Rod knock or Hydraulic valve noise?

Long story short I'm new, experienced mechanic, and looking at a 90 B2600i.

It's got some horrid sounding clatter coming from the engine and I'm not convinced it's not a rod knocking. I was going to see if anyone has had experience with hydraulic valve clatter before and if what I'm hearing is in fact the valve train or the rod's playing taps?

Here's the video I took yesterday.

I watched and listened to the video. I don't have B2600i, but have owned a 1988 Mazda B2200 since 1994, and it sounds just like that. I even rebuilt the engine, but kept the same lifters, and still makes that noise most of the time.

Hydraulic lifter noise. Characteristic of Mazda trucks. Try new lifters if it matters to you.

Too slow at idle to be a rod. Definitely valve noise. Typical for high mileage Mazdas. Lifters are readily available, but I recommend verifying oil psi also.

Here is rod knock:



I concur with the other guys, it sounds like you have a collapsed lifter.

If my truck sits for a few days without running, it will sound like that,, but after it runs for 10 or 15 min, the noise goes away and doesn't return until I let it sit again!