In addition to head gaskets, head screws play a fundamental role in the perfect sealing of an engine system. An incorrect torque, an incorrect tightening sequence or even the reuse of screws that have already been torqued can result in a defect in the system's sealing, causing major problems for your engine.

SPAAL cylinder head screws | DYNAMIC follows all manufacturer standards and specifications, both in the materials used and their classification.

Identifying a Screw:

Stress strain curve

Types of grips:

Torque-only tightening:

Torque tightening is recommended for screws that only undergo elastic deformation during and after torque, that is, these screws elongate when torque is applied and return to their initial condition when the torque on them is removed. It is worth mentioning that there are almost no engines in Brazil that use screws that work only in the elastic region at the junctions between the head and block.

Tightening elastic screws requires that only deformation occurs within the elastic zone - with tension lower than its yield stress - thus not allowing permanent deformation of the screw. Elastic screws can be torqued to the specified tension using a simple torque wrench.

Tightening by torque angle

Torque angle tightening is specified for applications where the indicated tension is higher than the yield stress of the steel used in the screw. In these applications, deformation differs from elastic because after loosening the screw, it does not return to its initial state, stretching permanently.

The tightening of these screws known as “plastic” are precisely sized to work within the plastic region of deformation. The sizing of this tightening is done to achieve maximum efficiency of the screw without it breaking. When the screw works with this type of tightening, it loses memory of its initial length, making it impossible to reuse it after loosening.

Aiming for greater efficiency of these critical components, practically all cylinder head screws are originally sized and manufactured to work beyond the elastic region, undergoing permanent stretching. These screws must be torqued with a torque wrench until they reach flow, and with a tool that allows control of the tightening angle so that they reach the necessary elongation within the plastic region.

Attention: The torque sequence is as important as the specified torque value. Always use the correct torque sequence and torque values specified in our Light Line and Heavy Line torque table available by clicking here or described on the label of our head gaskets.



Screw head types

Screw class

Do you know what the numbers engraved on each screw mean (8.8, 10.9 and 12.9)?