Some BMW engines require the use of Torque-To-Yield (TTY) bolts, which are designed to stretch during the torque process. Torque sequencing of all cylinder heads is non-sequential, and usually hemispherical. The sequencing allows even distribution of pressure on the head gasket during the tightening process. Proper torque strength of cylinder head bolts ensures the gasket is evenly secured to the engine and helps prevent costly part failures. New cylinder head gaskets are recommended each time the cylinder head is removed.
Things You'll Need
- Socket wrench
- Torx-head sockets
- Torque wrench
Replace any TTY bolts used to secure the cylinder head to the engine. TTY bolts previously used will have stretched threads, even if the stretching is not visible to the eye. The re-use of TTY bolts might result in failure of the bolt during operation.
Determine the torque specifications for your specific engine. Torque specifications measure the rotation force required to secure the bolt in place. Rotational force is measured in foot-pounds (also known as Newton-meters). You will need a torque wrench to correctly tighten the bolts to the specified value.
Use Torx-head sockets when applicable. Some BMW engines utilize Torx-head 6-star pattern bolts. Torx drivers are commonly available in automotive parts and hardware stores.
Tighten each bolt in the correct order. The tightening order is referred to as the "Torque sequencing." Torque sequencing includes the order in which the bolts are tightened. It also includes the rotation force required to secure the bolt in place as well as the specific steps required between the tightening sequences. Some BMW engines require 15 minutes of engine warming followed by a re-tightening to specification. Engines might also require a specific amount of time before a re-check is performed. Torque specifications for the M-series engines are provided in the "Resources" section.
Tips & Warnings
- Do not lubricate bolts prior to or during the tightening process. Lubricated bolts allow greater torque to be applied than is measured by the torque wrench. Overtightened bolts might result in thread, bolt, or gasket failure during operation of the vehicle.
- Photo Credit Scott Olson/Getty Images News/Getty Images
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