GM Prizm/Nova 1985-1993 Repair Guide

Rocker Arms and Shafts



1985-88 VIN Code 4 Engine

See Figures 1, 2 and 3

  1. Remove the valve cover as described previously.
  3. Loosen each rocker support bolt little-by-little, in 3 steps, in the proper sequence.
  5. Remove the bolts and remove the rocker assembly from the head. Inspect the valve contacting surfaces for wear. Inspect the rocker-to-shaft clearance by wiggling the rocker on the shaft. Play should be virtually none; any noticeable motion requires replacement of the rocker arms and/or the shaft.
  7. Disassemble the rockers from the shaft. Check the contact surfaces for signs of visible wear or scoring.
  9. Using either an inside micrometer or a dial indicator, measure the inside diameter of the rocker arm. Using a regular micrometer, measure the diameter of the shaft. Maximum allowable difference (oil clearance) between the 2 measurements is 0.06mm.
  11. After replacing any needed parts, loosen the adjusting screw locknuts.
  13. The rocker shaft has oil holes in it. When assembling the rockers onto the shaft, make sure the holes point to the left, the right and down. (Said another way, when viewed from the end of the shaft, the oil holes are at 3, 6 and 9 o'clock.)

Failure to observe this positioning will cause the rockers to starve for oil, causing expensive and premature wear.

  1. Install the rocker assembly on the head. Tighten the retaining bolts in 3 steps and in the correct sequence. Torque the bolts to 18 ft. lbs. on the third pass.
  3. Set the motor to TDC and adjust the valves, using the procedures discussed in Engine Performance & Tune-up .

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Fig. Fig. 1: Rocker support bolt loosening sequence - 1985-88 VIN Code 4 engine

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Fig. Fig. 2: Oil hole positioning - 1985-88 VIN Code 4 engine

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Fig. Fig. 3: Tighten the rocker support bolts in this sequence - 1985-88 VIN Code 4 engine

1988-93 All Twin Camshaft Engines

The twin camshaft motors (one cam for the intake valves and one for the exhaust valves) use direct-acting cams; that is, the lobes of the camshaft act directly on the valve mechanism. These engines do not have rocker arms.