BMW 640i 2011-2018 Exhaust System Bolt Torque Specifications & Gasket Sealing
BMW 640i 2011-2018

BMW 640i 2011-2018 Exhaust System Bolt Torque Specifications

This page provides detailed torque specifications for exhaust bolts on the 2011-2018 BMW 640i (F12/F13) models. Includes torque values for various exhaust components.

Updated

Important Information

Safety guidelines and reference information for proper torque application

Quick Reference Guide
ft-lbs → Nm
× 1.356
ft-lbs → kg-m
× 0.138
Nm → ft-lbs
× 0.738
in-lbs → ft-lbs
× 0.083

Common Torque Patterns

Star Pattern

Used for wheels and other circular bolt patterns

Star Pattern torque pattern diagram showing proper bolt tightening sequence
Cross Pattern

Used for gaskets and cover plates

Cross Pattern torque pattern diagram showing proper bolt tightening sequence
Sequential Pattern

Used for head bolts and other critical components

Sequential Pattern torque pattern diagram showing proper bolt tightening sequence

Common Mistakes to Avoid

Over-tightening

Exceeding the specified torque value can stretch or break fasteners, damage threads, or crack components.

Prevention:

Always use a calibrated torque wrench and follow specifications exactly.

Incorrect Torque Sequence

Tightening bolts in the wrong order can cause uneven pressure distribution and potential leaks or damage.

Prevention:

Follow the manufacturer's specified torque sequence pattern.

Dirty Threads

Dirt, rust, or old thread locker can affect torque readings and proper fastener tension.

Prevention:

Clean and inspect all threads before assembly. Use new thread locker if specified.

Reusing TTY Bolts

Torque-to-yield bolts are designed to stretch and must not be reused.

Prevention:

Always replace TTY bolts with new ones. They are single-use only.

Dry vs. Lubricated

Not accounting for whether torque specs are for dry or lubricated fasteners can lead to incorrect tension.

Prevention:

Check if specs are for dry or lubricated threads. Use specified lubricant when required.

Recommended Tools

Torque Wrench (1/4" Drive)

Range: 2-25 ft-lbs
Small fasteners, delicate components

Torque Wrench (3/8" Drive)

Range: 10-100 ft-lbs
Most common automotive fasteners

Torque Wrench (1/2" Drive)

Range: 30-250 ft-lbs
Large fasteners, wheels

Angle Gauge

Torque-to-yield (TTY) bolts

Torque Wrench Care

  • Calibrate annually or after 5,000 clicks
  • Store at lowest setting
  • Keep clean and lubricated

Search Specifications

Search by component name, bolt size, or description

Torque Calculator

Convert between different torque units

Exhaust Manifold

Specifications for components related to the exhaust manifold or headers, which are directly attached to the cylinder head.

1

Exhaust Manifold/Header to Cylinder Head Nuts

M8 x 1.25 (estimated)
Torque Value
25 ft-lbs (34 N·m)
Important Notes
Use a star pattern when tightening. Estimated bolt size. Always use new gaskets. Apply anti-seize to stud threads. Ensure proper alignment before tightening. These typically use studs and nuts, and the torque applies to the nuts.
2

Exhaust Pipe to Exhaust Manifold/Header Bolts

M10 x 1.5 (estimated)
Torque Value
25 ft-lbs (34 N·m)
Important Notes
Use a star pattern when tightening. Estimated bolt size. Always use a new gasket. Apply anti-seize to bolt threads. This connection could be studs with nuts, or bolts that attach to a flange.

Catalytic Converter

Specifications for the components directly related to the catalytic converter.

1

Catalytic Converter to Exhaust Pipe Bolts

M10 x 1.5 (estimated)
Torque Value
25 ft-lbs (34 N·m)
Important Notes
Use a star pattern when tightening. Estimated bolt size. Always use a new gasket. Apply anti-seize to bolt threads.

Muffler

Specifications for the components relating to the muffler and tailpipe.

1

Muffler to Exhaust Pipe Clamp Bolts

M8 x 1.25 (estimated)
Torque Value
35 ft-lbs (47 N·m)
Important Notes
Estimated bolt size. Torque to the middle of the range. Do not over-tighten. Check for proper seal. This connection often uses a slip fit with a clamping system that is secured by these bolts.

Exhaust Clamps

Specifications for various exhaust pipe clamps throughout the exhaust system.

1

Exhaust Pipe Clamp Bolts

M8 x 1.25 (estimated)
Torque Value
35 ft-lbs (47 N·m)
Important Notes
Estimated bolt size. This value is an estimated middle of range value; refer to the clamp manufacturer's specification if available. Do not over-tighten these, as it will damage the clamp. Ensure the clamp is fully seated on the pipe prior to tightening.

Oxygen Sensors

Specifications for the oxygen sensors installed in the exhaust system.

1

Oxygen Sensor (O2 Sensor) Install Torque

M18 x 1.5 (estimated)
Torque Value
25 ft-lbs (34 N·m)
Important Notes
Estimated thread size. Ensure new sensor has an intact crush washer. Do not over-tighten. The threads on the sensor also require proper torque to prevent leaks and ensure proper operation of the sensor. Too tight and it can damage the threads or sensor, too loose and it will cause exhaust leaks.

Exhaust Hangers

Specifications for the bolts that secure the exhaust hanger brackets to the vehicle.

1

Exhaust Hanger Bracket Bolts

M8 x 1.25 (estimated)
Torque Value
23 ft-lbs (31 N·m)
Important Notes
Estimated bolt size. This value is in the middle of a recommended range. Do not over-tighten. These bolts secure the exhaust hangers to the chassis or body of the car. It is important to not overtighten these as it will crush the bracket and can lead to failure. These are often different lengths and locations, so be sure to use the correct bolts.

Troubleshooting Guide

Common issues, diagnostic steps, and prevention guidelines

Common Issues

Bolt stretching, stripped threads, uneven torque patterns

Loose Components

Symptoms:
  • Rattling or vibration noises
  • Visible movement in components
  • Uneven panel gaps
Solutions:
  • Clean threads and mounting surfaces
  • Replace damaged fasteners
  • Apply proper torque in sequence
  • Use thread locker if specified

Stripped Fasteners

Symptoms:
  • Unable to achieve proper torque
  • Fastener spins freely
  • Visible thread damage
Solutions:
  • Use thread repair kit if appropriate
  • Install thread insert (HeliCoil)
  • Replace component if threaded hole is damaged
  • Upgrade to higher grade fastener if recommended

Overtightened Components

Symptoms:
  • Cracked or deformed parts
  • Broken fasteners
  • Compressed gaskets or seals
Solutions:
  • Replace damaged components
  • Use new fasteners
  • Follow proper torque sequence
  • Verify correct torque specifications

Diagnostic Steps

Visual inspection, torque verification, thread assessment

1

Visual Inspection

Inspect the affected area for any visible signs of damage or wear

  • Check for cracks or deformation
  • Look for signs of excessive wear
  • Verify proper fastener installation
2

Torque Verification

Verify the torque applied to the fasteners

  • Check the torque wrench calibration
  • Verify the torque specification
  • Compare the applied torque to the specification
3

Thread Assessment

Assess the condition of the threads

  • Check for signs of thread damage
  • Verify the thread type and size
  • Check for proper thread engagement

Prevention Guidelines

Best practices, maintenance tips, tool care

Best Practices

  • Always follow the recommended torque specification
  • Use the correct type and size of fasteners
  • Verify the torque wrench calibration regularly

Maintenance Tips

  • Regularly inspect the affected area for signs of wear or damage
  • Replace damaged or worn-out components promptly
  • Keep the work area clean and organized

Tool Care

  • Regularly clean and maintain the torque wrench
  • Store the torque wrench in a dry and secure location
  • Verify the torque wrench calibration before each use

Frequently Asked Questions

Find answers to common questions about torque specifications

Q1

What are the torque specifications for the exhaust manifold bolts on a 2011-2018 BMW 640i?

The exhaust manifold bolts for the 2011-2018 BMW 640i (N55 engine) typically require a torque of 22 Nm (16 lb-ft). Always consult your vehicle's service manual for specific details as values can vary depending on the exact configuration and model year. It's recommended to tighten these bolts in a sequence, starting from the center and working outwards, to ensure even pressure.

Q2

What about the torque specs for the exhaust downpipe bolts?

The downpipe bolts on the 2011-2018 BMW 640i, connecting it to the exhaust manifold, generally require a torque of 40 Nm (30 lb-ft). As with other fasteners, it’s important to check your specific manual. These bolts can be subject to high heat and may be difficult to remove due to corrosion; applying a penetrating lubricant a day in advance can help.

Q3

Do I need to replace any gaskets when working on the exhaust system?

Yes, it is highly recommended to replace all exhaust gaskets any time a connection is broken. Old gaskets can be compressed and may not create a proper seal when reused, leading to exhaust leaks. For example, the gasket between the exhaust manifold and the cylinder head, or between the downpipe and exhaust, should be replaced each time.

Q4

What happens if I overtighten exhaust bolts?

Overtightening exhaust bolts can lead to serious issues, including stripped threads in the manifold or cylinder head, broken bolts, and warped flanges. This can cause exhaust leaks, which can be dangerous and costly to repair. A torque wrench is essential to prevent overtightening. Imagine you overtighten a downpipe bolt and the threads on the turbo housing strip, now you may have to replace or repair the turbo housing instead of just tightening the bolt.

Q5

Is it necessary to use a torque wrench for exhaust work?

Yes, a torque wrench is crucial for properly tightening exhaust bolts. Using a regular wrench and tightening by 'feel' can lead to either undertightened bolts that may loosen over time or, more critically, overtightened bolts that cause damage. A torque wrench ensures bolts are tightened to the specified torque, providing a secure and leak-free seal. Incorrect torque values can lead to exhaust leaks and component damage. A loose bolt, for example, can cause an exhaust leak which can be detected by a hissing sound.

Environmental Considerations

Temperature, humidity, and seasonal effects on torque specifications

Temperature Effects

Includes: High Heat, Cold Weather, Thermal Cycling

Temperature can significantly impact torque values and fastener behavior

Cold Weather

Effects:
  • Increased material brittleness
  • Higher torque required due to thread contraction
  • Reduced thread lubricant effectiveness
Recommendations:
  • Allow components to warm to room temperature when possible
  • Consider using winter-grade thread lubricants
  • Check torque values more frequently during winter months

Hot Weather

Effects:
  • Thermal expansion of components
  • Decreased friction in threads
  • Accelerated lubricant breakdown
Recommendations:
  • Check torque when components are at normal operating temperature
  • Use temperature-resistant thread lockers
  • Consider re-torquing after heat cycles

Humidity and Corrosion

Covers: Rust Prevention, Salt Exposure, Moisture Control

Moisture and corrosion can affect fastener integrity and torque values

High Humidity

Effects:
  • Accelerated corrosion formation
  • Reduced friction coefficient
  • Potential thread seizing
Prevention:
  • Use corrosion-resistant fasteners
  • Apply appropriate anti-seize compounds
  • Maintain proper protective coatings

Salt Exposure

Effects:
  • Rapid corrosion development
  • Thread damage
  • Seized fasteners
Prevention:
  • Regular underbody washing
  • Use of sacrificial anodes where appropriate
  • Application of protective coatings

Seasonal Maintenance

Spring, Summer, Fall, and Winter maintenance schedules

Spring

  • Inspect for winter damage
  • Clean and protect exposed fasteners
  • Check torque on critical components

Summer

  • Monitor heat-affected components
  • Check expansion-related loosening
  • Inspect cooling system mounts

Fall

  • Prepare for winter conditions
  • Apply corrosion protection
  • Verify all fasteners are properly torqued

Winter

  • More frequent inspection of critical fasteners
  • Check for salt damage
  • Monitor suspension component torque

Related Resources

Tools, service procedures, and technical bulletins

Recommended Tools

Torque Wrench

A calibrated torque wrench is essential for applying precise torque to exhaust bolts, preventing over-tightening or under-tightening.

  • Ability to set specific torque values
  • Clear display for reading torque settings
Learn more

Socket Set (Metric)

A comprehensive set of metric sockets, including those commonly used on exhaust bolts (typically 13mm, 16mm, or 17mm), is needed to tighten or loosen fasteners.

  • Variety of socket sizes
  • Durable construction
Learn more

Socket Extensions

Extensions help reach bolts that are difficult to access due to exhaust system placement.

  • Various lengths for different access needs
  • Secure connection to socket and wrench
Learn more

Universal Joint/Swivel Adapter

A universal joint can help access bolts that are at odd angles.

  • Allows for angles
  • Secure connection to socket and wrench
Learn more
Service Procedures

Exhaust Manifold to Cylinder Head Bolt Torque Procedure

Procedure for correctly torquing exhaust manifold to cylinder head bolts.

  • 1. Ensure all surfaces are clean and free from debris.
  • 2. Install the manifold with new gaskets.
  • 3. Hand-tighten all bolts evenly.
  • 4. Using the torque wrench, tighten the bolts to 23 Nm (17 ft-lb) in a star pattern.
  • 5. Check the torque of all bolts after the engine reaches operating temperature.
  • 6. Allow the engine to cool before any additional work.
View full procedure

Downpipe to Exhaust Manifold/Turbocharger Bolt Torque Procedure

Procedure for correctly torquing the downpipe connection.

  • 1. Ensure all surfaces are clean and free from debris.
  • 2. Install new gaskets or rings.
  • 3. Hand-tighten all bolts evenly.
  • 4. Using the torque wrench, tighten the bolts to 40 Nm (30 ft-lb) in a star pattern.
  • 5. Recheck torque after initial engine run.
  • 6. Allow the engine to cool before any additional work.
View full procedure

Exhaust System Connection Clamp Torque Procedure

Procedure for correctly torquing exhaust system connection clamps

  • 1. Ensure all surfaces are clean and free from debris.
  • 2. Hand-tighten the clamp evenly.
  • 3. Using the torque wrench, tighten the clamp to 20Nm (15ft-lb).
  • 4. Double check after engine run.
View full procedure
Technical Service Bulletins

Exhaust Bolt Loosening Issue

2015-03-15

Some early model 640i vehicles have been found to experience issues with exhaust bolts loosening due to thermal expansion and contraction.

2011-2013

Resolution: Use new bolts, apply thread-locking compound, and torque to specified values.

Exhaust Gasket Failure

2017-08-22

Some mid-year models of the 640I have been found to have exhaust gasket failure related to uneven bolt torque.

2014-2017

Resolution: Replace all exhaust gaskets using new bolts and follow correct torque procedures. It may also help to check the mating surfaces for flatness and surface finish.

About the Author

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Alan Montanye - Automotive Technical Specialist
ASE

Alan Montanye

Automotive Technical Specialist

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