What are checks to be carried out on connecting rod bolts?

Connecting rod bolts are critical fasteners in an engine, and failure can lead to catastrophic engine damage. When working with connecting rod bolts — whether during engine rebuild, inspection, or maintenance — several checks must be performed to ensure their integrity and proper function. Here's a breakdown of the essential checks:

🔧 1. Visual Inspection

Check for signs of wear or damage:

Cracks, nicks, dents, pitting, corrosion, or discoloration (overheating).

Thread condition:

Ensure threads are not stripped, galled, or stretched.

Use a thread chaser or gauge to verify clean and accurate threading.

📏 2. Dimensional Checks

Bolt Stretch / Elongation:

Measure the bolt's length before and after torquing. If the bolt has stretched beyond specification, it must be replaced.

Compare with manufacturer specs for acceptable elongation.

Shank diameter:

Check for uneven wear or thinning.

Use a micrometer to confirm dimensions.

🧪 3. Torque and Torque-to-Yield (TTY) Considerations

Check tightening method:

Some bolts are torque-to-yield (TTY) and must be replaced after each use.

Compare torque values:

Ensure correct torque specs from the manufacturer are being used.

Improper torque can lead to bolt failure or bearing damage.

🔍 4. Magnetic Particle Inspection (MPI) or Dye Penetrant Test (for critical applications)

Use non-destructive testing methods to detect subsurface cracks, especially in high-performance or race engines.

🧰 5. Fitment Check

Bolt fit into the rod and cap:

Ensure bolts fit snugly and seat properly.

Loose bolts can indicate rod distortion or wear.

  Most important point is shank diameter and elongation/length of bolt.