OLDSMOBILE 12353406 Harmonic Balancer Crankshaft Pulley Bolt Olds 3.8L

( Brand: Oldsmobile ), ( Manufacturer Part Number: 12353406 ), ( Part Type: Balancer Crankshaft Bolt ), ( Id: 235271c7-24c4-48bd-8475-babbcf668118 ), ( Interchange: 309-406b ), ( Partout Id: A-129790841 )

Review OLDSMOBILE Olds Harmonic Balancer Crankshaft Pulley Bolt Oem 3.8l fits 1986–1988

The **1986 1988 Oldsmobile 3.8L V6 Harmonic Balancer Crankshaft Pulley Bolt (Part #12353406)** is a precision-engineered fastener designed to secure the harmonic balancer assembly to the front of the engine s crankshaft pulley, ensuring smooth operation and optimal power transfer in the iconic L36 V6 powerplant. This bolt is critical for maintaining proper alignment and tension within the drivetrain, preventing excessive vibration, premature wear, and potential catastrophic failure of the harmonic balancer a component that absorbs engine torque fluctuations to enhance ride comfort and longevity. Crafted from high-strength, heat-treated alloy steel, the bolt is engineered to withstand the high torque loads and cyclic stress inherent in high-performance applications, including both stock and modified versions of the 3.8L engine found in vehicles like the Cutlass Supreme, Omega, and Regency. Its **M12 x 1.5 pitch thread** and **1.25-inch shank diameter** ensure a secure, interference-fit connection with the pulley s mounting flange, while its **fine-tuned preload specification** (typically around **80 100 ft-lbs of torque**) is essential for preventing loosening under vibration, a common issue in older GM V6 engines. This bolt is not interchangeable with aftermarket or generic replacements, as its precise dimensions and material properties are tailored to the original Oldsmobile design, which incorporates a **split-pin locking feature** or **tooth-locking mechanism** in the pulley hub to prevent rotation and ensure a permanent, vibration-resistant seal. For restoration projects or performance builds, sourcing an authentic **OEM 12353406 bolt** is recommended to avoid compatibility issues, as aftermarket alternatives may lack the necessary torque retention or dimensional accuracy, leading to premature failure or drivetrain misalignment. Proper installation requires the use of a **torque wrench** and a **split-pin tool** (if applicable) to secure the bolt in place, followed by a final check of the harmonic balancer s balance and the engine s overall drivetrain alignment. Whether replacing a worn bolt in a classic Oldsmobile or ensuring reliability in a rebuilt engine, this component is a small but indispensable part of maintaining the integrity of one of the most enduring and beloved V6 powerplants of the late 1980s.

### Pros and Cons of Buying a 1986-1988 Oldsmobile 3.8L Harmonic Balancer/Crankshaft Pulley Bolt (Part Number 12353406)

1. **Direct Fitment** The part is designed specifically for the 3.8L V6 engine found in 1986 1988 Oldsmobile models (e.g., Cutlass Supreme, 98, Calais). This ensures compatibility without modification, reducing the risk of installation issues.

2. **Reliability for the Application** Harmonic balancers and crankshaft pulley bolts are critical components that prevent excessive vibration and ensure smooth engine operation. A genuine or high-quality aftermarket part can prevent catastrophic engine damage from a failed balancer or loose bolt.

3. **Prevents Costly Repairs** A worn or cracked harmonic balancer can lead to engine damage if it shatters, while a loose crankshaft bolt can cause misalignment or even engine failure. Replacing this part proactively can save thousands in potential repairs.

4. **Ease of Installation** These parts are relatively straightforward to replace, especially if you have basic mechanical skills. Most require only a socket wrench, a new bolt, and possibly a torque wrench to ensure proper tightening.

5. **Availability of Genuine vs. Aftermarket Options** While genuine OEM parts may be harder to find, reputable aftermarket suppliers (e.g., Moroso, Fel-Pro, or local auto parts stores) offer compatible alternatives at a lower cost without sacrificing quality.

6. **Long-Term Engine Protection** A well-maintained harmonic balancer and properly torqued crankshaft bolt contribute to smoother engine performance and longevity, especially in high-mileage vehicles.

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1. **Age and Wear of the Part** Even if the part itself is new, the threads in the crankshaft or engine block may be worn or stripped over time. If the bolt was previously loose or the threads are damaged, the new bolt may not provide a secure fit, leading to future issues.

2. **Potential for Counterfeit or Low-Quality Parts** Purchasing from untrusted sellers (e.g., eBay without seller verification, unknown online marketplaces, or salvage yards) risks receiving a fake, reused, or substandard part. This could lead to premature failure or improper fitment.

3. **Cost Considerations** While this part is relatively inexpensive (typically $20 $60 depending on source), the labor cost to replace it (if not DIY) can add up, especially if the engine needs to be removed or additional work is required (e.g., replacing a damaged harmonic balancer).

4. **Limited Lifespan of the Harmonic Balancer** The harmonic balancer itself (not just the bolt) is a wear item. Even if you replace the bolt, the balancer may still be worn out and could fail soon after. If the balancer is cracked or rubberized, it should be replaced entirely for safety.

5. **Difficulty Finding Genuine OEM Parts** Oldsmobile (now part of GM) no longer produces these parts, and genuine OEM bolts/balancers may be discontinued. You may need to source from a salvage yard, GM parts depot (if available), or rely on aftermarket equivalents.

6. **Risk of Over-Tightening or Under-Tightening** If the bolt is torqued incorrectly (either too loose or too tight), it can strip threads or cause stress cracks. Following the manufacturer s torque specification (typically 80 100 ft-lbs for the crankshaft bolt) is critical.

7. **Additional Maintenance Needs** If the harmonic balancer is old, replacing just the bolt may not address underlying issues like a worn flexplate or damaged crankshaft keyway. A full inspection may be necessary to prevent future problems.

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Replacing the harmonic balancer crankshaft pulley bolt (part #12353406) on a 1986 1988 Oldsmobile 3.8L engine is a **practical and cost-effective preventive measure** to avoid engine damage. The bolt is a critical safety component, and its failure can lead to severe consequences. However, the success of the replacement depends on:

- **Source reliability** (prioritize reputable suppliers or salvage yards with verified parts).

- **Condition of the surrounding components** (inspect the harmonic balancer, flexplate, and crankshaft for wear).

- **Proper installation** (follow torque specs and ensure threads are undamaged).

If the harmonic balancer is visibly worn or cracked, it should be replaced alongside the bolt. For DIYers, this is a manageable project, but if unsure, consulting a mechanic is advisable.

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1. **Buy from a Trusted Source** Purchase the part from a well-known auto parts store (e.g., RockAuto, AutoZone, or a local GM dealer parts department) or a salvage yard with a return policy. Avoid unknown online sellers unless they have verified reviews and a warranty.

2. **Inspect the Harmonic Balancer** If the balancer appears cracked, rubberized, or damaged, replace it entirely. A new harmonic balancer (e.g., Moroso #12353406 or equivalent) is a small investment that prevents major engine damage.

3. **Check Threads and Crankshaft Condition** Before installing the new bolt, ensure the crankshaft threads are clean and undamaged. If they are stripped or corroded, consider machining or replacing the crankshaft.

4. **Use the Correct Bolt and Torque Specs** Confirm the bolt is the correct length and thread pitch (typically M12x1.5 or similar). Torque it to **80 100 ft-lbs** (check your service manual for exact specs). Do not reuse the old bolt unless it was never loose.

5. **Consider Professional Help if Needed** If you lack experience with engine work, a mechanic can ensure proper installation, especially if the harmonic balancer or flexplate needs replacement.

6. **Pair with Routine Maintenance** After replacement, monitor the engine for unusual vibrations or noises. Regularly check the harmonic balancer and crankshaft bolt during oil changes to catch issues early.

**Final Verdict:** This is a **worthwhile and necessary replacement** for safety and longevity, provided you source quality parts and address any underlying issues. Skipping this maintenance could lead to expensive repairs down the line.

Details:

Model: OLDS EIGHTY-EIGHT 88. TROFEO 86 rubber and steel, TORONADO INCL. OLDS CIERA 86 6-231 3.8L, rubber and steel. Search for more parts OLDS EIGHTY-EIGHT 88.

part #: 12353406 prices

• $170.00-$200.00

specifications cranshafengin:

• for makes: Olds, Oldsmobile
• for years: 1986-1988
• brand: Oldsmobile
• mpn: 12353406
• part type: Balancer Crankshaft Bolt
• id: 235271c7-24c4-48bd-8475-babbcf668118
• interchange: 309-406b
• partout id: A-129790841

seller cranshafengin:

• # reviews: 16785
• rating: 99.6%
• city: Brush, Colorado

payments cranshafengin:

• wallet: Google-pay
• credit card: Mastercard
• other

general cranshafengin:

• Car Truck Parts Accessories > Engines Engine Parts > Crankshafts
• condition: Used

shipping cranshafengin:

• cost: $0.00
• type: Fixed
• transit: 3-7 Days
• class: Standard
• service: Standard

offer cranshafengin:

• quantity: 1
• sold: 0
• started: May 26, 2026
• options: Ship-to-home
• availability: In Stock

returns cranshafengin:

• time: 30 Days
• paid by: Seller
• policy: Returns Accepted

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