Ford Sierra Manual

Cylinder head - inspection and renovation
SOHC engines / Cylinder head - inspection and renovation


Note: On engines fitted with hardened valve seats for use with unleaded petrol, valve and valve seat grinding and recutting cannot be carried out without the use of specialist equipment. Consult a Ford dealer for further advice.

1 This operation will normally only be required at comparatively high mileages.

However, if persistent pre-ignition (УpinkingФ) occurs and performance has deteriorated even though the engine adjustments are correct, de-carbonizing and valve grinding may be required.

2 With the cylinder head removed, use a scraper to remove the carbon from the combustion chambers and ports. Remove all traces of gasket from the cylinder head surface, then wash it thoroughly with paraffin.

3 Use a straight edge and feeler blade to check that the cylinder head surface is not distorted. If it is, it must be resurfaced by a suitably equipped engineering works.

4 If the engine is still in the vehicle, clean the piston crowns and cylinder bore upper edges, but make sure that no carbon drops between the pistons and bores. To do this, locate two of the pistons at the top of their bores and seal off the remaining bores with paper and masking tape. Press a little grease between the two pistons and their bores to collect any carbon dust; this can be wiped away when the piston is lowered. To prevent carbon build-up, polish the piston crown with metal polish, but remove all traces of the polish afterwards.

5 Examine the heads of the valves for pitting and burning, especially the exhaust valve heads. Renew any valve which is badly burnt.

Examine the valve seats at the same time. If the pitting is very slight, it can be removed by grinding the valve heads and seats together with coarse, then fine, grinding paste.

6 Where excessive pitting has occurred, the valve seats must be recut or renewed by a suitably equipped engineering works.

7 Valve grinding is carried out as follows.

Place the cylinder head upside down on a bench on blocks of wood.

8 Smear a trace of coarse carborundum paste on the valve seat face and press a suction grinding tool onto the valve head.

With a semi-rotary action, grind the valve head to its seat, lifting the valve occasionally to redistribute the grinding paste. When a dull matt even surface is produced on the mating surface of both the valve seat and the valve, wipe off the paste and repeat the process with fine carborundum paste as before. A light spring placed under the valve head will greatly ease this operation. When a smooth unbroken ring of light grey matt finish is produced on the mating surface of both the valve and seat, the grinding operation is complete.

9 Scrape away all carbon from the valve head and stem, and clean away all traces of grinding compound. Clean the valves and seats with a paraffin soaked rag, then wipe with a clean rag.

10 If the guides are worn they will need reboring for oversize valves or for fitting guide inserts. The valve seats will also need recutting to ensure that they are concentric with the stems. This work should be entrusted to a Ford dealer or local engineering works.

11 Check that the free length of the valve springs is as specified, and renew if necessary. Do not renew individual springs; if any springs are excessively worn, renew all the springs as a set.


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