Automotive Lower End Theory and Service

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GOALS

¦ Describe how to disassemble and inspect an engine. ¦ List the parts that make up a short block and briefly describe their operation. ¦ Describe the major service and rebuilding procedures performed on cylinder blocks. ¦ Describe the purpose, operation, and location of the camshaft. ¦ Describe the four types of camshaft drives. ¦ Inspect the camshaft and timing components. ¦ Describe how to install a camshaft and its bearings. ¦ Explain crankshaft construction, inspection, and rebuilding procedures. ¦ Explain the function of engine bearings, flywheels, and harmonic balancers. ¦ Explain the common service and assembly techniques used in connecting rod and piston servicing. ¦ Explain the purpose and design of the different types of piston rings. ¦ Describe the procedure for installing pistons in their cylinder bores. ¦ Inspect, service, and install an oil pump.

Fgr__1 A cutaway showing the fit of the piston assemblies and crankshaft in an engine block.

The lower end of an engine is the cylinder block assembly. This includes the block, camshaft, crankshaft, bearings, pistons, piston rings, and oil pump. Many of these parts are made by casting or forging. To cast is to form molten metal into a particular shape by pouring it into a mold. To forge is to form metal into a shape by heating it and pressing into a mold. Some forging is done with cold metals.

These manufactured parts then undergo a number of machining operations. Following are a few examples:

¦ The top of the block must be perfectly smooth so that the cylinder head can seal it.

¦ The bottom of the block is also machined to allow for proper sealing of the oil pan.

¦ The cylinder bores must be smooth and have the correct diameter to accept the pistons.

¦ The main bearing area of the block must be align bored (cut a series of holes in a straight line) to a diameter that will accept the crankshaft. Camshaft bearing bores must also be aligned.

When there is a major engine failure, shops either rebuild or replace the engine (Fgr__1). Most often the short block is repaired or replaced as an assembly. A basic short block consists of a cylinder block, crankshaft, bearings, connecting rods, pistons and rings, and oil gallery and core plugs. Parts related to the short block but not necessarily included with it are the flywheel and harmonic balancer. A short block may also include the engine's camshaft and timing gear. A long block is basically a short block with cylinder heads. These terms are commonly used when purchasing replacement engines.

SHORT BLOCK DISASSEMBLY

This section begins with the assumption that the engine has been removed and the cylinder head(s)

have been separated from the cylinder (engine) block.

However, few parts have been removed from the short block. If the oil pan and water pump are still attached to the block, remove them before proceeding.

Remove the harmonic balancer, also called a vibration damper. The harmonic balancer is an assembly of an inner hub bonded with rubber to an outer ring. Its purpose is to absorb the torsional vibrations of the crankshaft. Removal of the balancer requires the correct type puller (Fgr__2). If a jawed puller is used, it’s very likely that the rubber bonding will be damaged. This would make the balancer useless and can cause engine vibrations and crankshaft damage. Once the balancer is removed, carefully check the rubber for tears or other damage.

If there are any faults, replace the balancer.

On overhead valve engines, remove the timing cover. Under the cover are the timing gears. The timing sprocket on the crankshaft snout has a slight interference fit and can normally be pulled off by hand.

However, the camshaft sprocket and chain must be removed with the crankshaft sprocket. The camshaft sprocket is either press-fit or bolted to the camshaft.

Before removing the gears and chain, check the deflection of the timing chain. Depress the chain at its midway point between the gears and measure the amount that the chain can be deflected. If the deflection measurement exceeds specifications, the timing chain and gears should be replaced.

Loosen the camshaft sprocket and pull the timing gears and chain from the engine. Be careful not to lose the keys in each shaft or any shims that may be behind the sprockets.

Often the timing chain assembly has tensioners and guides. The timing gear assembly is normally replaced during an engine overhaul. The tensioners and guides wear and should be replaced as well.

The timing belt or chain on OHC engines has already been loosened before the cylinder head was removed. However, it may still be dangling around the crankshaft sprocket. Slip it off, if possible.

Unbolt the timing chain or belt cover and gently pry it away from the engine block and cylinder head. Remove the crankshaft position sensor, timing chain guide, chain tensioner slipper, and chain.

Pull the timing gear or sprocket off the crankshaft.

On some engines, the oil pump is driven by the crankshaft at the front of the engine. The pump should be unbolted and removed. Rotate the crank shaft counterclockwise to align the timing marks on the oil pump sprocket with the mark on the oil pump. Remove the attachment bolt for the sprocket and the chain tensioner plate and spring. Then remove the oil pump sprockets and chain. Remove the oil screen then the oil pump (Fgr__3). On some engines, the alignment of the inner and outer gears of the pump should be marked before removing the pump.

If the lifters have not been removed, do so now. Place them on a bench in the order they were removed. Carefully pull the camshaft out of the block.

Support the camshaft during removal to avoid dragging its lobes over the surfaces of the camshaft bearings. This can damage the bearings and lobes. Some engines require the removal of a thrust plate before removing the camshaft.

Fgr__2 The harmonic balancer should be removed with the correct puller.

Fgr__3 On some engines, the oil pump is driven by the crankshaft at the front of the engine.

Fgr__4 The balance shaft housing must be unbolted in the prescribed order to prevent shaft and housing warpage.

Fgr__5 A ridge reamer should be used on all cylinders before removing the pistons.

Fgr__6 Normal cylinder wear. Dana

Corporation -- Ring ridge

0.009 (0.2286 mm) Wear

0.003 (0.0762 mm)

Wear

Upper end of top ring travel

Area of greatest wear

Piston skirt travels in area of least wear

Upper end of piston skirt travel

Lower end of bottom ring travel

Fgr__7 Check all connecting rods and main bearing caps for correct position and numbering. If the numbers are not visible, use a center punch or number stamp to number them. Matching numbers.

Fgr__8 The bearings on the left have no babitt left, and the ones on the right are slightly worn and scored.

Fgr__9 Inspect each crankshaft journal for damage and wear. By Dana Corporation

Cylinder Block Disassembly:

Rotate the engine on its stand so that the bottom is facing up. Remove the oil pan if it was not removed previously. Then remove the oil pump as directed in the service manual. Be careful not to lose the drive shaft while pulling the pump off the engine.

If the engine has balance shafts, check the thrust clearance of the shafts before removing the assembly. Set a dial indicator so it can read the back-and forth movement (end play) of the shaft. Measure the total distance that the shaft is able to move in the housing. Compare that reading to specifications. If the reading is more than the specified maximum, the balance shaft housing and bearings should be replaced. Unbolt the housing following the sequence given in the shop manual (Fgr__4).

Remove the housing cover. Then lift the balance shaft(s) out of the housing. Inspect the bearings for unusual wear or damage. Keep the bearings in their original location or mark them for identification.

Check the journals of the balance shafts for scratches, pitting, and other damage. If a bearing or journal is damaged, replace the bearings and/or balance shaft.

Rotate the engine so the bottom is at the bottom again. Rotate the crankshaft so that the piston of one cylinder is at BDC. Carefully remove the cylinder ridge with a ridge reamer tool. Rotate the tool clockwise with a wrench to remove the ridge (Fgr__5). Don’t cut too deeply, because an indentation may be left in the bore. Remove just enough metal to allow the piston assembly to slip out of the bore without causing damage to the bore.

The ridge is formed at the top of the cylinder.

Because the top ring stops traveling before it reaches the top of the cylinder, a ridge of unworn metal is left (Fgr__6). Carbon also builds up above this ridge, adding to the problem. If the ridge is not removed, the piston's ring lands may be damaged as the piston is driven out of its bore.

Repeat the process on all cylinders. After removing the ridges, use an oily rag to wipe the metal cut tings out of the cylinder. The cuttings will stick to it.

Rotate the engine to put the bottom side up.

Check all connecting rods and main bearing caps for correct position and numbering. If the numbers are not visible, use a center punch or number stamp to number them (Fgr__7). Caps and rods should be stamped on the external flat surface. If the rods are already numbered or marked, make sure the marks designate the cylinder where the rods should be installed. They may have been installed incorrectly or they may have been taken from another engine.

Re-mark them to show their current location.

To remove the piston and rod assemblies, position the crankshaft throw at the bottom of its stroke.

Remove the connecting rod nuts and cap. Remember that the caps and rods must remain as a set. Tap the cap lightly with a soft hammer or wood block to aid in cap removal. Cover the rod bolts with protectors to avoid damage to the crankshaft journals. Carefully push the piston and rod assembly out with the wooden hammer handle or wooden drift and support the piston by hand as it comes out of the cylinder. Be sure that the connecting rod does not damage the cylinder wall during removal. With the bearing inserts in the rod and cap, replace the cap (numbers on the same side) and install the nuts. Repeat the procedure for all piston and rod assemblies.

In the specified order, loosen and remove the main bearing cap bolts and main bearing cap. Keeping the main bearing caps in order is very important.

The location and position of each main bearing cap should be marked. Most high-performance engines have a main bearing girdle or bearing support. These use at least four bolts at each main bearing. It’s important that the recommended bolt loosening sequence be followed.

After removing the main bearing caps, carefully take out the crankshaft by lifting both ends equally to avoid bending and damage. Store the crankshaft in a vertical position to avoid damage.

Remove the rear main oil seal and main bearings from the block and caps. Examine the bearing inserts for signs of abnormal engine conditions such as embedded metal particles, lack of lubrication, anti freeze contamination, oil dilution, and uneven wear (Fgr__8). Also inspect them for any unusual signs of wear, and check them for indications that they are over- or undersized. Then carefully inspect the main journals on the crankshaft for damage (Fgr__9).

Engine blocks have core plugs, also called expansion plugs. Sand cores are used when a block is made.

These cores are partly broken and dissolved when the hot metal is poured into the mold. To get the sand out, the block is made with holes. These core holes are machined and core plugs are installed to seal them (Fgr__10). Blocks are also made with passageways for oil. These are machined in after the block is made and are sealed with plugs.

The block cannot be thoroughly cleaned unless all core plugs and oil plugs are removed. To remove cup type "freeze"/core plugs, drive them in on a slant and use channel lock pliers to pull them out. Flat-type plugs can be removed by drilling a hole near the center and inserting a slide hammer to pull it out. On some engines, the cup-type plug can be easily removed by driving the plug out from the backside with a long rod.

Sometimes removing threaded front and rear oil gallery plugs can be difficult. Using a drill and screw extractor can help.

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SHOP TALK Using heat to melt paraffin into the threads of oil plugs will make removal much easier. As the part is heated, it will expand and the paraffin will leak down between the threads. Because the paraffin serves as a lubricant, you will be able to loosen the plug. Hot paraffin burns, so wear gloves when handling it.

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After cleaning, the block and its parts must be visually checked for cracks or other damage.

CYLINDER BLOCK

The cylinder block houses the areas where combustion takes place. It’s normally a one-piece casting that is machined so that all the parts contained in it fit properly. Blocks may be cast from different materials such as iron, aluminum (Fgr__11), magnesium, or possibly, in the future, plastic. A few engine blocks have an exterior made of magnesium and the interior (cylinders, coolant passages, etc.) of a cast-iron insert.

Some late-model blocks are made of two pieces: an upper unit that contains the cylinders and a lower one that surrounds the crankshaft (Fgr__12). Other blocks have main cap girdles (also referred to as the bedplate) integrated in the housing to provide added strength.

Cast-iron blocks are very strong but heavy. Many engines have an aluminum block to reduce the vehicle's overall weight. Certain materials are added to aluminum to make it stronger and less likely to warp from the heat of combustion. The cylinder walls of aluminum blocks may be treated with a special coating or may have a sleeve or liner to serve as cylinder walls.

Cylinder Liners:

Most aluminum blocks have cylinder liners (Fgr__13). The liners are normally made of a cast iron alloy. On some engines, the liners can be replaced and/or machined if they are damaged. Most are very thin and cannot be serviced and the block must be replaced if the walls are damaged. Liners are pressed into the block or are placed in the mold before the block is cast. The liners have ribs on their outside diameter. These ribs hold the liner in place and increase its ability to dissipate heat to the block. There are two types of sleeves: wet and dry. The dry sleeve is supported from top to bottom by the block. The wet sleeve is supported only at the top and bottom. Cool ant touches the center part of a wet sleeve.

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Fgr__14 If the engine has water jacket spacers, they must be removed before cleaning the block and to prevent damage to them.

A - A Cross section Water jacket spacer

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Lubrication and Cooling

A cylinder block contains a series of oil passages that allow engine oil to be pumped through the block and crankshaft and on to the cylinder head. Water jackets are also cast in the block around the cylinder bores.

Coolant circulates through these jackets to transfer heat away.

Some engine blocks are cast with a plastic spacer for the water jackets (Fgr__14). The spacers pro vide a uniform distribution of heat throughout the cylinders by directing the flow of coolant toward the normally hotter areas. For example, a spacer is used to direct coolant away from the center of the cylinder bore to the top and bottom of the bore. The top and bottom of the bore are normally the hotter areas, so suppressing the coolant flow to the center may result in the center having the same temperature as the top and bottom.

Other Features

An engine block has other features. Many of these are machined areas on which to mount other parts.

These areas typically include threaded bores.

Brackets and housings may also be cast onto the basic block. Some blocks have air passage holes near the bottom to allow for any pressure buildup caused by the pumping action of the pistons. The bottoms of the pistons are moving with pumping action at the same time the tops are moving through their strokes.

CYLINDER BLOCK RECONDITIONING

Before doing any service to the block, clean all threaded bores with the correct-size thread chaser to remove any burrs or dirt. Use a bottoming tap in any blind holes. These bores should be slightly chamfered to eliminate thread pulls and jagged edges. If there is damage to the threads, they should be repaired. To restore damaged threads in an aluminum part, a threaded insert should be installed in the bore.

Check the block for cracks and other damage.

Cast-iron blocks can be checked by magnafluxing.

Aluminum blocks are checked for cracks with penetrant dye and a black light. Some cracks can be repaired; however, if they are in critical areas, the block should be replaced.

Fgr__15 Checking for deck warpage with a straightedge and feeler gauge.

Fgr__16 A scored cylinder wall.

Deck Flatness

The top of the block where the cylinder head mounts is called the deck. To check deck warpage, use a precision straightedge and feeler gauge. With the straight edge positioned diagonally across the deck, the amount of warpage is determined by the size of feeler gauge that fits into the gap between the deck and the straightedge (Fgr__15).

Some engines have special deck flatness requirements. Always refer to the manufacturer's specifications. If the deck is warped beyond limits, the block should be decked or replaced. Decking requires a special grinder that will shave off small amounts of metal, leaving a flat surface. Some manufacturers don’t recommend decking, especially if the block is aluminum. If the block has more than one deck surface (such as a V-type engine), each deck should be machined to the same height. If the deck is warped and not corrected, the valve seats can distort when the head is tightened to the block. Coolant and combustion leakage can also occur.

Cylinder Bore Inspection

Inspect the cylinder walls for scoring, roughness, or other signs of wear. Dirt can accelerate ring and cylinder wall wear. It also can get caught in the piston rings and can grind away at the metal surfaces.

Scuffed or scored pistons, rings, and cylinder walls (Fgr__16) can act as passages for oil to bypass the rings and enter the combustion chamber. Scuffing and scoring occur when the oil film on the cylinder wall is ruptured, allowing metal-to-metal contact of the piston rings on the cylinder wall. Cooling sys tem hot spots, oil contamination, and fuel wash are typical causes of this problem.

Most cylinder wear occurs at the top of the ring travel. Pressure on the top ring is at a peak and lubrication at a minimum when the piston is at the top of its stroke. A ridge of unworn material will remain above the upper limit of ring travel. Below the ring travel area, wear is negligible because only the piston skirt contacts the cylinder wall.

A properly reconditioned cylinder must have the correct diameter, have no taper or out-of-roundness, and the surface finish must be such that the piston rings will seat to form a seal that will control oil and minimize blowby.

Taper is the difference in diameter between the bottom of the cylinder bore and the top of the bore just below the ridge (Fgr__17). Subtracting the smaller diameter from the larger one gives the cylinder taper. Some taper is permissible, but normally not more than 0.006 inch (0.1524 mm). If the taper is less than that, re-boring the cylinder is not necessary.

Cylinder out-of-roundness is the difference of the cylinder's diameter when measured parallel with the crank and then perpendicular to the crank (Fgr__18). Out-of-roundness is measured at the top of the cylinder just below the ridge. Typically the maximum allowable out-of-roundness is 0.0015 inch (0.0381 mm). Normally a cylinder bore is checked for out-of-roundness with a dial bore gauge (Fgr__19). However, a telescoping gauge can also be used.

When using a dial bore gauge or a telescoping gauge, make sure the measuring arms are parallel to the plane of the crankshaft. The best way to do this is to rock the gauge until the smallest reading is obtained.

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Fgr__13 A cylinder block and cylinder liner for a late-model aluminum V8 engine. By Chrysler LLC

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Core plugs Fgr__10 Core plugs in an engine block.

Fgr__11 An engine block for a 12-cylinder engine. By BMW of North America, LLC Fgr__12 Aluminum engine blocks are often two-piece units. By Toyota Motor Sales, U.S.A., Inc.

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Cylinder bore taper

Cylinder walls A C

Fgr__17 To check for taper, measure the diameter of the cylinder at A and C. The difference between the two readings is the amount of taper.

Cylinder bore Cylinder block

Fgr__18 To check cylinder out-of-roundness, measure the bore in different locations. By Ford Motor Company

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Fgr__19 Cylinder bore is checked for out of-roundness with a dial bore gauge.

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50°-60° Crosshatch pattern; Intersect angle

Fgr__20 Ideal crosshatch pattern for cylinder walls. By Chrysler LLC

Fgr__21 The desired cylinder wall finish for most types of piston rings.

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Fgr__22 Using a resilient-based, hone-type brush, commonly called a ball hone.

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Cylinder Bore Surface Finish:

The surface finish on a cylinder wall should act as an oil reservoir to lubricate the piston rings and prevent piston and ring scuffing. Having the correct cylinder wall finish is important. Piston ring faces can be damaged and wear prematurely if the wall is too rough. A surface that is too smooth won’t hold enough oil and scuffing may occur.

The desired finish has many small crisscross grooves (Fgr__20). Ideally, these grooves cross at 50- to 60-degree angles, although anything from 20 to 60 degrees is acceptable. This finish leaves millions of tiny diamond-shaped areas to serve as oil reservoirs (Fgr__21). It also provides flat areas or plateaus on which an oil film can form to separate the rings from the wall. If the angle of the crosshatch is too steep, the oil film will be too thin, causing ring and cylinder scuffing. If the angle is too flat, the pistons may hydro plane and excessive oil consumption will result.

Cylinder Deglazing-- If the inspection and measurements of the cylinder wall show that surface conditions, taper, and out-of-roundness are within acceptable limits, the cylinder walls may only need to be deglazed. Combustion heat, engine oil, and piston movement combine to form a thin residue, glaze, in the cylinders. Glazed walls allow the piston rings to slide over them and prevent a positive seal between the walls and the rings.

It’s easy to confuse glaze with the polished surface that appears in the cylinders after the engine has some miles on it. Often, glazing can be removed by wiping the cylinders with denatured alcohol or lacquer thinner. Fine honing stones can also remove glaze and leave the walls with a desired finish. Often, technicians use a ball hone to deglaze (Fgr__22) and create the desired pattern on the walls of the cylinder. On many newer engines, deglazing with a ball hone or stones is not recommended. Always check the manufacturer's recommendations before deglazing or honing the cylinder walls.

Cylinder Honing:

A cylinder hone usually has three or four stones. The hone is spun by an electric motor and is moved up and down the cylinder's bore.

Springs push the stones against the walls. As they rotate, a small amount of metal is removed from the walls. Honing oil flows over the stones and onto the cylinder wall to control the temperature and to flush out any metallic and abrasive residue. To achieve the correct wall finish, the correct type of stones should be used. Stones are classified by grit size: The lower the grit number, the coarser the stone. The type of piston ring that will be installed normally dictates the desirable grit.

Cylinder honing machines are available in manual and automatic models (Fgr__23). Automatic models allow the technician to dial in the desired crosshatch angle. When honing a cylinder by hand, use a slow-speed (200-450 rpm) electric drill. Mount the honing tool into the drill and insert it into the bore. Adjust the stones so they fit snugly to the narrowest section of the cylinder. Move the drill and the hone up and down in the bore with short strokes.

Never remain in one spot too long. Squirt some honing oil on the walls and occasionally stop honing and clean the stones. Continue until the desired results are achieved.

Cylinder Boring --When cylinder surfaces are badly worn or excessively scored or tapered, a boring bar or boring machine is used to cut the cylinders for over size pistons or sleeves. A boring bar leaves a pattern on the cylinder wall similar to uneven screw threads.

These can cause poor oil control and excessive blowby. Therefore, always hone a cylinder after it has been bored.

Fgr__23 Automatic cylinder hone machine.

Fgr__24 Torque plates are fastened to the block during cylinder boring and honing to prevent block distortion during the machining process. By Jasper Engines & Transmissions

Fgr__25 An exaggerated view of crankcase housing misalignment.

Fgr__26 A line boring machine for correct crankshaft saddle alignment.

Fgr__27 Checking bore alignment with a straightedge and feeler gauge. By Federal-Mogul Corp.

CAUTION! Always wear eye protection when operating deglazing, honing, or boring equipment.

When engines are bored, oversized pistons and rings are used. These are available as 0.020_ (0.50 mm), 0.030_ (0.77 mm), 0.040_ (1.0 mm), and 0.060_ (1.5 mm) oversized.

Torque plates simulate the weight and structure of a cylinder head. They are used by engine rebuilding shops and are fastened to the cylinder block to equalize or prevent twist and distortion when honing or boring a cylinder.

After servicing the walls, use plenty of hot, soapy water; a stiff-bristle brush; and a soft, lint-free cloth to clean the walls. Then rinse the block with water and allow it to thoroughly dry. Put a light coat of clean engine oil on the walls to prevent rust.

Lifter Bores

Carefully check each valve lifter bore for cracks and evidence of excessive wear. Oblong or egg-shaped bores indicate wear. If the bores are rusted, glazed, or have burrs and high spots, they can be honed with a brake wheel cylinder hone. Be careful not to remove more than 0.0005 inch of metal while honing. If the bores exceed allowable wear limits or are damaged, the engine block should be replaced.

Checking Crankshaft Saddle Alignment--If the block is warped and its main bearing bores are out of alignment (Fgr__25), the crankshaft will bend as it rotates. This causes bearing failure and possibly a broken crankshaft. Blocks that are not severely warped can be repaired by line boring them. This is a special machining operation in which the main bearing bores are cut to an oversize in order to keep perfect alignment (Fgr__26). Badly warped blocks are replaced.

The alignment of the crankshaft saddle bore can be checked with a precisely ground arbor placed into the bearing bores. The arbor is rotated in the bores; the effort required to rotate it indicates the alignment of the bores.

Saddle alignment can also be checked with a metal straightedge (Fgr__27). Place the straightedge in the saddles. Attempt to slide a feeler gauge that is half the maximum specified oil clearance under the straightedge. If this can be done at any saddle, the saddles are out of alignment and the block must be line-bored.

The roundness of the bearing saddles should be checked with a dial bore gauge or telescoping gauge and micrometer. To do this, install and tighten the main bearing caps, then measure the inside diameter in many places in each bore.

Installing Core Plugs:

After the block has been serviced and cleaned, new oil and core plugs should be installed. The plugs' bores should be inspected for any damage that would interfere with the proper sealing. Make sure the plugs are the correct size and type. Coat the plug or bore lightly with a non-hardening oil-resistant (oil gallery) or water-resistant (cooling jacket) sealer. The oil plugs are threaded into their bores. If the threads are dam aged, run a tap through the bore.

If the bore for a core plug is damaged, it should be bored out for an oversized plug. Oversize (OS) plugs are identified by the OS stamped on the plug. The correct way to install a core plug depends on the type of plug.

Disc- or Dished-Type --These fit in a bore with the dished side facing out (Fgr__28A). With a hammer, hit the center of the disc's crown and drive the plug in until just the crown becomes flat. This allows the plug to expand properly and have a tight fit.

Cup-Type--These are installed with the flanged edge outward (Fgr__28B). The bore for these plugs has its largest diameter at the outer (sealing) edge.

The outside of the cup must be positioned behind the chamfered edge of the bore to effectively seal the bore.

Expansion-Type--These are installed with the flanged edge inward (Fgr__28C). The bore for these plugs has its largest diameter at the back of the bore.

The base of the plug must be positioned at the rear of the bore to seal it.

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Fgr__29 A camshaft for a V8 engine. Melling Automotive Products

Fgr__30 Typical valve timing diagram. INTAKE VALVE CLOSES OVERLAP 21° 15°

Fgr__28 Core plug installation methods: (A) dished, (B) cup, and (C) expansion.

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Next: Automotive Lower End Theory and Service--part 2

Prev.: Engine Disassembly and Cleaning



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