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Marine Risers and Manifolds


Maintaining a wary attention on raw-water cooled manifolds and risers can possibly prevent the untimely loss of your engine.

picture of a corroded riser

Pop Quiz: the master of a 30' powerboat hops aboard their vessel one-day to go for a cruise, but their inboard V-8 engine is slow to begin. With regards to finally does start, he notices a definite knocking noise which he's never heard before. He continues to run the engine shortly, and shuts it down to research the main cause. Ultimately he eliminates the spark plugs and finds out water in no. 2 and #4 cylinders (hmm ...). Later, once the motor is torn-down for inspection, it's discovered that the # 4 piston connecting pole is bent while the cylinder walls tend to be rusted as a result of water intrusion. How performed water get into the cylinders? (Hint: it is not said to be indeed there.)

There are numerous options, however, if you guessed "Act of God, " attempt once again. Much more likely, saltwater passed into the cylinders through a leak either in the raw-water cooled exhaust "manifold" or perhaps the "riser." Once water gets inside cylinders, the end result is generally catastrophic motor failure. It could ruin every day, and much of summertime once busy mechanics circumvent to an overall total engine reconstruct (if at all possible) or replacement. Because the engine is frequently the single most high-priced part of your ship, it seems sensible to inspect or change the risers and manifold occasionally before an interior drip takes place, which is much more a concern of "when" than "if." Once it happens, there was generally little or no warning prior to the motor is destroyed.

Maintaining The Water And Gas Separated

Exhaust manifolds and risers tend to be huge metal castings that carry hot fatigue gasses away from the engine block on inboard machines. All V-8 motors, for example, have another exhaust manifold across the side of every cylinder lender. The riser, which will be shaped like an inverted "U, " can be situated within aft end of each and every manifold (e.g., on Chrysler machines), and sometimes it's predicated on the top of manifold (age.g., on MerCruiser engines). Occasionally the riser slopes down through the end of this manifold, if the motor sits sufficient over the waterline, in which particular case it's called an elbow. The exhaust hose pipe is then connected to the aft end associated with riser or shoulder.

The thing that makes these cast-iron components unique is that they are a double-walled pipeline within another pipe. This arrangement permits hot fatigue gasses inside interior pipeline becoming enclosed by an external water-filled pipe, called a water-jacket, which stays cool enough to touch. During the aft end for the riser, water through the water-jacket combines with and cools the hot gasses before continuing from exhaust overboard discharge. Without cooling aftereffect of the water, the exhaust gas would overheat the manifold and risers and burn through the fatigue hose in short order.

Keeping the cooling water and fatigue gasses divided until they exit the riser is essential. If water finds a way in to the gas-only chamber before the end of riser considering a drip within the water-jacket, it could seep into the cylinders whenever motor has reached sleep and either seize the pistons with corrosion, or develop a "hydro-lock" problem. That takes place because liquid can't be compressed inside cylinders, so that the engine suffers massive and usually irreparable harm whenever you you will need to begin it. Both lead to the early death of your motor.



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