Cylinder block/crankcase casting - cleaning and inspection

Engine removal and overhaul procedures / Cylinder block/crankcase casting - cleaning and inspection

Cleaning
1 Remove all external components and electrical switches/sensors from the block.

For complete cleaning, the core plugs should ideally be removed. Drill a small hole in the plugs, then insert a self-tapping screw into the hole. Extract the plugs by pulling on the screw with a pair of grips, or by using a slide hammer (see illustration).

7.1 Using a slide hammer to remove a core plug

2 Scrape all traces of gasket and sealant from the cylinder block/crankcase, taking care not to damage the sealing surfaces.

3 Remove all oil gallery plugs (where fitted).

The plugs are usually very tight - they may have to be drilled out, and the holes retapped.

Use new plugs when the engine is reassembled.

4 If the casting is very dirty, it should be steam-cleaned. After this, clean all oil holes and galleries one more time. Flush all internal passages with water until the water runs clear.

Dry thoroughly, and apply a light film of oil to all mating surfaces and cylinder bores, to prevent rusting. If you have access to compressed air, use it to speed up the drying process, and to blow out all oil holes and galleries. Warning: Be sure to wear eye protection when using
compressed air!

5 If the castings are not very dirty, you can do an adequate cleaning job with hot, soapy water and a stiff brush. Take plenty of time, and do a thorough job. Regardless of the cleaning method used, be sure to clean all oil holes and galleries very thoroughly, and to dry all components well. Protect the cylinder bores as described above, to prevent rusting.

6 All threaded holes must be clean, to ensure that fixings are tightened to the correct torque during reassembly. To clean the threads, run the correct-size tap into each of the holes to remove rust, corrosion, thread sealant or sludge, and to restore damaged threads (see illustration). If possible, use compressed air to clear the holes of debris produced by this operation. Note: Take extra care to exclude all cleaning liquid from blind tapped holes, as the casting may be cracked by hydraulic action if a bolt is tightened in a hole containing liquid.

7.6 Clear out threaded holes using the correct size of tap

7 Apply suitable sealant to the new oil gallery plugs, and insert them into the holes in the block. Tighten them securely.

8 If the engine is not going to be reassembled immediately, cover it with a large plastic bag to keep it clean; protect all mating surfaces and the cylinder bores as described above, to prevent rusting.

Inspection
9 Visually check the casting for cracks and corrosion. Look for stripped threads in the threaded holes. If there has been any history of internal water leakage, it may be worthwhile having an engine overhaul specialist check the cylinder block/crankcase with professional equipment. If defects are found, have them repaired if possible, failing this the cylinder block should be renewed.

10 Check the cylinder bores for scuffing or scoring. Any evidence of this kind of damage should be cross-checked with an inspection of the pistons: see Section 5 of this Chapter. If the damage is in its early stages, it may be possible to repair the block by reboring it.

Seek the advice of an engineering workshop before you progress.

11 To allow an accurate assessment of the wear in the cylinder bores to be made, their diameter must be measured at a number of points, as follows. Insert a bore gauge into cylinder bore No 1 and take three measurements in line with the crankshaft axis; one at the top of the bore, roughly 10 mm below the bottom of the wear ridge, one halfway down the bore and one at a point roughly 10 mm the bottom of the bore. Note: Stand the cylinder block squarely on a workbench during this procedure, inaccurate results may be obtained if the measurements are taken when the engine mounted on a stand.

12 Rotate the bore gauge through 90°, so that it is at right angles to the crankshaft axis and repeat the measurements detailed in paragraph 11 (see illustration). Record all six measurements and compare them with the data listed in the Specifications Section. If the difference in diameter between any two cylinders exceeds the wear limit, or if any one cylinder exceeds its maximum bore diameter, then all four cylinders will have to be rebored and oversize pistons will have to be fitted.

Note that the imbalances produced by not reboring all the cylinders together would render the engine unusable.

7.12 Bore measurement points

13 Use the piston diameter measurements recorded earlier (see Section 5) to calculate the piston to cylinder clearances. Compare these with the specified maximum and determine whether reboring and oversize pistons are required.

14 Place the cylinder block on a level work surface, crankcase downwards. Use a straight edge and a set of feeler blades to measure the distortion of the cylinder head mating surface in both planes, A maximum figure is not quoted by the manufacturer, but use the figure of 0.05 mm as a rough guide. If the measurement exceeds this figure, repair may be possible by machining - consult your dealer for advice.

15 Before the engine can be reassembled, the cylinder bores must be honed. This process involves using an abrasive tool to produce a fine, cross-hatch pattern on the inner surface of the bore. This has the effect of seating the piston rings, resulting in a good seal between the piston and cylinder. There are two types of honing tool available to the home mechanic, both are driven by a rotary power tool, such as a drill. The ‘Bottle Brush’ hone is a stiff, cylindrical brush with abrasive stones bonded to its bristles. The more conventional surfacing hone has abrasive stones mounted on spring loaded legs. For the inexperienced home mechanic, satisfactory results will be achieved more easily using the Bottle Brush hone. Note: If you are unwilling to tackle cylinder bore honing, an engineering workshop will be able carry out the job for you at a reasonable cost.

16 Carry out the honing as follows; you need one of the honing tools described above, a power drill/air wrench, a supply clean rags, some honing oil and a pair safety glasses.

17 Fit the honing tool in the drill chuck.

Lubricate the cylinder bores with honing oil and insert the honing tool into the first bore, compressing the stones to allow it to fit. Turn on the drill at its slowest speed and as the tool rotates, move it up and down in the bore at rate that produces a fine cross-hatch pattern on the surface. The lines of the pattern should ideally cross at about 50-60” (see illustration)., although some piston ring manufacturers may quote a different angle; check the literature supplied with the new rings.

7.17 Cylinder bore honing pattern

Warning: Wear safety glasses pro tact your eyes from debris flying off the honing tool.

18 Use plenty of oil during the honing process. Do not remove any more material than is necessary to produce the required finish. When removing the hone tool from the bore, do not pull it out whilst it is still rotating; maintain the up/down movement until the chuck has stopped, then withdraw the tool whilst rotating the chuck by hand, in the normal direction of rotation.

19 Wipe out the oil and swarf with a rag and proceed to the next bore. When all the bores have been honed, thoroughly clean the whole cylinder block in hot soapy water to remove all traces of honing oil and debris. The block can be considered clean when a clean rag, moistened with new engine oil does not pick up any grey residue when wiped along the bore.

20 Apply a light coating of engine oil to the mating surfaces and cylinder bores to prevent rust forming. Store the block in a plastic bag until reassembly.