1970 Corvette: Service Bulletin: Water Pump Bearing and/or Shaft Failures

Subject:   Water Pump Bearing and/or Shaft Failures
Model and Year:   V-8 Engines with Fan Clutch
Source:  Chevrolet Dealer Service Technical Bulletin
Bulletin No:   71-T-37
Section:   VI
Date:    June 23, 1971

TO:  ALL CHEVROLET DEALERS

Investigation has shown that water pump bearing and/or shaft failures may occur if excessive run-out exists at the fan clutch.

Interim 1970, two (2) modifications were made in an effort to maintain total run-out within .006 inch.

Modifications include:

1. Elimination of the water pump pulley center reinforcement.  (Excessive run-out may be induced, as reinforcement may not "rest" flat).
2. Matching of high and low points of water pump hub and fan clutch hub to produce lowest amount of total run-out.  This is accomplished by placing a dab of paint on hub assemblies and aligning paint marks during assembly.

For service, since excessive run-out could be induced when the water pump, pulley and/or fan clutch is replaced and randomly assembled, the following procedure has been developed.  Use of this procedure will indicate run-out and provide a method of correction if it is excessive.

Chevrolet Motor Division
General Motors Corporation

SERVICE PROCEDURE

Passenger Car

During replacement of the water pump or related parts, the water pump pulley should be inspected to determine if the pulley has a reinforcement on the surface which contacts the water pump hub.  Pulleys with a welded reinforcement should be replaced with a 1971 pulley (refer to chart).  All mating surfaces (Water pump hub and fan clutch hub) should be inspected for smooth mating surfaces and reworked as necessary.  Except for the fan belt, components should then be assembled to the engine as specified in Section 6K of the Chassis Service Manual.  Check radial run-out according to the listed procedure below.

Trucks

During replacement of the water pump on trucks, the pulley should be inspected for a loose reinforcement  (cracked weld) and replace if necessary.  Inspect for smooth mating surfaces (water pump hub and fan clutch hub) and rework as necessary.  Except for the fan belt, components should then be assembled to the engine as specified in Section 6K of the Chassis Service Manual.  Check radial run-out according to the listed procedure below.

Procedure for Indicating Radial Run-Out

1. Secure the fan blade to prevent rotation.  (See Figure 1).
2. Mount a dial indicator (.001 graduations) to the engine and place the indicator pointer on the fan blade spider.  Preferably on the longest band or space on the spider.  (See Figure 2).
3. Rotate the water pump pulley in one direction and note the total amount of indicator needle movement.  This represents the total radial run-out.  Mark the point on the pulley at which the highest reading is obtained.
4. If the total indicator reading is less than .006 inch, the assembly is within specification.  Install fan belt and adjust.  If the total indicator run-out exceeds .006 inch, proceed to Step "E".
5. Divide the total indicator reading in half and obtain this thickness from shim stock (1/2 x 3/4) and rework per Figure 3.  Place this shim pack between the water pump pulley and fan clutch hub at the bolt closest to the point marked on the pulley in Step "C".  If the mark on the pulley is between two bolts so that it is difficult to determine which bolt is closes, place two shim packs; one under each bolt on either side of the mark.  (See Figure 4).

Bolt Torque Sequence

1. When one shim pack is used, first, torque the bolt over which the shim pack has been placed; second, the bolt opposite the first; and finally, the other two.  Recommended torque is 25 lbs. ft.
2. When two shim packs are used, each bolt must be torqued partially; then to full torque alternating between opposite bolts; then the other two bolts in the same manner.  Recommended torque is 25 lbs. ft.  NOTE :  Excessive run-out may result if the above sequence and recommended torque is not used.

F.  Recheck total indicator run-out to verify that run-out is within .006 inch.  Install fan belt and adjust.