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The following technical bulletins were published by AERA.


Crankshafts Used In Industrial Applications On
GM (Chevrolet) 5.7L (350 CID) Engines

When the GM (Chevrolet) 5.7L (350 CID) industrial engine is used in some applications such as lift trucks, the only crankshaft that is applicable has the forging number 1182.  Dimension A of the rear flange is slightly smaller than that of other crankshafts used in General Motors 5.7L (350 CID) engines.

The larger flange crankshafts will not pass through the center hole of the bell housing.  This is very critical when an oil clutch system is used.

                                                                     The AERA Technical Committee


                                       Timing Chain Tensioner Usage On
                                       Pre-1986 GM 3.8L (231 CID) Engines

General Motors recommends the removal of the factory timing chain guide assembly on remanufactured pre-1986 3.8L (231 CID) engines. Engines manufactured as of the 1986 model year no longer use the stationary chain guide assembly from the factory.  Production rebuilding shops have eliminated the stationary guide on all even fire GM 3.8L  engines, as it is no longer necessary.

The spring loaded tensioner has been retained, and should be reinstalled on remanufactured engines.

Over the years, engine rebuilders have noticed excessive wear of the front camshaft bearing on this engine.  Some rebuilders have been reducing the tension of the spring on the tensioner.  Doing so reduces bearing load and wear, especially during engine start up when little or no oil remains on the bearing.  Using an oil filter with an anti-drain back valve in the filter is also

The use of a tri-metal cam bearing has also proven effective in this engine.

                                                                             The AERA Technical Committee


                                         Narrow Timing Assemblies On
                             General Motors 2.8L (173 CID) VIN W Engines

In order to squeeze the 2.8L (173 CID) V6 engine into the 1986 and later high performance Chevrolet Cavalier Z24, General Motors narrowed the timing sprockets and chain assembly to fit behind a slimmer front cover.

As of the 1987 model year, GM also changed the Celebrity to use the narrow chain assembly and cover.

The standard timing chain assembly will not fit behind this special shallow cover.  Use the following aftermarket or GM part numbers when assembling this engine:

                              GM             Aftermarket

     Chain:                   14102671       C371
     Camshaft Sprocket:       14074399       S620
     Crankshaft Sprocket:     14100571       S619

                                                                        The AERA Technical Committee


                                 Fastener Tightening Specifications On
                                     1992 GM 4.3L Engines (VIN W & Z)

The AERA Technical Committee has been made aware that some of the torque	 procedures used on the GM 4.3L engines (VIN W and Z) are somewhat different than what we have been accustomed to in the past.

The connecting rod bolts of the 1992 GM 4.3L engine requires a seating torque of 20 lbs. ft. plus an additional 70 degrees.  Additionally,  the balance shaft drive gear bolt on the high output (HO) engine requires a torque of 15 lbs. ft. plus an additional 35 degrees.  

The torque-turn method is not a new concept and is used with many different types of bolts.  This method of tightening is not exclusive to torque to yield fasteners, in fact, it is rapidly becoming the recognized method of tightening for all fasteners in the automotive industry.

Notice should be taken that the degrees of additional turn are not readily measured by the use of the hex points on the bolt or nut.  General Motors indicates that precise measurement of the additional turn is critical for successful tightening of these fasteners.  

AERA is aware of at least one manufacturer which produces a torque angle meter to accurately measure the additional turn after the initial seating torque.                      
                                                                          The AERA Technical Committee


                Premature Valve Guide Failures On
          1987-90 GM 5.0 & 5.7L (305 & 350 CID) Engines

Some General Motors 5.0 & 5.7L engines used in trucks with a gross vehicle weight of less than 8500 lbs may exhibit premature exhaust valve guide failures.

These premature valve guide failures have been attributed to rougher than normal finishes of the exhaust valve stem causing excessive clearances.  Engines originally manufactured in Flint, MI were equipped with these valves.  On cylinder heads that are being rebuilt.  Check the engine's date code pad at the front of the right cylinder head bank for a V as the first character, example: V1201ABC (see illustration).  The letter V identifies the Flint, MI facility.  On engines manufactured in Flint, MI, be sure to check the surface finish of any exhaust valve that is to be reused, or simply replace it.

Engines manufactured in St. Catharines, engine code K, as well as all engines with a GVWR above 8500 lbs used exhaust valves from a different manufacturer and have not exhibited this problem to date.

                                                                               The AERA Technical Committee


                                                 Cracked Lifter Bore On
                                               GM 2.5L (151 CID) Engines

AERA members have reported a crack on the inside of the number six lifter bore on General Motors 2.5L (151 CID) engines.

To-date, all of the blocks found to have this crack carry the casting number 10038893.  The crack causes engine oil from the lubricating oil supply to mix with coolant. 

Cylinder blocks with this crack are no longer serviceable and must be replaced since no repair is available. 

                                                           The AERA Technical Committee


                                     Rough Idle & Poor Performance On
                                               1990-91 GM 4.3L Engines

AERA member machine shops have reported customer complaints of rough idle and poor performance on some General Motors vehicles equipped with 4.3L engines.  The engines also exhibited low manifold vacuum and some valve train noise.  

Close investigation of the valve train and camshaft revealed an irregular pattern on the trailing side of the camshaft lobes (see illustration).  The leading side of the lobe was machined to a smooth surface finish as one would expect.

AERA has learned that the roller lifter camshaft used in this engine is manufactured from a steel billet.  The billet is rough machined by a milling process before the lobes and journals are finish ground.  In the cases reported to AERA, too much material was milled from the trailing side of the camshaft lobes to be able to properly finish grind the lobe's profile.

This rough and bumpy profile of the trailing side of the lobe causes the hydraulic lifter to pump up, keeping the valve from fully closing.  The only repair possible is to replace the camshaft.

                                                                          The AERA Technical Committee

June 1991 - TB 780



                              Timing Of The Force Balancer Assembly On
                                                   GM 2.5L Engines

In order to reduce engine vibration, starting in 1988, General Motors has equipped some 2.5L engines with force balancer shaft assemblies.  

Since the balance shaft assembly rotates at twice engine rpm, correct timing of the assembly is very important.  Begin by rotating the crankshaft so number #1 cylinder is at top dead center (TDC); the crankshaft counter weights will be at bottom dead center (BDC).  Install the balance shaft assembly with its weights
positioned as close to bottom dead center (BDC) as possible.  

Install the retaining bolts and snug them to 9 lbs.ft. (12 Nm) in sequence 3, 1, 2, 4 (see illustration).  Following the same sequence torque the short bolts to 15 lbs.ft. (20 Nm) plus 60 degrees and the long bolts to 11 lbs.ft. (15 Nm) plus 90 degrees.  
For additional information see AERA Technical Bulletins: TB 720, 690 & 511
                                                                                The AERA Technical Committee


                                       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


                                             Distributor Gear Wear On
                                  GM 4.1L (HT-4100 Cadillac) Engines

Premature distributor gear wear has been noted on GM 4.1L (HT-4100 Cadillac) engines.

Since there is no direct lubrication of the distributor gear, General Motors has revised the gear to help eliminate this problem.  The revised gear carries GM Part #10499813 and can be identified by a cut ring on the body section of the gear.

Since the cam bearing housing bores are fully grooved, AERA members have enhanced lubrication of the gear.  Drill a small (1/32) hole from the groove of the last cam bearing housing bore forward toward the distributor opening of the cylinder block. 
Inserting the distributor into the block can be of assistance in locating this hole.

                                                                      The AERA Technical Committee

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