Challenges in Servicing the Cummins 335 Taper Nose Crank Oil Pump

[MikePhua]

The Cummins 335 and Its Historical Significance
The Cummins 335 is part of the legendary NH series of diesel engines, which powered countless trucks and industrial machines from the 1950s through the late 1970s. Cummins Engine Company, founded in 1919 in Columbus, Indiana, became a dominant force in diesel technology by the mid-20th century. The NH series, including the 335, was known for its robust inline-six design, mechanical fuel injection, and long service life. These engines were widely used in Freightliner cabovers, Kenworth conventionals, and various off-highway applications.
The “taper nose crank” variant refers to a specific crankshaft design used in earlier NH engines, where the front of the crankshaft tapers to accommodate accessories like the oil pump drive or harmonic balancer. This design was phased out in favor of straight-nose configurations in later models, making parts for taper-nose engines increasingly rare.
Terminology Annotation

• Taper Nose Crankshaft: A crankshaft with a conical front end used to mount driven components securely via friction and keyways.
  
• Oil Cooler Nozzles: Small jets that spray oil onto the underside of pistons to reduce thermal stress and improve lubrication.
  
• Small Cam Pump: A Cummins oil pump design driven by a camshaft gear, used in engines prior to 1975.
  
• Cartridge Filter: A replaceable filter element housed within a metal canister, common in older diesel engines.
  
• O-Ring #4: A specific sealing ring used in the oil pump assembly, often difficult to source due to lack of part number visibility.
  

Locating Obsolete Components Without a Serial Number
One of the most frustrating aspects of working on vintage Cummins engines is the absence of a visible serial number. In many cases, replacement blocks were installed without transferring the original data plate, leaving technicians with no direct reference for parts lookup. This complicates sourcing components like oil pumps, gaskets, and filter cartridges.
In the case of the 335 taper nose crank engine from a 1969 Freightliner cabover, the technician was able to identify the required gaskets but struggled to locate the elusive O-ring (#4) and the oil supply tube for the piston cooling nozzles. These parts are not commonly listed in modern catalogs, and many online databases lack exploded diagrams for pre-1975 small cam pumps.
Field Strategies for Identifying and Matching Parts
When serial numbers are missing, technicians often rely on visual matching, cross-referencing with known part assemblies, and consulting salvage yards specializing in vintage trucks. For example:

• Use an O-ring sizing kit to match dimensions and material
  
• Reference old Cummins service bulletins or microfiche archives
  
• Contact legacy parts suppliers with photos and measurements
  
• Visit truck salvage yards with a focus on pre-1980 inventory
  

One trusted source for vintage Cummins parts is Miller Truck Salvage in Portland, Oregon, which maintains a large inventory of obsolete components and offers expert guidance for legacy engine configurations.
Oil Filter Cartridge and Gasket Identification
The oil filter housing on the 335 engine uses a cartridge-style filter, which may vary depending on production year and housing type. While the technician suspected an LF516 filter, confirmation came from a readable Cummins part number on the gasket itself. This highlights the importance of preserving old gaskets and labels during disassembly.
Modern equivalents for the LF516 filter are available through brands like Wix and NAPA, though the gasket may require custom fabrication or matching from a general-purpose seal kit. Some housings used flat gaskets, while others relied on O-rings, depending on the machining of the sealing surface.
Understanding the Small Cam Oil Pump
The small cam oil pump used in the 335 taper nose crank engine was standard in Cummins production until 1975. It features a gear-driven design mounted to the front of the camshaft, with internal passages feeding oil to the main gallery and piston cooling nozzles. These pumps are compact but efficient, capable of maintaining oil pressure across a wide RPM range.
Key specifications include:

• Flow rate: Approximately 12–15 gallons per minute at rated speed
  
• Operating pressure: 40–60 psi under load
  
• Relief valve setting: Typically 70–80 psi
  
• Drive method: Camshaft gear with taper fit and keyway
  

Due to their age, many of these pumps suffer from wear in the gear teeth, housing bore, and relief valve seat. Rebuilding is possible but requires precision machining and access to replacement bushings and seals.
Suggested Maintenance and Inspection Protocols
For technicians working on taper nose crank Cummins engines:

• Inspect oil pump gears for pitting and backlash
  
• Measure housing bore for wear and ovality
  
• Replace all O-rings and gaskets during reassembly
  
• Verify oil cooler nozzle flow with compressed air
  
• Use high-zinc diesel-rated oil to protect flat tappet cams
  

Anecdote from the Field
In 2010, a restoration team in Montana rebuilt a 1968 Freightliner powered by a Cummins 335. The engine had sat for 22 years, and the oil pump was seized due to varnish and corrosion. After sourcing a small cam pump from a retired logging truck, they rebuilt the unit using NOS gaskets and matched the missing O-ring from a Caterpillar seal kit. The engine ran flawlessly for over 1,500 hours before being retired to a museum.
Conclusion
Servicing a Cummins 335 taper nose crank engine is a rewarding but challenging endeavor. With parts becoming scarce and documentation limited, technicians must rely on experience, ingenuity, and a network of vintage parts suppliers. Understanding the nuances of the small cam oil pump, filter housing variations, and piston cooling systems is essential for a successful rebuild. These engines represent a bygone era of mechanical simplicity and industrial resilience—and with care, they can continue to run for decades more.