Opel Corsa B 1993–2000 Service and Repair Manual: Engine components - examination and renovation

Crankshaft

1. Examine the crankpin and main journal surfaces for signs of scoring or scratches, and check the ovality and taper of the crankpins and main journals. If the bearing surface dimensions do not fall within the tolerance ranges given in the Specifications at the beginning of this Chapter, the crankpins and/or main journals will have to be reground.

2. Big-end and crankpin wear is accompanied by distinct metallic knocking, particularly noticed when the engine is pulling from low revs, and some loss of oil pressure.

3. Main bearing and main journal wear is accompanied by severe engine vibration rumble - getting progressively worse as engine revs increase - and again by loss of oil pressure.

4. If the crankshaft requires regrinding take it to an engine reconditioning specialist, who will machine it for you and supply the correct undersize bearing shells.

5. On some engines, the crankshaft journal diameters are machined undersize in production to allow for greater manufacturing tolerances.

Big-end and main bearing shells

6. Inspect the big-end and main bearing shells for signs of general wear, scoring, pitting and scratches. The bearings should be matt grey in colour. With lead-indium bearings, should a trace of copper colour be noticed, the bearings are badly worn as the lead bearing material has worn away to expose the indium underlay. Renew the bearings if they are in this condition or if there are any signs of scoring or pitting.

You are strongly advised to renew the bearings - regardless of their condition - at time of major overhaul. Refitting used bearings is a false economy.

7. The undersizes available are designed to correspond with crankshaft regrind sizes. The bearings are in fact, slightly more than the stated undersize as running clearances have been allowed for during their manufacture.

Cylinder bores

8. The cylinder bores must be examined for taper, ovality, scoring and scratches. Start by carefully examining the top of the cylinder bores. If they are at all worn a very slight ridge will be found on the thrust side. This marks the top of the piston travel. The owner will have a good indication of the bore wear prior to dismantling the engine, or removing the cylinder head. Excessive oil consumption accompanied by blue smoke from the exhaust can be caused by worn cylinder bores and piston rings.

9. Measure the bore diameter across the block and just below any ridge. This can be done with an internal micrometer or a dial gauge. Compare this with the diameter of the bottom of the bore, which is not subject to wear. If no measuring instruments are available, use a piston from which the rings have been removed and measure the gap between it and the cylinder wall with a feeler blade.

10. Refer to the Specifications. If the cylinder wear exceeds the permitted tolerances then the cylinders will need reboring.

11. If the cylinders have already been bored out to their maximum it may be possible to have liners fitted. This situation will not often be encountered.

Connecting rods

12. Examine the mating faces of the big-end caps to see if they have ever been filed in a mistaken attempt to take up wear. If so, the offending rods must be renewed.

13. Check the alignment of the rods visually, and if all is not well, take the rods to your local agent for checking on a special jig.

Pistons and piston rings

14. If the pistons and/or rings are to be re-used, remove the rings from the pistons.

Three strips of tin or 0.38 mm feeler blades should be prepared and the top ring then sprung open just sufficiently to allow them to be slipped behind the ring. The ring can then be slid off the piston upwards without scoring or scratching the piston lands.

15. Repeat the process for the second and third rings.

16. Mark the rings or keep them in order so they may be refitted in their original locations.

17. Inspect the pistons to ensure that they are suitable for re-use. Check for cracks, damage to the piston ring grooves and lands, and scores or signs of picking-up the piston walls.

18. Clean the ring grooves using a piece of old piston ring ground to a suitable width and scrape the deposits out of the grooves, taking care not to remove any metal or score the piston lands. Protect your fingers - piston rings are sharp.

19. Check the rings in their respective bores.

Press the ring down to the unworn lower section of the bore (use a piston to do this, and keep the ring square in the bore).

Measure the ring end gap and check that it is within the tolerance allowed (see Specifications). Also check the ring's side clearance in its groove. If these measurements exceed the specified tolerances the rings will have to be renewed, and if the ring grooves in the pistons are worn new pistons may be needed.

20. Proprietary piston rings are available which are reputed to reduce oil consumption due to bore wear without the expense of a rebore. Depending on the degree of wear, the improvement produced by fitting such rings may be short-lived.

21. If new rings (or pistons and rings) are to be fitted to an existing bore the top ring must be stepped to clear the wear ridge at the top of the bore, or the bore must be de-ridged.

22. Check the clearance and end gap of any new rings, as described in paragraph 19. If a ring is slightly tight in its groove it may be rubbed down using an oilstone or a sheet of carborundum paper laid on a sheet of glass. If the end gap is inadequate the ring can be carefully ground until the specified clearance is achieved.

23. If new pistons are to be installed they will be selected from the grades available (see Specifications), after measuring the bores as described in paragraph 9. Normally the appropriate oversize pistons are supplied by the repairer when the block is rebored.

24. Removing and refitting pistons on the connecting rod is a job for your dealer or specialist repairer. Press equipment and a means of accurately heating the connecting rod will be required for removal and insertion of the gudgeon pin.

Camshaft and bearings

25. With the camshaft removed, examine the bearings for signs of obvious wear and pitting.

If there are signs, then the three bearings will need renewal. This is not a common requirement and to have to do so is indicative of severe engine neglect at some time. As special tools are necessary to do this work properly, it is recommended that it is done by your dealer. Check that the bearings are located properly so that the oilways from the bearing housings are not obstructed.

26. The camshaft itself should show no marks on either the bearing journals or the profiles. If it does, it should be renewed.

27. Examine the skew gear for signs of wear or damage. If this is badly worn it will mean renewing the camshaft.

28. The thrust plate (which also acts as the locating plate) should not be ridged or worn in any way. If it is, renew it.

Timing chain sprockets and tensioner

29. Examine the teeth of both sprockets for wear. Each tooth is the shape of an inverted V and if the driving (or driven) side is concave in shape, the tooth is worn and the sprocket should be renewed. The chain should also be renewed if the sprocket teeth are worn. It is sensible practice to renew the chain anyway.

30. Inspect the chain tensioner, which is automatic in operation. The most important item to check is the shoe which wears against the chain. If it is obviously worn, scratched or damaged in any way, then it must be renewed. Check the spring for signs of wear and renew the unit if generally worn or defective, or when a new chain is being fitted.

Valve rocker arms, pushrods and tappets

31. Each rocker arm has three wearing surfaces, namely the pushrod recess, the valve stem contact, and the centre pivot recess. If any of these surfaces appear severely grooved or worn the arm should be renewed. If only the valve stem contact area is worn it is possible to clean it up with a fine file.

32. If the rocker ball is pitted, or has flats in it, this should also be renewed.

33. The nut on the rocker stud is a self-locking type. If it has been removed or adjusted many times, the self-locking ring may have become ineffective and the nut may be slack enough to turn involuntarily and alter the tappet clearance.

34. The rocker studs should be examined to ensure that the threads are undamaged and that the oil delivery hole in the side of the stud at the base of the thread is clear. Place a straight-edge along the top of all the studs to ensure that none is standing higher than the rest. If any are, it means that they have pulled out of the head some distance. They should be removed and replaced with an oversize stud. As this involves reaming out the stud hole to an exact size to provide an interference fit for the replacement stud, you should seek professional advice and assistance to ensure that the new oversize stud is securely fitted at the correct angle.

35. Any pushrods which are bent should be renewed. On no account attempt to straighten them. They are easily checked by rolling over a perfectly flat surface such as a sheet of glass.

36. Examine the bearing surfaces of the tappets which lie on the camshaft. Any indentation in these surfaces or any cracks indicate serious wear and the tappets should be renewed. Thoroughly clean them out, removing all traces of sludge. It is most unlikely that the sides of the tappets will prove worn but, if they are a very loose fit in their bores and can readily be rocked, they should be exchanged for new ones. It is very unusual to find any wear in the tappets, and any wear present is likely to occur at very high mileages, or in cases or neglect. If the tappets are worn, examine the camshaft carefully as well!.

Flywheel

37. If the teeth on the flywheel starter ring are badly worn, or if some are missing, then it will be necessary to remove the ring and fit a new one.

38. Either split the ring with a cold chisel after making a cut with a hacksaw blade between two teeth, or use a soft-headed hammer (not steel) to knock the ring off, striking it evenly and alternately at equally spaced points. Take great care not to damage the flywheel during this process, and protect your eyes from flying fragments.

39. Clean and polish with emery cloth four evenly spaced areas on the outside face of the new starter ring.

40. Heat the ring evenly with a flame until the polished portions turn dark blue. Alternatively heat the ring in a bath of oil to a temperature of 200ºC. (If a naked flame is used take adequate fire precautions.) Hold the ring at this temperature for five minutes and then quickly fit it to the flywheel, so the chamfered portion of the teeth faces the gearbox side of the flywheel. Wipe all oil off the ring before fitting it.

41. The ring should be tapped gently down onto its register and left to cool naturally when the contraction of the metal on cooling will ensure that it is a secure and permanent fit.

Great care must be taken not to overheat the ring, indicated by it turning light metallic blue.

If this happens the temper of the ring will be lost.

42. If the driven plate contact surface of the flywheel is scored or on close inspection shows evidence of small hair cracks, caused by overheating, it may be possible to have the flywheel surface ground provided the overall thickness of the flywheel is not reduced too much. Consult a specialist engine repairer and if it is not possible, renew the flywheel complete.

43. If the needle bearing in the centre of the crankshaft flange is worn, fill it with grease and tap in a close-fitting rod. Hydraulic pressure will remove it. Tap the new bearing into position and apply a little grease.