Cylinder Head Bolt Torque Specificationsby Tony Oldhand
A crucial component of engine building is setting the torque on head bolts. Torque refers to how tight a bolt should be. When setting the torque, reliance on the specifications set by design engineers is vital. One essential tool you must have is a good quality torque wrench. Without one, you are like a ship without a compass at sea.
Internal combustion engines run the gamut from small handheld model airplane units to large ship engines. For head bolts, no "one size fits all" approach to the torque specifications applies. One technical manual at Brigham Young University states that you must follow the manufacturer's instructions. This is absolutely essential, since you can destroy the engine if you do not follow instructions to the letter. You must have a good quality torque wrench--and know how to use it--to accomplish this task.
In the instruction manual, a torque sequence is specified. You must adhere to this. Torque sequence refers ro the pattern in which you tighten the bolts. The overall goal is to spread the torque evenly as you are tightening the bolts. Usually, you start at one bolt, and you work your way around in a circular pattern. Doing so ensures that your head won't be warped during the tightening sequence.
The manufacturer usually stipulates that you must tighten the bolts in incremental steps. For example, suppose the final torque on a bolt is 40 foot-lbs. The manufacturer may state to bring all the bolts to 10 foot-lbs. first, following the torque sequence. In the second step, bring the torque to 20 foot-lbs. In the third step, bring it up to 40 foot-lbs. Bringing the torque up in incremental steps prevents head warping as well.
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