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How do I determine the correct bearings for my engineblock?

For the VG30DE(TT) Nissan does this through grades. During manufacture, casts like the block are made and then machined to a specified tolerance. To make it even tighter, there are generally 4 thicknesses of bearing available to make the clearance spot on and even across all contact with the crank. There are numbers stamped in conspicuous places on the block, crank, rods and piston tops to match up components. Nissan also supplies color codes on the bearings themselves.

Grade numbers are stamped on the oil pan mating surface on the bottom of the block next to each main bearing. Nothing stamped = 0, otherwise there will be a 1 or a 2 stamped as shown above. Write the numbers down F1234 IE: F0021.

The front counterweight lobe on the crank will have a series of grade numbers stamped on it as shown above. Specifically:

   1 1
 F2 2 

If there were 0's or blanks, they would be above the ones. The stamp is a block of 0's over 1's over 2's. Write these numbers down under the block numbers like gradeschool addition F1234 IE F2121 in the photo. Add them up

F0021
F2121
_____
 2142

The grades front to rear are 2, 1, 4 & 2.

For a TT, the part numbers per grade are:

Main 1 (Front):
Grade 0 = 12207-30P00
Grade 1 = 12207-30P01
Grade 2 = 12207-30P02
Grade 3 = 12207-30P03
Grade 4 = 12207-30P04

Main 1 is 12207-30P02

Main 2 and 3:
Grade 0 = 12207-30P20
Grade 1 = 12207-30P21
Grade 2 = 12207-30P22
Grade 3 = 12207-30P23
Grade 4 = 12207-30P24

Main 2 is 12207-30P21, while Main 3 is 12207-30P24

Main 4 (Rear)
Grade 0 = 12263-30P00
Grade 1 = 12263-30P01
Grade 2 = 12263-30P02
Grade 3 = 12263-30P03
Grade 4 = 12263-30P04

Finally, Main 4 is 12263-30P04

For a NA, the part numbers per grade are:

Main 1 (Front):
Grade 0 = 12207-30P00
Grade 1 = 12207-30P01
Grade 2 = 12207-30P02
Grade 3 = 12207-30P03
Grade 4 = 12207-30P04

Main 2 and 3:
Grade 0 = 12207-30P20
Grade 1 = 12207-30P21
Grade 2 = 12207-30P22
Grade 3 = 12207-30P23
Grade 4 = 12207-30P24

Main 4 (Rear)
Grade 0 = 12263-30P00
Grade 1 = 12263-30P01
Grade 2 = 12263-30P02
Grade 3 = 12263-30P03
Grade 4 = 12263-30P04

These parts are complete bearings (top + bottom). The 4th bearing looks alot different from the others, it has a 'thrust' portion on it. These are the surfaces that control forward and aft movement of the crank.

Mains on the crank are calculated, on to the connecting rods:

Each connecting rod has their position numbers stamped on the sides for both the rod and the cap (1-6).

On the opposite side, the connecting rod will have a 'F' and a grade number stamped on it. Like the block, nothing = 0. As shown above there may be 0s stamped otherwise there will be a 1 (there are no 2s). Ive' been told to ignore the numbers on the lower cap, just use the numbers on the connecting rod itself next to the F. The connecting rod bearings are sold in halves, not complete like the mains. So the top and bottom could be different numbers for different grades although I haven't seen it before. Write down all the grades F123456 IE F100001

The rear counterweight lobe on the crank has the connecting rod grades stamped on it. Nothing=0, although there's no F in this grid, so I think 0s might always be accounted for. The 'top' of the number grid is away from the center of the crank as shown in the image (the mains are the other way). Since the 1s have no sarifs, it might be difficult to know what end of the order is the front. Make another grid like the one for the mains:

F100001
 011111
_______
 111112

The grades for the connecting rod ends are 1, 1, 1, 1, 1 & 2.

Grade 0 = 12111-31P00 x2
Grade 1 = 12111-31P01 x2
Grade 2 = 12111-31P02 x2
Grade 3 = 12111-31P03 x2

5 Grade 1's are required 12111-31P01 x 10 and 1 Grade 2 is required 12111-31P02 x 2.

Connecting rod bearing are sold as halves, so make sure to order 2 of each grade.

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DamonZ