When installing cylinder head bolts, what is the recommended lubricant application?

• A. A thin film of engine oil
• B. Dry
• C. Lock-tite
• D. Dielectric grease

Answer: (A)

The main idea is to control friction so the torque you apply translates to the correct clamping force. A light film of engine oil on the bolt threads (and under the bolt head) provides a consistent friction level, allowing the torque specification to produce the intended clamp for the cylinder head. If you go dry, friction is higher, which can throw off the torque reading and compromise the clamping. Using a threadlocker or dielectric grease changes the friction or is meant for electrical components, and isn’t appropriate for head bolts. So a thin film of engine oil is the proper method.