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Chevrolet / Chevy Corvair Engine Information

The following technical bulletins were published by AERA.


                                     A Principal Cause Of Bent Push Rods

When installing new push rods and rocker arm assemblies with or without new hydraulic lifters and new camshaft, it is natural to be so absorbed with getting the correct end of each push rod into the lifter socket and getting all of the rocker arm sockets engaged with the push rods at the same time, that no thought is given to the fact that whatever position the camshaft is in, there are several cam lobes holding lifters up, so the valves will be in the open position.
Furthermore, since the rocker arm and shafts supports too rapidly, as with an impact wrench. Pulling down the shaft too quickly does not give time for the lifters on the open valves to leak down to the normal operating position of the socket. Consequently with oil being  practically non-compressible, the valve lift may be excessive for a couple of minutes. Several valve springs may be compressed solid and/or several valves may contact a piston head with enough force to bend the push rod. More damage can be done if the engine crankshaft is turned over before the lifters have leaked down to normal lift.

The above gives an understanding of why the rocker arm shaft support bolts must be tightened slowly and uniformly to prevent damage such as bent push rods. 

In the case of Chevrolet Corvair, extra precaution is necessary, because the upper end of the push rods run in a guide plate that prevents sideways movement of the push rods and the rocker arms, which are mounted on individual studs. If tightening down a rocker arm too rapidly bends a push rod, it will bind in the guide hole, causing scoring and rapid wear. Also the end of the
Corvair push rods having a small hole on the side must be nearest the rocker arm to provide lubrication for the rocker arm and the guide hole.

                                                                               The AERA Technical Committee


                                     Cylinder Head Torquing Procedure On
                                   Chevrolet 2.3L (140 CID) Corvair Engines

Chevrolet Motor Division revised the cylinder head torquing procedure for 1961-1969 Corvair engines. Recommendations are as follows:

When torquing Corvair cylinder heads, an accurate torque wrench is required and it is essential that the procedure outlined below be followed step by step in order that the gaskets will be properly compressed at the torque limits specified.

     1. Install (or loosen if head has not been removed) all cylinder head nuts and 
         studs to finger tight.
     2. Using the sequence shown in Figure 1, tighten all cylinder head studs and 
         nuts to 20 ft.lbs.
     3. Repeat step 2 to 30 ft.lbs.
     4. Repeat step 2 to 40 ft.lbs.
     5. Repeat step 2 to stabilize the torque at 40 ft.lbs.
     6. Install rocker arms and adjust valves to specifications.
     7. Install valve rocker covers.

                                                                                The AERA Technical Committee


                                      New Cylinder Liner O-Ring Seals On
                                      Cummins NH/NT 6 Cylinder Engines

Cummins Engine Company has released new O-ring seals for the cylinder liners in NH/NT 6 cylinder engines.  The new seals are made of an EP material and have a smaller diameter cross-section.

The new seal replaces both the old center seal #3008998 and the old lower seal #183049.  The new seal carries Cummins part #3032874 and is black in color with one blue dot.

The new O-ring seals are not to be intermixed with the former seals on the same liner.  Cylinder liner deformation will result.  You can use the former seals and new seals in the same engine as long as they are used in the correct combinations on each liner.  The illustration below shows the correct combinations.

                                                                       The AERA Technical Committee


                                               Oil in Cooling System on
                                         VW 1.5L & 1.6L Diesel Engines

AERA members have reported instances of engine oil in the cooling system on VW 1.5L diesel engines.  According to AERA sources, the problem is related to a crack in the cylinder head bolt hole located near the oil gallery feeding the cylinder head.

The oil feed gallery in the block is located on one side of the center head bolt hole and a coolant jacket is on the opposite side of the bolt hole.  Pressurized engine oil is diverted through a slot in the head gasket and is feed up the side of the head bolt to the cylinder head.  The oil also follows the bolt back down to the bottom of the bolt hole.  Should the crack in the head bolt hole extend to the coolant jacket, oil can mix with engine coolant.

This problem is generally found on engines equipped with 11mm head bolt holes.  Later design engines utilize 12mm head bolts and do not exhibit this defect.  At the time of this writing no successful repair procedure is available.

                                                                       The AERA Technical Committee


                                        Cylinder Head Specifications on
                                              Case 207 Diesel Engines

The following cylinder head specifications should be considered when remanufacturing Case Model 207 diesel engine cylinder heads.

The minimum cylinder head thickness has been established at 3.968 with a new head measuring 4.000 +/- .005.  Heads are measured from the deck surface to the rocker cover rail.

Valve recession should be checked and adjusted if necessary to a maximum recession of .015, below the deck surface, for both intake and exhaust valves.  Valves on new cylinder heads are generally flush with a +/- .005 tolerance.

                                                                       The AERA Technical Committee


                                         Main Bearing Saddle Repair Kits

The Cummins Engine Company has made main bearing saddle repair kits available for several engines.  These kits can be used to salvage cylinder blocks when a main bearing has spun and the main bearing saddle has been damaged.

Each kit contains an 1/8 drill bit, two hold down bolts (one for the lock ring and one for the other side of the saddle), a quantity of rivets and the appropriate number of repair sleeves.  Semi-finished or good used main bearing caps are also needed to complete the repair.

A main bearing saddle can be successfully repaired by following this procedure.
                                                                                                                            Remove the main bearing cap from the saddle to be repaired.  Using the appropriate align bore tooling remove .050 of material out of the saddle.  This will enlarge the main bearing bore by .100.

Clean the saddle and lock tang area.  Install the repair sleeve and align the lock tang slot of the sleeve with the one in the block.

From the repair kit, install the washer marked L on the lock tang side of the saddle.  Install the second washer on the opposite side.  Install the hold down screws and torque to 20 lbs.ft. (Figure 1).

Mount the 1/8 drill bit in a right angle drill, so that the drill extends 1/4 beyond the chuck jaws.

Using the 4 holes in the repair sleeve as a guide, drill through each of the holes into the saddle.  The proper hole depth is achieved when the chuck jaws contact the repair sleeve.

Clean the 4 holes and install the supplied rivets (Figure 2).  Peen the rivets until they are flush with the repair sleeve.

Remove the temporary hold down bolts and trim the ends of the repair sleeve so they are flush with the main bearing saddle.

Clean the main bearing bolt holes and install a good used or semi-finished main bearing cap.  Torque the main bearing bolts to specifications.

Using the appropriate align boring tools, refinish the main bearing housing bore to specifications.  Approximately .050 of material should be removed from the repair sleeve.
Main bearing bore repair kits or sleeves may also be available from several aftermarket sources.

                                                                        The AERA Technical Committee


                          Overheating Of Engines With Electric Cooling Fans

Ever since gasoline prices have shot up, vehicle manufacturers have downsized cars and their engines.  One of the best ways of making a car smaller is to turn the engine sideways under the hood.  This has instituted the use of one or more electric cooling fans to move air through the radiator.  Diagnosing overheating conditions on engines with electric cooling fans requires a few extra steps to ensure that the electrical control system for the fan is operating properly.

o    Perform all of the tests associated with normal
     installations, for example:  check antifreeze level,
     thermostat, water pump and hoses.

o    Check that the cooling fan is moving air through the
     radiator.  With the fan turned on air should never blow out
     through the front of the vehicle.  If there is more than one
     fan, be sure to check both.  It's possible for the
     electrical leads to be reversed during installation causing
     the fan to move air in the opposite direction.

o    If the vehicle is equipped with two fans, be sure that both
     of them work.  If the vehicle is equipped with air
     conditioning, one of the fans may only operate when the air
     conditioning is on.  Consult the service manual if you are
     not sure.

o    Fans are controlled by a temperature sending unit.  Check a
     suspected faulty sensor by bridging the two connections.  If
     the fan comes on, then the sensor is at fault.

o    Verify that the fan comes on at the temperature listed in
     the service manual.  Replace the sensor if the proper
     temperatures are not maintained.

For additional information see AERA Technical Bulletins: TB 706,
SB 158 & SB 137

                                                                         The AERA Technical Committee

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