The engine’s cylinder block is the basic foundation for virtually everything in an engine project, and as such, it affects almost every part in the engine, either directly or indirectly. Improved performance is the typical goal of an engine project, and to accomplish this basic goal, all parts used in the engine must work together.
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All parts need to be compatible, but they should also be complementary. You may take the engine apart and put it back together several times before you arrive at the final assembly steps to complete the engine. As you begin building your foundation, use a notebook to keep track of everything that you see and do, from casting numbers to bore sizes, etc., for every part that you use. Once the engine is together, it can be very difficult to gain this information and it may be helpful for any troubleshooting that is required.
Basic block design could be considered similar to architecture because it defines how the block is laid out. An engine family such as the LA-engine and the Magnum extension tend to share many features that define them. The LA-engine small-block family is a basic 90-degree V-8. This angle is best for dynamic balance considerations and also makes for a very rigid block.
Cylinder numbering begins with the driver-side front cylinder; number-2 is the passenger-side front cylinder. The A-engine has a production deck height of 9.60 inches; the Magnum group uses 9.585 inches. Small-block race blocks have deck heights as low as 9.0 inches. Both groups of small-blocks share the 4.46-inch cylinder bore centers and the 6.125-inch camshaft centerline height. The LA-engine block is lighter than the original A-engine block and weighs about 160 pounds. The newer 1973–1974 thinwall cast versions are about 4 to 8 pounds lighter, which carries over to the Magnum blocks.
Although there are four different cylinder bore sizes, Chrysler made two basic blocks. One is the 273, 318, and 5.2L block; the other is the 340, 360, and 5.9L block. Most A-engines use a motor-mount design that attaches to the sides of the block close to the front, and the mount ears and bolts are parallel to the cam centerline. The 273 and 318 share the same arrangement.
However, the 340 and 360 share the same driver’s side configuration, but the passenger’s side has the three-bolt pattern reversed.
The Magnum engine, originally used in trucks, had a three-bolt pattern on each side, and these mounts bolted into the side of the block itself. This bolt pattern is located in the center of the block starting just above the pan rail. In addition, these Magnum blocks had the ears cast in and machined for the earlier system.
Both groups of blocks have three core plugs per side; the 318 group has them wide-spaced, and the 340–360 group has each core plug aligned with the center of the water jacket between two cylinders.
The easiest way to identify a small- block Mopar is to compare the casting numbers. Each casting is unique. In other words, you can’t machine out the 273 bores to make a 318. You also can’t make a 340 out of a 318.
These rules don’t apply to 340 and 360 blocks. You could probably bore out the 360 block to the 340 stock bore size of 4.04 inches, but the 360 has a large main bearing diameter crank. The large main bearing diameter makes the long-stroke 360 (3.58 inches) much stiffer. In addition, the 340 oil pan’s front and rear sealing surfaces are the same as the 318’s; the 360’s are smaller.
The 1970 340 T/A is the trick block for racing applications because it has thick bulkheads on the number-2, -3, and -4 main bearing bulkheads. The added thickness allows for vertical four-bolt main caps to be added to these center mains. None of the Magnum blocks have this thick bulkhead.
In the mid-1970s, Chrysler offered a four-bolt main race block known as the X-block (it had a large “X” on the passenger-side front wall of the casting). In the mid-1990s, Mopar Performance and Chrysler revised this race block and offered the R1 through R4 race blocks. These were generally called the R-blocks and all featured four-bolt mains.
When you are selecting a block for your particular build, remember that for all fi ve of my performance packages, the standard 340/360 or Magnum block can be used as long as the bore size is limited to .020/.030 overbore for the last two packages. An R-block is not required as long as the blocks are limited in overbore. If a big-bore engine is desired, an R-block is required, and the siamesed-bore version allows the largest bores. The 340 resto block is a version of the R-block. If your 340 or 360 block is already overbored too far, sleeve the bore back to 4.020 inches (360) or 4.04 inches (340).
The original race block for Mopar small-blocks was the 340 T/A in 1970. It was produced for only one year. When NASCAR began handicapping the big-blocks, both Hemi-head and wedge-head designs in the early 1970s, the NASCAR teams began using the T/A blocks, but they had to remove them from actual Trans-Am cars. This was a lot of extra work! To solve this problem, Chrysler introduced the X-block, which had all the features of the T/A block plus a few more. This X-block was readily available to racers and was very successful.
When the government issued the loan guarantee to keep Chrysler operating, the X-block tooling was lost during the confusion it created. In the late 1980s, the demand for a race block began to build, so Mopar Performance introduced the new “R1” block, which replaced the X-block. Then came the R2, R3, and R4. Each one has its name cast into the passenger-side front wall of the block.
Some of these R-blocks are cast with siamesed-bores, which means that the bore walls of adjoining cylinder bores are merged together, with no gap. This siamesed situation exists at three places per side (cylinder bank). This siamesed-bore alignment generally allows the actual cylinder bores to be larger because there is no water-jacket between the cylinders.
R-blocks can be converted to a six-bolt cylinder head by adding two more head bolts to the stock four-bolt pattern. This is a critical upgrade for super-high compression ratios, such as 13:1. A study showed that four-bolt heads were bending the head over the gasket’s sealing ring. The two extra head bolts keep the gasket material farther away from the bore. The bolts and gasket support help maintain a flat deck surface with high clamping loads.
One boss was added straight up in the tappet chamber and one was added straight down on the outside of the block. In some cases these bosses are left unmachined or are machined off if not desired. If they are machined, they do not have to be used. If you use them, you must use a six-bolt–style head gasket. All of these race blocks (X and R versions) are cast-iron blocks made with high-nickel-alloy cast iron.
Most LA-engine small-blocks were built at the Mound Road Engine plant in Detroit, then added to the Windsor engine plant in Canada, and later the Toluca plant in Mexico. Many A-engine blocks were cast at Chrysler’s Indianapolis, Indiana, foundry, which was closely involved in the early stages of the R-family of blocks.
Mopar Performance began offering aluminum small-blocks designed for racing in the early 1990s. They are designed and built for the serious Sprint Car and drag racer who competes in classes that allow aluminum blocks. The latest version weighs approximately 95 to 100 pounds, a weight savings of more than 25 pounds over the previous version. These blocks were offered in two basic deck heights, 9.00/9.10 and 9.56 inches. They are shipped with one of several options in bore size.
By about 2005, Mopar Performance offered more than 20 different blocks for the small-block. All were designed for racing; many options were available for virtually any engine project.
The amount of overbore depends on the block itself and when the block was built. Early 273 and 318 blocks (pre-1973–1974) can generally be overbored about .060 inch. Early 340 blocks can be overbored about .040 inch, or 4.080-inch actual bore size. The 360 is a gray area, but I use the 340 as a guide and limit overbore to .040 inch, or an actual bore size of 4.04 inches. All newer blocks, A-engines, and Magnums are thinwall casting designs, and overbore should be limited to .020 to .030 inch.
All race blocks can be overbored more than production blocks. You can overbore the resto block to 4.08 inches with the siamesed-bore versions able to be overbored the most (approximately 4.22-inch max for the siamesed-bore versions). When pushing the boundary of bore size and overboring, it is best to sonic-test the block before you begin any boring operation.
Most race blocks are bored or rough bored to approximately 4.00 inches. There are many reasons to use a race block even if the bore size is less than 4.00 inches (such as the 318’s 3.91 inches). If you plan to race a small-bore engine, such as 3.91 inches or even 3.63 inches, you should not use the production block. It is a better package to use the race block with the proper-size sleeves.
The two basic main sizes are the 273/318/340 and 5.2L engines. The 360 and 5.9L use a larger main. The 360 has a large 3.00-inch main; the other group is small at 2.69 inches. The main cap bolt spacing on the 360/5.9L is also wider, or spread. Magnum engines have a small dowel that locates the number-5 main cap. Magnums also use smaller main cap bolts in the number-5 cap. Typically the main caps are made of high-nickel cast iron. If the main caps have been replaced or damaged, or if they bind during crank rotation, the mains should be align-bored, which is a machine shop operation.
Most A-engine blocks were built at 9.60-inch block height; Magnum engines were built at 9.58 inches. Race blocks can be about 9.00- to 9.10-inch block height. Do not try to mill a production block to this height. Deck milling on production blocks should be limited to about .060 inch.
You need to determine if the engine was rebuilt or repaired in the past and whether the block was decked .060 inch at that time. If the block has been decked by .060, the actual deck now is 9.54 inches. You should not take off another .060 inch because the deck becomes too thin and causes head gasket sealing problems that you will not be able to fix. This is one reason that it is so important to measure the block’s actual height before you start machining.
The A-engine/Magnum engine can generally accept long-stroke cranks. Most of them use a 3.31-inch stroke; the 360/5.9L uses a longer 3.58-inch stroke. The performance aftermarket offers 4.00-inch strokes that are easy fits. Because the camshaft sits so high above the crank, long-strokes do not cause the connecting rods to hit the camshaft lobes. The pan rail and the bottom of the cylinder bore (pulling the skirt too far out the bottom) are still concerns with strokes longer than 4.00 inches.
A-engine and Magnum blocks oil in basically the same way. The difference comes in oiling the head and valvetrain. The A-engine oils the valvetrain and head through the head; Magnum engines oil the valvetrain and head through the pushrods.
Basically, the oil pump feeds the oil fi lter and then pushes oil to the passenger-side main oil galley. From the main oil galley, the oil feeds the passenger-side tappets and the main bearings. Then it crosses to the driver-side oil galley and oils the driver-side tappets. Then, from the mains, the oil goes to the camshaft bearing.
On the A-engine, the oil goes to the rockers and the head from the cam bearing and through passages in the block and head to the rocker shaft. On Magnum engines, the oil goes to the head and rockers through the pushrods from each tappet.
The aftermarket (specifically Schumacher Creative Services) makes mounts/brackets to use with either the 340/360 or 273/318 ears. Race blocks use the 340–360 ears but are often machined off to lighten the engine. Aluminum blocks are designed for mounting by motor plates.
Cores are used to make all cast parts, including cylinder blocks. A core is typically made of hardened sand and is used to make an internal passage or relief such as the water jacket. A special bonding agent holds together the hard sand. Cores don’t typically bend but they do break And when cores break, the broken pieces usually tear large holes and/or create solid chunks where they aren’t supposed to be, and then the block has to be scrapped.
Today, block castings are machined on CNC-machines, and this precision machining process centers the actual machining on the cylinder bore and centers the wall thickness. This centering process tends to reduce or cancel out the effects of any core shift. In addition, foundries today try to design the cores so that they are locked in place and can’t move once assembled. The foundry uses sonic testing to help find any broken or damaged core blocks and keep them from getting into the machining process.
Find a machine shop that has a history of machining Mopar engines and that engine builders recommend highly. As such, a machine shop familiar with the A-engine small-block design will perform the best job. This basic process actually starts with a close inspection followed by many accurate measurements. The measuring process usually starts with a thorough cleaning of the various parts. With new parts you tend to know more about them when you bring them to the machine shop; in some cases you may have purchased them already machined. Race blocks are often shipped rough-bored so your machine shop can finish them to your specifications.
Honing plates should always be used when boring and honing the cylinder block. These put the cylinder head stresses into the cylinders, so that it simulates what the cylinder walls do with the head installed. During this process the cylinder bore’s diameter is measured with a dial-bore gauge. The machine shop leaves about .001 to .002 inch of material for the final honing operation.
Once cleaned, the machine shop can tell how flat the deck surface is and if there is any damage (scratches, etc.) that needs to be fixed. You probably don’t need to deck a new block. The decking process tends to remove .010 to .020 inch, unless a special amount is requested. Typically, production blocks can have up to .060 inch milled off without causing problems.
Sometimes a used block has distorted or damaged main bearing caps and saddles. If you’ve measured the caps and saddles and determined that they need honing or boring, a machine shop needs to perform this service. Align-boring trues them so the crankshaft performs at its best and does not bind.
Generally, the last step in the engine disassembly process is to spin the crank once the rod-and-piston assemblies are removed. The engine builder tends to notice a tight spot during the general disassembly, but the final spin is confirmation. If no tight spot is observed during the disassembly process, the align-boring operation is not required. It is required if the block has been welded upon or suffered a major failure.
Sonic testing uses sound waves to determine the cylinder wall thickness around the bore. Thus it tells you how thick the bores actually are and if there is any core shift, and if there is core shirt, which direction it is in. If you are building many engines, buy a high-quality sonic tester; otherwise have your machine shop sonically test the block. The major thrust area on the driver’s side of each bank should be tested.
By determining bore thickness, you can figure out how much overbore is safe and where to stop. If you have two or more blocks, it tells you which one is best. Always sonic test before you start the overboring process. If a cylinder is found to be too thin, re-sleeve the cylinder or use a different block.
You can use sleeving as a repair or as a bore change.
Once the block is cleaned, the machine shop may tell you that one or two of the block’s cylinder bores are damaged and need to be fixed. Basic wear and/or scoring in the bore are the most common causes. No matter the reason, sleeving by a machine shop should fix it. If the process is executed properly, the rebuilt engine should be as good as new.
There are no 318 race blocks and the smallest 340/360 race block bore is 4.00 inches. The 318 block cannot be bored out to a 4.00-inch bore (3.97 inches on pre-1973 blocks but only 3.94–3.95 on 1973 and newer thinwall cast blocks). Perhaps your current race engine is worn-out; its last rebuild was at the maximum bore size for this block and it is time for another rebuild. Do you scrap the block? Sleeving all eight cylinders is one solution.
What if you want a race block with a bore of 3.97 inches (a .060-inch 318)? For small bores or worn bores, sleeving is a reasonable approach. For example, if you want to build a 310-ci A-engine with the readily available 3.31-inch stroker based on the 360/5.9L block (original 4.00-inch bores), you need a 3.86-inch bore. Sleeving is the only way to accomplish this bore size.
The typical main cap is made of cast iron (high-nickel alloy), similar to the block. Most race blocks use four-bolt caps, which may be steel or ductile iron. The number-3 cap is specially machined to accept the thrust bearing on the front and rear faces. The most complicated cap is the number-5.
Heavy-Duty Main Caps
All production blocks have cast-iron main caps with a tensile strength of approximately 241,000 psi. The tensile strength of ductile cast iron is about 413,000 psi, or more than 70 percent higher. Making main caps out of ductile cast iron results in a big strength gain.
Most R-family race blocks use special upgraded heavy-duty caps (ductile iron or steel). Also, the 360 and 5.9L engines, which have the larger main diameters, should also have the main cap bolts spread .31 inch farther apart than other engines.
Heavy-duty main caps, such as those offered by ProGram Engineering, should be used on nitrous and supercharged applications. For naturally aspirated engines, the switch is related to RPM and stroke length. Install heavy-duty main caps if mechanical roller cams are used or if the valve lift is more than .600 inch.
Four-Bolt Main Caps, Vertical
The key to installing or using a four-bolt main cap is to have the material added to the main bulkhead to allow this modification. Only the 340 T/A block and the new X- and R-block have the added material on main bulkheads number-2, -3, and -4. The majority of R-blocks come with four-bolt caps.
Special Features and Operations
The A-engine small-block started production in 1964 and the Magnum engine’s production ended in about 2003. That’s almost 40 years of production. Over such a long period of time, some problems inevitably pop up, and they may only apply to a few engines.
When race cams became much bigger, valvespring open loads went from 750 to 1,000 pounds. And this creates two problems. First, the cam’s nose must fit through the inside diameter of the cam bearing, but bigger cams have bigger and thus higher-lift cam lobes. To gain the higher lift, using the standard or 50-mm bearings, the cam lobe’s base circle has to be ground down. Obviously with less material, the cam becomes weaker.
Second, the higher spring loads caused deflections, and that inhibits engine performance. So racers went to 60-mm roller cam bearings, and an R3 race block was required. The large bearing diameter allows the lobe to become larger without grinding down the base circle. This bigger base circle makes the cam stiffer and stronger.
Standard cam bearings from manufacturers such as Clevite, Speed-Pro, and Dura-Bond work fine for all street/strip applications. Although not required, you should replace the cam bearings in used blocks. Roller cam bearings are not required for the street or street/strip engines but need to be used in race engines with mechanical roller cams with valve lifts more than .650 inch.
A small, threaded, solid plug is at the bottom of the water jacket, near the pan rail, on each side of the block. They are only removed when the block is cleaned or hot-tanked. If the engine is to be raced, consider replacing this solid plug with a block drain, available at any standard auto parts store.
A few blocks are cast with the bore walls joined. These special blocks are called siamese-bored blocks. The bore walls of adjacent cylinders are joined solid. This allows for slightly larger bores. It also makes the cylinder bores somewhat stiffer. The negative thing is that they cut off water flow around the cylinders, especially on the two center cylinders on each bank.
Bolts hold the Magnum engine; race heads use main cap bolts that are longer than the standard long bolts in production A-engine heads. ARP, A1, and other aftermarket companies sell studs that replace these bolts, and provide higher clamping force.
The studs’ biggest advantage comes into play if you race the engine and normally pull the caps to check the bearings or pull the head to check seats or guides or to modify it. Typical street or dual-purpose engines are assembled and run for many thousands of miles over a long time. Because the engines tend to be disassembled infrequently, there is very little wear and tear on the threads by the bolts.
Written by Larry Shepard and Posted with Permission of CarTechBooks
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