and make sure its doing its job. Does it flop around wen it runs?