Is it possible to replace engine bearings without removing engine (VQ35DE)?
How can I tell if engine bearings are in need of replacement?

 

Yes, but most likely something is going to have to be machined if you are in need of replacing the bearings.

Tolerances have to be checked to see if bearing fall in the appropriate range

 

Machined? Why?

 

If not, it is going to require machine work.

 

Oh. I see. Thanks. Do you know how much labor it's going to be to get it changed (without) machining?
Gee. I hope it's not the bearings.
BTW. How to tell if they're worn? Is that a thing that can be inspected only when diassembling the bottom of the engine?

 

There's something that needs to be asked before doing anything at all....

WHY do you suspect worn bearings?

And yes, you need to disassemble the entire block to inspect/measure. Think about it.... in order to drop the crank, you need to unbolt all the connecting rods (that's after dissassembling everything below and outside!), undo all the bearing caps and hope the pistons don't drop out once the crank is out. Oh, and let's not forget you're going to want to service the crank and re-do all of the rod bearings "while yer at it".

Then, in Chiltonesque wording, "assembly is the reverse of dis-assembly".... that is, once you figure out how to support the weight of the crank while you re-install all the bearing caps and reattach all the con rods with new bearings.

All while laying on your back on the cold garage floor.

Paints a grim picture? Well, uh, yeah.....

Frankly, I can't even fathom trying to do a crank bearing replacement in-car.... easier just to pull the motor and do it right.

VOE? Yeah, sorta..... (and no, I didn't try to do this but did enough similar stuff I no longer wish to consider.)