Hi All- Back from the UK and I wanted to bring you up to date on this project to get more advice. To recap, raw water was not coming out the transom port and the engine was on its way to overheating. After much good advice and confirming the water pump was working, I removed the hose at the entry to the exhaust riser and found lots of water coming out when the engine was run briefly. That points to the problem likely to be the exhaust riser itself being plugged and restricting water flow. This seems a common problem on Yanmar's but I had not heard of it as a routine problem on Universals (M4-30). But it is 25 years old. I finally got the old riser removed yesterday and it does appear blocked in that if I run water into the input port, nothing comes out of the exit port. I have a new one on order from a Universal parts distributor.
The advice I need is on the re-installation. There is a mounting flange that adapts the manifold to the riser. Large threaded pipe carries the gasses out of the manifold and interfaces the flange to the riser. I cut that with a hacksaw to get the riser off. A new flange, gasket, and connecting pipe will all come with the replacement kit. There are three threaded rods coming out of the manifold that the flange mounts to, with three nuts- two on top and one underneath. The two on top came off easily. The one on the bottom was difficult to access, but even with heat or impact or breaker bar and a week of PB Blaster, it would not budge. I ended up cutting the threaded pipe between the flange and the riser to get the whole thing off to get better access, but still no movement of the nut. The threaded rod is threaded into the manifold at the other end, and one might think that it might unscrew, but it didn't move either. I am not sure if that is reverse threaded or same thread in two directions so not sure how I would remove that to replace it. The nut is now so deformed from heat and force, that it is no longer straight sided. What are my options now? I can try grinding, but not sure how to approach that and with what bit on my Dremel. How do I get the residual nut metal off without destroying the threads? If I can get the nut off with only some damage to the threads, can I use a die to clean the threads? If I cut the nut off with the rod, how do I attach the lower part of the flange to the remains of the threaded rod? Thanks- Dave David Knecht S/V Aries 1990 C&C 34+ New London, CT
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