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The following technical bulletins were published by AERA.

OIL LEAKS AT OIL FILTER ADAPTOR

                                       Oil Leaks At Oil Filter Adapter On
                                      1989-91 GM 4.3L (262 CID) Engines

General Motors 4.3L (262 CID) engines installed in 1989-91Chevrolet S-10 and GMC S-15 trucks may experience oil leaks at theoil filter adapter.

Engines in these applications use a remote oil filter assembly that requires an oil filter adapter to be installed at the oil filter mounting area of the cylinder block (see illustration). The original gasket fails to seal properly and may also cause the adapter bolts to lose torque.  Simply retorquing the bolts may stop the leak, but will not result in a permanent repair. Replacement of the gasket and adapter is recommended.  The revised gasket carries GM Part #10172754 and the adapter GM Part #10172750.  

Position the gasket on the adapter and hold it in place with petroleum jelly.  Do not use any type of sealer on the gasket or the adaptor.  Each of the remote filter lines is fitted with an O- ring.  Be sure to torque the two mounting bolts to 13-18 lbs.ft. and the remote line bolts to 22-29 lbs.ft.

                                                                           The AERA Technical Committee

VALVE BRIDGE CAUTIN FOR 7.8L DIESEL ENGINES

                                                 Valve Bridge Stud Caution For
                                   1998-2003 Isuzu 7.8L 6HK1-TC Diesel Engines

The AERA Technical Committee offers the following information regarding a caution for bridge studs on 1998-2003 Isuzu 7.8L 6HK1-TC diesel engines. It has been reported valve bridge studs have moved during engine operation and cylinder head service work.

Damage will result to either the rocker arm or valve rocker bridge if the stud installed height is higher than 1.496" (38.000 mm).  The correct installed bridge stud height is listed as 1.457-1.496" (37.000-38.000 mm). These studs are pressed into the cylinder head casting and use of special tool # J43268 will locate the studs to the correct height. 

This engine built by Isuzu is used in the following vehicle models sold by Isuzu, Chevrolet Trucks and GMC Trucks.

1999-2003 Chevrolet & GMC F-Model (T-Series) Medium Duty Tilt Cab Models.
2000-2003 Chevrolet & GMC WT 5500 Medium Duty Tilt Cab Models.
2003 Chevrolet & GMC C6500-C8500 Series Models (Some Topkick & Kodiak).
1998-2002 Isuzu FSR/FTR/FVR Commercial Vehicles.
2000-2003 Isuzu, Some FRR Commercial Vehicles.

                                                                        The AERA Technical Committee

CYLINDER HEAD IDENTIFICATION

                                       Cylinder Head Identification On
                                      1977-78 GM (GMC) 5.0, 5.7 & 6.6L
                                     (305, 350 & 400 CID) Truck Engines

New lightweight cylinder heads for small block V-8 engines were released for interim 1977 & 78 production. The new heads are about six pounds lighter due to changes in internal coring of the water passages and slight modifications to the outer configuration (Fig. 1) on reverse side.

These lightweight heads were used together with current or heavy heads due to production requirements and machining capacities at the casting and manufacturing plants. Therefore, 1977 and 1978 small block V-8 engines may be assembled with either heavy or light heads, or a mixture of both.

Also, the lightweight heads consist of a 1st and 2nd design due to differences in the machining of the exhaust valve spring seats:

Lightweight Head - 1st Design

Exhaust valve spring seats are machined to 1977 or heavy head specifications (part #3911068 spring and damper assembly for intake valve and part #6263796 spring and damper assembly for exhaust valve).

Lightweight Head - 2nd Design

This head incorporates machining that allows the intake valve spring assembly (part #3911068) to be used at both intake and exhaust valve locations.

Valve Spring Identification

Part #3911068 intake spring can be identified by 1 lavender stripe approximately 2.03 free height. If the springs are identifiable by color, the cylinder heads can be identified by measuring from the top of the exhaust valve guide to the valve spring seat (exhaust spring only).

If the dimension is .75, use part #6263796 valve spring in the 1st design head.
If the dimension is .84, use part #3911068 valve spring in the 2nd design head.

                                                                             The AERA Technical Committee

V-6 BALANCE AND ASSEMBLY INFORMATION

                                             Balance & Assembly Data On
                    GM (GMC) 5.0, 5.8 & 6.6L (305, 351 & 401 CID) V-6 Engines

The following information was compiled to eliminate torsional engine vibration due to mismatching of parts or the use of pistons not balanced to the proper weight.

Although all three engines have used two or three different pistons, only the popular ones have been listed and can be used as listed in sets since the basic difference is in compression ratio, and the weights have remained constant.

Design characteristics make it possible to assemble with any crankshaft, connecting rod and pin combination in any given engine; however, vibration problems can arise since there are weight variations in the rods, pins and pistons. For this reason, the correct combination of rods, pins, pistons and crankshaft is a must.

Note that there are fourteen different crankshafts, three different connecting rods, and two different pins used in the 5.0, 5.8 & 6.6L (305, 351 & 401 CID) engines. 

The 5.0L (305 CID) engine uses five of these crankshafts, two of the connecting rods, one of the pins and one piston. 

The 5.8L (351 CID) engine uses seven of the crankshafts, all three of the connecting rods, both pins and three pistons. The three pistons used in this engine are all the same weight and compression ratio, and therefore, can be interchanged in less than set quantities as long as the correct pins are used.

The 6.6L (401 CID) engine uses three of the crankshafts, two of the connecting rods, one pin and one piston.

Note that the 2366209 crankshaft used in both the 5.8L (351 CID) and the 6.6L (401 CID) engine. This is accomplished by using the P4563 pin in the 5.8L (351 CID) engine which offsets the heavier piston weight of the 6.6L (401 CID). This is the only crankshaft that is interchangeable.

The next pages list the various combinations that can be used for each of the engines. Following are lists of the various pistons, pins and connecting rods and their weight specifications along with the balance formula for the V-6 engines.

Only Zollner piston and piston pin numbers and piston weights are listed in this bulletin since that company is the original piston supplier for the engines listed.

          GM (GMC) 5.0L (305 CID) Engine

Crankshaft Con Rod  Con Rod   Piston #  Piston Pin #
Forging #  Part #   Forging # Zollner   Zollner
----------------------------------------------------------

2367417   2389553   2389554   4564      P-4564
2454191   2389553   2389554   4564      P-4564
8874436   2389553   2389554   4564      P-4564
2475795   2477175   2470891   4564      P-4564
65828     2477175   2470891   4564      P-4564


          GM (GMC) V-6 5.8L (351 CID)

Crankshaft Con Rod  Con Rod   Piston #  Piston Pin #
Forging #  Part #   Forging # Zollner   Zollner
----------------------------------------------------------

2366209   2389553   2389554   4563-6*   P-4563
2454192   2389553   2389554   4563-12** P-4564
8875589   2389553   2389554   4594      P-4564
2475793   2477175   2470891   4594      P-4564
2475793   2477425   2474281   4594      P-4564
651826    2477175   2470891   4594      P-4564
651827    2477175   2470891   4594      P-4564

* Piston # 4594 can be used in place of Piston # 4563-6 if used
with pin # P-4563

** Piston # 4594 can be used in place of Piston # 4563-12


          GM (GMC) V-6 6.6L (401 CID)

Crankshaft Con Rod  Con Rod   Piston #  Piston Pin #
Forging #  Part #   Forging # Zollner   Zollner
----------------------------------------------------------

2366209   2389553   2389554   4565      P-4564
2475794   2477425   2474281   4565      P-4564
652794    2477425   2474281   4565      P-4564


Piston #  Piston         Piston Pin #        Pin
Zollner   Weights        Zollner        Weights
-------------------------------------------------------

4564      1128 g +/- 2        P-4564         318 g
4563-6    1380 g +/- 2        P-4563         516 g
4563-12   1380 g +/- 2        P-4564         318 g
4594      1380 g +/- 2        P-4564         318 g
4565      1560 g +/- 2        P-4564         318 g

* All oversize pistons are balanced to this standard weight and
weigh the same as a standard size piston.


GM (GMC)  GM (GMC)  Pin End        Crank End
Rod       Rod       Of Rod         Of Rod
Part #    Forge #   Weights        Weights
-----------------------------------------------------------

2389553   2389554   380 g +/- 2.5       966 g +/- 2.5
2477175   2470891   410 g +/- 2.5       1145 g +/- 2.5
2477425   2474281   390 g +/- 2.5       1155 g +/- 2.5


                 GM (GMC) V-6 Balancing Formula


The bobweight formula is 50% of the reciprocating weight and 100%
of the rotating weight of each piston-rod assembly. Determine the
bobweight (6 required) as follows:

Reciprocating  Grams

Piston                  
Ring Set                
Pin                     
Pin End Of Crod         
Lock                    

          Total          Divide Total by 2 =          


Rotating            Grams

Crank End Of Rod         
Bearings                 
Oil Estimate            

          Total                                   
                                                  

Bobweight Total 
(50% of Reciprocating + 100% Rotating)            


The 478 diesel uses the same crankshaft as does the 478 gas
engine. You must mount the flywheel and the dampener on the
crankshaft for balancing the diesel engine. The flywheel and the
dampener are counterweighted to offset the additional piston and
rod weight. Use exactly the same formula as above.

                                     The AERA Technical Committee

REAR CRANKSHAFT OIL SEAL LEAK

                                   Rear Crankshaft Oil Seal Leak On
                               1992-1994 4BD2TC GM Diesel Engines

The AERA Technical Committee offers the following information for rear crankshaft oil seal leaks on 1992-94 4BD2TC GM diesel engines*. This four cylinder turbocharged diesel engine is used in GMC and Chevrolet W4 model trucks. If this leaking condition can be verified as coming from the rear main seal, installing a revised oil seal may resolve the leak. 

The installed position of this seal, Part #97072823, is critical to assure an effective seal. When correctly installed, the seal depth should be .445-.468 (11.3-11.98 mm) below the rear face or the crankshaft. The use of tool number J41269 (Figure 2) is also advised to minimize seal distortion during installation.

Trucks that are equiped with an automatic transmission require the removal of the pilot bushing before installing a new seal. After installing the new seal, install the flywheel/flexplate and torque the mounting bolts to 115 ft. lbs.

* This engine is built for GM by Isuzu Motors.

                                                                          The AERA Technical Committee

BALANCING V-6 ENGINES

                          Balancing On
                       GM (GMC) V6 Engines

Much confusion exists on the proper bobweight formula for balancing the GM (GMC) V6 engines. For this reason balancing requests for these engines have been turned down or a marginal job performed.

During the Open Forum at the St. Louis Convention, questions were asked concerning balancing the subject engines. At that time no atisfactory answer was given. The following information is now available.

The bobweight formula is 50% of reciprocating weight and 100% of the rotating weight of each piston-rod assembly. Determine the bobweight (6 required) as follows:

Reciprocating            Grams

Piston                              _____
Ring Set                          _____
Pin                                    _____
Pin End Of Con Rod       _____
Lock                                 _____
     Total               _____     Total divided by 2 =     _____

Reciprocating

Crank End Of Rod         _____
Bearings                 _____
Oil Estimate             _____
     Total               _____                              _____

Bobweight Total ( 50% Reciprocating + 100 Rotating)         _____

Naturally, all piston-rod assemblies are matched in weight.

Approximate bobweight amounts are as follows:

5.0L (305 CID) Gas       2222 grams
5.8L (351 CID) Gas       2355 grams
6.6L (401 CID) Gas       2454 grams
7.8L (478 CID) Gas       2482 grams
7.8L (478 CID) Diesel    3041 grams

The 7.8L (478 CID) diesel uses the same crankshaft as does the 478 gas, however, you must mount the flywheel and dampener on the crankshaft for balancing. The flywheel and dampener are counterweighted to offset the additional piston-rod weight. Use exactly the same formula as above.

                                                                                 The AERA Technical Committee

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