396ci Chevy Big Block - Engine-Building Tips

When selecting a salvage-yard crankshaft, carefully check the surface condition of each journal. Many machinists claim that any surface imperfection that you can catch your fingernail on will require machine work. Also, tap the end of the crankshaft lightly on some concrete and listen to the sound it makes. If it rings like a tuning fork, fine—if it buzzes or has a dull sound, you may be holding a cracked casting. Regardless, you should send any salvage-yard crank to a reliable shop to have it Magnafluxed. We sent this one to Lopez Crankshaft in Santa Fe Springs, California for reconditioning, including resurfacing of the journals. Competent shops will also radius all the oil passages in the crankshaft to aid in lube dispersal.

We started with a discarded 396ci block that had been sitting around for years. Before any machine work was performed, the cylinder-bore diameters were measured to determine if they had been over-bored previously. Since the block’s condition was questionable, we had it acid-dipped and Magnafluxed to expose any cracks. The casting marks identify this as a “pass. perf.” 396 (denoting passenger car, high performance), and the canister-style oil filter mount indicates mid-’60s vintage. Examine the area around the starter mounting-pad for cracks. If necessary, it’s possible to repair small chips using a brazing rod and a carbon rod and then retapping the starter mounting holes.

Since we’re taking our 396 0.030-inch oversize, each cylinder was bored 0.025-inch over and then honed the remaining 0.005 inch, using several steps with progressively finer stones.. This is called Plateau-honing. The cylinder diameter is measured with a bore gauge.

It is essential that all of the main journal saddles share the same axis. If they don’t, excessive friction can result at the main bearings. This can cause a drag that will diminish power output and wear the bearings prematurely. Even if each main saddle measures to the proper specification, there’s no guarantee that they all line up with each other. Align-honing mildly machines the main saddles simultaneously with a common bar, thus making certain that all saddles are aligned. Prior to starting this operation, tap and clean all main-cap bolt-holes. A flat file is used on the surface where the caps sit to deburr this area.

Here’s a tip: Prior to align-honing, we bolted a cutaway oil pump on so that the rear main cap would take the shape it will be in when the engine is assembled. If the rear main cap is machined without it, the distortion that results from tightening the oil pump later on can pull the cap out of round.

Surfacing, or square-decking, the engine block often illustrates the lack of precision on an OEM factory casting. Here the block is located off the main saddles to ensure equal dimensions from deck to deck and front to rear. Equal deck heights and equal combustion chambers will improve peak performance.

When your block is returned from a machine shop, check to see if the top edge of each cylinder has been chamfered (machined to a slight radius or 45-degree step) rather than displaying a sharp 90-degree edge. A conical stone chamfers and deburrs the edge of the cylinder, making installation of the pistons easier.

During the honing phase, a torque plate should be bolted to the block to simulate the distortion that occurs when the cylinder head is torqued down. This operation guarantees that the cylinder bores will be perfectly round when the engine is assembled. If the bores are honed without a torque plate, the distortion that occurs when the head is installed can pull the bores out of round, compromising the piston ring seal.

A balance card records the weight of the rotating assembly—the crank, the rods, and the pistons with rings and bearings are measured in grams. All parts are balanced to within half a gram, or roughly the weight of a dollar bill.

The lightest piston sets the weight that every other piston must match, since material is never added to a piston during the balancing process, only removed. Material is removed from the wrist pin lugs where it will not impair the overall strength of the piston. Not only are the total weights of each rod matched, but so is the weight of each end of each rod. This is accomplished by grinding material from the pad at each end. Before the crankshaft is balanced, bob weights filled with lead shot to match the weights of the reciprocating components (pistons, rods, rings, etc.) are added to each throw.

Camshaft bearings have small oil holes that must align with the oil feed holes in the cam bearing journals. It’s easy to misalign the bearings, which would result in an oiling deficiency that would likely destroy the camshaft during the first few seconds after initial firing. Make sure all cam-bearing oil holes line up completely with the corresponding feed holes.

The end of the crankshaft is marked with a reference point to help identify where it’s out of balance during the spin process. A strobe light will freeze the mark when the imbalance is straight up.

Most quality camshafts kits, like our Edelbrock Performer, include break-in lube, usually in paste form. We used a liquid moly lube on the cam bearing journals. Once the cam is in place (but prior to installing the lifters), it’s important to rotate the cam. When everything is installed properly it should rotate freely.

A.

B.
Crankshaft assembly begins with a thorough cleaning in the solvent tank. Run a bore brush into the chamfered oil passages, then double-check the journal size (A). It’s also a good idea to torque the main caps to the block and measure the journal diameters (B).

Bearing surfaces can be finessed with a well-worn Scotchbrite pad. Use a quality lube or racing oil on bearing surfaces during assembly. Do not use a common grease that might trap dirt or grit.

A torque wrench set at 100 lb-ft takes the Chevy big-block main bolts to proper torque. Not all engines are the same. Check your engine’s specs for the proper torque setting.

Before proceeding, we check the crankshaft endplay using a dial indicator—0.003 to 0.007 inch is the acceptable range for this big-block.

Before installing the pistons we check the ring gap—0.004-inch per inch of bore is a general assembly guideline for proper ring gap.

There’s no tool like a quality piston and ring installation tool—it will facilitate piston installation and prevent damage to the rings.

Here’s a Top 10 Assembly Tip—Drill a 0.040-inch hole in the front oil galley plug that threads into the front of the engine block to duplicate the factory plugs. The small hole allows air to escape from the lifter galley, and it allows engine oil to lubricate the timing chain and gears.

We’ve pointed out the keyways on the crankshaft timing gear to enhance visibility. Performance timing sets often have multiple keyways to allow cam timing adjustment. For our street performance engine, we’ll use the standard “straight up” marks. It’s a good idea to use a little Loctite on the cam gear fasteners.

The degree wheel is installed to verify the positioning of the cam in reference to the crankshaft. Some builders will use the wheel to alter the cam timing, but for our application, the cam manufacturer’s specs should work well.

The thrust button on the end of the cam is used to keep the cam from walking—moving fore and aft in its journals. Excessive cam movement can change the distributor timing and rob your engine of power. A dial indicator at the rear cam bearing measures the amount of endplay after test-fitting the cam button and timing cover.

With the timing chain cover and oil pan in place, turn the crankshaft through several cycles to make sure there is no interference. This is especially important when a stroker motor is assembled, as the longer stroke places the connecting rods closer to the oil pan rails. Occasionally it is necessary to grind extra clearance reliefs in the oil-pan rails of the block, and the oil pan may also need massaging. Our stock-stroke 396 had no clearance issues.

Making massive amounts of horsepower and building a marathon motor aren’t always compatible goals, but many of the basic machine processes and engine building techniques for the two are the same. Regardless of the brand you prefer, exacting machine work and assembly are crucial to the success of the project.

We’ve combined precision machine work with a host of aftermarket speed equipment for an engine that will offer spirited performance and reliability over a long period. Few novice builders can perform their own machine work, but we’ll show you what to look for when a professional shop, like Carco Engine and Machine, does it. Most important is the machine work on the rotating assembly that will reduce friction and wear on cylinder walls and bearings. We’ve also included a variety of proven aftermarket items that enhance performance and increase longevity.

The 396ci Chevy big-block and crankshaft we used were salvaged some time ago, but they still have excellent potential. Follow along as we present the machine prep and buildup of our 396 and demonstrate some affordable and time-honored engine building techniques.