08-12-2025, 06:56 PM
Background: The Pony Engine Dilemma
Older Caterpillar dozers like the 17A were originally equipped with pony engines—small gasoline-powered units used to crank the main diesel engine. While historically effective, pony engines are notorious for being temperamental, especially after long periods of inactivity or exposure to moisture. Issues like worn carburetors, magneto failures, and cold-start difficulties have led many operators to consider replacing them with electric starter motor systems.
Terminology Explained
The Caterpillar 17A dozer, unlike the earlier 3T model, has a symmetrical bolt pattern on its flywheel housing, which simplifies the starter motor conversion. Unlike the 3T, which requires a custom adapter plate, the 17A can accept a starter motor directly using a conversion drive-end housing that matches the larger bolt circle.
The preferred starter motor for such conversions is the Delco Remy 40MT or 50MT, depending on torque requirements. These motors are robust, widely available, and compatible with 24V systems commonly used in heavy equipment.
Key Conversion Components
One operator working on a remote prospecting lease in Western Australia shared his experience converting a D7 3T dozer to electric start. With no charging circuit onboard, he relied on a solar charging station and manually removed batteries for charging. The system worked flawlessly, starting the dozer multiple times daily. Inspired by this success, he sought to convert a newly acquired 17A dozer, which had persistent pony engine issues.
Challenges with Pony Engines
Some operators have experimented with Honda engine conversions, using belt drives to spin the diesel starter armature. While effective in certain contexts (e.g., Amish farms), this method is less practical for frequent use or remote operations due to complexity and reliability concerns.
Technical Parameters and Suggestions
Converting a Caterpillar 17A dozer from pony engine to electric starter motor is a practical and proven upgrade. It eliminates cold-start frustrations, reduces maintenance, and improves operational readiness—especially in remote or rugged environments. While the conversion requires careful matching of components and some machining, the long-term benefits far outweigh the initial effort.
As one seasoned operator quipped, “I used to spend half the day coaxing the pony to life—now I just turn the key and get to work.”
Older Caterpillar dozers like the 17A were originally equipped with pony engines—small gasoline-powered units used to crank the main diesel engine. While historically effective, pony engines are notorious for being temperamental, especially after long periods of inactivity or exposure to moisture. Issues like worn carburetors, magneto failures, and cold-start difficulties have led many operators to consider replacing them with electric starter motor systems.
Terminology Explained
- Pony Engine: A small auxiliary engine used to start a larger diesel engine
- Starter Motor Conversion: Replacing the pony engine with a direct electric starter system
- Flywheel Ring Gear: A toothed ring mounted on the flywheel that engages with the starter motor’s pinion gear
- Helical Pinion Gear: A gear with angled teeth used in starter motors to mesh smoothly with the flywheel
- Adapter Plate: A machined plate used to mount a starter motor to an engine not originally designed for one
The Caterpillar 17A dozer, unlike the earlier 3T model, has a symmetrical bolt pattern on its flywheel housing, which simplifies the starter motor conversion. Unlike the 3T, which requires a custom adapter plate, the 17A can accept a starter motor directly using a conversion drive-end housing that matches the larger bolt circle.
The preferred starter motor for such conversions is the Delco Remy 40MT or 50MT, depending on torque requirements. These motors are robust, widely available, and compatible with 24V systems commonly used in heavy equipment.
Key Conversion Components
- Starter motor: Delco Remy 40MT or 50MT
- Voltage: 24V system with dual 12V batteries
- Pinion gear: 11-tooth right-hand helical gear
- Drive-end housing: Custom machined to match 17A bolt circle
- Flywheel ring gear: Must match starter pinion specifications
One operator working on a remote prospecting lease in Western Australia shared his experience converting a D7 3T dozer to electric start. With no charging circuit onboard, he relied on a solar charging station and manually removed batteries for charging. The system worked flawlessly, starting the dozer multiple times daily. Inspired by this success, he sought to convert a newly acquired 17A dozer, which had persistent pony engine issues.
Challenges with Pony Engines
- Carburetor wear due to vibration
- Magneto moisture sensitivity
- Cold-start difficulty in winter
- Time-consuming maintenance (e.g., cleaning points, replacing insulation tape)
- Inconsistent ignition performance
Some operators have experimented with Honda engine conversions, using belt drives to spin the diesel starter armature. While effective in certain contexts (e.g., Amish farms), this method is less practical for frequent use or remote operations due to complexity and reliability concerns.
Technical Parameters and Suggestions
- Starter torque: 15–20 ft-lbs for 40MT; up to 25 ft-lbs for 50MT
- Battery capacity: Minimum 150Ah per 12V battery
- Cable gauge: 2/0 AWG recommended for starter circuit
- Flywheel ring gear pitch: Must match pinion gear helix and tooth count
- Mounting bolt circle: Verify symmetry and diameter before ordering housing
- Clean flywheel teeth and inspect for wear before mounting starter
- Use anti-corrosion grease on electrical terminals
- Secure battery cables with vibration-resistant clamps
- Test starter motor on bench before installation
- Ensure proper alignment of pinion gear with flywheel ring gear
- Check starter motor brushes and solenoid annually
- Maintain battery health with regular charging and load testing
- Inspect mounting bolts and housing for vibration loosening
- Keep starter motor housing clean and dry to prevent corrosion
Converting a Caterpillar 17A dozer from pony engine to electric starter motor is a practical and proven upgrade. It eliminates cold-start frustrations, reduces maintenance, and improves operational readiness—especially in remote or rugged environments. While the conversion requires careful matching of components and some machining, the long-term benefits far outweigh the initial effort.
As one seasoned operator quipped, “I used to spend half the day coaxing the pony to life—now I just turn the key and get to work.”
