Why Upgrade to a Forged Crankshaft?

Swapping a factory cast crank for a forged crankshaft in your Nashville engine is one of the most consequential bottom-end upgrades you can make. Forged steel crankshafts are significantly stronger and more fatigue-resistant than cast iron units, allowing your engine to handle higher cylinder pressures, elevated rpm, and forced induction without bending or breaking. The forging process aligns the metal grain structure along the crank's contours, creating a part that can withstand substantially more stress than a cast equivalent. For any build targeting north of 600 horsepower, or if you plan to spin your engine past 7,000 rpm consistently, a forged crank is not optional—it’s mandatory for reliability.

This guide walks through the entire installation process for a Nashville engine platform, covering preparation, removal of the old crank, proper installation technique, reassembly, and the critical break-in procedure. The information applies to most V8 and inline configurations used in Nashville builds, though always cross-reference with your engine’s specific service manual.

Tools and Parts Required

Before you begin, gather everything you need. Having the right tools on hand prevents frustrating interruptions and ensures every step is done to spec.

Essential Parts

  • Forged crankshaft – Select a unit from a reputable manufacturer (e.g., Callies, Eagle, Lunati, or K1) that matches your engine’s stroke, journal size, and balancer register. Confirm the crank is designed for your specific Nashville engine family.
  • Main bearing set – Use high-quality tri-metal bearings (King, Clevite, or ACL). Avoid economy bearings in a high-stress build.
  • Thrust bearing – Many forged cranks require a specific thrust bearing width; verify with your crank manufacturer.
  • Rear main seal – Use the seal type recommended for your block (one-piece or two-piece). Consider upgrading to a premium PTFE or Viton seal.
  • Timing gear set – If replacing the crank gear, ensure it’s compatible with the keyway size on the new crank.
  • Harmonic balancer – A new or correctly sized balancer matched to your crank snout is essential.
  • ARP main studs or bolts – Forged cranks often require ARP fasteners for proper clamping force. Do not reuse old torque-to-yield bolts.
  • Engine assembly lube – Use a dedicated break-in lube with high moly content (e.g., Comp Cams, Red Line, or Lucas).
  • Sealant and gaskets – High-quality RTV sealant (The Right Stuff or Permatex ultra black) and a complete gasket set.
  • PlastiGauge – For verifying main bearing oil clearance.

Tool List

  • Socket set (deep and shallow) and combination wrenches (metric and SAE, depending on engine)
  • Engine hoist or stand (the engine should be out of the vehicle for this job)
  • Torque wrench with range up to 150 ft-lbs, calibrated within the last 6 months
  • Dial bore gauge or micrometer set (0–4 inches) for checking journals and bearing bores
  • PlastiGauge kit (0.001–0.003 inch range)
  • Pry bar or crank turning tool
  • Dead-blow hammer (plastic or brass)
  • Cleaning supplies: brake cleaner, lint-free shop towels, plastic scraper
  • Feeler gauges
  • Engine assembly stand (360° rotation is ideal)
  • Service manual for your specific Nashville engine

Preparation Before Installation

Preparation is the difference between a smooth install and a nightmare. Take your time here.

Workspace Setup

Set up your workspace in a clean, well-lit area. Cover the floor with cardboard or plastic sheeting to absorb drips. Organize your tools on a magnetic tray or pegboard so you’re not hunting for socket sizes. If you’re working in a Nashville winter, give yourself time for parts to come to room temperature before measuring clearances—thermal expansion can throw off your readings.

Engine Removal

For most Nashville engine builds, you’ll need to pull the engine from the vehicle. Disconnect the battery (negative terminal first), drain the oil and coolant, and remove any accessories blocking access to the bellhousing bolts. Follow your service manual for the exact removal sequence. Once the engine is on a stand, strip it down to a short block: remove cylinder heads, oil pan, timing cover, and front accessory drive. This gives you unobstructed access to the crankshaft.

Inspect the Block and All Parts

Before you so much as loosen a main cap, inspect everything. Look for cracks in the main bearing webs, especially around the thrust bearing area. Check the oil passages for debris or sludge. If the block hasn’t been cleaned in a hot tank or with a pressure washer, now is the time. A single piece of casting flash can ruin a main bearing in minutes.

Inspect the new forged crankshaft out of the box. Check each journal for nicks or burrs. If you see any, lightly dress them with a fine India stone. Measure each journal diameter with a micrometer and record the values—you’ll need them for clearance checks.

Removing the Old Crankshaft

With the engine stripped down, removal is straightforward, but you need to pay close attention to orientation and cleanliness.

Disassembly Steps

  1. Remove the harmonic balancer bolt and balancer using a puller. Do not pry on the balancer—you can damage the crank snout.
  2. Unbolt the timing cover and remove it. Note the position of the timing chain and gears; if you’re reusing them, mark the chain orientation.
  3. Remove the oil pump and pickup tube.
  4. Unbolt the main caps. Use a marker to number each cap and its corresponding bolt location (e.g., “1,” “2,” etc.)—caps are not interchangeable.
  5. Tap the main caps loose with a dead-blow hammer if they’re stuck. Do not pry between the cap and block.
  6. Lift out the old crankshaft. If it fights you, check that you haven’t missed a bolt or that the timing gear isn’t hung up on the keyway.
  7. Remove the main bearings from the block and caps. Keep them in order in case you need to reference wear patterns.

Crankcase Cleaning

Once the old crank is out, thoroughly clean the crankcase. Scrape off any old gasket material. Wipe down all surfaces with brake cleaner and a lint-free towel. Blow out every oil passage with compressed air. Do this twice. Any debris left behind will circulate through your new bearings and can cause failure within the first 30 seconds of startup.

Measuring and Setting Main Bearing Clearances

This step separates a professional build from an amateur one. Improper oil clearance is the #1 cause of forged crank failure.

Check Main Bore Alignment

Install the main caps (without bearings) and torque them to spec. Use a dial bore gauge to check that the main bores are round and aligned. Maximum allowable out-of-round is typically 0.001 inch. If your block is distorted, you may need align-honing before proceeding.

PlastiGauge Procedure

  1. Place the main bearings into the block and caps. Ensure the tangs are seated correctly. Do not use assembly lube yet.
  2. Lay the new forged crankshaft into the block (clean and dry).
  3. Place a strip of PlastiGauge across each main journal, parallel to the crank centerline.
  4. Install the main caps with bearings (finger-tight, then torque to spec in the correct sequence).
  5. Remove the caps and measure the flattened PlastiGauge against the scale on the package. Target clearance is typically 0.0020–0.0025 inches for street/strip builds. For forced induction or high-rpm use, 0.0025–0.0030 inches may be appropriate.

If clearance is too tight, you may need different bearing shells (e.g., go from standard to +0.001 inch undersize). If clearance is too loose, you can move to a thicker bearing shell or consider align-honing the block. Never attempt to set clearance by mixing bearing halves from different sets.

Journal Inspection

While the crank is out, run a micrometer over every rod and main journal. Check for taper and out-of-round. Forged cranks from top manufacturers should be within 0.0005 inch of spec, but it pays to verify. If your crank is out of spec, return it before installation.

Installing the Forged Crankshaft

With clearances verified and everything surgically clean, you can proceed to final installation.

Pre-Lubrication

Liberally apply engine assembly lube to all main bearing shells (both block and cap sides). Cover the entire surface of each shell. Do not skip this step—dry startup will destroy bearings immediately. Also coat the thrust bearing flange surfaces. Apply lube to the main journals on the crankshaft itself.

Lowering the Crank

Lower the forged crankshaft into the block carefully. If the stroke is longer than factory, double-check that the connecting rods (once installed) will clear the block windows. Rotate the crank a few degrees to seat the bearings. The crank should spin freely with little resistance at this point.

Thrust Bearing Alignment

Align the thrust bearing surfaces so they are centered on the crank thrust face. After torquing the main caps, use a feeler gauge to measure crankshaft end-play. Spec is usually 0.004–0.008 inches. If it’s too tight, the thrust bearing is misaligned; loosen the caps and re-center. Too much end-play may require a different thrust bearing or crank machining.

Torque Main Caps

Install main caps in their correct positions and orientations (arrows pointing toward the front of the engine, if marked). Use new ARP main studs or bolts lubed with ARP Ultra-Torque. Tighten in three stages following the factory or fastener manufacturer’s torque sequence: typically 30 ft-lbs, then 60 ft-lbs, then final torque (often 80–100 ft-lbs for ARP studs). Use a degree wheel if the fasteners call for angle-torque. After final torque, rotate the crank again. It should still turn freely without binding. If it feels tight, stop and investigate—do not force it.

Reassembling the Engine

With the crank installed and clearances confirmed, you can reassemble the bottom end and surrounding systems.

Rear Main Seal Installation

Install the rear main seal according to your engine type. For one-piece seals, lubricate the lip and press it in evenly using a seal driver. For two-piece seals, the upper half goes into the block and the lower half into the cap. Apply a thin bead of RTV at the seams where the cap meets the block to prevent oil leaks. Do not over-tighten the cap or you’ll pinch the seal.

Timing Gear and Chain

Install the timing gear on the crank snout. Ensure the keyway is fully seated and the gear slides on by hand—if you need a hammer, the keyway or bore is wrong. Use the timing marks on the gears to align the cam and crank sprockets. Install the timing chain and adjust tensioner if applicable. Torque the cam bolt to spec.

Oil Pump and Pan

Install the oil pump with a new pickup tube. The pickup screen should sit about ¼ to ⅜ inch from the bottom of the oil pan. Pack the oil pump with assembly lube or petroleum jelly to ensure prime (never use grease—it can block passages). Install the oil pan with a new gasket and RTV at the corners where the timing cover meets the block. Torque the pan bolts in a crisscross pattern to prevent warping.

Pistons and Connecting Rods

With the crank installed, you can now install the piston/rod assemblies. Ensure the rod bearings are the correct size for your crank journals and that the rods are clocked correctly (bearing tangs on the same side). Torque the rod bolts in stages with the proper lubricant. After each rod is installed, rotate the crank to verify free movement.

Final Steps Before Startup

Clean and Inspect Again

Before closing up the top end, wipe down everything one more time. Check for any tools, rags, or debris in the lifter valley or behind the timing cover. This is not paranoia—forgotten objects in an engine cause catastrophic failure.

Prime the Oil System

Use a primer tool (or a drill with a priming shaft) to pressurize the oil system before ever turning the key. Spin the pump until you see oil at every rocker arm or top-end oil point. This step ensures the main bearings and rod bearings have oil immediately on startup, preventing galling.

Install Cylinder Heads and Accessories

Install the cylinder heads with new head gaskets, torqued to spec in the correct sequence. Reinstall the intake manifold, timing cover (if not already done), water pump, harmonic balancer, and belts. Torque the balancer bolt to the manufacturer’s specification (often 200+ ft-lbs for large V8s).

Refill Fluids

Fill the engine with break-in oil (high-zinc, high-phosphorus conventional oil, not synthetic). Fill the coolant system with a 50/50 mix of distilled water and ethylene glycol antifreeze. Do not use tap water—minerals can deposit in cooling passages.

Break-In and Testing Procedure

The first 20 minutes of engine operation are critical for a forged crankshaft. The bearings and crank journals must seat properly under load.

Initial Start

Connect a mechanical oil pressure gauge directly to a port near the filter (do not rely on the dash gauge). Crank the engine with the ignition disabled until you see oil pressure, then enable the ignition and start. Bring the engine up to 2,000–2,500 rpm immediately. Do not let it idle. Vary the rpm between 2,000 and 3,000 for the first 20 minutes. Watch for oil pressure (should be 50–70 psi cold), coolant temperature, and any unusual noises. If you hear knocking, shut it down immediately and investigate.

Initial Inspection

After the first 20-minute break-in, shut the engine off. Check for oil leaks at the rear main, timing cover, oil pan, and oil filter. Check coolant level. Let the engine cool completely, then re-torque the cylinder heads (if the manufacturer requires it) and check valve lash.

Test Drive

For the first 500 miles, avoid sustained high-rpm operation and wide-open throttle. Vary engine speed frequently. Change the oil and filter at 500 miles, then again at 1,500 miles. After the second oil change, you can switch to a high-quality synthetic oil if desired. A forged crank does not require extended break-in beyond this point, but the bearings do need time to fully seat.

Common Pitfalls to Avoid

  • Skipping clearance checks – Assuming a new forged crank will fit without checking clearances is a fast track to spun bearings. Always measure.
  • Ignoring thrust bearing alignment – An incorrectly centered thrust bearing will fail within minutes, often taking out the entire bottom end.
  • Insufficient lubrication during assembly – Assembly lube is not optional. Use it generously on every bearing surface.
  • Reusing old fasteners – Main bolts are often torque-to-yield and should never be reused. Even studs should be replaced if they show signs of fatigue or corrosion.
  • Neglecting oil priming – Starting a fresh engine without oil pressure can cause bearing damage in under two seconds. Always prime the system first.

Maintenance After Installation

Once the break-in is complete, maintain your engine with these practices to maximize the life of your forged crankshaft:

  • Use a high-quality oil filter (Wix XP, Mobil 1, or Royal Purple) and change oil every 3,000–5,000 miles for street use, or after every race day for competition.
  • Monitor oil pressure regularly. A sudden drop can indicate bearing wear.
  • Avoid extended idling, which can cause oil film breakdown on bearing surfaces.
  • Keep the engine properly warmed up before high-rpm operation.
  • Use a vibration damper matched to your crank and engine rpm range. A mismatched balancer can induce harmonic fatigue that cracks the crank over time.

Additional Resources

For deeper technical detail, consult these industry references:

Conclusion

Installing a forged crankshaft in your Nashville engine is a substantial upgrade that delivers real, measurable gains in strength and reliability. The process demands patience, precision, and attention to detail—particularly when it comes to bearing clearance and thrust alignment. But the payoff is an engine that can handle significantly more power and rpm without bottom-end failure. Take your time with each step, reference your service manual for torque specs and sequences, and never cut corners on cleanliness or lubrication. A correctly installed forged crank will provide tens of thousands of miles of trouble-free performance in your Nashville build.