If you have a W50, most have a rubber end cap that you can remove to get inside the raw water HX. It's held on by a large hose clamp. Be very careful when re-installing that end cap. It has a groove on the inner side that must be perfectly aligned with the flow divider plate inside. If not aligned correctly, you'll get raw water bypassing the tubes which can significantly reduce the cooling capacity. It's so hard to do that I don't try it.
Anyway, if you do need to or want to remove the HX, you need to remove the exhaust manifold with the HX attached. No way around it. I've done it about 4 times and it's not too bad if you know what to do. I just did it this last winter and this is what I recall:
1. On my boat, the supply and return hoses to the water heater are in the way, so I need to remove these from the engine, and pull them aft out of the way. You will drain the antifreeze from the engine when you do this.
2. Next, remove all hoses from the exhaust manifold/mixing elbow and the HX. This process will also drain the antifreeze from the engine. There are 3 hoses for the HX: fresh water (anti freeze side) to the HX, raw water supply from raw water pump and a raw water hose from the HX connected to the oil cooler. I find it easier to remove the hose from the oil cooler and leave the hose stub attached to the HX --- makes it easier to reinstall due to clearances and interferences. On my boat there are 2 hoses connected to the exhaust manifold/mixing elbow assembly: 1 raw water supply to the mixing elbow from the oil cooler, and the large exhaust connection to the water lift muffler. I can't remove the large exhaust hose yet, without removing the manifold assembly, but you can loosen the hose clamps in preparation.
3. There are 6 fasteners that attach the exhaust manifold to the head. There are 2 bolts ( 1 on the forward side, and 1 on the aft side). Remove both bolts. I believe they need a 7/16" wrench. Use the box end to break them free, and the open end/box end to remove them. There also are 4 threaded studs all located on the inner sections. These have 1 nut and washer each. Again, use the box end to break them free, and the open end/box end to fully remove them.
4. Once all fasteners are fully removed (2 bolts, and 4 nuts/washers), lift out the exhaust manifold/HX assembly (slightly upward and outward). It's tight, and you'll probably have to flex it at the exhaust line to break that connection, but it's very doable. The full assembly probably weighs about 30 lb.
Reassembly is done in the reverse except:
1. I've found that it's much easier if you put the 4 nuts with washers in their studs first. The exhaust manifold flange is slotted so that the manifold will slide onto these studs. There's very little clearance since you have to angle the manifold outboard port slightly to get by a ridge on the head. Engage the threads only about 1/2 to 1 thread, and hold the washers in place with some grease. Once you get the manifold on the studs, tighten the nuts just enough so they won't accidentally fall off. Now make sure the manifold is fully lowered so that studs rest on the top of the manifold flange groove. On my boat I need to whack it a few time with a rubber mallet to get the assembly full inserted into the exhaust hose. Don't fully tighten these nuts yet.
2. Now, try to install the fore and aft bolts. If the manifold is fully lowered on the studs, they should go right in. On the aft bolt, where's there's not a lot of room; I had to push/hold the bolt in place with a large flat screw driver, while turning it with the wrench.
3. Once you have all 6 fasteners installed, fully tighten all of them.
4. Reinstall the all hoses, and refill the engine with antifreeze.
It's not too bad if you use this approach. It now takes me about 1/2 hour to get it off, and probably 45 minutes to get it back on. My first time, without knowing this process it took me at least 4 times as long, learning on the way.
Good luck.
_________________ Jim Voelxen Odyssey #191 Home Port: Osterville, MA
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