Shim Adjustment in the Caterpillar 3306 Engine

[MikePhua]

The Legacy of the 3306 Diesel Platform
The Caterpillar 3306 engine is one of the most widely deployed heavy-duty diesel engines in the world. Introduced in the 1970s as a successor to the 3304, the 3306 quickly became a staple in construction equipment, trucks, marine vessels, and generators. With a displacement of 10.5 liters, inline-six configuration, and bore-stroke dimensions of 120.65 mm × 152.4 mm, it offered a balance of torque, reliability, and serviceability. Caterpillar, founded in 1925, built its reputation on engines like the 3306, which powered everything from graders to drilling rigs across six continents.
Over the decades, millions of 3306 units were sold globally, and many remain in service today. Their mechanical simplicity and modular design make them ideal candidates for rebuilds and long-term fleet use.
Terminology Note

• Cylinder Liner: A replaceable sleeve inserted into the engine block to form the cylinder bore.
  
• Shim: A thin metal spacer used to adjust the height or position of a component.
  
• Counterbore: A recessed area in the engine block where the liner flange seats.
  
• Liner Protrusion: The amount the liner flange extends above the deck surface of the block, critical for head gasket sealing.
  

Why Shim Adjustment Matters
In the 3306 engine, cylinder liner protrusion is a critical parameter that affects head gasket sealing, combustion chamber integrity, and long-term durability. If the liner sits too low, combustion gases can leak past the gasket, leading to overheating, loss of compression, and coolant intrusion. If it sits too high, the head may not seat properly, causing warping or uneven torque distribution.
To achieve correct protrusion, shims are placed beneath the liner flange in the counterbore. These shims come in various thicknesses and allow precise adjustment without machining the block. According to AERA technical guidance, the target protrusion range is 0.0013 to 0.0069 inches (0.033 to 0.175 mm), with no more than 0.002 inches (0.050 mm) variation between adjacent liners.
Measuring and Selecting Shims
Before installing shims:

• Clean the counterbore thoroughly to remove carbon and corrosion
  
• Measure the depth at four points using a dial gauge
  
• Average the readings and compare against the liner flange thickness
  
• Select shim thickness to achieve desired protrusion
  

Available shim sizes typically include:

• 0.003 inch (0.076 mm)
  
• 0.005 inch (0.127 mm)
  
• 0.010 inch (0.254 mm)
  
• 0.015 inch (0.381 mm)
  
• 0.020 inch (0.508 mm)
  

In a rebuild shop in Ohio, a technician discovered that one liner sat 0.004 inches lower than the others due to a worn counterbore. By installing a 0.010-inch shim, he restored uniform protrusion and avoided head gasket failure during break-in.
Installation Tips and Common Pitfalls
When installing shims:

• Use a light coat of assembly lube to hold shims in place
  
• Avoid stacking more than two shims per liner to reduce movement risk
  
• Torque the liner clamp evenly to seat the flange
  
• Recheck protrusion after installation
  

Common mistakes include:

• Failing to clean the counterbore, leading to false measurements
  
• Using damaged or bent shims
  
• Ignoring adjacent liner height variation
  
• Overlooking block warpage
  

A rebuild in Australia failed due to uneven liner heights caused by improper shim selection. The head gasket blew after 50 hours of operation, requiring a full teardown and re-machining of the block.
Machining Alternatives and Counterbore Repair
If protrusion cannot be corrected with shims alone, machining the counterbore is an option. This involves:

• Cutting the counterbore to a uniform depth
  
• Installing repair sleeves if the bore is oversized
  
• Rechecking liner fit and protrusion
  

Machining should be done with precision equipment and verified using micrometers and dial indicators. A mining operation in Chile invested in a portable counterbore cutter and reduced engine rebuild time by 30%, improving fleet uptime.
Field Experience and Operator Stories
A logging crew in British Columbia rebuilt a 3306 powering their skidder. They used shims to correct liner protrusion and documented each measurement. After 2,000 hours, the engine showed no signs of gasket wear or combustion leakage.
Meanwhile, a marine technician in Florida rebuilt a 3306 for a tugboat. He discovered that salt corrosion had eroded one counterbore. By machining and shimming the liner, he restored proper sealing and avoided costly downtime during hurricane season.
Conclusion
Shim adjustment in the Caterpillar 3306 engine is a vital step in ensuring long-term reliability and performance. Whether rebuilding in a shop or repairing in the field, precise measurement and careful shim selection can prevent head gasket failures, combustion leaks, and premature wear. With millions of 3306 engines still in service, mastering this technique remains essential for diesel technicians and rebuilders worldwide.