Mopar Small-Blocks. Larry Shepard
Чтение книги онлайн.
Читать онлайн книгу Mopar Small-Blocks - Larry Shepard страница 9
Название: Mopar Small-Blocks
Автор: Larry Shepard
Издательство: Ingram
Жанр: Сделай Сам
isbn: 9781613253533
isbn:
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.
The backsides of the motor mount ears are machined to hold tolerance on mount location and thicknesses. The three ears form a sort of box with one corner missing. The change from 340/360 to 318/273 on one side is that the missing corner ear switches location, so the mounts are not interchangeable. The aftermarket mounts (from Schumacher) make a full box bracket and include all four holes to fit either engine.
Magnum blocks may have both styles as shown. This Magnum block (5.2L) has the four ears, machined on the rear, and the bolts into the side of the block (only two are showing) so it could be used with either style of mount.
The Magnum engine uses bolts (three per side) directly into bosses in the middle of each side of the block. The three bolts are spaced around the right core plug: one to the bottom, one to the upper left, and one to the upper right, both just below the pan rail. Remember, the block is upside down.
Core shift occurs when a core such as the water-jacket core moves or shifts relative to the cylinder bores or if the core breaks, which allows the ends to shift. If the core shifts, thin sections will be on one side of the bore and thick sections will be on other sides of the bore. Remember that the core is a solid piece so if it shifted, then all sides will be shifted in the same direction. For example, if cylinder number-1 has the core shifted upward and cylinder number-3 has it shifted downward, then it probably isn’t a core shift!
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.
All production small-block engines use the same ten-bolt-per-bank head bolt pattern, which is four bolts around each chamber for exceptional clamping strength. Some race blocks use the eighteen-bolt-per-bank head bolt pattern, which has six bolts around each chamber. If you have a six-bolt race block and your application does not require the two extra head bolts, you can use four-bolt heads and four-bolt gaskets and not install bolts on the two extra holes per cylinder. All high-performance packages that I put together use 11.5 CR max, and the current MLS gaskets from Fel-Pro or Cometic will easily seal this with the standard four-bolt system. The six-bolt system is not required for street/strip.
Although the Magnum group and A-engine water pumps look similar when installed on the engine, they are not because the Magnum group does not have an attachment hole in the right side of the cover for the mechanical fuel pump (all MPI) and the A-engine cover has a hole with two attaching bolts for the mechanical pump. In addition, the two water pumps run in opposite directions and the vanes that direct the water into the pump that are cast into the cover are tipped in opposite directions.
Once you decide to deck the block, be sure to address the head dowel pins, two per bank. They are pressed into the deck surface and must be removed before the milling machine can deck the block. They should be installed after the milling is complete. I recommend new ones. If they are being replaced, check the height before removing and set the new ones to the same height.
All Magnum engines have a two-bolt crank sensor mount at the right rear of the block next to the bellhousing face. The bosses are machined for a two-bolt attachment and the sensor itself can look directly at the ring gear wheel. This sensor would not be used if you do not use fuel injection (MPI) but is mandatory if you plan on using Multi-Point Injection. If you want to add the Magnum-style fuel injection to an A-engine, consider duplicating this boss, location, and basic setup.
The 48-degree tappets were created to offer the perfect valvetrain. The race blocks can be machined with either the standard 59-degree tappets or the 48-degree tappets. Once machined, they can’t be changed. Similar to the 50- and 60-mm cam bearings, the biggest advantage for the 48-degree tappets comes about with high cam lifts, high valvespring loads, and high engine RPM.
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.
You can make many measurements on the block, such as bore size (diameter in inches) or center-to-center distance (4.46 inches on small-blocks) and many others. The dial vernier is the quick and easy way to get rough ideas of what you are dealing with. The machine shop will use a dial bore gauge for the fine-tuning measurements. This is usually the preliminary step to boring/honing the block.