Beta diesel engone stack tube removed, cleaned and replaced with new O-rings

Middle of January 2017 - Tied up in Marina Mazatlán, Mexico

 We did this heat exchanger stack tube cleaning on the Beta diesel engine sitting at the dock in Marina Mazatlin. Made for low stress as we did not have to go anywhere.
 Front of Beta engine. The black around the stack tube is the seal.
Front of Beta engine heat exchanger.

 Front of Beta engine.
 Rear of Beta engine heat exchanger before removing housing
that holds in the stack tube in the heat exchanger.

Engine stack tube housing end from back of engine. It contains the engine zinc.
We believe this is made of bronze and resists the saltwater corrosion well.
I am holding the rear of the stack tube housing up-side-down. The impeller pumps the salt water through some piping to the stack tube end cap housing. The end cap housing separates the stack tube so that the incoming salt water flows through the bottom half and then at the other end on the front of the heat exchanger the stack tube has another end cap so the salt water is forced back out the top half of the stack tube and then out the exhaust. This cools the antifreeze which this stack tube is surrounded by.  

You can see the corrosion around the aluminum heat exchanger housing.
The black ring is the seal. The seals should be replaced each year. These seals I left in too long. They have been in 2-3 years as I mistakenly thought they got replace at 750 engine hours. I'll need to read the manuals each time or set up a better engine maintaince schedule. However no harm no foul. There was no damage done to the housing and new seals will seal up just fine. 
Dirty stack tube. We did not have a problem with the Beta engine over-heating last season but it does look like it needs cleaning.
Some slimy water from stack tube.
 The rubber seal rests against the area shown.
Skewer stick Debbie gave me to clean the stack tube. It goes in about 3\4 of the way so we needed to slide in from both sides. Did one side at a time.

Here is the engine zinc and we were having problems sealing it. We were having to use Teflon tape to seal it when screwing it in. It seems our zinc template for cutting off the new zinc ended up getting too long. Then we would use it to cut the new zinc and the new zinc would be too long. You can see the zinc butting up against the edge of the housing, preventing it from screwing in all the way. Just not quite screwing in all the way I think. Next time we will cut the zinc a bit shorter and try it. I thought we had tried a shorter zinc but it still leaked but possibly we did not try a shorter one?
Zinc butting up against housing.
This time this whole procedure went perfect. It helps to be at the dock in a marina.
No pressure. The first time we did this we did it at anchor in Barra-Bahia de Navidad and there are a few tricks to it. I did it three times or more before getting it in and not leaking. Each time we had to replace the antifreeze as the salt water mixed with it.

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