BMW i8 2014-2020 Drivetrain Bolt Torque Specifications & Fastener Values
BMW i8 2014-2020

BMW i8 2014-2020 Drivetrain Bolt Torque Specifications

Comprehensive list of drivetrain bolt torque specifications for the 2014-2020 BMW i8 (I12/I15) including transmission, differential, and axle fasteners.

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

Flywheel And Clutch

Torque specifications for components directly related to the flywheel and clutch assembly which are essential for transferring power from the engine to the transmission. This section includes critical fasteners that must be torqued correctly for reliable power transfer.

1

Flywheel Bolts

M12 x 1.25
Torque Value
48 ft-lbs (65 N·m)
Important Notes
Tighten bolts in a star pattern to ensure even clamping pressure. It is recommended to use new bolts.
2

Clutch Pressure Plate Bolts

M8 x 1.25
Torque Value
23 ft-lbs (31 N·m)
Important Notes
Tighten bolts in a star pattern to ensure even clamping pressure. Ensure clutch disc is properly aligned before torquing. Estimated value, refer to manufacturer's specific torque spec for your clutch model.

Transmission

Torque specifications for components directly related to the transmission assembly, including mounting to the engine, oil pan, and access plugs. Correct torque values in this section are crucial to prevent leaks and damage, and ensure the transmission operates correctly.

1

Transmission Bellhousing Bolts

M10 x 1.5
Torque Value
37 ft-lbs (50 N·m)
Important Notes
Tighten the bellhousing bolts in a crisscross pattern to ensure even clamping. Ensure proper alignment of the bellhousing and engine block.
2

Transmission Mounting Bolts

M12 x 1.75
Torque Value
37 ft-lbs (50 N·m)
Important Notes
Ensure proper alignment before tightening to prevent any stress on the mounts.
3

Transmission Oil Pan Bolts

M6 x 1.0
Torque Value
7 ft-lbs (10 N·m)
Important Notes
Use a crisscross pattern to tighten the oil pan bolts. Over-tightening can cause leaks. Use a new gasket when reassembling.
4

Transmission Drain and Fill Plugs

M18 x 1.5
Torque Value
37 ft-lbs (50 N·m)
Important Notes
Use new sealing washers or O-rings to ensure a leak-proof seal. Do not over-tighten to prevent damaging the housing.

Driveshaft And Axles

Torque specifications for components related to the driveshaft, axles, and CV joints that transfer power from the transmission to the wheels. Proper torque values are crucial for safe operation and the prevention of vibrations and component failure.

1

Drive Axle/Half Shaft Bolts

M10 x 1.5
Torque Value
74 ft-lbs (100 N·m)
Important Notes
Ensure proper alignment of the axle to the transmission flange or hub before tightening the bolts. Tighten in a star pattern.
2

CV Joint/Axle Nut

M24 x 1.5
Torque Value
180 ft-lbs (244 N·m)
Important Notes
This nut is critical for wheel bearing preload. Always use a new nut when reassembling. This is a high torque fastener.
3

Propeller/Drive Shaft Bolts

M10 x 1.5
Torque Value
37 ft-lbs (50 N·m)
Important Notes
Tighten the bolts in a star pattern to ensure even clamping pressure. Ensure proper driveshaft alignment.

Differential

Torque specifications for components related to the differential, which transmits power to the rear wheels and adjusts for wheel speed differences during turning. Proper torque values are critical to ensure the differential operates correctly and does not leak.

1

Differential Drain/Fill Plug

M18 x 1.5
Torque Value
37 ft-lbs (50 N·m)
Important Notes
Use new sealing washers or O-rings to ensure a leak-proof seal. Do not over-tighten to prevent damaging the housing.
2

Differential Mounting Bolts

M12 x 1.75
Torque Value
74 ft-lbs (100 N·m)
Important Notes
Ensure proper alignment of the differential to the chassis or subframe before tightening the bolts. Some mounts may need shimming for correct alignment.

Starter Motor

Torque specifications for the starter motor mounting bolts. While not directly involved in ongoing power transfer, the starter is essential for initiating engine operation. Correct torque ensures the starter is securely mounted and functions reliably.

1

Starter Motor Mounting Bolts

M10 x 1.5
Torque Value
37 ft-lbs (50 N·m)
Important Notes
Ensure the starter motor is aligned correctly with the engine block. Do not over-tighten these 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

Why is using the correct torque specification so important?

Using the correct torque specification is crucial to ensure the bolts hold the drivetrain components together with the appropriate clamping force. Under-torquing can lead to loosening, joint failure, and potential component damage or separation. Over-torquing can stretch or weaken the bolt, leading to failure and damage to the threads and mating surfaces. Both scenarios can cause drivetrain malfunctions, potential accidents, and costly repairs. Imagine a driveshaft bolt coming loose mid-drive; the consequences could be severe.

Q2

What happens if I don't have a torque wrench?

While a torque wrench is the ideal tool for accurate tightening, you should not attempt to guess torque values. If you absolutely must proceed without one, be extremely cautious and make sure to tighten all bolts consistently, but still try to find a professional who can do the job with the required tools as soon as possible. Improper tightening without a torque wrench can damage the vehicle and can void any warranty.

Q3

Can I reuse drivetrain bolts on my BMW i8?

Generally, it's highly recommended to replace drivetrain bolts, particularly those used in critical areas like the transmission and differential, whenever they are removed. These bolts can stretch upon tightening, rendering them unreliable for reuse. Reusing them can lead to improper clamping force and potential failure. While some bolts *might* be reusable, always refer to the official BMW service manual for specific guidance, and when in doubt, replace them with new bolts of the correct specification. Some bolts are one time use.

Q4

How often should I check the torque on my i8's drivetrain bolts?

It's recommended to check the torque on drivetrain bolts during regular maintenance intervals or any time the drivetrain has been disassembled and reassembled. Specifically, a good time to check is after any work that requires removing or loosening any drivetrain component such as a transmission service or replacement of suspension components which might impact the drivetrain. Follow BMW's maintenance schedule in your owner's manual as a starting point, and consider checking more frequently if you drive aggressively or expose the car to severe conditions (like track days).

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 (1/2" Drive)

A calibrated torque wrench is essential for applying precise torque to drivetrain bolts. A 1/2" drive is suitable for most fasteners found on the BMW i8 drivetrain.

  • Wide torque range
  • Audible click when torque is reached
  • Calibration certificate recommended
Learn more

Torque Wrench (3/8" Drive)

A smaller 3/8" drive torque wrench is useful for lower torque specifications on smaller components of the drivetrain.

  • Precise torque application for smaller bolts
  • Good for limited access areas
  • Calibration certificate recommended
Learn more

Socket Set (Metric)

A comprehensive set of metric sockets is required to fit the various bolt heads within the drivetrain assembly.

  • Wide range of socket sizes
  • 6-point and 12-point options
  • Durable construction
Learn more

Extension Bars

Extension bars are needed to access recessed bolts or bolts located in tight spaces within the drivetrain assembly.

  • Various lengths available
  • Secure connection to sockets
  • Made from hardened steel
Learn more

Universal Joint Adapter

A universal joint adapter allows access to bolts at angles, which is common in drivetrain assemblies.

  • Flexibility in access angles
  • Durable construction
  • Provides reliable torque transfer
Learn more
Service Procedures

Rear Differential Bolt Torque Check and Tightening

Procedure for inspecting and tightening the bolts securing the rear differential to the chassis and subframe on the BMW i8.

  • Locate all the rear differential mounting bolts.
  • Using the appropriate socket, check the torque of each bolt against the specified values.
  • If any bolt is below the torque specification, carefully tighten it to the correct torque setting.
  • Re-check all bolts to ensure proper torque.
  • Note any loose or damaged bolts, and replace as necessary.
View full procedure

Front Electric Motor Mount Bolt Torque Procedure

Procedure for tightening the bolts that secure the front electric motor to the chassis or subframe. This requires specific torque specifications for both the motor and it's mounting plate.

  • Locate all the electric motor mount bolts and plate bolts.
  • Use a 3/8" torque wrench to torque the smaller plate mounting bolts to spec.
  • Use the 1/2" torque wrench to apply torque to the main motor mounting bolts per specification
  • Double check the torque values and ensure all bolts are properly tightened.
  • Verify alignment of motor after tightening.
View full procedure

Driveshaft and Axle Bolt Torque Specifications

Guidance for proper torqueing of the bolts that secure the driveshafts to the differential or wheels.

  • Identify the bolts that connect the driveshaft to the differential and wheel hubs
  • Use the appropriate size socket to check torque values.
  • Using the appropriate torque wrenches and extensions as necessary, tighten to spec.
  • Ensure no bolts are damaged or stripped, replacing any necessary hardware.
View full procedure
Technical Service Bulletins

Driveshaft Bolt Loosening Issues

2017-03-15

Certain 2014-2017 BMW i8 models may experience loosening of the driveshaft bolts due to improper initial torque application and bolt stretching.

2014-2017

Resolution: Replace all driveshaft bolts with new, updated bolts and torque to the new specified torque using the torque-angle method.

Rear Differential Mounting Bolt Inspection

2018-11-20

A technical bulletin recommending periodic inspection of the rear differential mounting bolts for signs of loosening or damage.

2014-2020

Resolution: Inspect rear differential bolts every 15,000 miles or at annual services. Replace any damaged or suspect bolts and torque all bolts to the specified values.

Front Motor Mounting Plate Bolt Update

2019-05-01

A revised mounting bolt and torque specification was released for the front electric motor plate bolts due to stress cracks.

2014-2019

Resolution: Replace original mounting plate bolts with updated part number and torque to updated specifications, following correct tightening sequence.

About the Author

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Alan Montanye - Automotive Technical Specialist
ASE

Alan Montanye

Automotive Technical Specialist

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