What size is the crankshaft bolt on a 350 Chevy?

The crankshaft pulley bolt on a typical Chevy 350 small-block is a 3/4-inch diameter bolt with a 16 threads-per-inch (UNC) pitch, most commonly installed as a Grade 8 fastener about 2.5 to 3 inches long. Exact length can vary by damper design and year, so you should verify the specification for your specific engine.

Understanding the exact bolt size matters because the bolt must seat correctly through the harmonic balancer and into the crankshaft snout to secure the pulley or dampener. Although 3/4-16 UNC is the standard in many Chevy small-block 350 applications, variations exist based on damper type, spacer usage, and production year. Rely on the vehicle’s service manual or OEM dampener spec when in doubt.

Standard size and variations

Below is a quick guide to the typical characteristics of the crankshaft pulley bolt used on most Chevy 350 engines, along with notes on when things might differ.

• Thread size and type: 3/4"-16 UNC bolt, designed for the Chevy small-block’s harmonic balancer interface.


• Common length: roughly 2.5 to 3 inches (about 64 to 76 mm) overall. Some dampers or snout configurations may use slightly shorter (around 2.25–2.75 inches) or slightly longer bolts.


• Material and strength: usually a high-strength bolt such as Grade 8 steel; OEM bolts may be zinc-coated or otherwise finished for corrosion resistance.


• Important caveat: Always confirm the exact length for your particular damper and year. Using the wrong length can prevent proper seating or cause damage to the crankshaft or balancer.

In practice, the bolt’s size is dictated by the damper design and how far the balancer sits from the crankface. If you’re replacing a damaged bolt, using a new Grade 8 3/4"-16 UNC bolt in the typical length range is the safest starting point, and you should consult the service manual for the precise specification for your engine’s year and damper combination.

Installation and verification tips

To ensure you have the correct bolt and installation tolerances, follow these guidance steps before reassembly.

1. Inspect the crank snout and harmonic balancer seating surface for damage and debris.


2. Measure the depth from the balancer face to the end of the threaded portion to confirm the required bolt length for your engine.


3. Use a new bolt (do not reuse stretched fasteners) and apply any original thread locker or lubricant per the service manual.


4. Torque the bolt to the recommended specification for your year/model, then verify the balancer seating with a dial indicator or by ensuring the balancer is flush against the timing cover surface.

Note: Flywheel and flexplate bolts are separate fasteners with their own sizes and torque specs; do not substitute a crankshaft pulley bolt for those applications. Always distinguish between the pulley/damper hardware and flywheel hardware when servicing engine internals.

Verification for your specific engine

Because Chevy small-blocks span several decades and various dampers, your best approach is to confirm the exact bolt size for your particular 350 by consulting:

• The vehicle’s owner’s manual or service manual for the year and damper type.


• OEM damper part number or a reputable aftermarket damper specification sheet.


• Measurements taken from the existing assembly if the manual is unavailable (length and engagement depth) to ensure a proper match.

In short, the most common configuration for a Chevy 350 is a 3/4"-16 UNC Grade 8 bolt around 2.5–3 inches long, but always verify against your exact model and damper setup to avoid fitment issues or damage during service.

Summary

For a standard Chevy 350 small-block, expect a 3/4"-16 UNC, Grade 8 bolt, typically 2.5–3 inches in length, to secure the harmonic balancer/pulley. Length can vary with damper design and year, so always check the specific service manual or damper specification for your engine to ensure the correct fastener is used and torqued to the proper value.

What size bolt for sbc harmonic balancer?

The SBC (Small Block Chevy) harmonic balancer bolt size is 7/16-20 with a fine thread. This bolt size is standard for many SBC engines, including the 280, 305, 350, and 383 models. Various lengths are available, such as 2.250 inches or 2.470 inches, so ensure the length is appropriate for your specific application.
 

• Thread Size: 7/16"-20 fine thread
• Common Lengths: 2.250" or 2.470" (underhead length)
• Material: High-strength alloy steel (Grade 8 or higher) is recommended for performance applications

What size is a crankshaft bolt?

There is no single crankshaft bolt size, as it varies widely by vehicle and engine, but common examples include 15/16 inch (or 33mm) for some older American engines, 1-1/16 inch (12-point) for GM LS engines, and metric sizes like 16mm x 1.5mm for some Honda Accords. The exact size and type (like thread pitch and length) are critical and should be confirmed for your specific application.
 
Common examples

• Ford: 15/16 inch
• GM LS engines: 1-1/16 inch, 12-point socket (M16 x 2.0)
• Honda: 16 x 49mm
• Small-block Chevy: 7/16-20 inch thread, 2.2 inches long, with a 3/4 inch hex head 

How to find the correct size

1. Consult your vehicle's service manual: This is the most accurate source for your specific make and model.
2. Search online for your specific engine: Use search terms like "[Your Year] [Your Engine] crankshaft bolt size."
3. Measure the existing bolt: If you have the old bolt, you can measure its diameter, length, and thread pitch. 
4. Use a socket to find the hex size: Try a standard set of sockets (both metric and standard/SAE) to see which one fits the bolt head. 

What size is the main journal on a 350?

The main journal size for a standard 350 Chevy engine is approximately 2.45 inches in diameter. The rod journals are a smaller 2.10 inches in diameter.
 

• Main journal diameter: 2.452.452.45 inches (62.2362.2362.23 mm)
• Rod journal diameter: 2.102.102.10 inches (53.3453.3453.34 mm)
• Other specifications:
  • Stroke: 3.483.483.48 inches
  • Bore: 4.004.004.00 inches

What size is the crank bolt on a Chevy 350?

The crank bolt for a Chevy 350 is most commonly a 7/16-inch fine thread (7/16−207 / 16 minus 207/16−20), typically 2.25 inches long, with a 6-point hex head. However, the bolt may differ depending on the specific engine and accessories, and some aftermarket or big block applications might use different sizes, like 1/2-20. It's crucial to confirm the size for your specific engine and application before purchasing a replacement. 
Common bolt specifications

• Thread size: 7/16−207 / 16 minus 207/16−20 (fine thread)
• Under-head length: 2.252.252.25 inches
• Head style: 6-point or 12-point hex
• Material: Grade 8 steel is recommended for strength 

This video shows how to remove the crankshaft pulley and harmonic balancer on a Chevy 350: 58sThe Burnout ShowYouTube · May 4, 2023
Important considerations

• Confirm your application: While 7/16−207 / 16 minus 207/16−20 is standard, some applications or aftermarket cranks may use a different thread, such as a 5/85 / 85/8 inch socket size on a larger bolt. Always verify the size for your specific engine. 
• Check accessories: The length of the bolt can vary depending on the number and type of pulleys being used. Aftermarket pulleys, especially aluminum ones, may require a longer bolt. 
• Use the correct tools: A 6-point or 12-point socket is necessary to prevent slipping. Using a specialized harmonic balancer installation tool is recommended for proper and safe installation.