I was driving along, minding my own business...

Ok I was rodding the **** out of my engine a few times last week - it's a d16y7 boosted 6 psi, stock internals. I noticed a klunk a few times I started it in the mornings. Then one afternoon it suddenly and while cruising around 60mph it started rattling.

I trailered it home and I've narrowed it down. I checked the valve lash and it was all good. Compression was about 145 on 1-3 cold. 4 was at 120 so I put a little oil in there and it went to 130. Also if I idle the engine without a spark plug in cylinder 4 it doesn't rattle. With a spark plug in there, connected or not it will make the loud tapping noise.

I don't know for sure what broke but my guess is a bearing on rod. It's time to build my engine I guess.

 

And the answer is

Spun rod bearing. Poor crank

 

that sucks. does that mean your swapping a motor in it then?