Does a 5.9 Valve Cover Fit on a 6.7?

Discover if a 5.9 valve cover fits on a 6.7 Cummins engine with our detailed guide. Learn key differences, compatibility, and expert tips for modifications.

Jan 8, 2025 - 12:50
Jan 20, 2025 - 20:40
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Does a 5.9 Valve Cover Fit on a 6.7?
Does a 5.9 Valve Cover Fit on a 6.7

The question of whether a 5.9 valve cover fits on a 6.7 engine is a common one among diesel enthusiasts and Cummins owners. While the 5.9L and 6.7L engines are closely related in terms of design and engineering, there are key differences that impact compatibility. In this article, we’ll explore the specifics of the 5.9 and 6.7 valve covers, the dimensions, modifications, and what you need to know to make an informed decision.


Understanding the Basics: 5.9L vs. 6.7L Cummins Engines

The 5.9L Cummins engine, produced from 1989 to 2007, is renowned for its simplicity, durability, and reliability. On the other hand, the 6.7L Cummins engine, introduced in 2007.5, features updated technology, increased displacement, and a focus on emissions compliance.

Key Differences Between the 5.9L and 6.7L:

  • Displacement: The 5.9L has a displacement of 359 cubic inches, while the 6.7L offers 408 cubic inches.
  • Emission Controls: The 6.7L includes systems like EGR and a diesel particulate filter, which are absent in the 5.9L.
  • Valve Cover Design: These engines have different head designs, which directly impact the compatibility of components like the valve cover.

Dimensions and Design of the Valve Covers

Valve covers are engineered to match the specific dimensions and architecture of the cylinder head. While the 5.9L and 6.7L Cummins engines share a family lineage, their valve covers are not directly interchangeable without modification.

5.9L Valve Cover:

  • Made for simpler cylinder head designs.
  • Lightweight aluminum or composite construction.
  • Dimensions and bolt patterns align specifically with the 5.9L head.

6.7L Valve Cover:

  • Designed to accommodate advanced emission systems.
  • Slightly larger due to the increased displacement and design differences.
  • Features additional ports and fittings to support emission components.

Will a 5.9 Valve Cover Fit on a 6.7?

In short, a 5.9 valve cover does not fit directly on a 6.7 engine without modifications. The primary reasons include differences in bolt patterns, overall dimensions, and functionality requirements. However, with some customization, it is possible to adapt the 5.9 valve cover to a 6.7 engine.

Challenges to Consider:

  1. Bolt Pattern Misalignment: The bolt pattern on the 6.7 cylinder head is different, requiring either an adapter plate or machining adjustments.

  2. Sealing Issues: Ensuring a proper seal is critical to prevent oil leaks. The gasket surfaces differ between the two engines.

  3. Emission System Compatibility: The 6.7 valve cover includes ports and fittings to support systems like the EGR. A 5.9 valve cover lacks these features.


How to Adapt a 5.9 Valve Cover for a 6.7

While not straightforward, adapting a 5.9 valve cover for use on a 6.7 engine can be accomplished with the right tools and expertise. Below are the general steps to consider:

1. Verify Fitment and Dimensions

Start by measuring the dimensions of both valve covers to identify the areas where modifications are needed. Pay close attention to bolt hole alignment.

2. Use an Adapter Plate

Custom adapter plates can bridge the gap between the 5.9 valve cover and the 6.7 cylinder head. These plates are machined to align with both bolt patterns.

3. Modify the Valve Cover

In some cases, it may be necessary to drill new bolt holes or reshape the valve cover for a snug fit. Work with a professional machinist to ensure accuracy.

4. Address Emission System Needs

If the vehicle is equipped with a functioning emissions system, additional modifications may be required to integrate the necessary ports and fittings.

5. Test for Leaks

After installation, run the engine and inspect for oil leaks. Replace the gasket if necessary and ensure all bolts are torqued to specification.


Why Choose a Custom Solution?

For enthusiasts who want the aesthetics of a 5.9 valve cover or are retrofitting an older design, customization is a viable route. However, for most practical applications, using the correct 6.7 valve cover is more efficient and ensures better compatibility.


Alternative Options for Customization

If you're looking to enhance the appearance or performance of your 6.7 engine, consider aftermarket valve covers designed specifically for the 6.7. These options provide the desired visual appeal without the need for extensive modifications.

Benefits of Aftermarket Valve Covers:

  • Customizable designs and finishes.
  • Improved oil sealing and durability.
  • Compatibility with emission systems.

Conclusion

While the idea of fitting a 5.9 valve cover on a 6.7 engine may be appealing for customization or aesthetic reasons, it is not a direct fit. Modifications, including adapter plates and machining, are required to make it work. For most applications, sticking to the proper valve cover for your engine is the best choice.

If you’re considering this modification, ensure you have the tools, expertise, or access to professional assistance to avoid complications. Always prioritize compatibility and performance over aesthetics to keep your engine running smoothly.

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