Nissan Pick-ups and Pathfinder 1970-1988

Pistons and Connecting Rods

Print

REMOVAL & INSTALLATION



See Figures 1, 2, 3, 4 and 5

All Engines

Before removing the piston assemblies, connecting rod bearing clearance and side clearance should be checked. Refer to the Connecting Rod Inspection procedure in this section.

  1. Remove the cylinder head as outlined in the appropriate procedure earlier in this section.
  2.  
  3. Remove the oil pan and pump.
  4.  
  5. Position a cylinder ridge reamer into the top of the cylinder bore. Keeping the tool square, ream the ridges from the top of the bore. Clean out the ridge material with a solvent-soaked rag, or blow it out with compressed air.
  6.  
  7. Remove the oil strainer if it is in the way. Unbolt the connecting rod caps, after matchmarking each cap to its connecting rod.
  8.  
  9. Place pieces of rubber hose over the rod bolts, to protect the cylinder walls and crank journals from scratches. Push the connecting rod and piston up and out of the cylinder from the bottom using a wooden hammer handle.
  10.  

It is advisable to number the pistons, connecting rods and bearing caps in some manner so that they can be reinstalled in the same cylinder, facing the same direction, from which they were removed.


CAUTION
Use care not to scratch the crank journals or the cylinder walls.

  1. Mark each connecting rod with the number of the cylinder from which it was removed. Number stamps are available at most hardware or auto supply stores.
  2.  

To install:
  1. Apply a light coating of engine oil to the pistons, rings, and outer ends of the wrist pins.
  2.  
  3. Examine the piston to ensure that it has been assembled with its parts positioned correctly (see the illustrations). Be sure that the ring gaps are not pointed toward the thrust face of the piston and that they do not overlap.
  4.  
  5. Place pieces of rubber hose over the connecting rod bolts, to keep the threads from damaging the crank journal and cylinder bore. Install the pistons, using a ring compressor, into the cylinder bore. Be sure that the appropriate marks on the piston are facing the front of the cylinder. (see Identification And Positioning)
  6.  

It is important that the pistons, rods, bearing, etc., be returned to the same cylinder bore from which they were removed.

  1. Install the connecting rod bearing caps and tighten them to the torque figures given in the Torque Specifications chart.
  2.  

Be sure that the mating marks on the connecting rods and rod bearing caps are aligned.

  1. Install the oil pump. Install the oil pan.
  2.  
  3. Install the cylinder head.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the cylinder block-Z20, Z22, Z24 and Z24i engines (L-series engines similar)



Click image to see an enlarged view

Fig. Fig. 2: Exploded view of the cylinder block-VG30i engines



Click image to see an enlarged view

Fig. Fig. 3: Exploded view of the cylinder block-SD22 and SD25 engines



Click image to see an enlarged view

Fig. Fig. 4: Removing the piston and connecting rod assembly from the cylinder block



Click image to see an enlarged view

Fig. Fig. 5: Installing the piston and connecting rod

IDENTIFICATION AND POSITIONING



See Figures 6, 7, 8, 9, 10, 11, 12 and 13

The pistons used in gasoline engines are marked with a notch in the piston head. When installed in the engine, the notch markings must be facing towards the front of the engine. Additionally, late model VG30i engines have a W mark on the piston skirt and this must face forward. The pistons used in diesel engines are less obvious-they have no marking-instead, they have a leaf-type combustion chamber cut into the piston head, the stem of this leaf must face the the right (passenger) side of the truck.

The connecting rods should be installed in the engine with oil hole facing the right side of the engine. Most connecting rods also have the cylinder number stamped into the side of the rod and cap, these numbers should face the left side of the engine. Also, as with the pistons, late model VG30i engines have a W stamped into the connecting rod which should face the front of the engine.

It is advisable to number the pistons, connecting rods and bearing caps in some manner so that they can be reinstalled in the same cylinder, facing the same direction, from which they were removed.

The piston rings must be installed with their gaps in the correct position.



Click image to see an enlarged view

Fig. Fig. 6: Piston ring positioning-L16, L18, L20B, Z20, Z22, Z24 and Z24i engines



Click image to see an enlarged view

Fig. Fig. 7: Piston and connecting rod positioning-all gasoline engines



Click image to see an enlarged view

Fig. Fig. 8: Piston ring positioning-1986-87 VG30i engines



Click image to see an enlarged view

Fig. Fig. 9: Piston ring positioning-1988 engines



Click image to see an enlarged view

Fig. Fig. 10: Piston and connecting rod positioning-1988 VG30i engines



Click image to see an enlarged view

Fig. Fig. 11: Piston ring positioning-SD22 and SD25 engines



Click image to see an enlarged view

Fig. Fig. 12: Piston and connecting rod positioning-SD22 and SD25 engines



Click image to see an enlarged view

Fig. Fig. 13: Piston and connecting rod offset-SD22 and SD25 engines

PISTON RING REPLACEMENT



See Figure 14

The cylinder walls must be de-glazed (honed) when the piston rings are replaced. De-glazing ensures proper ring seating and oil retention.

Using a piston ring expander, remove the rings one by one. Always remove and replace the rings of each piston before going on to the next. This helps avoid mixing up the rings. When the rings have been removed from each piston, perform the end-gap check, piston inspection and piston cleaning procedures detailed later in this section. The rings are marked on one side, the mark denoting the up side for installation.

Install the rings using the ring expander, starting with the top compression ring and working down. Make sure the marks are facing up on each ring. Position the rings so that the ring and gaps are set as in the illustrations. Never align the end-gaps!



Click image to see an enlarged view

Fig. Fig. 14: Removing the piston rings

WRIST PIN REMOVAL & INSTALLATION



See Figure 15

Wrist pin and/or connecting rod small-end bushing wear can be checked by rocking the piston at a right angle to the wrist pin by hand. If more than very slight movement is felt, the pin and/or rod busing must be replaced.

The pistons on the engines covered here must be heated in hot water to expand them before the wrist pins can be removed and installed. The four cylinder pistons must be heated to 176°F (80°C), and all six cylinder pistons must be heated to 140°F (60°C). This job can be performed at a machine shop if the idea of boiling pistons in the kitchen doesn't appeal to you. If you decide to do it, however, remember that each piston, pin and connecting rod assembly is a matched set and must be kept together until reassembly.

  1. Using needlenose or snapring pliers, remove the snaprings from the piston (if so equipped).
  2.  
  3. Heat the piston(s) in hot water (as noted above depending on engine).
  4.  
  5. Using a plastic-faced hammer and driver, lightly tap the wrist pin out of the piston. Remove the piston from the connecting rod.
  6.  
  7. Assembly is in the opposite order of disassembly. The piston must again be heated to install the wrist pin and rod. Once heated, (while wearing protective gloves) it should be able to be pushed into place with your thumb when heated. When assembling, make sure the marks on the piston and connecting rod are aligned on the same side as shown.
  8.  



Click image to see an enlarged view

Fig. Fig. 15: Rock the piston at a right angle to the wrist pin to check pin and small end bushing wear

CLEANING AND INSPECTION



See Figures 17, 18, 19, 20, 21, 22, 23, 24 and 25

Clean the piston after removing the rings, by first scraping any carbon from the piston top. Do not scratch the piston in any way during cleaning. Use a broken piston ring or ring cleaning tool to clean out the ring grooves. Clean the entire piston with solvent and a brush (NOT a wire brush).

Once the piston is thoroughly cleaned, insert the side of a good piston ring (both No. 1 and No. 2 compression on each piston) into its respective groove. Using a feeler gauge, measure the clearance between the ring and its groove. If clearance is greater than the maximum listed under Ring Side Clearance in the Piston and Ring chart, replace the ring(s) and if necessary, the piston.

To check ring end-gap, insert a compression ring into the cylinder. Lightly oil the cylinder bore and push the ring down into the cylinder with a piston, to the bottom of its travel. Measure the ring end-gap with a feeler gauge. If the gap is not within specification, replace the ring; DO NOT file the ring ends.



Click image to see an enlarged view

Fig. Fig. 17: Ridge caused by cylinder wear



Click image to see an enlarged view

Fig. Fig. 18: Removing the ridge with ridge reamer



Click image to see an enlarged view

Fig. Fig. 19: Check the piston ring side clearance



Click image to see an enlarged view

Fig. Fig. 20: Check the piston ring end-gap



Click image to see an enlarged view

Fig. Fig. 21: Clean the piston ring grooves



Click image to see an enlarged view

Fig. Fig. 22: Measuring the piston-A is the skirt dimension



Click image to see an enlarged view

Fig. Fig. 23: Measure the cylinder bore with dial gauge



Click image to see an enlarged view

Fig. Fig. 24: Cylinder bore measuring points



Click image to see an enlarged view

Fig. Fig. 25: Measuring the cylinder liner projection on the diesel engine

CYLINDER BORE INSPECTION



Place a rag over the crankshaft journals. Wipe out each cylinder with a clean, solvent-soaked rag. Visually inspect the cylinder bores for roughness, scoring or scuffing; also check the bores by feel. Measure the cylinder bore diameter with an inside micrometer, or a telescope gauge and micrometer. Measure the bore at points parallel and perpendicular to the engine centerline at the top (below the ridge) and bottom of the bore. Subtract the bottom measurements from the top to determine cylinder taper.

Measure the piston diameter with a micrometer; since this micrometer may not be part of your tool kit as it is necessarily large, you may have to have the pistons miked at a machine shop. If you obtain a micrometer, take the measurements at right angles to the wrist pin center line, about an inch down the piston skirt from the top. Compare this measurement to the bore diameter of each cylinder. The difference is the piston clearance. If the clearance is greater than that specified in the Piston and Ring Specifications chart, have the cylinders honed or rebored and replace the pistons with an oversize set. Piston clearance can also be checked by inverting a piston into an oiled cylinder, and sliding in a feeler gauge between the two.

CONNECTING ROD INSPECTION AND BEARING REPLACEMENT



See Figures 26, 27, 28 and 29

Connecting rod side clearance, along with big-end bearing inspection and replacement should be performed while the rods are still installed in the engine. Determine the clearance between the connecting rod sides and the crankshaft using a feeler gauge. If clearance is below the minimum tolerance, check with a machinist about machining the rod to provide adequate clearance. If clearance is excessive, substitute an unworn rod and recheck; if clearance is still outside specifications, the crankshaft must be welded and reground, or replaced.

To check connecting rod big-end bearing clearances, remove the rod bearing caps one at a time. Using a clean, dry shop rag, thoroughly clean all oil from the crank journal and the bearing insert in the cap.

The Plastigage® gaging material you will be using to check clearances with is soluble in oil; therefore any oil on the journal or bearing could result in an incorrect reading.

Lay a strip of Plastigage® along the full length of the bearing insert (along the crank journal if the engine is out of the truck and inverted). Reinstall the cap and torque to specifications listed in the Torque Specifications chart.

Remove the rod cap and determine the bearing clearance by comparing the width of the now flattened Plastigage® to 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 degrees and retest, to determine journal eccentricity.

Do not rotate the crankshaft with the Plastigage® installed.

If the bearing insert and crank journal appear intact and are within tolerances, no further service is required and the bearing caps can be reinstalled (remove Plastigage® before installation). If clearances are not within tolerances, the bearing inserts in both the connecting rod and rod cap must be replaced with undersize inserts, and/or the crankshaft must be reground. To install the bearing insert halves, press them into the bearing caps and connecting rods. Make sure the tab in each insert fits into the notch in each rod and cap. Lube the face of each insert with engine oil prior to installing each rod into the engine.

The connecting rods can be further inspected when they are removed from the engine and separated from their pistons. Rod alignment (straightness and squareness) must be checked by a machinist, as the rod must be set in a special fixture. Many machine shops also perform a Magnafluxing service, which is a process that shows any tiny cracks that you may be unable to see.



Click image to see an enlarged view

Fig. Fig. 26: Check the connecting rod length (arrow)



Click image to see an enlarged view

Fig. Fig. 27: Check the connecting rod side clearance with a feeler gauge



Click image to see an enlarged view

Fig. Fig. 28: Match the connecting rod to the cylinder with a number stamp



Click image to see an enlarged view

Fig. Fig. 29: Match the connecting rod and cap with scribe marks

 
label.common.footer.alt.autozoneLogo