Engine assembly depends on fasteners producing the correct clamping force. That depends on two things: using a bolt of the right strength, and tightening it the right way. Gasket leaks, warped covers and stripped threads are often traced back to fasteners rather than the gasket or part itself.
Reading SAE (Inch) Bolt Markings
SAE bolts are identified by radial lines on the head:
- No marks: Grade 2 — low strength, not suitable for most engine applications.
- 3 lines: Grade 5 — medium strength, common in general automotive use.
- 6 lines: Grade 8 — high strength, used where higher clamp load is required.
Reading Metric Bolt Markings
Metric bolts are stamped with a property class number on the head:
- 8.8: comparable in use to SAE Grade 5.
- 10.9: comparable in use to SAE Grade 8.
- 12.9: very high strength, often used in critical internal applications.
Always replace a bolt with one of the same grade or class, length and thread pitch. A lower-grade bolt can stretch or break; a bolt that is too long can bottom out in a blind hole and give a false torque reading.
Torque Basics
- Clean threads: chase threads in the block and head and clean bolt threads. Dirt, rust and old sealant absorb torque and reduce clamp load.
- Follow the lubrication spec: torque values are given for dry, oiled or specially lubricated threads. Using oil or moly lube on a bolt specified dry can over-tighten it significantly.
- Sealant on bolts into coolant: bolts that enter water jackets usually require thread sealant to prevent seepage.
- Tightening sequence: follow the specified sequence and steps for heads, manifolds, oil pans and covers to clamp the gasket evenly.
- Torque-angle and TTY bolts: follow the torque-plus-angle procedure exactly and replace torque-to-yield bolts as specified.
- Calibrated tools: use an accurate torque wrench, and use an in-lb wrench for small cover bolts that are easy to over-tighten.
Why It Matters for Gaskets
Gaskets are designed to seal at a specific clamping load. Too little load and the joint leaks; too much and the gasket can be crushed, a cover can distort or threads can pull out of aluminum. Correct fasteners and torque are part of every good seal.
Evergreen Gaskets
Every Evergreen gasket is engineered with Eversealed Technologies, matching the sealing material to each engine application. Use the Evergreen eCatalog to find the right gasket set for your engine. Browse Evergreen head bolt sets.
