REMOVAL & INSTALLATION
See Figures 1 through 7
Before removing the crankshaft check the main bearing clearances.
- Remove the piston and connecting rod assemblies.
- Check crankshaft thrust clearance (end-play) before removing the crankshaft from the block. Using a prybar, carefully pry the crankshaft the extent of its travel forward, and measure thrust clearance at the center main bearing (No. 4 bearing on V6 engines, No. 3 on 4-cylinder engines) with a feeler gauge. Pry the crankshaft the extent of its rearward travel, and measure the other side of the bearing. If clearance is greater than that specified, the thrust washers must be replaced (see the main bearing installation procedure found later in this information).
- Using a punch, mark the corresponding main bearing caps and saddles according to position: one punch on the front main cap and saddle, two on the second, three on the third, etc. This helps ensure correct reassembly.
Most of the engines covered by this manual utilize a single main bearing cap assembly. Obviously, for these engines it is unnecessary to individually matchmark the bearing caps to each cylinder, but care should be taken that the proper orientation of the assembly is noted during removal. And, if bearing inserts are to be reused, they MUST be reinstalled in their original saddles.
- Remove the main bearing caps after they have been marked.
- Remove the crankshaft from the block.
- Follow the crankshaft inspection, main bearing clearance checking and replacement procedures before reinstalling the crankshaft.
Crankshaft inspection and servicing should be handled exclusively by a reputable machinist, as most of the necessary procedures require a dial indicator and fixing jig, a large micrometer, and machine tools such as a crankshaft grinder. While at the machine shop, the crankshaft should be thoroughly cleaned (especially the oil passages), Magnafluxed (to check for minute cracks) and the following checks made: main journal diameter, crank pin (connecting rod journal) diameter, taper and out-of-round, as well as run-out. Wear, beyond specification limits, in any of these areas means the crankshaft must be reground or replaced.
MAIN BEARING CLEARANCE CHECK
See Figures 8 and 9
Checking main bearing clearances is done in the same manner as checking connecting rod big-end clearances.
- With the crankshaft installed, remove the main bearing cap. Clean all oil from the bearing insert in the cap and from the crankshaft journal, as the Plastigage material is oil-soluble.
- Lay a strip of Plastigage along the full width of the bearing cap (or along the width of the crank journal if the engine is out of the truck and inverted). On engines which utilize a single main bearing cap assembly, you can save time by placing the gauging material on all bearing caps and checking them all together.
- Install the bearing cap and torque to specification.
Do not rotate the crankshaft with the Plastigageinstalled.
- Remove the bearing cap and determine bearing clearance by comparing the width of the now-flattened Plastigage with the scale on the Plastigage envelope. Journal taper is determined by comparing the width of the Plastigage strip near its ends. Rotate the crankshaft 90 and retest, to determine journal eccentricity.
- Repeat the previous steps for the remaining bearings. (If your engine uses a main bearing cap assembly, it is easier to check all bearings at the same time since the entire assembly must be bolted and unbolted for the clearance check). If the bearing journal and insert appear in good shape (with no unusual wear visible) and are within tolerances, no further main bearing service is required. If unusual wear is evident and/or the clearances are outside specifications, the bearings must be replaced and the cause of their wear must be found and corrected.
MAIN BEARING REPLACEMENT
See Figures 10, 11, 12 and 13
Main bearings can be replaced with the crankshaft either in the engine (with the engine still in the truck) or out of the engine (with the engine on a work stand or bench). Both procedures are covered here. The main bearings must be replaced if the crankshaft has been reground; the replacement bearings are available in various undersize increments from many auto parts jobbers or your local Nissan dealer.
- Remove the crankshaft from the engine block.
- Remove the main bearing inserts from the bearing caps and from the main bearing saddles. Remove the thrust washers from the No. 3 (4-cylinder engines) or No. 4 (V6 engines) crank journal.
- Thoroughly clean the saddles, bearing caps, and crankshaft.
- Make sure the crankshaft has been fully checked and is ready for reassembly. Place the upper main bearings in the block saddles so that the oil grooves and/or oil holes are correctly aligned with their corresponding grooves or holes in the saddles.
- Install the thrust washers on the center main bearing, with the oil grooves facing out.
- Lubricate the faces of all bearings with clean engine oil, and place the crankshaft in the block.
- Install the main bearing caps in numbered order with the arrows or any other orientation marks facing forward. Torque all bolts except the center cap bolts in sequence in two or three passes to the specified torque. Rotate the crankshaft after each pass to ensure even tightness.
- Align the thrust bearing by prying the crankshaft the extent of its axial travel several times with a prybar. On the last movement, hold the crankshaft toward the front of the engine and torque the thrust bearing cap to specifications. Measure the crankshaft thrust clearance (end-play). If the clearance is outside specifications (too sloppy), install a new set of oversize thrust washers and check the clearance again.
On engines with a single main bearing cap assembly, it is much more difficult to replace bearings with the engine and crankshaft still installed. If this is attempted, make sure the crankshaft is safely supported while the bearing cap assembly is removed.
- Remove the main bearing caps and keep them in order.
- Make a bearing roll-out pin from a cotter pin as shown.
- Carefully roll out the old inserts from the upper side of the crankshaft journal, noting the positions of the oil grooves and/or oil holes so the new inserts can be correctly installed.
- Roll each new insert into its saddle after lightly oiling the crankshaft-side face of each. Make sure the notches and/or oil holes are correctly positioned.
- Replace the bearing inserts in the caps with new inserts. Oil the face of each, then install the caps in numbered order with the arrows or other orientation marks facing forward. Torque the bolts to specification in two or three passes of the appropriate sequence.