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Isuzu I-MARK Engine Information

The following technical bulletins were published by AERA.


                                      Cylinder Head Bolt Caution On
                                                Isuzu 2.6L Engines

A loose head bolt has been found to be the cause of coolant leaks on some Isuzu 2.6L engines.  The leakage occurs at the center head bolt on the exhaust manifold side of the engine and seems to be caused by high engine temperatures.  This heat may cause the head bolt to stretch and lose its clamping ability, allowing coolant to seep past the head gasket and into the combustion chamber.  If the loosened bolt is not replaced, there is a possibility th at coolant deposits will accumulate on the exhaust valve's seating ace.

Correction of this situation requires removal of the cylinder head and complete inspection of the exhaust valves for deposits.  Install a new head gasket and replace all head bolts.  See the illustration below and torque bolts in sequence to 58-72 ft. lbs.  All components must be torqued to specification prior to
adjusting the valve train.  The engine may be rotated by the using a 17 mm wrench/socket on the power steering pulley nut.  Cold valve adjustment specification for both intake and exhaust is .008.
                                                                               The AERA Technical Committee


                                         Crankshaft Specifications On
                                       1985-89 Isuzu 2.0L VIN F Engines

The AERA Technical Committee offers the following crankshaft specifications for 1985-89 Isuzu 2.0L VIN F engines. It appears that depending upon the 
source, different crankshaft journal diameters have been published. The amount of difference is slight, but could cause an engine failure if the incorrect 
specifications are used to grind the crankshaft.

The correct diameter for the connecting rod journal is 1.9262-1.9268 (48.925-48.940 mm). The correct diameter for the main bearing journal is 2.2016-
2.2022 (55.921-55.936 mm). 

     Crankshaft Specifications                                                        Oil Clearance

     Connecting Rod Journal        1.9262-1.9268                           .0007-.0020
                                                   (48.925-48.940 mm)      
      Main Bearing Journal           2.2016-2.2022                            .0008-.0020
                                                   (57.980-58.00 mm)
      Stroke                                    3.2283 (82.00 mm)
      End Play                            .002-.010 (.051-.254 mm)

Previously published information indicated the main journal diameter could be as much as .0016 larger than the above specifications. Whereas, the rod 
journal may have been as much as .0014 (.0356 mm) larger. If an engine is assembled with either of these situations, there may be insufficient bearing 
oil clearance.

                                                                         The AERA Technical Committee


                                       Engine Overheating Problems On
                                            1989 Isuzu 2.6L Engines
AERA machine shops have reported engine overheating problems on 1989 Isuzu 2.6L engines used in Troopers and Pick Ups.  Though the cooling system was filled during engine installation, the overheated engines have a low coolant level when inspected.  Before disassembling the engine, consider that the cooling system may not have been properly filled during installation.

Isuzu recommends the following fill procedure:

1) Make sure that the thermostat jiggle valve is positioned at the top of the 
    thermostat housing (Figure 1).

2) Remove the thermal valve from the thermostat housing. Remove the radiator 
    cap and set the temperature control lever to the highest heat position.

3) Fill the cooling system until coolant flows from the thermal valve opening.

4) Apply a thread locking compound to the thermal valve and install it into the 
    thermostat housing.  Finger tighten the valve using the metal housing.  Rotate 
    the valve one additional revolution and align it as show in Figure 2 below.

5) Start the engine and let it reach normal operating temperature.  Check the 
     coolant level in the radiator and refill as necessary.  If no air bubbles are 
     present in the filler neck, install the radiator cap.

                                                                             The AERA Technical Committee


                      Oil & Coolant Leaks From Cylinder Head Cracks On
                                               Isuzu 2.6L Engines

AERA members report a condition that may exist on 2.6L Isuzu engines where there is oil in the coolant or coolant in the oil.  This may be caused by a crack in the oil gallery feed line to the third camshaft journal.  The crack usually occurs after severe overheating of the engines, but has also been reported when no
evidence of overheating exists. 

Reports indicate this type of crack can be found between the oil gallery and the water jacket on the top side of the cylinder head, near the valve springs.  The crack is usually visible with the naked eye, and is easily found through pressure testing.  This condition is very similar to cracks found in earlier 1.9L Isuzu cylinder heads.

Welding attempts to repair this condition have not proven successful as the oil line does not travel in straight lines and re-establishing them is difficult.  AERA is not aware of any other repairs being made at this time and replacing the head
seems to be the only alternative.  

                                                                     The AERA Technical Committee


                                 Valve Lash Adjustment On
                            1986-92 Isuzu 2.3 & 2.6L Engines

AERA member have expressed some confusion on the correct valve lash
adjustment procedure on 1986-92 Isuzu 2.3 & 2.6L engines. It appears that previous service manual information may lead a technician to an incorrect adjustment.

The service manual indicates that valve lash on the #1 cylinder should be adjusted when all timing marks are lined up. The camshaft however, is in the valve overlap position at the number one cylinder. If the adjustment is made as indicated in the manual, excessive valve lash will result. These engines are actually timed off the #4 cylinder and those valves can be adjusted when all timing marks are lined up.

To correctly adjust the valves, first look to see that the cam lobes are pointing down in the cylinder you are adjusting. The correct adjustment is made on a cold engine and is .008 for both valves on the 2.6L engine. The adjustment for the 2.3L engine is .006 for intake valves and .010 for exhaust valves.
                                                                               The AERA Technical Committee


                                             Rear Engine Oil Leaks On
                                            1988-92 Isuzu 2.6L Engines

AERA members have reported engine oil leaks at the rear on 1988-92 Isuzu 2.6L engines.  Most of those leaks have been associated with the rear crankshaft area.  While the most likely source of leakage would be the rear crankshaft seal, this has not been the cause of most complaints.

This engine uses a crankshaft with flexplate/flywheel mounting bolt holes exposed to the crankcase.  That design requires sealer on bolt threads, before they are torqued to 43 ft/lbs.  Failure to apply sealer on the bolt threads will allow engine oil to seep around the bolt threads and leak externally.

Another possible cause of oil leakage is between the rear main bearing cap and block mating surfaces.  It appears that some castings are somewhat irregular, therefore requiring a small amount of silicone sealer at time of assembly. 

                                                                    The AERA Technical Committee


                             No Oil Pressure At Engine Restart On
                                 1988-94 Isuzu 2.6L VIN E Engines

The AERA Technical Committee offers the following information on no oil pressure at engine restart on 1988-94 2.6L VIN E engines. This condition has 
occurred on engines that have been recently rebuilt or the oil pump has been replaced. The affected engines have lost the oil prime after the engine has been stopped for a period of time (overnight).

The cause of this condition is an air pocket that is trapped in the engine oil pump. Oil pressure can generally be established by pressurizing the system 
before starting the engine. Doing so has not solved the problem, it has only prolonged its re-occurrence. 

To remove the trapped air in the oil pump, some AERA members have used an unconventional method of priming the oiling system. The use of vacuum has been advantageous in engines that exhibit this condition. Vacuum applied to a nipple installed into the oil pressure sending unit hole while cranking the engine 
over has proven to remove the trapped air. In many instances that procedure has been successful and a  no pressure situation has not re-occurred at 

                                                                           The AERA Technical Committee


            Oil Pipe Interference On
  1986-87 Isuzu 2.2L VIN U Turbo Diesel Engines

AERA members are cautioned to check for oil pipe 
interference during assembly procedures on 1986-87 
Isuzu 2.2L VIN U turbo diesel engines. This 
interference is located between the connecting rod(s) 
oil pipe nozzles. Isuzu made modifications to the 
connecting rods for this engine creating the possible 
interference (See AERA Technical Bulletin TB 836).

As shown in the illustration below, a clearance of 
.060 (1.5mm) is recommended between the rod and 
nozzle. To obtain the clearance, grind the nozzle on a 
bench grinder until the desired clearance is obtained.

Failure to check and adjust this clearance during 
engine assembling may create an engine noise and 
possible engine damage.

                         The AERA Technical Committee

March 1998 - TB 1548



                               Engine Front Oil Leak On
                  1986-94 Isuzu 2.3 & 2.6L VIN L & E Engines

The AERA Technical Committee offers the following information regarding a oil leak on 1986-94 VIN L & E Isuzu engines. Some engines have exhibited an engine oil leak at the front crankshaft oil seal retainer. The cause of this leakage has been attributed to cracks or splits in the retainer gasket allowing oil to pass through the gasket.

To reduce the possibility of this reoccurring, Isuzu now offers a revised gasket that is made from a material that is resistant to cracks or splitting. This gasket is available with Part #8971434780 from Isuzu. Aftermarket suppliers for this oil seal retainer gasket have not exhibited this type of leak when their gaskets are used.

Installation of this gasket requires only a minimal torque of 14 ft. lbs. to the four mounting bolts shown in the illustration below. Any over torque of those 
bolts may cause distortion, allowing oil leakage.

                                                                               The AERA Technical Committee


                                           Connecting Rod Failures On
                                     1986-1987 Isuzu C223T 2.2L Engines

AERA members remanufacturing 1986-87 Isuzu C223T, 2.2L turbo-charged diesel engines should replace connecting rods which have the casting number FM3066 with a later, heavier design, Part #8-9432-4210-1.  The revised connecting rod carries the casting number FM3234.

The earlier design connecting rod may have improperly-machined rod bolt seating surfaces which may cause the bolts to break, resulting in severe engine damage.  Isuzu has extended the short block warranty to 5 years or 75,000 miles, whichever occurs earlier, to the original purchaser of vehicles equipped with this engine.

Refer to the illustration below when mounting the piston to the connecting rod.  Torque the connecting rod nuts to 58-65 lbs.ft.

                                                                          The AERA Technical Committee

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