Inside th 420a Engine by Allpar

This is a full article located on Allpar.com This outlines bits of information that make understanding the 420a origin better.

http://www.allpar.com/mopar/2dohc.html

Double Overhead Camshaft (DOHC) 2.0 Liter Engine

The Neon, Dodge Avenger, and Chrysler Sebring featured (as base engine on the Avenger/Sebring and optional engine on the Neon through 1999) the Chrysler-designed DOHC 2.0 engine. Displacement is 1996 cm(cubed) (121.8 in(cubed)). The engine is slightly over square with a bore of 87.5 mm (3.44 in.) and a stroke of 83 mm (3.26 in.) Compression ratio is 9.6:1. The engine is designed to run on regular-grade unleaded gasoline.
The engine has a very high specific output of 70 bhp/liter for brisk performance. Typical ratings are:
140 bhp @ 6000
130 lb-ft @ 4800 rpm
104 kW @ 6000
178 N-m @ 4800 rpm

Cylinder head, cylinder block, and bedplate

A low profile, cast aluminum cross-flow cylinder head has pent-roof combustion chambers housing four valves per cylinder. Dual camshafts run in six bearings with removable caps that are machined in head base material. Powdered metal valve seat inserts and valve guides are pressed into the head. Spark plugs thread into the center of the combustion chamber through wells cast into the head.
To provide turbulence in the cylinders that contributes to the rapid combustion necessary for low emissions and efficient operation on regular-grade gasoline, the intake ports cause the incoming air to "tumble" from top to bottom of the cylinders. The degree of tumbling action was balanced against the conflicting need for high air flow to obtain high power output.
The thin-well cast in iron block is only 212 mm (8.35 in.) high to clear the low hood. The block ends at the centerline of the crankshaft. Bore spacing of 96 mm (3.78 in.) allows room for coolant to flow around all cylinders. The top deck is open to reduce weight. For light weight, cylinder walls do not allow for a larger bore.
A bedplate beneath the block supports the crankshaft and provides needed structural stiffness for durability at high rpm's and quiet operation. A perimeter wall and three transverse webs make up the bedplate. Main bearing caps are integral with the transverse webs. The bedplate attaches to the base of the block via 20 bolts -- 10 along the outer walls and 10 straddling the main bearings. The bedplate also provides a flat sealing surface for the oil pan.

Intake and exhaust manifolds

A two-piece cast aluminum intake manifold features 18.5 in. (470 mm) primary runners to enhance low-speed torque. The runners are curved to provide as much length as possible in the compact engine compartment of the Avenger and Sebring. A tapered plenum and elbow section deliver air from the throttle body to the runners. Recirculated exhaust gas (EGR) for NOx emission control enters the manifold at the base of the throttle body.
A compact, light weight nodular cast iron exhaust allows exhaust gas to heat catalytic converter to operating temperature quickly for low emissions.

Valve Train
Four valves per cylinder are actuated by dual overhead camshafts. Valve seat outer diameters are 1.36 in. (34.5 mm), intake, and 1.16 in. (29.5 mm), exhaust. All valves have 0.25 in. (6 mm) chrome plated stems. Intake valve lift is 0.31 in. (7.8 mm) and exhaust valve lift is 0.28 in. (7.0 mm). Valves have a 48 degree included angle; exhaust valves forward, intakes rearward. Each valve is operated by an end- pivot rocker arm. Each 0.79 in. (20 mm) roller cam follower runs on roller-bearings. Each rocker pivots on an inboard-mounted, fixed hydraulic lash adjuster. Barrel-shaped single valve springs provide control of valve actuation to 7200 rpm.
The nodular iron camshaft is hardened after machining to provide the requisite durability characteristics for roller followers. A state-of- the-art cog belt drives the camshaft. The belt system is designed to last the life of the vehicle without adjustment or replacement. High belt loads associated with operating 16 valves dictated a special high temperature rubber material and unique belt construction. A spring- loaded automatic tensioner with hydraulic damping forces an idler pulley against the back of the belt, maintaining proper tension for the life of the vehicle. Low inertia powdered metal sprockets, one for each cam, are spaced away from the block to reduce belt operating temperature. A two piece molded plastic cover completely encloses the belt to prevent damage from foreign matter. It includes a removable inspection plate.

Internal engine parts

Pistons are cast from a eutectic aluminum alloy that contains 12% silicon for wear resistance. They have an elliptical shape to control expansion during warm up to minimize noise and avoid low temperature scuffing. The pin is offset 0.04 in. (1 mm) to reduce noise. The tops of the pistons include valve clearance notches that allow increased valve lift. Piston pins are press-fitted into the rods. Ring line-up is conventional, with two compression rings and a three-piece oil ring.
Connecting rods and rod caps are initially formed as one-piece powdered metal forgings. Molding them from powder before forging assures excellent dimensional and weight control with minimum machining. Powdered metal rods are lighter than conventional forgings, especially at the piston end, resulting in low reciprocating weight and smooth high rpm operation. Weight is lower because the rods are made without the excess material that is partially machined away as part of the normal balancing process on conventional rods. The cap is separated from the rod by a unique process. The uneven surface that results from the breaking process provides perfect rod to cap alignment at assembly. Rod cap retention screws thread directly into the connecting rod for simplicity and light weight.
The nodular cast iron crankshaft is fully counterweighted -- it has counter weights on both sides of each crank pin -- to balance bearing loads for smooth, quiet operation yet weighs only 15 kg (33 pounds). Counterweights opposite each crankpin allow bearing diameters to be reduced from past practice for less friction aiding fuel economy and power. Main and rod bearings are 2.05 in. (52 mm) and 1.88 in. (48 mm) in diameter, respectively -- 0.4 in. (10 mm) and 0.15 in. (4 mm) smaller, respectively, than past practice. Main and rod bearing journal tolerances are reduced from past practice for quieter operation and longer life.
A conventional inertia-ring vibration damper is mounted on the nose of the crankshaft. Pulley grooves machined into the inertia ring drive the alternator and accessory belts. In addition to reducing engine noise and vibration, the damper reduces load variation on the belts for longer belt life.
The camshaft needs no bearing inserts: it operates directly in the cylinder head. Main and rod bearing shells are aluminum base material with a high load capacity.

Lubrication System

The powdered metal gerotor oil pump mounts in an aluminum housing attached to the front of the block and is driven by the crankshaft. The system for returning oil from the head prevents aeration during high-rpm operation. Oil drains from the head along the right (rearward facing) side of the block, because the block is inclined in that direction. The crankcase is ventilated through openings left side of the head. Oil capacity is four quarts plus filter. SAE 5W-30 oil, grade SP/SG is recommended. A half-quart oil filter mounts vertically to an extension of the bedplate.
The oil pan is stamped from acoustically damped material -- two sheets of steel sandwiching a layer of sound deadening mastic -- to reduce noise transmission. The pan is basically full depth throughout its length, allowing ample clearance between crankshaft and oil to avoid aeration

Cooling Systems

The water pump scroll is integral with the block to reduce complexity. The pump is driven by the timing belt. The thermostat housing, cooling system filler neck, radiator hose nipple and overflow nipple are combined in a single cast aluminum part that attaches to the thermostat base on the cylinder head. The filler neck is on this housing rather than the radiator because the low hood line makes this the highest point in the cooling system and therefore the appropriate place for filling or refilling the system after maintenance or repair. A pressure radiator cap attaches to the filler neck. This cap maintains constant pressure in the cooling systems when the engine is running to enhance cooling and reduce water pump cavitation. This cap is smaller than a conventional radiator cap to avoid using an incorrect cap.
A check ball in the thermostat allows air in the coolant to escape when the system is cool but seals to assure rapid engine warm-up. The vent also aids in refilling the system after maintenance or repair by preventing air entrapment. By allowing air to escape, the vent also helps prevent large variations in coolant temperature during warm-up previously cause by trapped air.
The cast aluminum cylinder head cover has a black enameled finish. Raised nomenclature on the cover -- "DOHC 2.0L 16 Valve" -- has a silver finish.

Sealing Features

The crankshaft rear main seal is pressed into the block and bedplate assembly rather than into a bolt-on housing, eliminating a potential leakage path. The seal includes a Teflon(R) lip for long life.
The oil pump cover houses the crankshaft front main seal.
Oil pan and cylinder head cover gaskets are state-of-the-art molded silicone with steel backbones and compression limits.
Bed plate construction makes oil pan sealing easier by providing a flat, continuous, machined sealing surface.
The top surface of the cylinder head is machined flat for easy sealing.
Spark plug wells are sealed to the cylinder head covers by individual molded seals.
A molded silicone rubber gasket that is integral with the thermostat provides a high-integrity seal between the thermostat housing and cylinder head.
The oil pan drain plug includes a molded seal to prevent leakage.
The camshaft sensor is sealed to the cylinder head with an O-ring

Fuel Injection System

Sequential multi-port injection uses injectors that direct a separate spray to each intake valve to provide balanced fuel delivery to all cylinders. Sequential injection improves throttle response and overall driveability compared to single-point or simple multiple-point injection.
The fuel injection system uses speed-density control -- engine speed and intake manifold pressure as primary determinants of fuel injection rate and timing. Intake manifold pressure is determined by a manifold absolute pressure (MAP) sensor. The injection system uses the same speed, timing and cylinder selection sensors as the ignition system. These direct-acting sensors provide both greater accuracy and quicker response than a conventional distributor.
The throttle body has a 2.05 in. (52 mm) bore to minimize restriction at high rpm. To enhance manual transaxle driveability, the throttle body has a contoured bore in the off-idle area that reduces the slope of the airflow vs. throttle angle curve making low-throttle "launches" easier. Also with manual transaxle, the throttle is operated by a progressive cam that provides relatively slow initial response to pedal movement. With automatic transaxle, the cam provides throttle response proportional to pedal movement.

Ignition System

The Avenger and Sebring 2.0-liter engine has a direct (distributorless) ignition system that provides the following benefits compared to distributor systems:
quick starts because camshaft and crankshaft sensors give early recognition of which cylinder is to be "fired"
simplification because the distributor and related parts are eliminated
greater accuracy because ignition and fuel injection timing signals are taken directly from the crankshaft and camshaft
reduced maintenance because timing adjustment is never required
improved idle quality because timing variation is reduced
improved engine response and idle quality because DIS sensors update data flowing to the PCM (power train control module) more frequently than conventional systems to accurately reflect changing speed and load conditions
high reliability through use of proven "Hall-effect" sensors
Two sensors provide data for operation of the system: a crankshaft timing sensor and a camshaft reference sensor. The timing sensor, which is inserted through the side of the block, senses two patterns of four slots each in the #2 crankshaft counterweight, spaced 180 degrees apart. These slots provide data for engine speed and timing calculations. Their position on the crankshaft establishes basic timing for the engine. Sensing directly from the crankshaft provides greater accuracy than prior systems that sensed from starter ring gear or torque converter drive plate. Individual slots are spaced 20 degrees apart. Spark advance and injection timing are computed from these points. One slot, called the "signature" slot, is 60 degrees wide; the others are approximately 5 degrees wide. The unique sensor output coming from the signature slot is used in combination with the output from the camshaft sensor to determine which cylinder is ready for fuel and ignition.
The camshaft sensor is mounted at the rear of the exhaust camshaft, outside the cylinder head. It is triggered by a ring magnet in the end of the camshaft. The magnet has four poles arranged asymmetrically at 150 degree and 210 degree intervals. Correlation between the magnet poles and the "signature" slot is established in less than one crankshaft revolution, allowing injection and ignition to begin.
A knock sensor permits fine tuning of engine operation rather than just responding to engine-damaging knock.
The four-lead DIS coil module is attached directly to the cylinder head cover, providing very short secondary wire leads.

Idle speed control

The PCM determines idle speed. It actuates a stepper motor and by-pass valve in the throttle body to change idle air flow. In addition to customary warm-up and basic idle speed control, a switch on the power steering high-pressure hose detects higher hydraulic pressure that occurs during steering action and compensates by increasing idle speed. Air conditioning compressor operation has the same effect. To maintain smooth operation, the PCM idle speed control system opens the valve in anticipation of compressor engagement or (with automatic transaxle) a shift out of Neutral.

Other Components

The generator is driven by a poly-vee belt from the crankshaft damper. The power steering pump and air conditioning compressor are driven by a separate poly-vee belt. The belt is also adjusted manually by means of a pivoting bracket.
A lightweight two-piece plastic air cleaner housing is remotely mounted and houses a panel-type filter. Air is ducted to the throttle body by a flexible molded hose.
To minimize oil pullover at high rpm, the crankcase ventilation system includes an oil separator in the cylinder head cover. The separator has baffles that inhibit the flow of oil to the intake manifold. Oil drains out of the baffling on a long, narrow plate pinned to the inside of the cover.
The optional automatic speed control system uses a vacuum servo supplied by manifold vacuum to open the throttle via cable. It allows the car to maintain any selected speed between 35 to 85 mph (56 to 137 km/hr.) A vacuum reservoir helps operate the servo on steep grades. An intermediate link between the speed control cable and the throttle cable allows the driver to increase speed, if desired, independent of speed control operation. The system cancels speed control action if the brake is applied, if engine or vehicle speed rises quickly indicating wheel spin or an out-of-gear condition, or if vehicle speed drops suddenly, indicating rapid deceleration.