30/04/2021
The Perkins 4.107 and 4.108 are two closely related diesel engines that have powered a wide range of vehicles and equipment over the years. While they share a common heritage, several key differences set them apart, with the 4.108 generally considered an improvement upon its predecessor. Understanding these distinctions is vital for anyone involved in maintaining, restoring, or specifying these reliable powerplants.
A Tale of Two Engines: Perkins 4.107 and 4.108
Both the 4.107 and 4.108 are four-cylinder, naturally aspirated diesel engines produced by Perkins Engines, a company renowned for its robust and dependable diesel engines. They were widely used in marine applications, agricultural machinery, industrial equipment, and even some light commercial vehicles. The 4.107 was introduced first, and the 4.108 followed, incorporating several enhancements based on the experience gained with the earlier model.
The Core Difference: Wet vs. Dry Liners
The most significant and fundamental difference between the Perkins 4.107 and 4.108 lies in their cylinder liner design. This seemingly small detail has considerable implications for engine construction, maintenance, and longevity.
Perkins 4.107: Wet Liners
The Perkins 4.107 features wet liners. In this design, the cylinder liners are in direct contact with the engine's coolant. They are sealed at the top and bottom with O-rings and fit into the engine block, allowing the coolant to flow around them. This direct contact with the coolant facilitates efficient heat transfer away from the combustion chamber, helping to keep the engine running cooler.
Advantages of Wet Liners (4.107):
- Improved Cooling: Direct contact with coolant allows for more effective heat dissipation.
- Easier Replacement: Wet liners can often be removed and replaced more easily than dry liners, which can be beneficial during major overhauls.
Disadvantages of Wet Liners (4.107):
- Potential for Coolant Leaks: The O-ring seals at the top and bottom of the liner are potential points of failure, which could lead to coolant entering the crankcase or combustion chamber.
- Block Corrosion: Over time, the engine block surrounding the liners could be susceptible to corrosion if the coolant is not properly maintained.
Perkins 4.108: Dry Liners
In contrast, the Perkins 4.108 employs dry liners. These liners are pressed or interference-fit into the engine block, and they do not come into direct contact with the coolant. Instead, the engine block itself is water-cooled, with coolant passages surrounding the dry liners. The heat from combustion is transferred through the liner to the engine block and then to the coolant.
Advantages of Dry Liners (4.108):
- Reduced Leakage Risk: Eliminates the potential for coolant leaks at the liner seals, contributing to a more robust and less prone-to-failure design.
- Greater Block Integrity: The engine block is less exposed to coolant, potentially reducing the risk of corrosion in the immediate vicinity of the cylinders.
- Potentially More Robust: The interference fit can provide a very strong and stable cylinder wall.
Disadvantages of Dry Liners (4.108):
- More Difficult Replacement: Replacing dry liners can be a more involved process, often requiring specialized tools and techniques to press them out and in.
- Slightly Less Efficient Cooling (Potentially): While still very effective, the indirect contact with coolant might, in some extreme scenarios, offer marginally less direct heat dissipation compared to wet liners. However, Perkins' design mitigated this significantly.
Other Notable Modifications in the 4.108
Beyond the fundamental change in cylinder liner design, the Perkins 4.108 received several other important upgrades:
Strengthened Cylinder Head Studs/Bolts
The 4.108 featured improvements in the size and strength of the cylinder head studs and bolts. This enhancement was crucial for better clamping force on the cylinder head, ensuring a more secure seal and greater resistance to the stresses of combustion. Stronger fasteners contribute to overall engine reliability and longevity, reducing the likelihood of head gasket failure.
Revised Cooling System (Later Models)
On later production runs of the 4.108, Perkins introduced an all-new cooling system. This often involved replacing the front-mounted header tank with a more integrated system. The exact configuration could vary, but these revisions aimed to improve the efficiency and reliability of the cooling system, potentially leading to more consistent operating temperatures and reduced risk of overheating.
Comparative Table: Perkins 4.107 vs. 4.108
| Feature | Perkins 4.107 | Perkins 4.108 |
|---|---|---|
| Cylinder Liners | Wet Liners (Direct coolant contact) | Dry Liners (Interference fit, indirect coolant contact) |
| Cylinder Head Fasteners | Standard | Improved size and strength |
| Cooling System (Later Models) | Standard | Revised/All-new system (often without front header tank) |
| Primary Advantage | Good cooling efficiency | Enhanced reliability and robustness, reduced leak potential |
| Maintenance Consideration | Potential for coolant seal leaks | More complex liner replacement |
Why the 4.108 Became More Prevalent
The modifications made to the 4.108, particularly the switch to dry liners and the strengthening of critical components, made it a more robust and reliable engine. While the 4.107 was a capable unit, the 4.108 addressed some of its potential weaknesses. The reduced risk of coolant leaks associated with dry liners was a significant factor in its favour for many manufacturers and end-users. This improved durability and reduced maintenance headaches contributed to the 4.108 often being the preferred choice for new applications and a popular upgrade path.
Frequently Asked Questions
Q1: Are the Perkins 4.107 and 4.108 interchangeable?
While they are very similar, direct interchangeability can be complex due to the differences in cylinder liners and potentially other minor mounting or ancillary differences. It is crucial to consult the specific application's requirements and the original engine specifications. In many cases, modifications would be needed to swap one for the other.
Q2: Which engine is considered more powerful?
Both engines typically produced around 40-50 horsepower, with minor variations depending on the specific tune and application. The focus of the 4.108's development was more on reliability and robustness than a significant power increase.
Q3: Can I fit 4.108 dry liners into a 4.107 block?
This is generally not a straightforward conversion. The engine blocks are machined differently to accommodate the wet liners of the 4.107 and the dry liners of the 4.108. It would likely require significant machining of the block, which is often not cost-effective or practical.
Q4: What are common issues with these engines?
Common issues for both engines, typical of older diesel engines, can include worn piston rings, valve seat wear, injection pump issues, and cooling system problems (especially leaks in the 4.107's wet liner seals). The 4.108, with its dry liners, is less prone to the specific coolant seal leaks but can still suffer from general wear and tear.
Conclusion
The Perkins 4.107 and 4.108 are both respected workhorses in the diesel engine world. The 4.108 represents an evolution of the 4.107, bringing key improvements in cylinder liner design, fastener strength, and cooling system technology. These enhancements made the 4.108 a more durable and reliable option, solidifying its reputation and widespread adoption. Whether you are maintaining a classic boat, a vintage tractor, or any equipment powered by these engines, understanding these differences will help ensure you are providing the best possible care.
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