The Differences Between Early SZ Cars and the Later 20K Series One of the most-often-asked questions regarding used SZ cars is, “Which one offers the most reliability and robust engineering for the least amount of money?” The answer that is usually heard is, “If you’re going to buy one it must be a 20,000 series”. We have all heard this over and over. The term, “20,000 Series” refers to cars built beginning in the 1987 model year which have a chassis number higher than 20,001 and lower than 27799. It’s important to note that there are some early 1987 cars that are NOT 20,000 series cars. You must look at the chassis number to be sure. The series continued through the 1989 model year. It was succeeded by the 30,000 Series, which began in 1990. The usual reasons cited for buying a 20,000 series car are the addition of ABS and an improved electrical system. While those items are both true, there were many more important improvements to the cars. The changes resulted in greater fuel efficiency, greater engine power, vastly improved reliability, simplified servicing, and a reduction of the number of engine components. In this article, we will find out in detail why these cars are the best choice for someone shopping for a modern car from the eighties. The information found here is compiled from Rolls-Royce’s technical service bulletin TSD 4742, An Introduction to the Specification Changes for Silver Spirit, Silver Spur, Bentley Eight, Bentley Mulsanne, and the Bentley Turbo R. AIR CONDITIONING A new design of compressor was fitted. The new Sandin compressor was smaller and lighter than the previous type. Despite it’s smaller size, it had equal capacity and greater reliability. A new six row evaporator matrix was used. The new design provided greater efficiency. In addition, a newly designed fan speed module, a new electrically operated heater tap, and a revised air ducting system for the rear occupants were introduced. A multi-function resistor block located in the engine compartment above the former toe board connections replaced the fan speed module with variable resistors, finned to dissipate heat. The entire system was controlled by a new microprocessor based servo unit which provided much more precise control of the selected temperatures with improved reliability through simplified construction. Finally, an additional position was available on the control panel. In the ‘Economy’ position, the system cuts out the compressor and uses ambient air only ENGINE

In the new design, the main bearing caps are retained by set bolts instead of the studs and nuts of the previous design. Also, the main bearing shells were now of a common width. The rear main bearing now used the same bearing shells as the other four bearings. A new timing cover casting was introduced which featured an integral oil filter mounting pedestal. This change improved oil integrity by reducing the number of joints involved. In addition, a hydraulic thermal switch opens when the oil temperature reaches a predetermined temperature, allowing flow to the oil cooler when the engine comes to temperature. A new induction manifold was introduced. The manifold is a single tier design, which has improved gas flow characteristics. The design also incorporates a plenum chamber necessary for the revised fuel system. The new design also incorporates external coolant galleries which provide improved coolant circulation, giving more even running temperatures, especially around the rear cylinders. The tappet cover was redesigned to accommodate the plenum chamber which was incorporated in the new induction manifold. Finally, engine starting was improved with the introduction of a new starter motor. The new starter is smaller and lighter than the old one and is also quieter. A new cylinder head was introduced which featured revised cooling passages and round section inlet ports, which improve gas flow. All 20,000 series cars were fitted with a revised firing order camshaft which resulted in an improved firing load distribution between the main bearings. The camshaft is the same as the one that was introduced on 1986 turbo charged cars in the home market. The new firing order is: A1, A3, B3, A2, B2, B1, A4, B4. A new throttle body deign was fitted. The new design was a four barrel design which allows the overall height to be kept to a minimum while permitting efficient air flow and minimal load on the throttle flaps. This is sometimes referred to as a staged four barrel. A new piston design was employed which had many improvements. The primary advantages were reduced weight and lower friction. This is a result of the skirt design which is diamond cut for better oil retention and break-in-material gathering. This prevents material build up and a change in piston dimensions. Engine refinement at idle was enhanced by the introduction of a new flywheel design. The result was greater mass incorporated in the outer rim of the flywheel. The oil cooler was repositioned. The new location is behind the front air dam. The new location reduced engine operating temperatures.

FINAL DRIVE All twenty thousand series cars feature a number of changes to the final drive assembly. Firstly, to compliment the increase in engine power, a new higher axle ratio gearing has been introduced. The new ratios are as follows: All non-turbocharger cars- 2.69:1 All turbocharger cars- 2.28:1 Also, a number of changes to the design were introduced. The principal changes are a revised design of axle casing and differential housing to accommodate the new crown wheel and pinion gears. Also, the coupling flange splines were changed from straight to involute helical splines. This change results in the flange press-on load being greatly reduced, making service easier. FUEL AND IGNITION SYSTEM Major changes have been made to the fuel system on twenty thousand series cars. The principal change on all normally aspirated cars is the use of Bosch K-Jetronic continuous fuel injection. Normally Aspirated Engines The K-Jetronic system is both manually and hydraulically controlled which requires no form of drive. The amount of air drawn into the engine serves as a measure for the correct quantity of fuel to be injected. Depending on the operating mode of the engine, the K-Jetronic system meters the optimum amount of fuel required. The system provided more efficient utilization of the fuel than is possible with a conventional carburetor, resulting in greater specific power and fuel economy. The basic principal of operation is as follows: Air is drawn into the engine through the air meter. The airflow causes the air sensor plate to deflect downwards. This movement is transmitted through to the fuel distributor control plunger, causing the plunger to be moved upwards. In doing so, the control edge of the plunger uncovers metering slicks (one for each cylinder) machined in the plunger barrel. This determined the cross sectional flow area to the injectors, allowing the correct amount of fuel to be supplied to the cylinders. The system is similar to that already fitted to cars for use in North America, Japan, and Australia. However, the use of a three-way exhaust catalytic converter and closed-loop mixture control, together with air injection and exhaust gas recirculation (EGR) is necessary to meet emissions regulations.

Elapsed O2 time indicator is eliminated with 12v warming coil supplied to quicken the O2 warming time. This extinguishes the facia light faster. The O2 sensor has longer life and higher durability. This feature began in the 1986 model year. Textron by Chevron, fuel injector cleaner additive, should be used to clean the injectors at service. Turbocharged Engines On Turbo charged motor cars, the operating parameters of the engine, such as engine temperature and power output are far higher than on normally aspirated engines. Because of this, Turbocharged motor cars are fitted with the Bosch KE-jetronic (E stands for electronic) fuel injection system. This system uses the same basic mechanical and hydraulic functions as the K-Jetronic system, but also incorporates electronic control of the mixture for starting, the post start phase and warm-up operation as well as acceleration and full load operation. A chain of sensors provide information on water temperature, throttle position, manifold pressure, engine speed, and air sensor plate rate of movements. This information is processed by an electronic control unit (ECU) which then provides a signal to the electro hydraulic actuator(EHA) mounted on the fuel distributor. The EHA then electronically controls the mixture strength as required. This provides more precise control than is available with a purely mechanical system. All Cars In addition, all 20,000 Series motor cars are fitted with an in-tank mounted fuel pre-pump. The prepump is used to raise the pressure of the fuel entering the main fuel pump. This increase in pressure alleviates the possibility of fuel cavitation occurring at higher fuel temperatures and so reduces operation noise. An improved fuel level sender unit is now fitted. This new unit provides more accurate fuel level indication. Ignition System-Naturally-Aspirated Engines All 20,000 Series motor cars with naturally aspirated engines feature a revised ignition system. The changes include a new design of ignition amplifier module and improved ignition leads. Other improvements include a seven pin diagnostic plug to aid engine tuning. The plug is fitted adjacent to the alternator. The signal for the plug is provided by a sensor mounted in the rear of the crankcase.

Turbocharged Motor Cars On turbocharged motor cars, a completely new ignition system has been introduced. The new ignition system is a digital electronic system which accurately controls the ignition timing and advance characteristics during all operating g conditions. The principal components of the new system are a twin 4 cylinder distributor, twin ignition coils and amplifiers and an electronic control unit. The electronic control unit receives information from a chain of sensors on the engine, the most important inputs being r.p.m. and induction manifold pressure. The ECU processes these inputs, and using one of any four pre-programmed ignition advance ‘maps’ provides precise ignition timing during all conditions. It should be noted that the ignition timing is not adjustable. Under no circumstances should any attempt be made to rotate the ignition distributor housing. Service personnel should also note the following precautions when working on the system: 1. DO NOT disconnect the electronic control unit with the ignition switched on. 2. DO NOT disconnect the battery with the engine running. 3. DO NOT use a starting aid of greater than 16 volts DC. 4. Always ensure that the correct polarity of the connections is observed. Failure to do so can result in the destruction of the ignition amplifiers, coils, and ECU. 5. DO NOT remove the high tension cable from the ignition coil/s to the distributor with the engine running. Spark Plugs All 20,000 Series motor cars are now fitted with NGK BPR5EV spark plugs. These plugs provide improved warm-up characteristics and reduced electrode erosion. Air Cleaner

All motor cars now feature a new design of air cleaner housing and element. The new design of the filter provides efficient filtering of the air, but with low restriction to the flow rate. This improves engine breathing, so allowing greater power output. Cooling System A number of changes have been introduced which further improve the efficiency of the cooling system. The principal change is the introduction of a new type of radiator. The new radiator is of larger capacity and features an aluminum matrix and plastic header tanks. In addition, a new larger diameter engine driven fan is used together with revised fan cowls. Finally, all motor cars are now fitted with twin ‘ARA’ type electric cooling fans mounted in front of the ACU condensor matrix. The entire cooling system is now pressurized including the recovery tank, which now has a pressurizing cap. Wiring New thinner-walled wiring has been introduced which reduces the size and weight of the main looms. Also, the main distribution loom is now common to all motor cars. Wires are now rated in millimeters, not standard. Connectors Revised wiring connectors are now used which provide more positive and reliable electrical connections. Also, the ‘toe board’ connections have been deleted and replaced by one -piece looms passing through ‘closed plates.’ This again improves reliability by removing a large number of mechanical joints. Fuses and Boards A revised fuse board has been introduced which now has only one thermal cut-out, which is used for the central door locking system. The other functions previously protected by thermal cut-outs have now been transferred to the fuses. The standardized fuses blow at rated ability and do not carry like the old fuses. NOTE: The gearbox cut-out is now by fuse No. A6.

In addition, new relays have also been introduced which feature integral diodes, therefore terminal terminals 85 and 86 are now polarity conscious. Battery The battery has been relocated and is now positioned in the rear of the boot floor panel. Alternator All 20,000 Series motor cars are fitted with an improved alternator. The new alternator provides increased output at idle r.p.m. and features a new digital regulator which has a lower cut in speed and an improved ‘load dump’ system which protects the alternator in the event of the battery becoming disconnected. This new Delco alternator cannot be substituted for previous retrofitted Delco alternators. They have too high of a gain at idle, which cuts out the starter relay. Cruise Control All 20,000 Series motor cars are now fitted with a new type of cruise control. The new system is a self-contained unit, which incorporates its own motorized drive and a direct mechanical linkage to the throttle. These features provide improved reliability and response time. Finally, a word of caution to service personnel when handling the various electronic control units or the ACU micro-processor now fitted to all 20,000 Series motor cars. These units can be damaged by static discharge. Because of this, when handling any of the components, avoid all contact with any external circuitry or connections. Also, when using the ACU system test equipment, the ‘anti-static’ wrist strap supplied with the equipment must be used. It is in fact, strongly recommended that this anti strap is also used when handlingany electronic control units (ECU). Electric Window Lift A new type of electric window lift motor has been introduced. The new motor is smaller and more powerful than the old type and also has an integral cut-out device (thermal circuit breaker).

In addition, the davail clutch mechanism is now deleted from the gearbox assembly. Steering System All 20,000 Series motor cars are now fitted with anew design of PAS pump. The new pump is mounted beneath the alternator adjacent to the timing cover and is fitted with a remotely-mounted header tank. This installation is similar to that use don turbocharged motor cars. Also a PAS oil cooler has been introduced. The new cooler is now located behind the front air dam, adjacent to the engine oil cooler where it receives an improved airflow. EXHAUST SYSTEM All 20,000 Series motor cars feature a new design of exhaust system. The new exhaust system is of more efficient design and is routed down the right hand side on all motor cars. In addition, the exhaust system is now secured to the motor car using an improved design of mounting. These mountings are of simpler construction, using rubber ‘hoops’ to secure the exhaust system to the mounting bracket. This type of mounting results in improved reliability and isolation between the body and exhaust. MANIFOLDS All motor cars feature revised exhaust manifolds. The new manifolds feature a two stud manifold to downtake clamping arrangement. This provides improved joint sealing and accessibility. Also, on turbocharged motor cars, the ‘B’ bank manifold is now a two piece design. This design has improved exhaust gas flow characteristics, so reducing back pressure and improving engine breathing. BODY A number of changes have been introduced to the front cross member area. These changes have been made to accommodate the revised engine and PAS cooler locations and also to further improve the air flow to the coolant radiator. Also, two new designs of air dam have been introduced. One is for normally aspirated motor cars, the other is for turbo charged motor cars only.

Both new air dams provide improved high speed stability and better air flow to the engine compartment. In addition, all 20,000 Series motor cars are now fitted with snow excluders to the front wings. Finally, the following new paint colors have been added. Rolls-Royce: College blue, Deep gold. Bentley: Silver, Graphite, Windsor, Windsor blue, Metalcraft bronze. INTERIOR Seats All naturally aspirated motor cars are fitted with revised front seat assemblies. The improvements include new head restraints with vertical adjustments, and new moldings for the cushions and squabs to improve comfort and lumbar support. On turbocharged motor cars, new sports style seats and head restraints to both front and rear have been introduced. The design of the new seats provides improved comfort and occupant location, particularly when cornering at higher road speeds. Also, all four door motor cars feature a new seat position adjusting mechanism. This new mechanism uses an eight way adjustable self contained electrical unit which includes seat rake adjustment. Control of the new seat mechanism is by new analogue design seat switches which are located in the forward section of the center console. In addition, all four door motor cars, except Bentley Eight, are fitted with an electronic memory seat control mechanism. The memory system allows four personally selected seat positions to be stored and recalled as required. The memory control switches are located beneath the analogue seat switches in the center console. NOTE: Memory will not work while the motor car is in any forward gear. A lithium batter allows the system to hold it’s memory for four weeks after the batter is disconnected. Steering Wheel

All turbocharged motor cars are fitted with a new design of steering wheel. The new ‘sports’ style wheel is of a three spoke pattern and is trimmed in hyde. In addition,, the indicator stalk has been modified to improve visibility of the indicator with the new type of steering wheel. Seat Belts A revised B/C post trim has been introduced. This change results in improved seat belt operation by reducing friction of the belts during extraction and retraction. TRANSMISSION All 20,000 Series motor cars are fitted with a revised gearbox. The principal change is the use of a new casing which now incorporates the dipstick tube. This new design provides easier fitting and improved oil integrity. The dipstick is physically longer and not interchangeable with previous models, but will bolt up. Do not retrofit. In addition, a new deeper sump pan is now fitted. This moves the oil level further away from the rotating parts of the gearbox, and so prevents ‘frothing’ should the oil level rise too high when hot. Also, internal modifications to the valve chest have been introduced which result in improved gear changes. Finally, the range of speedometer drive gears used has been revised to suit the new rear axle ratios. EMISSION CONTROL All 20,000 Series motor cars are fitted with a new crankcase breather system. The basic principal of operation is the same as before. However; the connection to the crankcase is now via the B bank oil filler only an the components of the system are contained in a new housing located to the rear of the ACU compressor. The new system is more efficient, particularly on turbocharged engines, where it is better able to control the crankcase depression at idle and lower power outputs. MINERAL OIL HYDRAULIC SYSTEM Height Control System All 20,000 series cars feature a revised hydraulic control system.

In the new system, only one height control valve is used to control both sides of the motor car. This valve is now located on the left hand side of the rear crossmember. The valve is actuated by means of a torsion bar, which is connected to the center of the rear anti roll bar at one end, the other end being supported in a bearing attached to the crossmember. During cornering, body roll will cause one end of the anti-roll bar to be deflected upwards whilst the other end will be deflected downwards by an equal amount. As one movement balances out the other, no movement occurs at the center of the anti-roll bar. However, when load is added to the motor car, both ends of the anti-roll bar will be deflected upwards, rotating the complete anti-roll bar, which in turn rotates the torsion bar so operating the height control valve. This system ensure that no undesirable reaction of the height control system occurs during cornering which would be detrimental to the stability and handling of the motor car. Front Brakes All 20,000 Series motor cars are fitted with a front brake pad warning wear warning system. A soft metal contact molded into the brake pad material contacts the brake disc when the pad has worn down to it's serviceable limit. This completes an electrical circuit, illuminating a light in the facia warning lamp cluster. Hydraulic System Reservoirs All 20,000 Series motor cars are fitted with a new design of hydraulic system mineral oil reservoir. The new reservoir is manufactured in opaque material and incorporates revised hydraulic connections, filler device and reservoir cover retention. Also includes in the design is a new mineral oil level indicator system. In the new system, two floats are used on the reed switch. The smaller upper float is used as a lost motion device which allows for the natural rise and fall of the fluid level which occurs due to the height control system struts charging or discharging. In this way, indications are only given when the system is genuinely under or over filled. Spare Mineral Oil The two 500 ml bottles of hydraulic system mineral oil supplied in the motor car have been relocated. These are now situated behind a hinged panel incorporated in the right-hand side luggage compartment trim panel.