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Topic: Marine Exhaust Systems

Question: What is the Difference Between Original Equipment and After Market Marine Exhaust Manifolds Products?

Response: The term "Original Equipment" versus "After Market" (sometimes referred to as Direct Replacement) in many cases refers to whether the part is "branded" by the engine manufacturer versus a replacement parts company. In most cases the replacement parts are very similar to the original equipment parts since most engine manufacturers "Outsource" the casting of their exhaust manifolds to a foundry that specializes in castings. In some cases the companies who manufacture the replacement products also produce the direct replacement parts as well.

Casting Techniques:
There are essentially two different casting methods being utilized today; green sand casting and evaporative pattern (Lost Foam) casting. The green sand method has been around for many years and represents the vast majority of products available today. The Lost Foam method although growing for iron produced products has mainly been used for aluminum castings over the years. Probably the most well known product related to marine parts customers would be the standard aluminum outboard engine block. Technically speaking the lost foam method is considerably different from sand casting in that the pattern used in producing the part is actually a direct representation of the actual part. Whereas with sand casting the cores create the void  where the actual metal fills to generate the part.

Casting Technical Information:
In terms of advantages it can be presented in several different ways. The main advantage with Lost Foam Casting lies in the fact that very consistent wall thicknesses can be generated. This allows the manufacturer to reduce the overall wall thickness and therefore reduce the weight/cost of the casting. At the same time these consistent wall thicknesses generate very consistent water flow jackets ensuring good coolant flow throughout the part. Two difficulties regarding Lost Foam casting in iron is with the melting point of iron being considerably higher than aluminum creates difficulty in preventing porosity (small holes) in the iron. The second difficulty is with controlling the amount of core float.

Corrosion:
The two primary failure modes with marine exhaust manifolds are associated with either corrosion related failure, or freeze damage. Regarding freeze damage one must always ensure the cooling water is drained before the onset of freezing weather. Regarding corrosion there are a couple of different methods of controlling the life of the parts.

 Alternative Materials - This is a very good option however very costly. Standard stainless steel systems generally sell for about 3 times the cost of cast iron or aluminum.

Coatings - Coatings are a very cost effective method of extending the life expectancy of iron or aluminum marine exhaust manifolds. There are several different coatings available ranging from galvanizing, to ceramic coating, to electro deposition plating. Since the determining factor regarding the life expectancy is not only how quickly the coating CORRODES but also how quickly the coating ERODES. In our experience the best combination for a coating strategy is with the following approach;

• Ceramic Coating (sacrificial). Since all coatings are porous some amount of the corrosive salt water will penetrate the coating and attack the base material. Therefore a sacrificial coating ensures that any corrosion that takes place does so to the coating before the actual base iron or aluminum material. In a nutshell this allows the coating to function as specified; extending the life of the casting.

• Electro Deposition Plating - This acts as a protective outside barrier to further extend the life of the casting by further preventing salt water from penetrating the ceramic coating.

In all cases when installing the system you do not need to use silicone type gasket sealers. The most important things to ensure when installing marine exhaust manifolds and risers is to make sure the fasteners are torque consistently such that the gaskets is compressed equally (criss-cross pattern). Torque the fasteners in 3 separate stages, the first just to "seat" the gaskets, then followed by the next two in equal amounts of half the total required torque. For example if the total required torque is 50 ft - lbs the first step would be to seat the gasket by tightening the fasteners to about 5 ft-lbs (criss-cross pattern). The next step would be to torque the fasteners to about 25 ft-lbs (criss-cross pattern), while the third step would be achieving the final specified torque in this case 50 ft-lbs (criss-cross pattern). After running the marine engine and allowing the cooling system to reach operating temperature, the marine exhaust manifold and riser fasteners should be re-torque'd to the specified torque. This ensures that good fastener retention is maintained after the marine engine completes the post installation thermal cycle.

Marine Exhaust Manifolds