The four- and six-cylinder single overhead camshaft engines described in this manual are very similar in design. Where there are differences between them, they will be pointed out.
The means by which the overhead camshafts are driven varies by engine type; the M10 and M30 engines use a timing chain, while the M20 and M40 engines use a timing belt.
Many major repairs can be done without removing the engine from the vehicle.
Before starting any work, clean the engine compartment and the outer surfaces of the engine using a degreaser. This will greatly simplify the implementation of upcoming procedures and reduce the risk of dirt entering the engine.
Depending on the components you intend to work on, it may be useful to remove the hood to provide better access to the engine during repairs (if necessary, see chapter Body). To avoid damage to painted surfaces, cover the fenders of the car with special covers, or, if they are not available, blankets or covers will do.
If oil, vacuum, exhaust or coolant leaks necessitate replacement of gaskets or seals, repairs can generally be made without removing the engine from the vehicle. At the same time, there is sufficient access to the gaskets of the intake pipeline and exhaust manifold, the oil pan, the crankshaft oil seals and the cylinder head.
With the engine installed on the vehicle, external components such as the intake piping and exhaust manifold, oil pan, oil and water pumps, starter, alternator, distributor and fuel system components can be easily removed for repair.
Removing the cylinder head does not require removing the engine. Maintenance of the camshaft, rocker arms and other valve train components is most easily done with the cylinder head removed; these procedures are described in the appropriate section. However, please note that on the M40 engine, the camshaft can be removed without removing the engine, since it is held by bearing caps.
In emergency situations, such as in the absence of the necessary equipment, without removing the engine, work such as repair or replacement of piston rings, pistons, connecting rods and bearings of the lower heads of connecting rods can be performed. However, this practice is not recommended, because this must be preceded by a great deal of preparatory work and a thorough cleaning of all the components involved.