Fiat-Allis 605-B Engine Timing: Precision, Pitfalls, and Practical Fixes

[MikePhua]

Understanding the Engine and Injection Timing
The Fiat-Allis 605-B wheel loader is powered by a 6-cylinder diesel engine, often paired with a mechanically governed rotary injection pump. Proper timing between the injection pump and engine crankshaft is critical for combustion efficiency, cold starting, and minimizing white smoke. When the pump is removed without marking its timing position, reinstallation becomes a challenge—especially if the engine was not set to top dead center (TDC) beforehand.
Terminology Notes

• BTDC (Before Top Dead Center): The crankshaft angle before the piston reaches its highest point; used to set injection timing.
  
• White Smoke: Unburned fuel vapor, often caused by late injection or poor atomization.
  
• Injection Advance: Adjusting timing to inject fuel earlier, improving cold starts and reducing smoke.
  
• Timing Window: A port or cover on the pump or flywheel housing used to observe timing marks.
  
• Serial Number Relevance: Timing specs may vary by engine serial number due to design changes.
  

Timing Specifications and Adjustments
For the Fiat-Allis 605-B with engine serial number 18Y04591, the correct injection timing is 26° BTDC. For later serial numbers, the spec drops to 20° BTDC. This difference reflects changes in combustion chamber design, injector spray pattern, or pump calibration.
To set timing:

• Rotate the engine to TDC on cylinder #1 (compression stroke).
  
• Align timing marks on the flywheel or front pulley with the pointer.
  
• Install the injection pump with its timing mark aligned to the housing.
  
• Fine-tune by rotating the pump slightly to advance or retard timing.
  

Field Anecdotes and Troubleshooting
One technician shared a case where a customer removed the pump without marking its position. After reinstalling, the engine ran but emitted heavy white smoke. Advancing timing from 19° to 22° BTDC had no effect. Only after confirming the correct spec of 26° BTDC for that serial number did the smoke clear.
Another mechanic recalled a similar issue on a Fiat-Allis 645B, where the pump was installed 180° out of phase. The engine cranked but wouldn’t start. After rotating the pump and rechecking the gear mesh, the machine fired up cleanly.
Common Mistakes and Solutions

• Mistake: Assuming all engines use the same timing spec.
  Solution: Always verify timing based on serial number and pump model.
  
• Mistake: Using visual alignment without confirming TDC.
  Solution: Remove valve cover and observe intake/exhaust valve overlap to confirm compression stroke.
  
• Mistake: Ignoring white smoke during startup.
  Solution: White smoke is a diagnostic clue—often pointing to late injection or poor compression.
  

Preventive Measures

• Mark pump and housing before removal
  
• Keep a log of timing specs by serial number
  
• Use a dial indicator or timing light for precise adjustment
  
• Replace worn injectors and check compression if smoke persists
  
• Avoid excessive cranking with incorrect timing—it can wash cylinders and damage rings
  

Historical Context and Design Evolution
Fiat-Allis engines from the 1970s and early 1980s often used Bosch or CAV rotary pumps. These pumps were reliable but sensitive to timing errors. Later models introduced electronic governors and improved combustion chambers, allowing for lower BTDC specs and cleaner emissions.
In military surplus units exported from Europe, timing plates were sometimes stamped in German or French, adding confusion during field repairs. One technician found a loader with a German timing plate but a U.S.-spec engine, requiring cross-reference with factory manuals.
Conclusion: Timing Is Everything
Engine timing on the Fiat-Allis 605-B is more than a technical detail—it’s the heartbeat of combustion. Whether you're chasing white smoke or rebuilding a pump, knowing your BTDC spec and verifying TDC are essential. As one veteran rebuilder put it, “If the pump’s good and the timing’s wrong, it’ll still run—but it’ll tell you something’s off with every puff of smoke.” Precision, patience, and a little diesel intuition go a long way.