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21.06.2021 10:17:19
Re: Mercruiser riser gaskets - Restricted vs. Open
See full version: Mercruiser riser gaskets - Restricted vs. Open
Re: Mercruiser riser gaskets - Restricted vs. Open
Re: Mercruiser riser gaskets - Restricted vs. Open
Re: Mercruiser riser gaskets - Restricted vs. Open [links]
I have option 4b from that bulletin. Raw water cooled with bypass from the thermostat to the front of the elbows. So, I put in the restricted gasket. [links]
Don, thanks for the bulletin.
You guys might want to look at this Merc service bulletin. here
Due to our engineering background at MerCruiser with Marine Exhaust Systems we’re regularly asked about the positioning of the Dry Joint Exhaust System full flow gasket versus the restrictor gasket, along with which directional orientation is correct for the restrcitor hole itself. Without going into too much detail this article will give you some background regarding the design intent of this system. Having been engineers for Mercruiser throughout the development of the Dry Joint Exhaust system, as well as the patenting (select link to view the patents) to release into these systems into production we have a very thorough background to address these questions.
The purpose of the restrictor hole is to prevent the cold bypass water as it enters the exhaust elbow, from back-flowing down and into the manifolds. If the restrictor hole is positioned incorrectly the cold bypass water will flow downward into the manifold and prevent the manifold temperatures from heating up enough to prevent condensation. [links]
The purpose of the restrictor hole is based on the desire to run the manifolds warm therefore preventing condensation from collecting in the exhaust manifolds. The intended design is such that the excess raw water supplied to the enigne is routed out through the fittings which are located in the exhaust elbows. Therefore the surface area exposed to the cold bypass water is minimized to only the exhaust elbows and not the manifolds or spacers. After the engine thermostat opens the heated water that flowed through the engine is then routed through the thermostat and out of the system while exiting through the fittings located in the bottom of the exhaust manifolds.
It is most commonly desired to minimize the total amount of surface area that gets exposed to the cold bypass water. With this in mind the desired approach is to put the restrictor gasket just below the exhaust elbow. Therefore no matter whether you run the 3″ or 6″ spacer the your cold bypass water is still limited to only the surface area of the exhaust elbow and not the exhaust manifolds. Then the exhaust manifolds and spacers get exposed to the heated water after it exits the thermostat.
If you want maximum performance over decades of use from your MerCruiser inboard engine, routine maintenance on your exhaust system is essential. Corrosion, plus the normal wear and tear of use, can damage your exhaust system, which could lead to poor performance and even serious engine problems. At NuWave Marine, you’ll find a large selection of MerCruiser exhaust system parts, including MerCruiser exhaust manifolds, risers, bellows, and every other replacement part you need to keep your motor in top shape. We carry OEM parts, as well as high-quality parts by Sierra and other leading names.
The exhaust riser is another key component that needs to be inspected as part of routine maintenance. At NuWave Marine you'll find the latest designs that collect hot gasses from the engine and cool them with a water-filled jacket. The efficient outflow of gasses makes your engine run better and can improve its power and lifespan. [links]
Whether you’re looking for a new MerCruiser transom assembly , or simply need a new MerCruiser exhaust elbow, NuWave Marine is your one-stop-shop for the highest-quality parts. From MerCruiser exhaust manifolds to complete MerCruiser outdrives and a variety of replacement parts, we have the components you need for yearly maintenance and complete rebuilds. You’ll spend less time in the shop and more time in the water with well-made MerCruiser parts from NuWave Marine. With over 35 years of experience building, servicing, and maintaining marine engines, we know the difference that quality parts can make when you need your boat's engine to perform its best.
Start with the fact that the Crusader had 4-bolt, stepped and stabilized main bearing caps, whereas the other engine had a 2-bolt, unstepped, unstabilized main bearing caps. As some of you may know, GM has long made two lines of basically the same engine, the better of the two being named the "TargetMaster" line of heavier duty, more precision engines for trucks. While I don't claim to be intimate with the GM product line of engines - the last time I personally rebuilt a TargetMaster was 10 years ago - there isn't any doubt in my mind that Crusader is using the TargetMaster line. The basic block was an all-around better block than it's competitor's. The basic differences were in the lower end, as well as obviously larger cooling passages.
Crusader's engines aren't widely used for race boat engine conversions like its competitors engines are, probably because Crusader doesn't get involved with the racing crowd. But it is interesting to note that when its competitor's engines are used by the race engine builders, they always add stabilizers to the main bearing caps. Sort of makes you wonder why they don't just use the better block in the first place, doesn't it? Well, part of the answer is that this is a high performance, not a heavy duty block, made for speed but not endurance.
Crusader solves this problem by including the cast iron risers on the fresh water side of the cooling system, so that without sea water going through them these risers can last ten years or more. Yes, it does mean that Crusader engines are more sensitive to overheating because more of the very hot exhaust system is being cooled by the FWC side of the system. But that's a small price to pay to avoid having to replace $2,000 worth of castings and risking major engine damage. This doesn't mean that Crusader engines are prone to overheating, at least not if you pay more attention to cooling system maintenance. This is because any reduction in heat transfer ability will result in a more rapid rise in temperature simply because more of the engine is being cooled by the FWC system. more