Tracking Down Cylinder Heads for the Detroit Diesel 2-71 Engine

[MikePhua]

The Detroit Diesel 2-71 and Its Industrial Legacy
The Detroit Diesel 2-71 is a two-cylinder, two-stroke diesel engine from the legendary GM Series 71 family, first introduced in the late 1930s. Designed for compact power delivery, the 2-71 was widely used in generators, pumps, welders, and small industrial machines. Its designation refers to two cylinders with 71 cubic inches of displacement per cylinder, totaling 142 cubic inches.
Detroit Diesel, originally a division of General Motors, built its reputation on rugged, high-revving two-stroke diesels that powered everything from military vehicles to tugboats. The 2-71, though less common than its larger siblings like the 6-71 or 8V-71, remains a cult favorite among restorers and collectors due to its simplicity and distinctive sound.
Terminology and Component Notes
- Cylinder Head: The cast iron component that houses intake and exhaust valves, injectors, and combustion chambers.
- Two-Stroke Diesel: An engine design where each piston completes a power cycle in one revolution, using ports and valves for scavenging.
- Blower: A gear-driven supercharger used to force air into the cylinders for scavenging and combustion.
- Valve Train: The assembly of rocker arms, pushrods, and valves that controls airflow and fuel delivery.
- NOS (New Old Stock): Unused parts manufactured during the original production run, often stored for decades.
The Challenge of Finding 2-71 Cylinder Heads
As of the 21st century, sourcing cylinder heads for the 2-71 has become increasingly difficult. With production long discontinued and many units scrapped or cannibalized, parts availability is limited. In some regions, quotes for replacement heads range from $3,000 to $5,000, shocking buyers who remember when these engines were considered disposable.
The scarcity is compounded by the fact that the 2-71 was never produced in the same volume as the 6-71 or 4-71. Many heads have been damaged by overheating, improper torqueing, or corrosion, making rebuildable cores rare.
Strategies for Locating Affordable Heads
Despite the challenges, several avenues remain viable for locating usable 2-71 heads:
- Contact diesel rebuilders who specialize in vintage Detroit engines

• Search industrial surplus dealers and military auction sites
  
• Explore international suppliers, especially in regions where 2-71-powered equipment was common (e.g., India, Southeast Asia)
  
• Look for NOS inventory in old warehouses or dealerships that once serviced Detroit Diesel fleets
  
• Network with restoration communities and diesel forums for leads
  

One buyer in Australia managed to locate a head listed for $500 USD, complete with valves, from a U.S.-based supplier. Even with freight costs, the total was significantly lower than local quotes. This underscores the importance of global sourcing when dealing with legacy equipment.
Rebuilding and Compatibility Considerations
When acquiring a used or NOS head, it’s essential to verify compatibility and condition. The 2-71 head must match the engine’s serial configuration, injector type, and valve geometry. Some heads may have been modified or machined for specific applications.
Inspection checklist:

• Check for cracks between valve seats and injector ports
  
• Verify flatness of the mating surface with a straightedge
  
• Inspect valve guides and seats for wear or pitting
  
• Confirm injector bore diameter and thread pitch
  
• Pressure test coolant passages for leaks
  

If rebuilding a head, use OEM-grade valve components and follow Detroit Diesel torque specifications. The head bolts must be torqued in sequence to prevent warping, and the gasket surface should be cleaned but not over-machined.
Historical Anecdotes and Collector Interest
In military diesel training programs during the 1960s and 70s, the 2-71 was often used as a teaching engine due to its simplicity and accessibility. One technician recalled rebuilding a 1-71 variant—an even rarer single-cylinder version—during his time in the armed forces. These engines were used in small generators and are now considered collector items.
A photo of a 1-71 surfaced in a restoration group, prompting admiration for its compact design. Some enthusiasts even display these engines in living rooms or workshops as mechanical art.
Preservation and Long-Term Support
To preserve a 2-71 engine:

• Run the engine monthly to keep seals lubricated and prevent fuel varnish
  
• Use high-detergent diesel oil and change it every 100 hours
  
• Monitor coolant chemistry to prevent internal corrosion
  
• Store the engine in a dry, ventilated space with intake and exhaust ports sealed
  
• Keep a log of parts sources and rebuild history for future reference
  

For those restoring vintage welders, pumps, or generator sets powered by the 2-71, maintaining a spare head is wise. As parts become harder to find, early acquisition ensures future serviceability.
Conclusion
The Detroit Diesel 2-71 may be small in size, but its legacy looms large in industrial history. Tracking down a cylinder head for this engine requires persistence, global outreach, and a bit of luck. Yet for those who succeed, the reward is more than mechanical—it’s the satisfaction of reviving a piece of engineering heritage. In the world of vintage diesels, the 2-71 is a reminder that even the smallest engines can leave the deepest impressions.