Tuesday, June 7, 2011

Cylinder block, crankshaft and bearing service

The engine is usually removed from the vehicle for any major service work on the cylinder block and crankshaft, although some jobs can be done with the engine in the vehicle.
As well as dismantling and reassembling procedures, service items include checking the cylinder bores for wear, reconditioning the cylinders by honing or boring, renewing cylinder sleeves, checking crankshaft journals for wear, and checking and replacing crankshaft bearings.
Some information on engine reconditioning will be included in upcoming posts. While major items are often handled by engine-reconditioning workshops, a general appreciation of these procedures is needed by all automotive technicians.

Fig 5.1
Servicing cylinder blocks
After the various components have been dismantled from the cylinder block, it should be cleaned and inspected. The block can be steam-cleaned, pressure- cleaned with water, or cleaned in a cleaning tank. Alternatively, solvent can be applied by spray gun or brush and jetted off with water. All old gaskets and sealing material must be removed from the machined surfaces.
For a thorough cleaning, the plugs that blank off oil passages should be removed and the passages blown through with compressed air. The passages must be free of sludge or deposits that could have been loosened during cleaning.
A general check of the cylinder block should be carried out, as shown in Figure 5.1. Checks include machined surfaces, threaded holes, and core plugs. The cylinders are checked for cracks, scores and wear.
·    Minute cracks will show up f the suspected area of the block is checked with one of the crack-detection methods.

Machined surfaces
Fig 5.2
Machined surfaces should be inspected for burrs, nicks and scratches. Minor damage can be carefully removed with a fine file or an oil stone.
The top of the cylinder block can be checked for flatness by using a straightedge and feeler gauge (Figure 5.2). This is done in a similar manner to that previously described for the cylinder head (Chapter 3). The surface can be machined to restore the flatness if necessary, but only a limited amount of metal (for example, 0.25 mm) should be removed.

·   For more information on bolts and threads see upcoming "General engine service."

Expansion or core plugs
Expansion plugs in the cylinder block should be replaced if they show any evidence of leaking. Most plugs can be removed by drilling or punching a hole in the centre, and then levering them out with a punch or small pry bar.
To install a new plug, scrape any rust from the recess in the block, coat the recess with a suitable sealing compound and place the new plug in the recess, convex side out. Tap the centre of the plug to make sure it is seated, then use a flat-ended punch and a hammer to drive against the centre of the plug and expand it into the recess.
Cup-shaped plugs are treated in a similar way, except that it is not necessary to expand them after they have been tapped into the recess in the cylinder block.

Checking and measurement of cylinders for service

The cylinders do not wear uniformly, but wear tapered and out-of-round. They must be measured accurately to find the amount of wear and to determine what reconditioning is needed.
If the wear is not excessive, new piston rings and bearings can be fitted and this will provide a satisfactory repair. However, if the cylinders have worn beyond a certain limit, new rings will not be sufficient and the cylinders will have to be reconditioned. 

See measuring cylinders>>>>>>>>>>>>>>

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