Heat Exchanger Zincs

[hcpookie]

I've been lurking for some time on this great site, but I can't find the answer to this particular question:

I checked the condition of my HE zinc. The brass plug is flush - no zinc protrudes at all. Obviously, I need to replace the HE zinc.

Looking at the catalog pic of a new zinc, there should be about 1 inch clearance for the pencil zinc. When I probe the hole with a small screwdriver, I can insert it no more than the depth of the brass plug. On my HE, the opening appears to be blocked by a blackish sediment that appears to be metallic, but I am hesitant to probe deeper for fear of dislodging the material. It "feels" hard like metal, not soft like mud... in short, I cannot physically install a brand new zinc due to this blockage.

PO had done an acid flush last Spring, and installed a closed-loop fresh water system.

I am assuming that the sediment is scale (and other stuff) from the acid flush. (Bad assumption?)

A few questions:

1. What do do about the accumulation at the zinc? Remove the HE and flush? Pick it out with needlenosed pliers? Another acid flush? Ignore it?

2. Could it be something other than scale? Perhaps the zinc broke off? It would seem that the zinc should protrude about 1" from the end of the brass plug....?

3. The dock is shutting off the fresh water supply this week for the Winter, so I will most likely have to remove it and do all this in my garage (yippee). Are there any other proactive maintenance actions I should perform while the HE is removed?

4. The zinc seems rather small - how long should these last in Chesapeake Bay waters?

TIA,
- Jerry

[Don Moyer]

Jerry,

I'm not sure of the design of your heat exchanger, but most models have an end plate which is removable for inspection and cleaning. I think your questions could best be answered if you would remove the end plate and inspect the inside of your exchanger. The nature of the restriction should be obvious from such an inside look.

Don

[hcpookie]

Don, thanks for the reply! I did not see an endplate. That will be the first thing I look for.

Not sure where to look for model info. Am I mistaking what's normally called the exhaust manifold by calling it a heat exchanger? It's the rectangular assembly with 'universal' cast into the side, bolted above the carb.

[Don Moyer]

Jerry,

Oops! Heat exchangers aren't usually made of cast iron with large letters (Universal). It sounds more like you're talking about the manifold itself. Manifolds have 1/8" pipe-threaded drain holes in the lower aft corner, but no accommodation for a zinc.

By the way, these drain holes are frequently blocked and extremely difficult to reopen, due to the fact that they only go into the manifold approximately 3/4" and then take a 90 degree turn toward the front of the manifold and up about 45 degrees toward the lower corner of the actual water jacket (another inch or so away). During a rebuild we remove the freeze plugs and drive a small metal shaft through this drain passage from inside the water jacket. I don't consider this to be worth the effort in terms of owner maintenance.


Don

[hcpookie]

Thanks, Don! That makes more sense now. The plug has had something inserted in the end, and I assume it was a zinc. This came from a rebuild shop, so perhaps it was convenient to plug this with whatever they found laying about. I will assume someone found a used-up zinc plug and used it. I may consider flushing the whole thing out again this spring.

Thanks again!
- Jerry