Development of Plastic Region Tightening Cylinder Head Bolts for New Diesel Engine

In developing the new 2.0-liter and 2-2-liter diesel engines, the plastic region tightening method was applied to the cylinder head bolts, with the following factors taken into consideration:

1. (1)
   Ease of precise fastening at expected preload
2. (2)
   Reliability against fatigue fracture
3. (3)
   Resistance to delayed fracture
4. (4)
   Reusability

This paper describes the effects on these factors of bolt form, i.e., thread length, shank diameter and threaded shank, heat treatment after or before thread rolling, and tensile strength.

Discussed also are reliable specifications based on the preload, gas pressure, and the load due to thermal expansion of the aluminum alloy cylinder head.