Engine Mechanical - 3.6L - Description and Operation: Other GMC Acadia I

Crankcase

The cylinder block is constructed of aluminum alloy by precision sand-casting with cast in place iron cylinder liners. Each steel main bearing cap incorporates 6 bolts bolting the cap into the engine block. Along with 2 outer and 2 inner bolts, 2 side bolts are used in the deep skirt block. To prevent aeration, oil return from the valvetrain and cylinder heads is channeled away from the rotating and reciprocating components through oil drain back passages incorporated into the cylinder heads and engine block. Pressure-actuated piston oil cooling jets are mounted between opposing cylinders. A knock sensor is located on each side of the exterior of the engine block. The crankshaft position sensor is located on the right side of the exterior of the engine block.

Crankshaft

The crankshaft is a hardened, forged steel design with 4 main bearings. Crankshaft thrust is controlled by the upper portion of number 3 main bearing. The crankshaft position reluctor wheel is pressed onto the rear of the crankshaft in front of the rear main journal. A micro encapsulated adhesive is used on the reluctor wheel to aid retention. The crankshaft is internally balanced, and has an integral oil pump drive machined into the nose in front of the front main journal.

Connecting Rods and Pistons

The connecting rods are steel and have full floating piston pins. The piston pins are a slip fit in the bronze bushed connecting rod. Round wire retainers are used to retain the piston pin into the piston. The cast aluminum pistons incorporate a polymer-coated skirt to reduce friction. The piston uses two low tension compression rings and one multi-piece oil control ring. The top of the piston contains a dished portion for the direct injection system to aid in fuel-air charge mixture and even combustion.

Camshaft Drive System

The camshaft drive system consists of one primary timing drive chain driven by the crankshaft sprocket. The primary timing drive chain drives two intermediate drive shaft sprockets. Each intermediate drive shaft sprocket drives separate secondary timing drive chains. Each secondary timing drive chain drives the respective cylinder head's intake and exhaust camshaft position actuators.

The primary timing drive chain uses two stationary timing drive chain guides and a hydraulically-actuated tensioner with built-in shoe. The tensioner minimizes timing drive chain noise and provides accurate valve action by keeping slack out of the timing drive chains and continuously adjusting for timing drive chain wear. The tensioner incorporates a plunger that adjusts out with wear allowing only a minimal amount of backlash. The tensioner is equipped with an oiling jet to spray oil onto the timing components during engine operation. The secondary timing drive chains use a stationary timing drive chain guide and movable timing drive chain shoe. The secondary timing drive chain shoe is under tension from a hydraulically-actuated tensioner. All tensioners are sealed to the head or block using a rubber coated steel gasket. The gasket traps an adequate oil reserve to ensure quiet start-up.

Camshaft Position Actuator System

The engine incorporates a camshaft position actuator for each intake and exhaust camshaft. Camshaft phasing changes the inlet and exhaust valve timing as engine operating conditions vary. Dual camshaft phasing allows the further optimization of performance, fuel economy and emissions without compromising overall engine response and driveability. Variable valve timing also contributes to a reduction in exhaust emissions. It optimizes exhaust and inlet valve overlap and eliminates the need for an exhaust gas recirculation (EGR) system.

The camshaft position actuator is a hydraulic vane-type actuator that changes the camshaft lobe timing relative to the camshaft drive sprocket. Engine oil is directed by a camshaft position actuator oil control valve to the appropriate passages in the camshaft position actuator. Oil acting on the vane in the camshaft position actuator rotates the camshaft relative to the sprocket. At idle, both camshafts are at the default or "home" position. At this position, the exhaust camshaft is fully advanced and the intake is fully retarded to minimize valve overlap for smooth idle. An internal lock pin locks the inner rotor to the outer camshaft position actuator housing at idle and maintains this position during start-up conditions. Under other engine operating conditions, the camshaft position actuator is controlled by the engine control module (ECM) to deliver optimal intake and exhaust valve timing for performance, driveability and fuel economy. The camshaft position actuator incorporates an integral trigger wheel, which is sensed by the camshaft position sensor mounted in the front cover to accurately determine the position of each camshaft. Each camshaft position actuator has a specific timing drive mark for right or left bank application, as the camshaft position actuators are common bank to bank. The exhaust camshaft position actuator has a different internal configuration than the intake camshaft position actuator since the exhaust camshaft position actuator phases in the opposite direction relative to the inlet camshaft position actuator.

The camshaft position actuator oil control valve (OCV) directs oil from the oil feed in the head to the appropriate camshaft position actuator oil passages. There is one OCV for each camshaft position actuator. The OCV is sealed and mounted to the front cover. The ported end of the OCV is inserted into the cylinder head with a sliding fit. A filter screen protects each OCV oil port from any contamination in the oil supply.

The camshaft front journal has several drilled oil holes to allow camshaft position actuator control oil to transfer from the cylinder head to the camshaft position actuator. The center camshaft bolt hole is counterbored to allow oil to flow around the camshaft bolt and to the camshaft position actuator. Oil in this oil passage is used to move the camshaft position actuator to the default or home position. Radially outward from the center of the journal is a set of 4 drilled camshaft position actuator oil holes. Oil in this group of oil holes is used to move the camshaft from the default position to a specific set position as determined by the ECM. Seal rings are used at the front and rear of the front camshaft journal to prevent oil leakage from the camshaft position actuator hydraulic system. The seal is made from a plastic compound that resists wear and has a diagonal end gap to enhance sealing. The camshaft position actuator is mounted to the front end of the camshaft and the timing notch in the nose of the camshaft aligns with the dowel pin in the camshaft position actuator to ensure proper cam timing and camshaft position actuator oil hole alignment.

Cylinder Heads

The cylinder heads are cast aluminum with powdered metal valve seat inserts and valve guides. Two intake valves and two exhaust valves are actuated by roller finger followers pivoting on a stationary hydraulic lash adjuster (SHLA). Separate exhaust and intake camshafts are supported by bearings machined into the cylinder head. The front camshaft bearing cap is used as a thrust control surface for each camshaft. In addition to the thrust bearing surfaces in the front camshaft bearing caps, there is a plastic thrust washer installed between the camshaft position actuator and the forward face of the cylinder head/camshaft thrust cap to supplement camshaft thrust control. Each spark plug is shielded by a tube that is pressed into the cylinder head. Each spark plug ignition coil is also mounted through the spark plug tube. The engine coolant temperature (ECT) sensor is threaded into the cylinder head. Longer intake ports are designed into the head for better airflow and eliminate the need for a separate lower intake manifold. With direct injection, the high pressure injectors are located in machined bores below the intake ports. A stainless steel, high pressure fuel rail is attached to the intake side of the head.

Induction System

A one piece, all-aluminum intake manifold is used to deliver a dry-air charge to the combustion chamber. Fuel is introduced directly to the cylinder during the intake stroke. As the piston approaches top-dead center, the air-fuel mixture is ignited by the spark plug. An electronically controlled throttle (ETC), through the ECM, coordinates the input from the driver with various control components.

Right and Left Bank Designation

Right hand (RH) and left hand (LH) designation through the engine mechanical section are viewed from the rear of the engine or from inside the vehicle.

New Product Information (LLT)

The purpose of New Product Information is to highlight or indicate important changes from the previous model year.

Changes may include one or more of the following items

1. Torque values and/or fastener tightening strategies
2. Changed engine specifications
3. New sealants and/or adhesives
4. Disassembly and assembly procedure revisions
5. Engine mechanical diagnostic procedure revisions
6. New special tools required
7. A component comparison from the previous year

New Sealants and/or Adhesives

There are no changes to the sealants and/or adhesives used for this model year. Refer to Adhesives, Fluids, Lubricants, and Sealers .

A Component Comparison from the Previous Year

1. RWD LLT applications use a unique low pressure fuel feed line with integral check valve this model year.
2. Some RWD LLT applications also use unique water outlets this model year.
3. The Camaro and G8 LLT applications use a specific crankshaft balancer.
4. All HFV6 engines use a new structural front engine cover for additional noise reduction.
5. All FWD applications use a new oil pan.
6. Spark plugs are changed to a different manufacturer for all applications.
7. 5W-30 oil is recommended for all applications.

Refer to Engine Component Description (LLT) for additional information.

Cleanliness and Care

An automobile engine is a combination of many of the following surfaces

1. Machined
2. Honed
3. Polished
4. Lapped

The tolerances of these surfaces are measured in the ten-thousandths of an inch. When you service any internal engine part, cleanliness and care are important. Apply a liberal coating of engine oil to the friction areas during assembly in order to protect and lubricate the surfaces on initial operation. Throughout this section, practice proper cleaning and protection procedures to the machined surfaces and to the friction areas.

Whenever you remove the valve train components, keep the components in order. Follow this procedure in order to install the components in the same locations and with the same mating surfaces as when removed.

Disconnect the negative battery cables before you perform any major work on the engine.

Separating Parts

In addition to the room temperature vulcanizing (RTV) sealant's sealing capabilities, the RTV sealants may form an adhesive bond between the components. This may make the components difficult to remove or to separate. If possible, bump the components sideways rather than using prying tools in order to remove the components. This technique prevents damage when the bonding strength of the RTV sealant is stronger than the component itself. Perform bumping at the bends or at the reinforced areas in order to prevent part distortion.

Gasket Reuse and Applying Sealant

1. Do not reuse any gasket unless specified.
2. Gaskets that can be reused will be identified in the service procedure.
3. Do not apply sealant to any gasket or sealing surface unless specified in the service procedure.

Separating Components

1. Use a rubber mallet in order to separate the components.
2. Bump the part sideways in order to loosen the components.
3. Bumping of the component should be done at bends or reinforced areas of the component to prevent distortion of the components.

Cleaning Gasket Surfaces

1. Use care to avoid gouging or scraping the sealing surfaces.
2. Use a plastic or wood scraper in order to remove all the sealant from the components. Do not use any other method or technique to remove the sealant or the gasket material from a part.
3. Do not use abrasive pads, sand paper, or power tools to clean the gasket surfaces. These methods of cleaning can cause damage to the component sealing surfaces. Abrasive pads also produce a fine grit that the oil filter cannot remove from the engine oil. This fine grit is an abrasive and can cause internal engine damage.

Sealant Types

Note. The correct sealant and amount of sealant must be used in the proper location to prevent oil leaks, coolant leaks, or the loosening of the fasteners. DO NOT interchange the sealants. Use only the sealant, or equivalent, as specified in the service procedure.

The following 2 major types of sealant are commonly used in engines

1. Anaerobic sealant room temperature vulcanizing (RTV)
2. Anaerobic sealant, which include the following: Gasket eliminator Pipe Threadlock

Anaerobic Type Room Temperature Vulcanizing (RTV) Sealant

Anaerobic type room temperature vulcanizing (RTV) sealant cures in the absence of air. This type of sealant is used where 2 components, such as the intake manifold and the engine block, are assembled together.

Use the following information when using RTV sealant

1. Do not use RTV sealant in areas where extreme temperatures are expected. These areas include: The exhaust manifold The head gasket Any other surfaces where a different type of sealant is specified in the service procedure
2. Always follow all the safety recommendations and the directions that are on the RTV sealant container.
3. Use a plastic or wood scraper in order to remove all the RTV sealant from the components.
4. The surfaces to be sealed must be clean and dry.
5. Use a RTV sealant bead size as specified in the service procedure.
6. Apply the RTV sealant bead to the inside of any bolt holes areas.
7. Assemble the components while the RTV sealant is still wet to the touch, within 3 minutes.
8. Tighten the fasteners in sequence, if specified, and to the proper torque specifications.

Anaerobic Type Gasket Eliminator Sealant

Anaerobic type gasket eliminator sealant cures in the absence of air. This type of sealant is used where 2 rigid parts, such as castings, are assembled together. When 2 rigid parts are disassembled and no sealant or gasket is readily noticeable, then the 2 parts were probably assembled using an anaerobic type gasket eliminator sealant.

Use the following information when using gasket eliminator sealant

1. Always follow all the safety recommendations and directions that are on the gasket eliminator sealant container.
2. Apply a continuous bead of gasket eliminator sealant to one flange. The surfaces to be sealed must be clean and dry.

Note. Gasket eliminator sealed joint fasteners that are partially torqued and the gasket eliminator sealant allowed to cure more than 5 minutes, may result in incorrect shimming and sealing of the joint. Do not overtighten the fasteners. Apply the gasket eliminator sealant evenly to get a uniform thickness of the gasket eliminator sealant on the sealing surface. Tighten the fasteners in sequence, if specified, and to the proper torque specifications. After properly tightening the fasteners, remove the excess gasket eliminator sealant from the outside of the joint.

Anaerobic Type Threadlock Sealant

Anaerobic type threadlock sealant cures in the absence of air. This type of sealant is used for threadlocking and sealing of bolts, fittings, nuts, and studs. This type of sealant cures only when confined between 2 close fitting metal surfaces.

Use the following information when using threadlock sealant

1. Always follow all safety recommendations and directions that are on the threadlock sealant container.
2. The threaded surfaces to be sealed must be clean and dry.
3. Apply the threadlock sealant as specified on the threadlock sealant container.
4. Tighten the fasteners in sequence, if specified, and to the proper torque specifications.

Anaerobic Type Pipe Sealant

Anaerobic type pipe sealant cures in the absence of air and remains pliable when cured. This type of sealant is used where 2 parts are assembled together and require a leak proof joint.

Use the following information when using pipe sealant

1. Do not use pipe sealant in areas where extreme temperatures are expected. These areas include: The exhaust manifold The head gasket Surfaces where a different sealant is specified
2. Always follow all the safety recommendations and the directions that are on the pipe sealant container.
3. The surfaces to be sealed must be clean and dry.
4. Use a pipe sealant bead of the size or quantity as specified in the service procedure.
5. Apply the pipe sealant bead to the inside of any bolt hole areas.
6. Apply a continuous bead of pipe sealant to one sealing surface.
7. Tighten the fasteners in sequence, if specified, and to the proper torque specifications.

Tools and Equipment

1. Special tools are listed and illustrated throughout this section, with a complete listing at the end of the section. These tools, or their equivalents, are designed to quickly and safely accomplish the operations for which they are intended. The use of these special tools also minimize possible damage to engine components. Some precision measuring tools are required for inspection of certain critical components. Torque wrenches and a torque angle meter are necessary for the proper tightening of various fasteners.
2. To properly service the engine assembly, the following items should be readily available: Approved eye protection and safety gloves A clean, well-lit, work area A suitable component cleaning tank A compressed air supply Trays or storage containers to keep components and fasteners organized An adequate set of hand tools Approved engine repair stand An approved engine lifting device that adequately supports the weight of the components