When working on diesel engines, especially Cummins engines, enthusiasts and mechanics alike often encounter questions about part compatibility. One of the common inquiries involves whether a valve cover from a 5.9L Cummins engine will fit a 6.7L Cummins engine. The short answer is: no, a 5.9L valve cover will not directly fit on a 6.7L Cummins engine. However, understanding why this is the case requires a closer examination of both engine models, their respective design differences, and what makes each unique. In this article, we’ll dive deep into the differences between the 5.9L and 6.7L Cummins engines and the specifics of their valve covers.
1. Overview of the 5.9L and 6.7L Cummins Engines
5.9L Cummins Engine:
The 5.9L Cummins engine, often referred to as the “B series,” was used in a wide variety of Dodge Ram trucks from 1989 to 2007, most notably in the 1994 to 2007 Dodge Ram 2500 and 3500 models. This engine has been highly regarded for its durability, power, and simplicity, which made it a popular choice for both commercial and recreational uses. The 5.9L engine is a six-cylinder, turbocharged, inline engine, and it’s known for being very robust, with many examples reaching high mileage without major issues.
6.7L Cummins Engine:
The 6.7L Cummins engine is the successor to the 5.9L and was introduced in 2007.5 (mid-year) in Dodge Ram 2500 and 3500 trucks, continuing to be used in Ram’s heavy-duty lineups today. This engine also features a six-cylinder, turbocharged, inline configuration, but with several key improvements over the 5.9L. The 6.7L was designed with more stringent emissions requirements in mind, which necessitated some design changes to meet modern diesel standards, including a larger displacement, a more complex fuel system, and upgraded turbocharging.
While both engines share a similar basic configuration, the 6.7L Cummins is a more refined, modern engine that is capable of producing more horsepower and torque than the 5.9L. Additionally, the 6.7L Cummins features changes to the components of the engine to meet more stringent emissions standards, and these design alterations result in differences that impact the compatibility of certain parts.
2. Valve Cover Design: 5.9L vs. 6.7L
The valve cover of an engine serves a crucial function: it houses the valve train components, provides a seal to prevent oil from leaking, and helps maintain engine cleanliness by keeping debris and contaminants out of the engine. Given the importance of this component, the valve covers on the 5.9L and 6.7L Cummins engines have some significant design differences.
Material and Construction Differences:
Both the 5.9L and 6.7L Cummins engines feature cast aluminum valve covers, but the overall design of these covers is different. For the 6.7L engine, the valve cover is larger, and it includes additional mounting points to accommodate different sensors, wiring harnesses, and components. The increased size of the 6.7L valve cover is in part due to the extra complexity of the engine and the increased internal components needed to meet emissions regulations.
In contrast, the 5.9L valve cover is more simplistic, with fewer features, fewer mounting locations, and a smaller overall size. The 5.9L engine was designed before the implementation of more stringent emissions controls, so it lacks the additional components that are found in the 6.7L engine. The 6.7L engine has provisions for things like a higher flow PCV (positive crankcase ventilation) system, additional wiring for sensors, and other emissions-related systems that the 5.9L does not need.
Bolt Pattern and Mounting Points:
One of the key differences that makes it difficult for a 5.9L valve cover to fit a 6.7L engine is the bolt pattern and the number of mounting points. The 5.9L Cummins engine features a simpler mounting system for the valve cover, with fewer bolts and a different arrangement when compared to the 6.7L engine. On the 6.7L, the valve cover includes more mounting points to accommodate additional engine components, such as the larger emissions systems and sensor wiring.
The bolt pattern between the two engines does not align, meaning that the holes in the 5.9L valve cover will not match the mounting points on the 6.7L cylinder head. This makes a direct swap of the valve covers impossible without significant modification, which is not ideal or recommended for most mechanics or DIY enthusiasts.
3. Emissions and Engine Management Differences
One of the main reasons why the 6.7L Cummins engine is not compatible with a 5.9L valve cover is the evolution of emissions systems between the two engines. As the diesel industry faced increasing pressure to reduce emissions, Cummins had to implement several new technologies into the 6.7L engine to meet stricter standards set by the Environmental Protection Agency (EPA) and other regulatory bodies.
Changes in Emissions Components:
The 6.7L Cummins engine has several new components related to emissions, including a more advanced turbocharger, intercooler, exhaust gas recirculation (EGR) system, and a diesel particulate filter (DPF). These components required changes to the valve cover design, as additional space and provisions had to be made for the sensors and connections related to emissions control.
The 5.9L engine, by contrast, uses a simpler EGR system and does not require the additional components that the 6.7L engine uses to meet emissions standards. The lack of these additional emissions systems means that the 5.9L valve cover is not designed to accommodate the extra fittings, sensors, and mounting points needed by the 6.7L engine.
Crankcase Ventilation:
Another significant change between the two engines is the crankcase ventilation system. The 6.7L Cummins has a more advanced PCV system to prevent excessive buildup of gases and contaminants in the engine. The design of the valve cover reflects these changes, incorporating additional passages and fittings to handle the increased volume of gases produced in the more emissions-strict 6.7L engine. The 5.9L, having been designed before the need for such advanced systems, has a simpler crankcase ventilation design, and its valve cover does not have the same provisions for this function.
4. Interchangeability of Parts: Why a 5.9L Valve Cover Doesn’t Fit a 6.7L
Given the differences in design between the 5.9L and 6.7L engines, it’s clear why a 5.9L valve cover cannot be directly swapped onto a 6.7L Cummins engine. Key factors that prevent this interchangeability include:
- Size and Shape: The 6.7L valve cover is larger to accommodate additional components like sensors, wiring, and emissions systems. The 5.9L cover is smaller and lacks provisions for these features.
- Bolt Pattern: The bolt pattern on the 5.9L valve cover does not align with the mounting points on the 6.7L cylinder head, making it physically impossible to mount the 5.9L valve cover onto the 6.7L engine without extensive modification.
- Emissions Systems: The 6.7L Cummins features more advanced emissions control systems, which require additional mounting points, fittings, and passages on the valve cover. The 5.9L lacks these emissions systems, so its valve cover is not designed to accommodate them.
- Crankcase Ventilation and Sensors: The 6.7L engine has a more complex PCV system and additional sensors that are mounted on or integrated into the valve cover, features that the 5.9L valve cover doesn’t have.
5. Conclusion
A 5.9L Cummins valve cover will not fit a 6.7L Cummins engine. The differences in engine design, emissions systems, and bolt patterns between the two models make such a swap incompatible without significant modification, which is not recommended due to the complexity and potential for engine issues. If you are working on a 6.7L Cummins engine and need a replacement valve cover, it is best to source one specifically designed for the 6.7L model to ensure proper fitment and functionality.
While the 5.9L and 6.7L engines share some similarities, they are different enough in design to require specific parts for each engine. When working on these engines, always verify compatibility before attempting to replace or upgrade engine components, as using incorrect parts can lead to performance issues, leaks, and even engine damage.
