What is the torque specification for cylinder head bolts in Newton meters?
2 Answers
Cylinder head bolts for the main bearing cap require 8 N·m of torque, while the small bearing cap bolts require 6 N·m. Relevant details about cylinder heads are as follows: 1. Overview: The engine cylinder head is a crucial structural component of an internal combustion engine. It seals the cylinder and forms the combustion chamber. In side-valve engines, the cylinder head is cast with features such as water jackets, inlet/outlet ports, spark plug holes, bolt holes, and the combustion chamber. Overhead-valve engine cylinder heads additionally incorporate valve mechanisms, intake/exhaust passages, and cooling water jackets. 2. Bolts and threaded holes: Friction exists between bolts and their threaded holes, with variations occurring between different bolt-hole pairs. This friction difference becomes more pronounced with reused fasteners. When tightening to the same torque wrench reading, these friction variations result in inconsistent clamping forces. The angle tightening method helps minimize this discrepancy.
Regarding the torque issue of cylinder head bolts, as someone who frequently helps friends with car repairs, I must say there's no fixed value. It depends on your specific car model and engine type. For instance, Japanese and German cars have different designs, resulting in significant variations in tightening torque, typically ranging from 80 to 120 Newton meters. However, the exact value must be checked in the vehicle's repair manual or consulted with a professional technician, as the manual contains precise data. Never tighten by feel—over-tightening can cause bolt breakage or cylinder block cracking, while under-tightening may lead to gasket oil leaks or combustion chamber gas leaks, potentially ruining the entire engine. I've seen cases where improper handling resulted in thousands spent on engine repairs. Therefore, always verify the manual data before starting, and use a torque wrench to gradually tighten in steps to the specified value, ensuring safety and reliability.
