Introduction

The auxiliary drive system in Detroit Diesel 92 Series engines is designed to provide power for various accessories such as hydraulic pumps, air compressors, and alternators. This article covers the auxiliary drive’s components, functionality, and maintenance requirements.

Auxiliary Drive Overview

The auxiliary drive system consists of several components that facilitate the operation of engine accessories. These include:

• Accessory Drive Gear
• Drive Hub
• Coupling Assembly
• Bearings and Oil Seals
• Drive Pulley and Belt System
• Mounting Assembly

This system is responsible for transferring rotational power from the engine’s camshaft or blower drive to the auxiliary components.

Auxiliary Drive Positions and Ratios

Detroit Diesel 92 Series engines are equipped with multiple auxiliary drive positions, allowing for flexibility in powering different accessories. The drive ratios vary depending on the application, ensuring the correct operational speed for each component.

Understanding Drive Ratios

The drive ratio determines the rotational speed at which the accessory operates relative to the engine’s RPM. A 1:1 drive ratio means the accessory spins at the same speed as the engine, making it ideal for alternators and hydraulic pumps that require constant, predictable speeds. In contrast, a 2.60:1 or 2.05:1 ratio allows for increased accessory speed relative to engine RPM, making it suitable for applications that demand higher rotational speeds, such as cooling fans and high-speed pumps.

Proper selection of an auxiliary drive position ensures that accessories receive adequate power without overloading the engine or compromising performance.

Mounting Locations and Drive Mechanism

The auxiliary drive system can be mounted in different positions depending on engine configuration and accessory requirements. There are three main types of mounting locations:

Front-Mounted Accessory Drive

The front-mounted auxiliary drive is commonly used for alternators, power steering pumps, and additional cooling fans. It draws power from key rotating engine components, ensuring consistent and efficient operation.

Key Components:

• Camshaft Pulley – Drives accessories requiring moderate rotational speed.
• Crankshaft Pulley – Provides a direct, high-power drive for high-load accessories.
• Water Pump Drive Gear – Used to power auxiliary components without direct crankshaft engagement.

The front accessory drive system includes a short drive hub, which is bolted to the water pump drive gear. A keyed pulley is secured with a bolt and lock washer, while a pressed-in oil seal prevents oil leakage.

Rear-Mounted Accessory Drive

The rear-mounted auxiliary drive is utilized for heavier-duty accessories such as hydraulic pumps and power take-off (PTO) applications. It uses the blower drive gear or left-bank camshaft gear to provide power.

• The accessory drive gear is attached to the cylinder block rear end plate.
• Lubrication is provided through an external oil line, ensuring longevity and reducing friction.

This configuration is ideal for applications requiring a stable and high-power auxiliary drive setup.

Blower Drive Integration

In some configurations, the blower drive gear is used as a power source for accessories. Instead of a conventional coupling, an accessory drive hub replaces the standard blower hub. This system transfers power through a slotted coupling, allowing for a direct and efficient power transfer to driven components.

Types of Auxiliary Drive Systems

Depending on the engine application and required accessory operation, different drive systems are used:

Direct-Driven Accessories

In this setup, accessories are directly flange-mounted on the flywheel housing. A coupling, splined to both the camshaft gear and the accessory shaft, transfers power directly from the engine.

Common Applications:

• Power take-offs (PTOs)
• Direct-drive hydraulic pumps
• Fixed-speed air compressors

Belt-Driven Accessories

Belt-driven auxiliary drive systems use a shaft and pulley system to transfer power from the engine to accessories. A drive shaft, supported by a bearing, connects to a drive pulley, which is linked to accessories via belts.

Advantages:

• Allows for adjustable accessory speeds by changing pulley sizes.
• Reduces direct engine load, improving component longevity.
• Can drive multiple accessories simultaneously.

Common Applications:

• Alternators
• Secondary cooling fans
• Air compressors

Left-Bank Accessory Drive

In certain configurations, a left-bank accessory pad is available in the flywheel housing. This pad allows for the installation of additional accessories that are driven by the left-bank camshaft gear.

This configuration is useful for:

• Additional hydraulic systems
• High-output alternators
• Specialty-driven components in marine and industrial applications

Auxiliary Drive Maintenance

Routine maintenance of the auxiliary drive system is essential to prevent failures and ensure smooth operation.

Inspection

1. Check for Wear – Inspect drive gears, bearings, and couplings for wear or damage. Excessive gear wear can lead to improper engagement and reduced efficiency.
2. Check for Leaks – Examine oil seals and gaskets for leaks. Worn-out seals can cause lubrication failure, leading to component damage.
3. Measure Gear Backlash – Ensure backlash between the accessory drive gear and camshaft gear remains within specifications (typically 0.002-0.008 inches, with a maximum allowable wear limit of 0.010 inches).

Repair or Replacement Procedures

Accessory Drive Removal

1. Loosen and remove the alternator adjusting strap and mounting bolts.
2. Remove the accessory drive pulley and belt.
3. Disconnect any components obstructing access to the auxiliary drive.
4. Remove bolts securing the drive assembly to the flywheel housing.
5. Carefully extract the drive unit.

Disassembly and Cleaning

1. Remove the pulley retaining nut and pulley.
2. Press the shaft from the hub and extract the bearing.
3. Clean all components thoroughly, inspecting them for wear, cracks, or corrosion.

Reassembly

1. Install new bearings and oil seals as needed.
2. Reassemble the hub, shaft, and pulley.
3. Secure all components using proper torque specifications.
4. Reinstall the accessory drive assembly onto the engine, ensuring proper alignment.

Common Issues and Troubleshooting

Despite regular maintenance, auxiliary drive systems can develop issues over time. Below are common problems and their solutions.

Excessive Gear Wear

• Symptoms: Increased backlash, excessive noise, presence of metal shavings in oil.
• Cause: Misalignment, lack of lubrication, or worn components.
• Solution: Replace worn gears, ensure correct lubrication, and check for proper alignment.

Oil Leaks

• Symptoms: Oil seeping from seals or pooling near the drive assembly.
• Cause: Worn or improperly installed oil seals and gaskets.
• Solution: Replace damaged seals and verify gasket installation.

Belt Slippage

• Symptoms: Squealing noise, reduced accessory performance, increased belt wear.
• Cause: Improper belt tension, worn pulleys, or degraded belt material.
• Solution: Adjust belt tension, inspect pulleys for wear, and replace old belts.

Conclusion

The auxiliary drive system in Detroit Diesel 92 Series engines plays a crucial role in powering essential accessories. Proper maintenance, timely inspections, and correct installation procedures ensure reliable operation and longevity. By understanding the drive locations, mechanisms, and troubleshooting techniques, operators can optimize the performance of their engines.

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