Disassembly Of Cylinder Head and Valves For Detroit Diesel 71 Series Inline Engines (271, 371, 471, 671)

October 28, 2024

Disassembly Of Cylinder Head and Valves For Detroit Diesel 71 Series Inline Engines (271, 371, 471, 671)

Detroit Diesel 671 Loaded Cylinder Head
Detroit Diesel 671 Loaded Cylinder Head

The cylinder head is one of the most critical components in the engine. It houses the valves and, in some cases, the injectors, and is responsible for controlling air intake, exhaust gases, and combustion pressure. Proper disassembly of the cylinder head and valves is essential for routine maintenance, repairs, or a full overhaul. This procedure must be done carefully to avoid damaging the head, valves, or block.

Safety Precautions:

  1. Use Lifting Assistance for Heavy Cylinder Heads:
    • Cylinder heads can be very heavy, especially when they include additional components like valves, rocker arms, and injectors. Use a hoist, engine lift, or seek assistance to avoid injury or damage to the head during removal.
  2. Wear Protective Gear:
    • Always wear gloves and safety goggles when working around the cylinder head to protect your hands from sharp edges and your eyes from debris or coolant.
  3. Cool the Engine Completely:
    • Make sure the engine is fully cooled before beginning work on the cylinder head. A hot engine can lead to burns, warping of the head, or improper torque readings during disassembly.

Disassembly Steps:

  1. Disconnect All External Components:
    • Before removing the cylinder head, you need to disconnect several key components:
      • Fuel Lines: Disconnect the fuel lines leading to the injectors, if equipped. Be sure to relieve fuel system pressure beforehand, as outlined in the Fuel Lines section, and cap the fuel ports to avoid contamination.
      • Air Intake and Exhaust Manifold: Remove the air intake piping and exhaust manifold from the head. Refer to the Exhaust Manifold section for detailed instructions.
      • Coolant System: Drain the coolant and disconnect any coolant lines connected to the cylinder head to prevent coolant from spilling during disassembly.
  2. Loosen the Cylinder Head Bolts:
    • The cylinder head is secured to the engine block with a set of bolts. These bolts must be loosened in a specific sequence to avoid warping the head or damaging the engine block.
    • Procedure:
      • Start by loosening the bolts from the outer edges and work your way toward the center in a criss-cross pattern. This ensures even pressure release.
      • Loosen the bolts gradually. Avoid removing one bolt completely while others are still tight. This helps prevent warping or cracking the head.
      • Use a torque wrench to ensure you loosen the bolts evenly, starting with just a partial turn on each bolt before fully removing them.
  3. Lift the Cylinder Head:
    • Once all the bolts are fully loosened, use an engine hoist or lifting assistance to carefully lift the cylinder head off the engine block. Be sure to lift it evenly to avoid damaging the head or gasket surface.
    • Tip: If the cylinder head is stuck due to old gaskets or sealants, gently tap it free with a rubber mallet. Avoid prying it loose with metal tools, as this can gouge or scratch the mating surfaces.
    • Handle with Care: The cylinder head is a precision component. Once removed, place it on a clean, padded surface to avoid damaging the sealing surface or the valves.
  4. Inspect the Cylinder Head and Gaskets:
    • With the head removed, inspect the gasket for signs of wear, corrosion, or leaks. If the gasket shows signs of failure, it will need to be replaced. Common signs include:
      • Blowouts: Gasket material missing between the cylinders or coolant passages indicates a failed gasket.
      • Oil or Coolant Leaks: Evidence of oil or coolant escaping through the gasket can be seen as discoloration or residue around the gasket area.
    • Check for Warping: Use a straightedge to check if the cylinder head is warped. Place the straightedge across multiple points on the head’s mating surface and use feeler gauges to measure any gaps. If the warping exceeds manufacturer specifications, the head may need to be machined.
  5. Remove the Valves and Valve Springs:
    • Once the cylinder head is off, you can begin disassembling the valves for inspection or replacement.
    • Valve Spring Removal:
      Detroit Diesel 71 Series Spring
      Detroit Diesel 71 Series Spring
      • Use a valve spring compressor to compress the valve springs and remove the retaining keepers. Be careful, as the springs are under tension and can fly off if not handled properly.
      • After compressing the spring, remove the valve retainer and carefully release the compressor to remove the spring.
      • Repeat the process for each valve.
  6. Remove the Valves:
    • After removing the springs, carefully lift each valve out of its guide. Inspect each valve for wear, burning, or pitting, particularly on the valve face and stem.
    • Tip: Label each valve so it can be reinstalled in its original location or replaced as needed.

Inspection Notes:

  1. Valve Face and Seat Inspection:
    • Inspect the valve faces for signs of wear or burning. If the valve faces are pitted or burned, they may need to be refaced or replaced.
    • Valve Seats: Check the valve seats in the cylinder head for wear or damage. Worn seats can lead to poor sealing, resulting in loss of compression and engine inefficiency. If necessary, recut the valve seats to ensure a proper seal.
  2. Valve Stem-to-Guide Clearance:
    • Measure the valve stem-to-guide clearance using a micrometer or dial gauge. If the clearance is excessive (typically beyond 0.0015 to 0.003 inches (0.038 to 0.076 mm)), the valve guides will need to be replaced or reamed.
  3. Cylinder Head Surface Inspection:
    • After removing the old gasket, inspect the mating surface on the cylinder head for any gouges, cracks, or irregularities. Clean the surface using a scraper or gasket remover, taking care not to scratch the surface.
    • If any warping is detected, consider having the head resurfaced by a machine shop.

Reassembly Notes:

  1. Install New Gaskets:
    • Always install new gaskets when reassembling the cylinder head. Reusing old gaskets can lead to leaks and poor compression. Be sure the gasket is properly seated and aligned with the engine block.
  2. Evenly Torque the Cylinder Head Bolts:
    • When reattaching the cylinder head, torque the bolts in the reverse order of disassembly, starting from the center and working outward in a criss-cross pattern. Gradually increase torque in stages according to the manufacturer’s specifications, typically in the range of 200-220 lb-ft.
  3. Reinstall Valves and Springs:
    • Use a valve spring compressor to reinstall the valve springs and retainers. Make sure each valve is properly seated in its guide and that the retainers are securely in place.
    • After installing the valves and springs, check the valve clearance and adjust it according to the engine specifications.

Additional Tips:

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