Introduction to Refurbishing Detroit Diesel Cylinder Blocks

Refurbishing Detroit Diesel V71 engine cylinder blocks (6V71, 8V71, 12V71, and 16V71) requires precision and adherence to technical specifications. The cylinder block is the main structural component, housing critical engine subassemblies. This guide provides step-by-step instructions for cleaning, inspection, machining, and assembly procedures tailored for machine shops.

Disassembly and Preparation

Preliminary Steps

1. Draining Fluids:
   • Completely drain lubricating oil, coolant, and any remaining fuel.
   • If equipped with a heat exchanger, drain both fresh water and raw water systems.
2. Engine Removal:
   • Secure the engine on an overhaul stand for stability and access.
   • Remove all external subassemblies, including the turbocharger (if equipped), exhaust manifolds, air compressors, and any ancillary equipment.
3. Cylinder Block Disassembly:
   • Remove all air box covers, fuel lines, lubricating oil lines, and electrical connections.
   • Detach the cylinder heads and pistons, keeping all components organized for inspection.

Cleaning Procedures

Thorough cleaning is essential to identify wear or defects. Use the following techniques:

1. Steam Cleaning:
   • Use a steam cleaner to remove heavy grease and dirt from external surfaces.
2. Solvent Tank Cleaning:
   • Immerse the block in a commercial heavy-duty solvent heated to 180-200°F (82-93°C).
   • Rinse with hot water and dry thoroughly with compressed air (maximum 40 psi).
3. Water Passage Descaling:
   • For scaled water jackets, use inhibited phosphoric acid followed by a neutralizing alkaline solution.
4. Rust Prevention:
   • Coat cleaned components with rust-preventive oil if not reassembled immediately.

Inspection Process

Inspect the cylinder block for cracks, wear, and dimensional accuracy. Key areas include:

Visual Inspection

1. Cylinder Bores:
   • Hone lightly to remove glazing.
   • Check for irregular wear patterns or damage.
2. Main Bearing Supports:
   • Verify alignment and ensure no visible damage or wear.
3. Oil and Coolant Passages:
   • Ensure all passages are clear and free of debris.

Dimensional Measurements

Use precise measuring tools such as dial bore gauges and micrometers to assess:

1. Cylinder Bore Diameter:
   • Measure at multiple positions (top, middle, and bottom) and angles (transverse and longitudinal).
   • Standard bore diameter: 4.6256–4.6275 inches.
2. Main Bearing Bore Alignment:
   • Ensure longitudinal alignment within 0.001 inches.
3. Counterbores:
   • Check depth and ensure it falls within the range of 0.4770–0.4795 inches.
4. Flatness of Deck Surface:
   • Maximum allowable warpage: 0.003 inches (transverse) and 0.006–0.009 inches (longitudinal, depending on engine model).

Pressure Testing

Pressure test the block for cracks or leaks:

1. Method A (Immersion):
   • Seal water inlets and outlets.
   • Submerge in 180°-200°F water and apply 40 psi of air pressure.
   • Observe for bubbles indicating leaks.
2. Method B (On-Engine):
   • Use a mixture of water and antifreeze in the water jacket.
   • Maintain 40 psi pressure for 2 hours and inspect for leaks in all accessible areas.

Machining and Repairs

Cylinder Bores

1. Honing:
   • Use 120-grit stones to achieve a smooth finish suitable for proper liner-to-block contact.
   • Maintain bore roundness and taper within 0.002 inches.
2. Boring Oversized Liners:
   • If required, bore to oversize specifications listed in the manual. Install oversized liners with a specified liner-to-block clearance of 0.000–0.0015 inches for new parts.

Deck Surface

1. Machining:
   • Correct warpage by removing no more than 0.008 inches of material.
   • Recheck all seal ring and counterbore depths after machining.

Main Bearing Bores

1. Line Boring:
   • If out of alignment, line bore to ensure proper crankshaft installation.

Crack Repairs

1. Welding:
   • Small cracks may be repaired using welding methods specified for cast iron.
   • Post-weld heat treatment is mandatory to prevent further stress.

Assembly and Testing

Preassembly Steps

1. Lubrication:
   • Coat all threaded holes, plugs, and fittings with pipe sealer.
2. Component Preparation:
   • Reinspect and clean all parts. Use new seals, gaskets, and hardware as required.

Installation

1. Liner Installation:
   • Position liners using appropriate tools to prevent distortion.
2. Torque Specifications:
   • Follow precise torque values for bolts and caps as outlined in the manual.
3. Final Assembly:
   • Install all subassemblies, ensuring proper alignment and fit.

Post-Assembly Testing

1. Dynamometer Test:
   • Run the engine under load conditions to verify functionality and seal integrity.
2. Final Inspection:
   • Check for leaks, noise, and proper operation before returning the engine to service.

Conclusion

Refurbishing a Detroit Diesel V71 cylinder block demands attention to detail and adherence to specifications. By following this guide, machine shops can ensure high-quality results that maximize engine performance and longevity.