Ford Sierra Manual

General information
SOHC engines / General information


1.6 litre engine
The 1.6 litre CVH engine was introduced in September 1991, to replace the 1.6 litre SOHC engine used previously in the Sierra range. The engine is broadly similar to the 1.8 litre (R2A type) CVH engine described below.

The main differences are outlined in the following paragraphs.

The centre main bearing is fitted with thrustwashers to control crankshaft endfloat, instead of a flanged bearing shell.

The hydraulic cam followers operate in a similar manner to those described for the 1.8 litre (R2A) engine but no rollers are fitted, and the base of each cam follower is in direct contact with the cam profile.

A distributorless ignition system is used and a blanking plate is therefore fitted to the cylinder head in place of the distributor drive. The electric fuel pump is mounted in the fuel tank.

A comprehensive emissions control system is fitted, comprising Central Fuel Injection (CFI), a sophisticated engine management system, a crankcase ventilation system, a catalytic converter, and a pulseair system (to reduce exhaust gas emissions).

Unless otherwise stated, all procedures are as described for the 1.8 litre (R2A) engine.

1.8 litre (R2A type) engine The CVH (Compound Valve angle, Hemispherical combustion chambers) engine is of four-cylinder, in-line, single overhead camshaft type. The engine was introduced to replace the 1.8 SOHC engine previously used in the range.

The crankshaft incorporates five main bearings. The centre main bearing has a flanged bearing shell (thrust bearing) fitted to the cylinder block to control crankshaft endfloat The camshaft is driven by a toothed belt and operates the compound angled valves via roller type hydraulic cam followers, which eliminates the need for valve clearance adjustment. The cam followers operate in the following way.

When the valve is closed, pressurised engine oil passes through ports in the body of the cam follower and the plunger into the cylinder feed chamber. From this chamber, oil flows through a ball type non-return valve into the pressure chamber. The tension of the coil spring causes the plunger to press the rocker arm against the valve and to eliminate any free play.

As the cam lifts the cam follower, the oil pressure in the pressure chamber increases and causes the non-return valve to close the port to the feed chamber. As oil cannot be compressed, it forms a rigid link between the body of the cam follower, the cylinder and the plunger which then rise as one component to open the valve.

The clearance between the body of the cam follower and the cylinder is accurately designed to meter a specific quantity of oil as it escapes from the pressure chamber. Oil will only pass along the cylinder bore when pressure is high during the moment of valve opening. Once the valve has closed, the escape of oil will produce a small amount of free play and no pressure will exist in the pressure chamber. Oil from the feed chamber can then flow through the non-return valve into the pressure chamber so that the cam follower cylinder can be raised by the pressure of the coil spring, thus eliminating any play in the arrangement until the valve is operated again.

As wear occurs between rocker arm and valve stem, the quantity of oil which flows into the pressure chamber will be slightly more than the quantity lost during the expansion cycle of the cam follower. Conversely, when the cam follower is compressed by the expansion of the valve, a slightly smaller quantity of oil will flow into the pressure chamber than was lost.

To reduce valve clatter when the engine is started, a small plastic stand pipe retains oil inside the plunger. When the engine is started, the reservoir in the plunger (and via the nonreturn valve, the pressure chamber) are immediately filled with oil. This reduces the noise often associated with hydraulic cam followers as they pressurise with oil after engine start-up.

The cam follower rollers run in needle bearings, which greatly reduces friction as the rollers follow the cam profile.

The distributor and fuel pump are driven directly from the camshaft and the oil pump is driven directly from the front of the crankshaft.

The cylinder head is of crossflow design, with the inlet manifold mounted on the righthand side and the exhaust manifold mounted on the left-hand side.

Lubrication is by means of a bi-rotor pump which draws oil through a strainer located inside the sump and forces it through a fullflow filter into the oil galleries where it is distributed to the crankshaft and camshaft.

The big-end bearings are supplied with oil via internal drillings in the crankshaft. The undersides of the pistons are supplied with oil from drillings in the big-ends. The hydraulic cam followers are supplied with oil from the camshaft bearings via short passages in the cylinder head.

A semi-closed crankcase ventilation system is employed whereby piston blow-by gases are drawn from the crankcase, through the camshaft cover via an external vent hose, out to an oil separator built into the base of the air cleaner.

1.8 litre (R6A type) engine The 1.8 litre (R6A type) CVH engine, introduced in March 1992, is a further development of the earlier 1.8 litre (R2A type) unit described above. Apart from minor engineering modifications to provide increased fuel economy, reliability and power output, the engine is mechanically identical to the earlier version.

In common with the 1.6 litre unit, a distributorless ignition system is used, together with a comprehensive emissions control system comprising Central Fuel Injection (CFI), a sophisticated engine management system, a crankcase ventilation system, a catalytic converter, and additionally, an exhaust gas recirculation (EGR) system.

Unless otherwise stated, all procedures are as described for the 1.8 litre (R2A type) engine.


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