GM Prizm/Nova 1985-1993 Repair Guide

Valve Springs and Valves

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REMOVAL & INSTALLATION



See Figures 1, 2 and 3

This procedure requires the use of a valve stem compressor. This common tool is available at most auto supply stores. It may also be possible to rent one from supplier.


WARNING
It is absolutely essential that all components be kept in order after removal. Old ice trays make excellent holders for small parts. The containers should be labeled so that the parts may be reinstalled in their original location. Keep the valves in numbered order in a holder such as an egg carton or an inverted box with holes punched in it. Label the container so that each valve may be replaced in its exact position. (Example: Exhaust #1, #2 etc.)



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Fig. Fig. 1: Typical valve and related components

1985-88 VIN Code 4 Engine
  1. Remove the head from the engine and remove the rocker arm and cam shafts, following procedures outlined in this section.
  2.  
  3. Using a valve spring compressor, compress the valve spring and remove the keeper at the top of the valve shaft.
  4.  
  5. Slowly release the tension on the compressor and remove it. Remove the spring retainer (upper cap), the valve spring, the valve stem oil seal and the lower spring seat.
  6.  
  7. The valve is then removed from the bottom of the head.
  8.  
  9. Repeat steps 2-5 for each valve in the head, keeping them labeled and in order.
  10.  
  11. Thoroughly clean and decarbon each valve. Inspect each valve and spring as outlined later in this section.
  12.  
  13. Lubricate the valve stem and guide with engine oil. Install the valve in the cylinder head and position the lower spring seat.
  14.  
  15. Coat the valve face and seat with a light coat of valve grinding compound. Attach the suction cup end of the valve grinding tool to the head of the valve (it helps to moisten it first).
  16.  
  17. Rotate the tool between the palms, changing position and lifting the tool often to prevent grooving. Lap in the until a smooth, evenly polished surface is evident on both the seat and face.
  18.  
  19. Remove the valve from the head. Wipe away all traces of grinding compound from the surfaces. Clean out the valve guide with a solvent-soaked rag. Make sure there are NO traces of compound in or on the head.
  20.  
  21. Proceed through the remaining valves, lapping them one at a time to their seats. Clean the area after each valve is done.
  22.  
  23. When all the valves have been lapped, thoroughly clean or wash the head with solvent. There must be NO trace of grinding compound present.
  24.  
  25. Lubricate the new valve stem seal with engine oil and install it onto the valve stem over the lower seat.
  26.  
  27. Install the valve spring and the upper seat, compress the spring and install the 2 keepers. Relax tension on the compressor and make sure everything is properly placed. Tap on the installed valve stem with a plastic mallet to ensure proper locking of the retainers.
  28.  
  29. Install the half-circle plug at the end of the head. Coat it with a silicone sealer before installation.
  30.  
  31. Complete the reassembly of the head by installing the camshafts and the manifolds.
  32.  



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Fig. Fig. 2: Installing the valve



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Fig. Fig. 3: Lapping a valve in by hand

Except 1985-88 VIN Code 4 Engine
  1. Remove the head following procedures outlined earlier in this section.
  2.  
  3. On 1989-90 VIN Code 6 engine and 1991-92 VIN Code 5 engine, remove the intake and exhaust manifolds.
  4.  
  5. Remove the camshafts following procedures outlined later in this section. Label the shafts and their retainers.
  6.  
  7. Remove the valve lifters and the adjusting shims.
  8.  
  9. On the 1988 VIN Code 5 engine and 1991-92 VIN Code 6 engine, remove the bond cable and the right engine hoist hook. Remove the temperature sensor bracket and the left engine hoist hook. For the 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines, simply remove the engine hoist hook(s).
  10.  
  11. Remove the spark plug tubes from the head, if so equipped.
  12.  
  13. Attach the spring compressor. For the 1988 VIN Code 5 engine and 1991-92 VIN Code 6 engine, use GM tool J-37134 or equivalent, and for the 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines, use J-8062 with a J-37979 adaptor or equivalent tools.
  14.  
  15. Compress the valve spring and remove the keepers at the top of the valve shaft.
  16.  
  17. Slowly release the tension on the compressor and remove it. Remove the spring retainer (upper cap), the valve spring, the valve stem oil seal and the lower spring seat. The valve is then removed from the bottom of the head.
  18.  
  19. Repeat steps 2-5 for each valve in the head, keeping them labeled and in order. On 1991-92 VIN Code 5 engine, remove the half-circle plug at the end of the head on.
  20.  
  21. Thoroughly clean and decarbon each valve. Inspect each valve and spring as outlined later in this section.
  22.  
  23. Lubricate the valve stem and guide with engine oil. Install the valve in the cylinder head.
  24.  
  25. Coat the valve face and seat with a light coat of valve grinding compound. Attach the suction cup end of the valve grinding tool to the head of the valve (it helps to moisten it first).
  26.  
  27. Rotate the tool between the palms, changing position and lifting the tool often to prevent grooving. Lap in the until a smooth, evenly polished surface is evident on both the seat and face.
  28.  
  29. Remove the valve from the head. Wipe away all traces of grinding compound from the surfaces. Clean out the valve guide with a solvent-soaked rag. Make sure there are NO traces of compound in or on the head.
  30.  
  31. Proceed through the remaining valves, lapping them one at a time to their seats. Clean the area after each valve is done.
  32.  
  33. When all the valves have been lapped, thoroughly clean or wash the head with solvent. There must be NO trace of grinding compound present. Lubricate the new valve stem seal with engine oil and install it onto the valve stem over the lower seat.
  34.  
  35. Install the valve spring and the upper seat, compress the spring and install the 2 keepers. Relax tension on the compressor and make sure everything is properly placed. Tap on the installed valve stem with a plastic mallet to ensure proper locking of the retainers.
  36.  
  37. On the 1988 VIN Code 5 engine, install the spark plug tubes, the engine hangers, the temperature sensor bracket and the bond cable. For the 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines, install the tubes and the hanger(s).
  38.  
  39. Install the valve lifters and the adjusting shims. Don't attempt to adjust the valves until after the head is bolted onto the engine.
  40.  
  41. On the 1991-92 VIN Code 5 engine, coat the half-circle plug with silicone sealant and install it in position.
  42.  
  43. Complete the reassembly of the head by installing the camshafts and the manifolds for the 1989-90 VIN Code 6 engine and 1991-92 VIN Code 5 engine, following procedures outlined in this section.
  44.  

INSPECTION AND MEASUREMENT



See Figures 4 through 8

Accurate measuring equipment capable of reading to 0.0001 (ten thousandths) inch is necessary for this work. A micrometer and a hole (bore) gauge will be needed.

Inspect the valve faces and seats for pits, burned spots, and other evidence of poor seating. If the valve face is in such poor shape that the head of the valve must be cut to true the contact face, discard the valve.

The correct angle for the valve face is given in the Valve Specifications Chart at the beginning of this section. It is recommended that any reaming or refacing be done by a reputable machine shop.



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Fig. Fig. 4: Valve refacings should be handled by a reputable machine shop

Check the valve stem for scoring and/or burned spots. If the stem and head are in acceptable condition, clean the valve thoroughly with solvent to remove all gum and varnish.

Use the micrometer to measure the diameter of the valve stem. Use the hole gauge to measure the inside diameter of the valve guide for that valve. Subtract the stem diameter from the guide diameter and compare the difference to the chart. If not within specifications, determine the cause (worn valve or worn guide) and replace the worn part(s).



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Fig. Fig. 5: Measure the diameter of the valve guide and the valve stem. The difference is the stem clearance

Using a steel square, check the valve spring for correct height and squareness. If the squareness is not within 2mm, replace the spring. If the free height of the spring is not within specification, replace the spring. The installed height of the spring must be measured with the spring under tension in the head. Assemble the valve and spring with the retainers and clips into the head; modify a small steel ruler to fit and record the distance from the bottom spring seat to the upper retainer. If not within specification, shim washers (one or more) any be added between the lower spring seat and the spring.

Use only washers designed for this purpose.



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Fig. Fig. 6: Checking the valve spring for squareness



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Fig. Fig. 7: Checking the spring free height



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Fig. Fig. 8: Measure the valve spring installed height (A) with a modified steel ruler

 
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