Crankshaft - refitting and running clearence check

Engine removal and overhaul procedures / Crankshaft - refitting and running clearence check

1 Crankshaft refitting is the first stage of engine reassembly following overhaul. At this point, it is assumed that the crankshaft, cylinder block/crankcase and bearings have been cleaned, inspected and reconditioned or renewed.

2 Place the cylinder block on a clean, level work surface, with the crankcase facing upwards. Unbolt the bearing caps and carefully release them from the crankcase; lay them out in order to ensure correct reassembly. If they are still in place, remove the bearing shells from the caps and the crankcase and wipe out the inner surfaces with a clean rag - they must be kept spotlessly clean.

3 Clean the rear surface of the new bearing shells with a rag and lay them on the bearing saddles. Ensure that the orientation lugs on the shells engage with the recesses in the saddles and that the oil holes are correctly aligned (see illustration). Do not hammer or otherwise force the bearing shells into place.

It is critically important that the surfaces of the bearings are kept free from damage and contamination.

10.3 Fitting the centre main bearing upper shell

4 Give the newly fitted bearing shells and the crankshaft journals a final clean with a rag.

Check that the oil holes in the crankshaft are free from dirt, as any left here will become embedded in the new bearings when the engine is first started.

5 Carefully lay the crankshaft in the crankcase, taking care not to dislodge the bearing shells.

Running clearance check
6 When the crankshaft and bearings are refitted, a clearance must exist between them to allow lubricant to circulate. This clearance is impossible to check using feeler blades, so Plastigage is used. This is a thin strip of soft plastic that is crushed between the bearing shells and journals when the bearing caps are tightened up. The change in its width then indicates the size of the clearance gap.

7 Cut off five pieces of Plastigage, just shorter than the length of the crankshaft journal. Lay a piece on each journal, in line with its axis (see illustration).

10.7 Lay a piece of Plastigage on each journal, in line with its axis

6 Wipe off the rear surfaces of the new lower half main bearing shells and fit them to the main bearing caps, again ensuring that the locating lugs engage correctly.

9 Wipe the front surfaces of the bearing shells and give them a light coating of silicone release agent - this will prevent the Plastigage from sticking to the shell. Fit the caps in their correct locations on the bearing saddles, using the manufacturers markings as a guide.

Ensure that they are correctly orientated - the caps should be fitted such that the recesses for the bearing shell locating lugs are on the same side as those in the bearing saddle.

10 Working from the centre bearing cap, tighten the bolts one half turn at a time until they are all correctly torqued to their first stage only. Do not allow the crankshaft to rotate at all whilst the Plastigage is in place.

Progressively unbolt the bearing caps and remove them, taking care not to dislodge the Plastigage.

11 The width of the crushed Plastigage can now be measured, using the scale provided (see illustration). Use the correct scale, as both imperial and metric are printed. This measurement indicates the running clearance - compare it with that listed in Specifications.

If the clearance is outside the tolerance, it may be due to dirt or debris trapped under the bearing surface; try cleaning them again and repeat the clearance check. If the results are still unacceptable, re-check the journal diameters and the bearing sizes. Note that if the Plastigage is thicker at one end, the journals may be tapered and as such, will require regrinding.

10.11 Measure the width of the crushed Plastigage using the gauge provided

12 When you are satisfied that the clearances are correct, carefully remove the remains of the Plastigage from the journals and bearings faces. Use a soft, plastic or wooden scraper as anything metallic is likely to damage the surfaces.

Crankshaft - final refitting 13 Lift the crankshaft out of the crankcase.

Wipe off the surfaces of the bearings in the crankcase and the bearing caps. Fit the thrust bearings either side of the No 3 bearing saddle, between cylinders No 2 and 3 (see illustration). Use a small quantity of grease to hold them in place; ensure that they are seated correctly in the machined recesses, with the oil grooves facing outwards.

10.13 Thrustwashers fitted to the No 3 bearing saddle

14 Liberally coat the bearing shells in the crankcase with clean engine oil (see illustration).

10.14 Liberally coat the bearing shells  in the crankcase with clean engine oil

15 Lower the crankshaft into position so that No 2 and 3 cylinder crankpins are at TDC; No 1 and 4 cylinder crankpins will then be at BDC, ready for fitting No 1 piston.

16 Lubricate the lower bearing shells in the main bearing caps with clean engine oil, then fit the thrustwashers to either side of bearing cap No 3, noting that the lugs protruding from the washers engage the recesses in the side of the bearing cap (see illustration). Make sure that the locating lugs on the shells are still engaged with the corresponding recesses in the caps.

10.16 Fitting the centre main bearing cap

17 Fit the main bearing caps in the correct order and orientation - No 1 bearing cap must be at the timing belt end of the engine and the bearing shell locating recesses in the bearing saddles and caps must be adjacent to each other. Insert the bearing cap bolts and hand tighten them only.

18 Working from the centre bearing cap outwards, tighten the retaining bolts to their specified torques. Where the torque is expressed in several stages, tighten all the bolts to the first stage, then repeat the exercise in the same sequence for the subsequent stage(s) (see illustration).

10.18 Tightening the main bearing bolts

19 Refit the crankshaft rear oil seal housing, together with a new oil seal; refer to Part A of this Chapter for details.

20 Check that the crankshaft rotates freely by turning it by manually. If excessive resistance is felt, re-check the running clearances, as described above.

21 Carry out a check of the crankshaft endfloat as described at the beginning of Section 6. If the thrust surfaces of the crankshaft have been checked and new thrust bearings have been fitted, then the endfloat should be within specification.