Rod / Main Bearing Replacement

[UNISA JECS]

Ok according to the FSM here is an example of how to get the bearing grade # for your "main" journal bearings.

Block #'s + Crank Counter Weight #'s = Grade #'s

Example:
22222 + 10111 = 32333

.................................................. .................................................. .
Here is an example oh how to get you "rod/pin" journal bearings.

Crank Counter Weight #'s = Grade #'s

Example:

1011 = 1011
.................................................. .................................................. ..

Ok now thats all fine and easy to do but in my experience on 3 SR's and now my KA not once have those numbers ever agreed with the actual part numbers on the bearings themselves, in fact all 3 SR's and my KA bearings had part numbers that were of the standard grade 0 respectivly accross the board for SR and KA.

So my question to anyone who may know, what gives? I dont think this can be coinincidental between 4 engines now? I also have yet to see a rod or main bearing with any indication of color coding either.

Straight from the FSM on how to get the grades and a FAST screen capture on rod bearing part numbers and there respective grades:

http://i167.photobucket.com/albums/u159/zilvia_album/SP32-20080314-180130-1.gif

ROD BEARING #'s:

http://i167.photobucket.com/albums/u159/zilvia_album/KA24DE%20REBUILD/SP32-20080313-214244.gif
http://i167.photobucket.com/albums/u159/zilvia_album/KA24DE%20REBUILD/SP32-20080313-214244.gif

[Xracer]

I use aftermaket bearings when i build motors, they only offer "standard" size or over sized breaings. Ive built 3 motors so far with aftermarket bearings in standard size and for each one the clearances were well within spec, nearly identical for each journal. I cant say that ive seen color codes on the OEM bearings either although i do know that they offer different grades to super fine tune clearances.

[Rambuck]

Yup. STD bearings are within spec. You can even get STD + 25 microns (0.001") aftermarket for a good crank that has been polished... However there is a good reason why you can expect 300k+ miles from a well-maintained Nissan without grinding the crank.

The OEM grades make a difference of only 3 microns (0.00012") in clearance. With six grades, you can cover the full range in allowed bearing clearance acceptable variance (up to 18 microns). For high performance, you would try to dial in a precise bearing clearance, uniformly equalized across all journals. You can make it tight (35 microns) or loose (53 microns) depending on your desired performance. Check your FSM to be sure of the numbers. These here are for my VQ30.

I'm surprised at your finding that your bearings weren't factory graded. So I checked my originals. They are all STD grade 0 as well. No problem sticking aftermarket STD bearings in there if the crank is still good. Just get a micrometer with 0.0001" accuracy and check.


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