3.7L Engine - Service Information: Overview RAM Pickup 2500

Scheme 9

The 3.7 liter (226 CID) six-cylinder engine is an 90° single overhead camshaft engine. (Scheme 9) The cast iron cylinder block is made up of two different components; the first component is the cylinder bore and upper block, the second component is the bedplate that comprises the lower portion of the cylinder block and houses the lower half of the crankshaft main bearings. The cylinders are numbered from front to rear with the left bank being numbered 1,3, and 5 and the right bank being numbered 2, 4, and 6. The firing order is 1 - 6 - 5 - 4 - 3 - 2. The engine serial number is located at the right front side of the engine block.

DESCRIPTION

The camshafts consist of powdered metal steel lobes which are sinter-bonded to a steel tube. Four bearing journals are machined into the camshaft. Camshaft end play is controlled by two thrust walls that border the nose piece journal.

The rocker arms are steel stampings with an integral roller bearing. The rocker arms incorporate a 2.8 mm (0.5 inch) oil jet hole in the lash adjuster socket for roller and camshaft lubrication.

Scheme 10

Note. Disconnect the battery negative cable to prevent accidental starter engagement.

1. Remove the cylinder head cover. Refer to «COVER(S), Cylinder Head, Removal, 3.7L»(ref-457795-S38087059622012030200000) for left cover and «COVER(S), Cylinder Head, Removal, 3.7L»(ref-457795-S11243807712012030200000) for right cover.
2. For rocker arm removal on cylinder No. 4, Rotate the crankshaft until cylinder No. 1 is at BDC intake stroke.
3. For rocker arm removal on cylinder No. 1, Rotate the crankshaft until cylinder No. 1 is at BDC combustion stroke.
4. For rocker arm removal on cylinders No. 3 and No. 5, Rotate the crankshaft until cylinder No. 1 is at TDC exhaust stroke.
5. For rocker arm removal on cylinders No. 2 and No. 6, Rotate the crankshaft until cylinder No. 1 is at TDC ignition stroke.
6. Using the Rocker Arm Remover/Installer (special tool #8516A, Remover/Installer)(2), press downward on the valve spring, remove rocker arm. see scheme 42

The valve guide seals are made of rubber and incorporate an integral steel valve spring seat. The integral garter spring maintains consistent lubrication control to the valve stems.

The valve springs are made from high strength chrome silicon steel. The springs are NOT common for intake and exhaust applications. The exhaust spring has an external damper. The valve spring seat is integral with the valve stem seal, which is a positive type seal to control lubrication.

The valves are made of heat resistant steel and have chrome plated stems to prevent scuffing. Each valve is actuated by a roller rocker arm which pivots on a stationary lash adjuster. All valves use three bead lock keepers to retain the springs and promote valve rotation.

Scheme 11

Note. Valve seats that are worn or burned can be reworked, provided that correct angle and seat width are maintained. Otherwise the cylinder head must be replaced.

Note. When refacing valves (4) and valve seats, it is important that the correct size valve guide pilot be used for reseating stones. A true and complete surface must be obtained.

1. Using a suitable dial indicator measure the center of the valve seat. Total run out must not exceed 0.051 mm (0.002 in).
2. Apply a small amount of Prussian blue to the valve seat, insert the valve into the cylinder head, while applying light pressure on the valve rotate the valve. Remove the valve and examine the valve face. If the blue is transferred below the top edge of the valve face, lower the valve seat using a 15 degree stone. If the blue is transferred to the bottom edge of the valve face, raise the valve seat using a 65 degree stone.
3. When the seat is properly positioned the width of the intake seat must be 1.75 - 2.36 mm (0.0689 - 0.0928 in.) and the exhaust seat must be 1.71 - 2.32 mm (0.0673 - 0.0911 in.).
4. Check the valve spring (6) installed height after refacing the valve and seat. The installed height for both intake and exhaust valve springs must not exceed 40.74 mm (1.6039 in.)
5. The valve seat and valve face must maintain a face angle of 44.5 - 45° angle.

Scheme 12

Note. The cylinder head(s) must be removed in order to perform this procedure.

1. Remove and isolate the negative battery cable.
2. Remove the cylinder head covers. Refer to «COVER(S), Cylinder Head , Removal , 3.7L»(ref-457795-S38087059622012030200000) for left cover or «COVER(S), Cylinder Head , Removal , 3.7L»(ref-457795-S11243807712012030200000) for right cover.
3. Remove the rocker arms and lash adjusters. Refer to «ROCKER ARM, Valve , Removal , 3.7L»(ref-457795-S05071015032012030200000) for left head and «ROCKER ARM, Valve , Removal , 3.7L»(ref-457795-S03147253012012030200000) for right head.
4. Remove the camshaft bearing caps and the camshaft. Refer to «CAMSHAFT, Engine , Removal , 3.7L»(ref-457795-S00941660302012030200000) for left head and «CAMSHAFT, Engine , Removal , 3.7L»(ref-457795-S12196500472012030200000) for right head.
5. Remove the cylinder head(s). Refer to «Cylinder Head, Left , Removal , 3.7L»(ref-457795-S33882215162012030200000) for left head and «Cylinder Head, Right , Removal , 3.7L»(ref-457795-S13300154642012030200000) for right head. NOTE: All valve springs and valves are removed in the same manner; this procedure only covers one valve and valve spring.
6. Using Valve Spring Compressor (special tool #C-3422-D, Compressor, Valve Spring) and Adapter (special tool #8519, Adapters, Valve Spring), compress the valve spring. NOTE: It may be necessary to tap the top of the valve spring to loosen the spring retainers locks enough to be removed.
7. Remove the two spring retainer lock halves. NOTE: The valve spring is under tension, use care when releasing the valve spring compressor.
8. Remove the valve spring compressor.
9. Remove the spring retainer, and the spring. NOTE: Check for sharp edges on the keeper grooves. Remove any burrs from the valve stem before removing the valve from the cylinder head.
10. Remove the valve from the cylinder head. NOTE: The valve stem seals are common between intake and exhaust.
11. Remove the valve stem seal. Mark the valve for proper installation.

The camshafts consist of powdered metal steel lobes which are sinter-bonded to a steel tube. Four bearing journals are machined into the camshaft. Camshaft end play is controlled by two thrust walls that border the nose piece journal.

The rocker arms are steel stampings with an integral roller bearing. The rocker arms incorporate a 0.5 mm oil jet hole in the lash adjuster socket for roller and camshaft lubrication.

The valve guide seals are made of rubber and incorporate an integral steel valve spring seat. The integral garter spring maintains consistent lubrication control to the valve stems.

The valve springs are made from high strength chrome silicon steel. There are different springs for intake and exhaust applications. The exhaust spring has an external damper. The valve spring seat is integral with the valve stem seal, which is a positive type seal to control lubrication.

The cylinder block is made of cast iron. The block is a closed deck design with the left bank forward. To provide high rigidity and improved NVH an enhanced compacted graphite bedplate is bolted to the block. The block design allows coolant flow between the cylinders bores, and an internal coolant bypass to a single poppet inlet thermostat is included in the cast aluminum front cover.

Scheme 13

Before honing, stuff plenty of clean shop towels under the bores and over the crankshaft to keep abrasive materials from entering the crankshaft area.

1. Used carefully, the Cylinder Bore Sizing Hone (special tool #C-823, Hone, Cylinder), equipped with 220 grit stones, is the best tool for this job. In addition to deglazing, it will reduce taper and out-of-round, as well as removing light scuffing, scoring and scratches. Usually, a few strokes will clean up a bore and maintain the required limits. CAUTION: DO NOT use rigid type hones to remove cylinder wall glaze.
2. Deglazing of the cylinder walls may be done if the cylinder bore is straight and round. Use a cylinder surfacing hone, Honing Tool (special tool #C-3501, Hone W/Oil, AMMCO Cylinder), equipped with 280 grit stones ((special tool #C-3501-3810, Stones, 220 Grit Honing)). about 20-60 strokes, depending on the bore condition, will be sufficient to provide a satisfactory surface. Using honing oil (special tool #C-3501-3880, Oil, Honing), or a light honing oil, available from major oil distributors. CAUTION: DO NOT use engine or transmission oil, mineral spirits, or kerosene.
3. Honing should be done by moving the hone up and down fast enough to get a crosshatch pattern (1). The hone marks should INTERSECT at 50° to 60° for proper seating of rings (2).
4. A controlled hone motor speed between 200 and 300 RPM is necessary to obtain the proper crosshatch angle. The number of up and down strokes per minute can be regulated to get the desired 50° to 60° angle. Faster up and down strokes increase the crosshatch angle.
5. After honing, it is necessary that the block be cleaned to remove all traces of abrasive. Use a brush to wash parts with a solution of hot water and detergent. Dry parts thoroughly. Use a clean, white, lint-free cloth to check that the bore is clean. Oil the bores after cleaning to prevent rusting.

The structural dust cover is made of die cast aluminum and joins the lower half of the transmission bell housing to the engine bedplate.

OPERATION

The structural cover provides additional powertrain stiffness and reduces noise and vibration.

The lubrication system is a full flow filtration pressure feed type.

ENGINE LUBRICATION FLOW CHART - BLOCK: TABLE 1

ENGINE LUBRICATION FLOW CHART - CYLINDER HEADS: TABLE 2

Scheme 14

Oil from the oil pan is pumped by a gerotor type oil pump (9) directly mounted to the crankshaft nose. Oil pressure is controlled by a relief valve mounted inside the oil pump housing.

The camshaft exhaust valve lobes and rocker arms are lubricated through a small hole in the rocker arm; oil flows through the lash adjuster then through the rocker arm and onto the camshaft lobe. Due to the orientation of the rocker arm, the camshaft intake lobes are not lubed in the same manner as the exhaust lobes. The intake lobes are lubed through internal passages in the camshaft. Oil flows through a bore in the No. 3 camshaft bearing bore, and as the camshaft turns, a hole in the camshaft aligns with the hole in the camshaft bore allowing engine oil to enter the camshaft tube. see scheme 121 The oil then exits through 1.6mm (0.063 in.) holes drilled into the intake lobes, lubricating the lobes and the rocker arms.

The oil pressure switch is a pressure sensitive switch that is activated by the engine's oil pressure (in the main oil gallery). The switch is a two terminal device (one terminal is provided to the wiring harness and the other terminal is the switch's metal housing that screws into the engine block).

The oil pressure switch is normally "Closed". The switch changes from a "Closed" circuit to an "Open" circuit, on increasing pressure of 7 psig. The oil pressure switch changes from an "Open" circuit to a "Closed" circuit, on decreasing pressure, between 2 psig and 4 psig.

The primary timing chain is a single inverted tooth chain type. The primary chain drives the large 50 tooth idler sprocket directly from a 25 tooth crankshaft sprocket. Primary chain motion is controlled by a pivoting leaf spring tensioner arm and a fixed guide. The arm and the guide both use nylon plastic wear faces for low friction and long wear. The primary chain receives oil splash lubrication from the secondary chain drive and designed oil pump leakage. The idler sprocket assembly connects the primary chain drive, secondary chain drives, and the counterbalance shaft. The idler sprocket assembly consists of two integral 26 tooth sprockets a 50 tooth sprocket and a helical gear that is press-fit to the assembly. The spline joint for the 50 tooth sprocket is a non serviceable press fit anti rattle type. The idler sprocket assembly spins on a stationary idler shaft. The idler shaft is a light press-fit into the cylinder block. A large washer on the idler shaft bolt and the rear flange of the idler shaft are used to control sprocket thrust movement. Pressurized oil is routed through the center of the idler shaft to provide lubrication for the two bushings used in the idler sprocket assembly.

There are two secondary drive chains, both are roller type, one to drive the camshaft in each SOHC cylinder head. There are no shaft speed changes in the secondary chain drive system. Each secondary chain drives a 26 tooth cam sprocket directly from the 26 tooth sprocket on the idler sprocket assembly. A fixed chain guide and a hydraulic oil damped tensioner are used to maintain tension in each secondary chain system. The hydraulic tensioners for the secondary chain systems are fed pressurized oil from oil reservoir pockets in the block. Each tensioner incorporates a controlled leak path through a device known as a vent disc located in the nose of the piston to manage chain loads. Each tensioner also has a mechanical ratchet system that limits chain slack if the tensioner piston bleeds down after engine shut down. The tensioner arms and guides also utilize nylon wear faces for low friction and long wear. The secondary timing chains receive lubrication from a small orifice in the tensioners. This orifice is protected from clogging by a fine mesh screen which is located on the back of the hydraulic tensioners.

Scheme 15

Note. This procedure must be performed with the timing chain cover removed.

1. Remove the timing chain cover. Refer to «CHAIN and SPROCKETS, Timing, Removal, 3.7L»(ref-457795-S04678736542012030200000).
2. To determine if the secondary timing chains are worn, rotate the engine clockwise until maximum tensioner piston (2) extension is obtained. Measure the distance between the secondary timing chain tensioner housing and the step ledge on the piston. see scheme 157 The measurement at point (A) must be less than 15mm (.5906 inches).
3. If the measurement exceeds the specification the secondary timing chains are worn and require replacement. Refer to «CHAIN and SPROCKETS, Timing, Removal, 3.7L»(ref-457795-S04678736542012030200000).