What is the 90 degree tightening method for cylinder head bolts?

First, tighten the torque wrench to the basic torque, eliminate the gap, and unify the starting point.

Rotate the bolt by another 90 ° to induce plastic elongation, resulting in a more stable pre tightening force that is not affected by friction and a more reliable seal.

Most of them are disposable bolts that usually need to be replaced after disassembly and cannot be reused.

Bolts must be new: Plastic deformed bolts must be replaced after disassembly, as old bolts are prone to breakage and insufficient pre tightening force.

The angle must be accurate: 90 ° is the final value, and twisting too much or too little will affect the sealing and strength.

Torque+rotation angle: Do not only look at torque without looking at angle, nor skip the basic torque and directly twist the angle.

Loosening sequence: When disassembling, reverse the tightening sequence and loosen step by step to avoid cylinder head warping. (The bolt tightening sequence shown in the manual)