The 2.4 Liter Four-Cylinder Engine
The Chrysler-engineered 2.4 liter four-cylinder entered production in December 1994 for minivans
and cloud cars, essentially a long-stroke 2.0-liter Neon engine
. While the Neon engine was criticized for being loud and somewhat uncouth, the 2.4 seemed to be quieter and gentler, and gained many fans.
There was some confusion with the launch of the "World Engine
," which also had 2.0 and 2.4 liter sizes; both were made and sold for a few years.
Compared with the original 2.0,
the 2.4 had a longer stroke, taller block, dual overhead camshaft cylinder head (optional on 1995-99 2.0 engines), and dual counter-rotating balance shafts to reduce engine vibration. The compression ratio was fairly high at 9.4:1, and the engine had a knock sensor to back off the timing if gasoline wasn't up to the task
Like the 2.0, it had a partially open deck, a bedplate, and powdered metal connecting rods; it shared the 2.0's crankshaft design, sealing features, fuel injection system, and direct ignition system.
With the higher compression and more advanced features, the 2.4 far surpassed the old Chrysler 2.5
in power and torque. The first generation engine's specs were (in the Plymouth Breeze, compared to the 2.5 in the 1994 Spirit):
| ||1996 2.4||1994 2.5|
Later versions, used in the Avenger/Sebring
and PT Cruiser
, had 150 hp - the same as the turbocharged
version of the old 2.5 - and still used regular gasoline.
All PT Cruisers sold in the US carried this 2.4 liter engine. Some complained that it had poor economy and power, but when General Motors produced a car similar in most dimensions to the PT Cruiser, it had almost identical economy and acceleration; the issue was most likely too much weight and not enough of a gear range.
The turbo 2.4
Mexican engineers turbocharged the 2.4 liter engine before Detroit started; but the Mexican and American turbo-fours were apparently developed independently (thanks, Paul Holmgren).
While the turbo-four engine was used in the Neon SRT4, Chrysler engineer Garry W. McKissick said it was created for the PT Cruiser GT. They looked at superchargers first; the reason for the change was likely lack of space.
The main difference between the PT Cruiser GT and Neon SRT versions was the intake manifold, which had to fit within tight constraints; the SRT group created their own intake. The development of the engine is detailed in this SAE paper
The 2.4 turbo in the Neon SRT-4
produced 215-235 horsepower and 245 lb-ft of torque. In the PT Cruiser GT (215 hp 2003-2005; 230 hp and 245 lb.-ft. from 2006 onwards), 0-60 times came in the low-to-mid 7s, versus the lighter Neon's 6s. It had forged C70-steel connecting rods supplied by Mahle.
The 2.4 turbo was superceded by a 2.4-turbo World Engine with 300 hp
Common 2.4 liter engine repairs
The 2.4 was generally a reliable engine, without major flaws; oil sealing was good,
head gaskets were well designed, and any flaws in the basic design (including fuel and spark systems) had presumably been worked out on the earlier 2.0 Neon engines.
Cam sensor repair
TWX wrote that in his 1997 Dodge Stratus, his oil light would come on and he'd get a single drip of oil when he parked. He concluded his oil pressure sending unit was bad; the part was only $10, and on the back side of the engine, above the CV shaft and difficult to reach.
"Ultimately I ended up having to use the socket (1 1/6" deep, six point if I remember correctly), a swivel head adapter, a two inch extension, and a 1/2" drive ratchet. There wasn't a lot of room to work, and the wiring harness blocks viewing the connector; a flashlight is a must. ... The oil pressure sending unit sits high enough that oil doesn't need to be drained to do this."
Dimensions and specifications
148.2 cubic inches / 2429 cc
Bore x stroke: 3.44 x 3.98
Block length x height: 16.43 x 9.36
Rod length: 5.94 (151)
The cylinder head is a low profile aluminum casting with pent-roof combustion chambers and four valves per cylinder. The valve included angle is 48 degrees, allowing large valves.
Dual camshafts run in six bearings with machined-in removable caps. 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.
Ports from each valve merge in the head, leading to a single branch (runner) in their respective manifolds. To provide turbulence, the ports cause incoming air to tumble from top to bottom. The degree of tumbling action was balanced against the need for high air flow.
Made of die cast aluminum, the cylinder head cover has an isolated mounting with an O-ring type, silicone perimeter gasket, and an integral DIS coil mount and PCV system.
The one-piece, cast aluminum intake manifold on first-generation cloud cars had a runner length of 15.7 inches, with tuned individual runners for each cylinder and an integral plenum chamber. Made of thin-wall cast nodular iron, the exhaust manifold had a four- into-one runner design. The four-bolt outlet flange mated with a sealed flex coupling flange on the exhaust pipe.
Later vehicles used a plastic intake manifold.
On the first models (no turbos), valve diameters were 1.40 inch (35.5 mm) intake and 1.20 inch (30.5 mm) exhaust, with 0.24 in. (6 mm) chrome plated stems. Exhaust valves were on the right (rearward) side of the head. Each valve was operated by an end-pivot rocker arm that has a 20 mm roller cam follower. Rockers pivoted on inboard-mounted, fixed hydraulic lash adjusters. Barrel-shaped single valve springs were good to 7200 rpm.
Post-hardened nodular cast iron camshafts provide a 236° intake duration and a 240° exhaust duration. The intake cam centerline was 113° ATDC, the exhaust was 110° BTDC, with 15 degrees of overlap. Intake valve lift was 0.33 inches (8.25 mm) and exhaust valve lift was 0.26 inches (6.5 mm).
The intake and exhaust cams had separate drive sprockets; a three-piece molded plastic cover, with inspection plate, completely enclosed the belt.
Electrical, injectors, and water pump
The base of the water pump housing was part of the block; the body was die cast aluminum, driven by the timing belt. Sequential multi-port injection (SMPI) used four dual-spray injectors; the engine's returnless fuel injection was safer and less complicated than traditional return systems.
Direct ignition eliminated the distributor. The PCM used a stepper motor and valve in the throttle body to change idle air flow. A switch on the power steering hose increased idle speed when the steering wheel was turned.
Single-size cast aluminum pistons had pop-up tops with valve cut outs for broken-belt valve clearance (which could be defeated if the two cams rotated independently). Piston pins were held in place by press fit to the connecting rods, which differed from those in the 2.0 liter engine only in length.
The nodular iron crankshaft had eight counterweights and a 75% balance ratio. Counterweights straddled each crank pin to balance the bearing loads for smooth operation, and to allow smaller, narrower bearings. Smaller diameters reduced friction. The main bearing diameter was 2.36 inches (60 mm), and the rod bearing diameter was 1.97 inches (50 mm). The crankshaft main bearing journals were 1.0 inch (25.5 mm) wide for low friction. The engine had a torsional vibration damper is used, with two poly-V pulleys that drive accessories.
The two counter-rotating, eccentric balance shafts, interconnected by gears, were driven by a short chain from the crankshaft, at double the engine speed. They were enclosed in an aluminum housing beneath the crankshaft, in the oil pan. The housing was bolted to the bottom of the main bearing webs of the bedplate and rest in the oil supply. When the engine is running, the balance shafts pumped oil out of the housing to minimize parasitic drag.
The camshafts had no bearing inserts; main and rod bearings had bi-metal inserts.
The powdered metal gerotor oil pump mounted in the front of the block, driven by the crankshaft. The oil return system was designed to prevent aeration during high-rpm running.
The block was inclined to the right (rearward in the car) to allow the oil to drain from the head. SAE 5W-30 oil, grade SG/SH was recommended. A half-quart oil filter mounted horizontally to an extension for access.
The oil pan was stamped of a sound-deadening metal-plastic-metal laminate material; a windage tray was integral with the oil-pan gasket.
The crankcase ventilation had an oil separator in the cylinder head cover with baffles to inhibit the flow of oil to the intake manifold, a problem in some past engines.
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