Hey guys, i have a serious crisis on my hands and could use ANY help.
i have a 93 300zx 2+2.
Just recently i spun a rod bearing and had to dig in and fix it.(Its a b!tch working on the z32's but im sure all of you already know this.)
We replaced the damaged bearing, but the connector cap and rod were all beat up, and had major damage. There were ridges on the cap and rod where the bearing would go.
So me and my dad ground it down so it was nice and even, replaced the bearing, put the rod back on the crank. I made sure there wasnt any loose rods(rod knock). Put the oil pan back on, changed the oil and filter she started up but had a knock.
the knock isnt noticeable when it starts up or idles,but when the revs hit 2500 it starts knocking. But as soon as you change gears it goes down, but picks up again at 2500. but in 3rd or 4th it wont start knocking untill about 32/3300 rpms.
I bought that lucas oil thickener or additive but it still knocks.
im completely dumbfounded by what the problem could be.
I hear it could be the rocker bar, could be a cracked connecting rod, the crank...etc etc.
what could this be?! do i have to tear apart the engine and rebuild it?!
PLEASE HELP!!!

 

Could be VTC gears, collapsed lifter, piston slap, something hitting the fan..etc You should try and narrow down the area where it's coming from. Also have you checked compression and checked your oil pressure?

 

Vtc gears? whats that?
Well the it sounds like it comes from the piston, or somewhere around cylinder 4(top right).
mainly sounds internal, but sounds like it could be coming from the bottom of the engine.
im almost positive it isnt anything hitting the fan, or itd be knocking all the time.
And if it were piston slap, what would need to be done to it?
the compression is fine, there isnt any loss of power or anything. and my oil pressure seems fine, it goes up to about 60 when driving around. should it be higher? its always been around 60 even since before i spun my bearing.

 

The VTC gears are the sprocket gears on the intake cams. There's a spring in there that wear and cause a tapping sound...more like a noisy lifter. I had one that was noisy and replaced both with the o-ring seal as well. Took care of the problem. The noise was noticeably coming from the front of the engine.

Try using a long screwdriver as a stethoscope to isolate where the noise is coming from.

 

Oh, alright. Well im thinking about posting a link to a video of my engine running, showing where the noise generally comes from, maybe then you'll know a little better if you can actually hear it. since we can explain back and forth all day but who knows if we're on the same page.
ill have it up by tonight, if not tomorrow morning.

 

 

Amazingly, my '93 Z32 is STILL passing emissions tests with front motor knocks, intermittently louder and quieter, they STOP completely over 2500 rpm...both while parked and at hwy speeds...would welcome any insight on this, been going on for almost three years...(do not drive this car much, use a '87 Z31 (ac works) and an HS130).....

 

Here is the title to a quick reply just made...Many Thanks ahead of time if somebody has insight on this unpleasant situation. It's very near time to replace the timing belt and sprockets, plugs, etc.... on this Z32, so will HAVE TO address this problem then anyway!....