Mopar Small-Blocks. Larry Shepard

and difficult to read.

       The main cap bolts are 1/2-13. The Magnum uses a slightly smaller head on the number-5 cap bolts (at the top). The most unique main cap bolts are the ones used on the number-2 and -4 mains on the 340/360 engines when the windage tray is used. The head of these bolts is thicker and is machined to accept to small screw that is used to hold the windage tray in position.

      Splayed Main Caps

      Many years ago, the splayed cap was used to add the four-bolt main caps to stock-style blocks. The angle was designed to go to the outer wall of the block, below the pan rail where there was enough material to hold this size of bolt. In these blocks, the bulkhead did not have enough material for four vertical bolts.

      At one time, the X and R race blocks were readily available with the added thickness in the bulkhead and the vertical four-bolt main caps, but the splayed cap is rarely used today.

      Neither approach works on the Magnum blocks because there is not enough material below the pan rail in the outer wall to support the 1/2-inch bolt. However, Chrysler/Mopar has tested the two-bolt Magnum blocks at very high outputs without problems (in the range of 500 to 550 hp).

       A splayed main cap is a style of four-bolt main cap, and it has the two outer bolts angled or machined at a different angle than the two inner bolts. With a splayed-style cap the outer two bolts also tend to be shorter so that the cap itself has a down-step from the standard height inner bolts. This step gives the splayed cap a unique appearance.

       You can convert your two-bolt main caps to four-bolt caps. To do so, the two outer holes are drilled at 7.06-inch centers and centered on the main bearing bore. Drill the 27/64-inch hole, 1.32-inch deep and then tap with a 1/2-inch-13 tap, 1.19-inch deep. At the top, or parting line surface, add a counterbore .52 inch in diameter, .12-inch deep (T/A and X+R blocks only).

      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.

      Cam Bearings

      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.

      Rear Main Seal

      The neoprene or rubber rear main seal replaced the rope seal that was installed on A-engines during the first few years of production. No one services the rope seal in gasket sets anymore. The rubber seal has a lip and must be installed in the proper direction. The rubber seal is better (with one exception).

      Little grooves are machined into the rear-seal groove-sealing surface on the crank (see Chapter 2). Grooves are not commonly found on a used crank. However, if you have a brand-new crank, there is a chance that these little grooves are cut too deep, too long, or have too sharp of an edge. In this situation, the rubber seal leaks. The solution is to install a rope seal. Contact Best Gaskets in California; they still offer rope seals.

      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.

      Block Drain

      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.

      Siamesed Bores

      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.

      Fasteners

      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.

       CHAPTER 2

       CRANKSHAFTS AND CONNECTING RODS

      A crankshaft’s main function is to change the pistons’ up-and-down motion into rotational motion, which can be measured as torque and horsepower. Each small-block crank has five main bearings and four journals with two rods per journal.

      The crankshaft is another engine part that you should take to a machine shop for inspection. A machine shop can repair almost any crankshaft if it is still in one piece. The most common problem is that small pieces of dirt pass through the engine over time and the dirt scratches the journals. The machine shop or crank grinder can typically repair this damage by carefully grinding the crank journals undersize. A common amount for this operation is .020 inch. The crank is then referred to as a 20-20 crank meaning the mains and rod journals are both .020-inch undersized. You use .020-inch undersize bearings with it.

Production Cranks

      The stroke measurement is often used to categorize small-block cranks. Mopar A and Magnum cranks fall into one of two groups. The 3.31-inch stroke for