Overhaul

Cylinder Head, Overhaul

- Remove the cylinder head, see Cylinder Head Gasket for procedure.

- Place the cylinder head on suitable blocks on a bench.

- Remove the spark plugs and the intake and exhaust manifolds.




- Mark the position of the camshaft caps relative to the head, remove the cap securing bolts and remove the caps (1 Fig. 1).

- Remove the camshafts.




- Using a magnet, lift out the cam followers (1 Fig. 2).

- Support the valves using a wooden block.

- Remove the valve springs, using Service Tool MS 1519A, valve spring compressor.

- Retrieve the collars, collets and spring retaining plates.

- Remove the valves, noting the relationship between valve and guide to ensure correct pairing during re-assembly.

- Remove the seals from the intake and exhaust valve guides and remove the cylinder head rear blanking plate.

- Clean all component parts.

- Check for wear and burning of valves or seats.

- Check the cylinder head face for distortion.

- If distortion is evident, a maximum of 0.25 mm may be removed by skimming the cylinder head.

- Taking care not to damage the inside surface of the combustion chambers, clean the intake and exhaust ports.

CAUTION: When using scrapers or wire brushes for removing carbon deposits, avoid scratching the valve faces and seats. A soft wire brush is the most suitable implement for this purpose.

- Clean all carbon and other deposits from the valve guide using a suitable valve guide brush. Thoroughly wash the cylinder head to ensure that all loose carbon is removed and dry the cylinder head with a high pressure air line.




- After cleaning and polishing each valve, examine the stems for straightness and wear, using a suitable dial gauge and vee-block see example at (Fig. 3).

- Examine the valve faces for burns, pitting and distortion. Renew any valves that are excessively worn, bent, or too badly pitted to be salvaged by refacing.

Note: No attempt should be made to clean up a burnt or badly pitted valve face by extensive `grinding in' of the valve to the seat.

- Lightly lap the valves into the seats with a fine grinding compound. The reseating operation should leave the finished surfaces smooth. Excessive lapping will groove the valve face resulting in a poor seat when the engine is hot.




- Fig. 1 shows:

A - Valve correctly seated
B - Undesirable condition
C - Rectified condition

- To test the valves for concentricity with their seats, coat the face of the valve with Prussian blue or similar, and rotate the valve against the seat. If the valve face is concentric with the valve stem, a mark will be made all around the face. Should a mark be made on only one side of the face, the face is not concentric with the valve stem. Clean the valve and again coat with Prussian blue and rotate the valve against the seat.

- Check that the valve guide is concentric with the valve seat, if not, the seat must be recut. Whenever valves are renewed the seats must be recut prior to lapping of the valves. Check valve guide wear by inserting a new valve into the guide to be checked, lift it 6 mm from its seat and rock it sideways.




- Movement of the valve across its seat (A Fig. 2) must not exceed 0.04 to 0.07 mm. Should the movement exceed this tolerance, the valve guide must be renewed. Ensure that the relevant valve guide is selected prior to fitting.

- When new guides are to be fitted they should always be one size larger than the old guide.

- Cylinder head bores will require reaming as follows: Remove the old valve guide and ream the cylinder head to the relevant dimension. Immerse the cylinder head in boiling water for 30 minutes. Coat the guide with graphite grease, and drive in the guide from the camshaft side until the snap-ring is seated in the groove.

Note: The interference should not be sufficient to require the use of excessive force when fitting the guide.




- After fitting a valve guide, the valve seat must be recut using Service Tool MS 204 (Fig. 3). Examine the valve seat inserts for pitting or excess wear. If renewal is necessary, proceed as follows.

- Remove the inserts by machining, leaving approximately 0.25 mm of metal which can easily be removed by hand without damaging the cylinder head. Measure the diameter of the insert recess in the cylinder head. Grind down the outside diameter of the new insert to a dimension 0.08 mm larger than the insert recess.

- Heat the cylinder head for 30 minutes from cold to a temperature of 150°C ). Fit the insert ensuring that it beds evenly in the recess. When the cylinder head has cooled, recut the valve seat using Service Tool MS 204. For correct valve seat angles see Service Data under Engine Specifications.

Note: If new valve inserts have been fitted, the clearance between valve stem and cam must be checked, see Service Data under Engine Specifications.

- The dimension must be taken between the valve stem and the back of the cam. Should this dimension not be obtained, metal must be ground from the valve seat of the insert.

Note: Use only suitable grinding equipment.

- Remove only very small amounts of metal from the valve seat at one time before rec1hecking the clearance.




- Examine the cam followers for wear on the top face. Check for any sign of barreling on the side faces (Fig. 1). Renew all followers that are worn or suspect. Wash the valves, springs, collets, followers and air dry.

- After the valve springs have been thoroughly washed, they must be examined for fatigue and distortion. Renew as necessary.

- Test the valve springs either by comparison with the figures given in Service Data under Engine Specifications, or by comparison with a new valve spring (using a recommended valve spring testing machine).




- To test against a new valve spring, insert both valve springs end to end between the test equipment. Apply a load to partly compress the springs and measure their comparative lengths (Fig. 2).

Note: `A' is the old spring.

- If the distance `A' is smaller than the distance `B', then `A' must be renewed.




Note: Spring distortion is determined by positioning the spring upright on a surface plate and checking the squareness of each end with a set square (Fig. 3). All valve springs which have diminished in length and/ or are not square must be renewed.

- Fit the valves into the guides and place the cylinder head on wooden blocks.

- Fit the valve spring seats, intake and exhaust valve guide oil seals, springs and collars.

- Compress the springs using Service Tool MS 1519A and insert the split collets.




- Refit the original shims (1 Fig. 4) in the valve collar recesses. (Ensure that the shims are seated correctly and fit the cam followers, see Valve Clearance Adjustment.

Note: If the cylinder head has been overhauled to the extent of having the valve seats recut, each shim should be O.O1O in. smaller than the original.

- Lubricate the camshafts and fit to the cylinder head, ensuring that they are fitted with the slots to the top. Fit the camshaft caps and torque tighten the securing bolts. Measure the valve clearance between the heel of the cam and the cam follower, turning the camshaft as necessary to measure all the clearances see Valve Clearance Adjustment.

Note: It is advisable to set the valve clearances to the upper limit to allow for the clamping effect experienced through torque tightening upon engine reassembly.

Note: A final check of the valve clearances should be done when the cylinder head is fitted and torque tightened to the cylinder block.

- Clean the cylinder head thoroughly and check the cylinder head and cylinder block for warping, bowing or cracks.

- Fit the cylinder head, see Cylinder Head Gasket for procedure.