I believe I developed a rod bearing noise a couple months back due to low oil level + detonation issues. Symptoms include:

- Noise evident when motor is warm/cold; does not vary;
- around 2500 - 4000 rpms when I 'float' the gas pedal in this range or decelerate; noise not present under load/acceleration;
- Noise consistent with rpms
- found to have EXTREMELY low oil level around time noise was discovered.

Of course, it could very well be piston slap, or 10 other possible noises depending on what you reference. Admittedly, I'm not very savvy when it comes to engine noises, and trying to firmly diagnose anything via the Internet is impossible.

I was thinking about dropping the oil pan one weekend and replacing the rod bearings myself? Has anyone tried this on the Z while the engine was still in place? If rods are bent, will new bearings do anything to stave off failure until a new block is purchased? Should I/can I replace anything else while I'm under the car? Will I even be able to tell if the bearings need replacement if I drop the oil pan? Will I need to also remove the upper oil pan?

I'm saving the pennies for a built block - teased the idea of putting in new rods/pistons while I was in there but I've never performed internal motor work myself and dunno that I'm brave enough to tackle it at the moment.

The other option is to keep my fingers crossed, hope for no immediate failure, and follow through on the block purchase.

Input is appreciated

 

You can't do rods and pistons from the bottom.

 

Also ---In an oil starvation situation, the farther u get from the lube source, the worst the damage. Ur going to have probable Cam Journal issues

 

Hey Joe,
The sound that you are describing could be indicative of a rod bearing failure, but given how easily the stock rods bend when encountering detonation or higher than normal levels of load, I would be willing to bet that some deformation of one or more rods is present.

We have pulled apart several vq35 motors; some water damaged, some fire damaged, some with a "spun bearing" and others that have been run with F/I without severe symptoms... several of these motors have had bent rods, twisted rods, or broken ringlands on the pistons.

You could definately replace the rod bearings from the bottom, but this would probably turn out to be an extreme waste of time, as I'm willing to bet, if a rod bearing did go, if that is what indeed is causing your suspicious sound, then the rod bearing's demise was predisposed by a less than perfect oem rod. Let's suppose that the rod is perfect, but the bearing is compromised from a low oil situation...then chances are the rod journal on the crank is not so happy, possible scoring present, if this is the case, replacing the bearings would not help, as the crank needs to be turned, at least .010 to reveal a new clean surface.

My advice:
Stop driving the car, as the motor sounds like it is unstable and will likely let something go soon...if the core is still rebuildable/tradeable for a core charge now, don't lose that , as a block with a hole in it, or heads that are chiseled away from an exploded piston are only good for oversized paper weights. Good luck, let me know if I can help and when you are ready.
We can ship you a motor in about a week. (or a sleeved shortblock immediately!!!)

-TODD

 

would be a royal PIA to do it from underneath and extremely messy. If you have to replace rod bearings and your motor is otherwise stock and you plan.or currently run FI, now is the time to just build a bottom end.

if your rods are bent replacing bearings won't do a thing for you - you have to replace the rod (and bearings)

 

thought that's what I said guess you are giving me a +1... glad we agree

 

 

Sadly, she's also my daily driver so I'll have to drive less aggressively until the piggybank is replenished. I'll keep my fingers crossed that it'll hold out until then

Thanks to everyone for the feedback!