What should be put on cylinder head bolts when installing?

• A. Lock-tite
• B. Dielectric grease
• C. Install dry
• D. Install with a thin film of engine oil

Answer: (D)

Torque-based clamping relies on proper thread lubrication to convert the applied torque into the correct clamping force. A thin film of engine oil on the cylinder head bolts reduces thread friction so the torque you apply corresponds to the intended clamp on the head. This helps prevent over- or under-tightening and avoids galling or binding on the threads. Using a locking compound would alter the friction and distort the torque-to-clamp relationship, dielectric grease isn’t for fasteners, and installing dry increases friction, throwing off the desired clamp. So the best practice is to install with a thin film of engine oil.