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Complete Guide to Installing Cylinder Head and Injectors On A Detroit Diesel 671

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Introduction

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This is your comprehensive, detailed procedure for removing, inspecting, and installing the cylinder head and fuel injectors on the Detroit Diesel 6-71, part of the legendary 71 Series inline two-cycle diesel engines. This guide integrates exact service practices, torque specifications, and critical dimensions pulled directly from the original Detroit Diesel manuals—an indispensable resource now that these manuals are out of print.

It’s written specifically for the 6-71 model, which is a 6-cylinder, 4.25″ bore by 5″ stroke engine with a 426 cubic inch displacement and a standard compression ratio of 17:1 or 18.7:1, depending on turbo configuration. This guide assumes a typical non-electronic mechanically governed engine, though most of the principles also apply to turbocharged and four-valve variants.

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Cylinder Heads & Related Components For Detroit Diesel 671 Non Turbo (2 Valve Head)

Cylinder Heads & Related Components For Detroit Diesel 671 Non Turbo (4 Valve Head)

Cylinder Heads & Related Components For Detroit Diesel 671 Turbo

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Safety Guidelines Before Starting

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Essential Precautions

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• Disconnect the battery completely by removing both cables to prevent accidental starting.

• Ensure the governor stop lever is in the no-fuel position, eliminating risk of the engine firing if the fan or flywheel is rotated.

• Wear proper personal protective equipment (PPE): safety glasses, steel toe boots, gloves, hard hat if overhead work is involved.

• Use a certified lifting device with a spreader bar. The lifter brackets must all be used to evenly distribute weight.

• Never use the blower air intake webs or other non-rated areas to lift the engine.

• Keep your workspace clean and ventilated, especially when using solvents or steam cleaning.

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Removing the Cylinder Head on the Detroit Diesel 6-71

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Preliminary Disconnections

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1. Drain the cooling system by opening the radiator/heat exchanger and cylinder block drains.

2. Drain the oil from the oil pan.

3. Disconnect fuel lines to the filter and cylinder head.

4. Remove the air cleaner or silencer assembly.

5. Remove the exhaust piping and then the exhaust manifold. If turbocharged, also remove turbo and associated plumbing.

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Preparing to Lift

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6. Remove the thermostat housing and water manifold.

7. Remove the valve rocker cover and the governor cover.

8. Disconnect the fuel control rod from the injector rack control tube lever and governor.

9. Remove the injector control tube and brackets as an assembly.

10. If doing a full overhaul, remove the injector pipes and injectors.

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Freeing the Head

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11. Loosen (3–4 turns) the bolts directly below the lifter brackets. These attach the balance weight cover and flywheel housing.

12. Remove the bolts securing the lifter brackets to the balance weight cover and flywheel housing.

13. With a torque wrench, record the existing torque on cylinder head bolts for diagnostic reference.

14. Remove the cylinder head bolts and nuts following a gradual crisscross pattern to relieve tension evenly.

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Lifting the Cylinder Head

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15. Use a chain hoist with hooks in the lifter brackets or rocker cover vent holes.

16. Slowly lift the head off the block, keeping it level.

17. Place the head valve-side down on 2-inch wooden blocks to protect injector tips and followers.

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Inspecting the Cylinder Block Before Installation

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Cleaning and Verifications

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• Thoroughly clean the block deck, counterbores, and bolt holes.

• Check the cylinder liner flange height using a dial indicator. The liner should protrude evenly above the block to specified height (approximately .002″ to .005″ above block deck, exact spec by liner class).

• Ensure piston crowns are clean and free of carbon buildup.

• Make sure push rods are threaded fully into their clevises so the adjuster end sticks out.

• Confirm all corner drive pins (oil gallery plugs) are flush or slightly below the top surface of the block.

• Inspect for cracks or corrosion, especially between water and oil passages.

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Installing the Cylinder Head on the Detroit Diesel 6-71

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Installing New Gaskets and Seals

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• Never reuse old gaskets or seals.

• Install new compression gaskets on each cylinder liner. These are laminated metal gaskets and must be matched to your liner classification.

• Insert new water and oil seals into the block’s counterbores. Use a light spray adhesive in the bores only to hold them, never on the seals.

• Install the perimeter oil seal ring in the groove around the top of the block with the colored side facing outward.

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Lowering the Cylinder Head

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• Insert guide studs (two corners) to help align the head.

• Using a chain hoist and spreader bar, lower the head carefully. As it gets within 1/2 inch of the block, visually recheck that the seals and gaskets remain seated.

• Lower completely into place, guiding evenly to avoid disturbing seals.

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Torquing the Cylinder Head Bolts

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Proper Torque Sequence

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• Install the bolts finger tight.

• Torque to 170-180 lb-ft (231-244 N-m) in three stages:

  • First pass: ~60 lb-ft

  • Second pass: ~120 lb-ft

  • Final pass: 170-180 lb-ft

• Follow the standard 6-cylinder Detroit Diesel torque pattern, starting at the center bolts and working outward in a spiral or crisscross pattern.

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Securing the Lifter Brackets

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• Tighten the two bolts directly under each lifter bracket, then secure the front and rear lifter brackets with new gaskets, torquing to 55-60 lb-ft (75-81 N-m).

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Installing the Injectors on the Detroit Diesel 6-71

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Preparing the Injector Tubes

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• Clean the injector tube bores using reamer J 5286-9, packing flutes with grease to catch debris.

• Only remove carbon. Excess metal removal affects the injector tip stand-out.

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Installing Injectors

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1. Fill each injector with clean fuel oil to lubricate the internal parts.

2. Insert the injector into the head, aligning the dowel pin with the locating hole.

3. Slide the rack control lever into the injector rack slot.

4. Install the injector clamp and torque to 20-25 lb-ft (27-34 N-m).

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Assembling the Rocker Arms

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• Position the rocker assembly. Tighten the bracket bolts to 90-100 lb-ft.

• Ensure the rack moves freely; overtightening can bind the rack.

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Installing Fuel Pipes and Adjusting Racks

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Fuel Pipes

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• Use new or undamaged Endurion®-coated nuts.

• Tighten to 130-160 lb-in (14.7-18.1 N-m).

• Never mix coated and uncoated nuts or reuse flared fuel pipes.

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Installing Injector Control Tube

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• Ensure the ball ends of the control levers engage the injector racks.

• After the return spring is hooked up, spin the control tube by hand. The racks should snap to the no-fuel position. If they stick, lightly tap to center.

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Adjusting Exhaust Valve Clearances and Injector Timing

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Setting Exhaust Valve Lash

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• With engine warm, adjust to .013″ clearance on the exhaust valves.

• Cold adjustment can be .016 ± .004″.

• Insert a feeler gauge under the rocker tip and adjust the push rod until it just passes.

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Timing the Injectors

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1. Place governor in no-fuel idle position.

2. Rotate the crankshaft until the exhaust valves are fully open on the cylinder you’re timing.

3. Insert the timing gauge into the injector follower.

4. Adjust the push rod until the gauge can just slide over the top.

5. Tighten the lock nut and recheck.

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Post-Assembly Checks

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• Reinstall the exhaust manifold, water manifold, thermostat housing, and fuel lines.

• Fill the cooling system and crankcase with fresh fluids.

• Slowly prime the fuel system.

• Perform a controlled engine run-in, monitoring for leaks at oil, fuel, and water connections.

• Recheck all torque specs after the first heat cycle.

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Final Recommendations

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• Use International Compound No. 2 on main bolts where specified to prevent galling, and a quality pipe sealant like Loctite on any plugs entering water, fuel, or oil galleries.

• Keep surfaces meticulously clean—minor debris under the cylinder head can lead to leaks, cracked heads, or “blow-by” under compression.

• Follow all specs precisely; Detroit Diesels rely heavily on exact clearances for proper combustion and scavenging.

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Conclusion

This detailed guide provides all the crucial steps, specifications, and sequences to correctly install the cylinder head and injectors on the Detroit Diesel 6-71 engine. When followed precisely, you’ll restore your engine to original durability and performance—ensuring proper sealing, fuel delivery, and valve timing.