BMW Crankshaft Crank Bolt 11231709037

( Manufacturer Part Number: 1231709037 ), ( Part Type: Crankshaft Crank Bolt ), ( Manufacturer Warranty: 1 Month ), ( Items Included: Bolts ), ( Material: Steel ), ( Vintage Part: Yes ), ( Performance Part: No )

Review BMW Crankshaft Crank Bolt fits E21 E12 E30 E34 E28

The **BMW 1231709037 crankshaft bolt** is a precision-engineered fastener specifically designed for the iconic E21, E12, E30, E34, and E28 series BMW engines, ensuring optimal performance, reliability, and longevity in high-stress applications. This critical component plays a pivotal role in maintaining the structural integrity of the crankshaft assembly, which is the heart of the engine, converting linear piston motion into rotational force. Manufactured to BMW s exacting specifications, this bolt is forged from high-grade alloy steel, treated with a proprietary heat-treating process to achieve an optimal balance of strength, durability, and resistance to fatigue and corrosion. The bolt features a **11mm nominal diameter** with a **1.5 pitch thread**, designed to withstand the immense torsional forces generated during engine operation, particularly under heavy loads, high RPM, or extreme temperatures. Its **torque-to-yield specification** ensures that it remains securely fastened without risking overtightening, which could lead to thread stripping or bolt failure a critical consideration in performance and turbocharged applications where engine stress is significantly elevated.

The **1231709037** part number denotes its compatibility across multiple BMW engine variants, including the **M10, M20, M40, M50, and M52** families, making it a versatile choice for restorers, tuners, and mechanics working on classic and modern BMWs alike. The bolt s design incorporates a **fine-pitch thread** for precise engagement with the crankshaft s mating surface, reducing the risk of loosening under vibration, a common issue in high-performance or modified engines. Additionally, the bolt is often paired with **BMW s proprietary locking compound or a torque-to-yield washer** (such as the **1231709038** or **1231709039** variants) to further enhance security and prevent loosening over time. For applications requiring enhanced corrosion resistance, some aftermarket alternatives may feature a **black oxide or zinc plating**, though the original BMW specification typically calls for a **natural or lightly passivated finish** to maintain optimal friction characteristics during installation.

When installing this crankshaft bolt, adherence to BMW s **torque specifications** (typically **100 120 Nm or 74 89 ft-lbs**, depending on the engine variant) is essential to prevent under- or overtightening. Improper torque can lead to catastrophic engine failure, as the crankshaft bolts are subjected to extreme cyclic loading during operation. For engines with higher displacement or forced induction, it is advisable to use **high-quality aftermarket bolts** from reputable manufacturers that meet or exceed BMW s original specifications, as these may incorporate additional safety features like **torque-to-yield properties** or **enhanced thread coatings** for improved longevity. Whether used in a **restoration project, engine rebuild, or performance upgrade**, this crankshaft bolt is a cornerstone of engine reliability, ensuring that the crankshaft remains securely assembled and the engine operates with the precision and efficiency BMW engines are renowned for.

### **Analysis of BMW Crankshaft Bolt (Part Number 11231709037) for E21, E12, E30, E34, and E28 Engines**

#### **Overview**

The part number **11231709037** refers to a **crankshaft bolt** (also known as a **main bearing cap bolt**) designed for several BMW engine variants, including:

- **E21 (M10/M11 engines, e.g., 2002, 2002ti, 2002t)**

- **E12 (M10/M11 engines, e.g., 2002, 2002ti)**

- **E30 (M10/M11/M50/M52 engines, e.g., 318i, 320i, 325i, 328i, 518i, 520i, 525i, 530i)**

- **E34 (M50/M52/M54 engines, e.g., 520i, 525i, 530i, 730i, 740i)**

- **E28 (M20/M50/M52 engines, e.g., 635CSi, 635i, 735i, 740i)**

These bolts are critical components that secure the **main bearing caps** to the crankshaft, ensuring proper engine alignment and preventing catastrophic failure if loose or damaged.

---

### **Pros of Buying This Part**

1. **OEM Quality and Fitment**

- BMW s original crankshaft bolts are **high-strength, precision-machined** components designed to meet strict torque specifications.

- They are **compatible with multiple engine variants** (M10, M11, M50, M52), making them a versatile choice for restorations or replacements.

- Using OEM bolts ensures **proper fitment** without the risk of cross-threading or improper seating.

2. **Reliability and Durability**

- These bolts are made from **high-grade steel** and are **heat-treated** for strength, reducing the risk of stretch or failure over time.

- Unlike aftermarket alternatives, OEM bolts are **not prone to premature wear**, which is critical in high-performance or heavily modified engines.

3. **Torque Specifications and Safety**

- BMW specifies **strict torque values** (typically **50-60 Nm** for M10/M11, **80-90 Nm** for M50/M52) to prevent overtightening or undertightening.

- Using the correct bolt ensures **even clamping force**, preventing **main bearing cap rotation** or **crankshaft misalignment**, which can lead to **seizures or catastrophic engine failure**.

4. **Ease of Availability**

- As an **OEM part**, it is widely available from **BMW dealerships, authorized distributors, and reputable aftermarket suppliers**.

- Replacement bolts are **not overly expensive** compared to full engine rebuilds, making them a cost-effective solution for maintenance.

5. **Prevents Common Engine Issues**

- **Main bearing wear**

- **Crankshaft misalignment**

- **Engine seizures**

- **Premature engine failure**

- Replacing worn or damaged bolts **prevents these issues**, extending the engine s lifespan.

6. **Compatibility with Retro or Modified Engines**

- Many **restoration projects** (e.g., E30 325i, E28 635CSi) require OEM bolts for **stock performance** or **high-mileage reliability**.

- Even in **modified engines**, using OEM bolts (with proper torque) ensures **structural integrity**.

---

### **Cons of Buying This Part**

1. **Cost Compared to Aftermarket Alternatives**

- OEM crankshaft bolts are **more expensive** than generic aftermarket bolts (e.g., **AC Delco, ACDelco, or generic high-strength bolts**).

- However, the **savings from avoiding engine damage** often justify the cost.

2. **Potential for Counterfeit or Low-Quality Parts**

- Some **eBay, Amazon, or unscrupulous sellers** may offer **fake OEM bolts** that do not meet BMW s specifications.

- **Risk of purchasing substandard bolts** that could fail under load.

- **Solution:** Purchase from **authorized BMW dealers, reputable distributors (e.g., RockAuto, BMW Parts USA), or trusted aftermarket suppliers (e.g., Fel-Pro, Mann Filter).**

3. **Torque Specifications Must Be Strictly Followed**

- **Overtightening** can **strip threads** or **deform the bolt head**.

- **Undertightening** can lead to **loose caps and engine damage**.

- Requires **a torque wrench** and **proper technique** (e.g., **staggered tightening sequence**).

4. **Limited Lifespan in High-Performance or Modified Engines**

- While OEM bolts are strong, **extreme modifications (forced induction, nitrous, high RPM tuning)** may require **aftermarket high-performance bolts** (e.g., **ARP, Mucoff, or EBC bolts**) for additional strength.

- **Stock bolts may not handle extreme stress** in **turbocharged or supercharged engines**.

5. **Replacement Requires Disassembly**

- Accessing crankshaft bolts requires **removing the engine cover, oil pan, and possibly the timing cover**, which is a **labor-intensive job**.

- **Not a quick fix** requires **mechanical skill** or professional help.

6. **Potential for Bolt Stretch Over Time**

- While rare, **high-mileage engines** may experience **bolt stretch**, reducing clamping force.

- **Solution:** Check torque **periodically** (especially in **high-mileage or modified engines**).

---

### **Comparison with Aftermarket Alternatives**

**Factor** **OEM Crankshaft Bolt (11231709037)** **Aftermarket High-Strength Bolt**

-------------------------- -------------------------------- --------------------------------

**Cost** Higher ( $10 $20 each) Lower ( $3 $8 each)

**Quality & Fitment** Perfect fit, OEM specs May vary (some are good)

**Strength** Sufficient for stock/modded Some exceed OEM (e.g., ARP)

**Availability** Widely available More options (but quality varies)

**Risk of Counterfeit** Possible if bought from unreliable sources Higher risk with cheap brands

**Best For** Stock restorations, high-mileage High-performance, turbocharged

---

### **Conclusion & Recommendation**

#### **When to Buy OEM (11231709037)**

- **Stock or high-mileage engines** (e.g., E30 325i, E28 635i) where **reliability and fitment** are critical.

- **Restoration projects** where **authentic parts** are desired.

- **Engines with moderate modifications** (e.g., mild tuning, stock turbo) where **OEM specs are sufficient**.

- **When purchasing from a trusted source** (BMW dealer, authorized distributor) to avoid counterfeits.

#### **When to Consider Aftermarket Alternatives**

- **High-performance or turbocharged engines** where **extra strength** is needed (e.g., **ARP, Mucoff, or EBC bolts**).

- **Budget-conscious buyers** who are **willing to verify quality** (e.g., **Fel-Pro or Mann Filter bolts**).

- **Engines with known bolt stretch issues** (e.g., **M50/M52 in high-mileage cars**), where **high-strength aftermarket bolts** may be preferable.

#### **Final Recommendation**

For **most E21, E12, E30, E34, and E28 owners** with **stock or mildly modified engines**, the **OEM crankshaft bolt (11231709037) is the best choice** due to:

**Guaranteed fitment and reliability**

**Proper torque specifications**

**Prevents engine damage from loose bolts**

**Widely trusted in restoration and classic BMW communities**

**However**, if the engine is **heavily modified (turbocharged, nitrous, high RPM tuning)**, **aftermarket high-performance bolts** (e.g., **ARP or Mucoff**) should be considered for **additional strength and safety**.

- **Buy from an authorized BMW parts dealer** or a **reputable online retailer** (e.g., **RockAuto, BMW Parts USA, eBay with verified seller ratings**).

- **Always check for authenticity** (e.g., **BMW part number stamping, correct thread pitch**).

- **Follow BMW s torque specifications** (use a **digital

Details:

Pulled from a 1991 E30 325e with 190k miles on it.

part #: 1231709037 prices

• $14.95-$52.16

specifications cranshafengin:

• for models: E21, E12, E30, E34, E28
• for makes: Bmw
• mpn: 1231709037
• part type: Crankshaft Crank Bolt
• manufacturer warranty: 1 Month
• items included: Bolts
• material: Steel
• vintage part: Yes
• performance part: No

returns cranshafengin:

• policy: No Returns

offer cranshafengin:

• best offers: True
• quantity: 1
• sold: 0
• started: February 12, 2026
• availability: In Stock
• options: Ship-to-home

shipping cranshafengin:

• type: Fixed
• cost: $9.95
• class: Standard
• carrier: USPS
• transit: 5-11 Days
• service: USPS Ground Advantage

payments cranshafengin:

• wallet: Apple-pay
• credit card: Visa
• other

seller cranshafengin:

• city: Denver, Colorado
• # reviews: 33
• rating: 97.1%

general cranshafengin:

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

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