View Single Post
  #8  
Old 09-06-2011, 10:55 PM
cn90 cn90 is offline
Officially Welcomed to the 'Fest
Location: Omaha NE
 
Join Date: Mar 2006
Posts: 12,832
Mein Auto: 1998 528i 5-sp 140K+
Quote:
Originally Posted by dvsgene View Post
...Typically, I see that only when a crush washer or something is involved (like a spark plug). Why not just specify a straight 60Nm instead of 30Nm with a twist unless there is something that moves during the final tightening.
Car mfgs use this technique all the time: torque to ___ Nm, then turn another 45, or 60, or 90, or 120 degrees. It is a common procedure for Torque-to-yield (TTY) bolts such as cylinder head etc.


---------
http://www.cdxetextbook.com/toolsEqu...torqgauge.html

Quote:
Originally Posted by cdxetextbook.com
Summary
Vehicle manufacturers specify torque values for certain fasteners. This is to make sure that fasteners are not over- or under-tightened. The torque wrench is used to apply a specified amount of torque to a fastener. The torque angle gauge is used to make sure there is equal tightness of fasteners on a component. The objective of this procedure is to show you how to use a torque angle gauge in conjunction with a torque wrench.

------------
http://www.aa1car.com/library/torque_wrench.htm

Quote:
Originally Posted by aa1car.com
TTY Head Bolts Usually Require Special Procedures

Many late model engines have "Torque to Yield" (TTY) head bolts that are designed to stretch slightly when tightened. The torque specifications for these bolts often involve extra procedures, such as gradually tightening down the bolts in steps until a certain torque value is reached, then giving the bolt and extra twist (specified in number of degrees) to achieve its final load.

For these kinds of applications, you will need an extra tool called an Angle Gauge (see photo below) or an electronic torque wrench that can also measure the degrees of rotation as a fastener is being tightened. If you are using an angle gauge, mount it on the end of your torque wrench. Zero the pointer, then note how many degrees you have rotated the fastener as you are turning it.

For example, a specification might say to tighten down the head bolts in three incremental steps, going from 15 to 30 to 45 ft.-lbs., then giving each bolt a 1/4 turn (90 degrees) to achieve the final load

Last edited by cn90; 09-06-2011 at 11:00 PM.
Reply With Quote