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Old 03-13-2013, 05:16 PM   #1
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Engine anode failure?

This zinc anode was in-service exactly 12 months. Look how it was chewed off at the base but the anode looks mostly intact. This is a Perkins 4.236. I would hope it would have wore down all over.
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Old 03-13-2013, 06:32 PM   #2
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In my experience, the anode will break off early about 50% of the time. If your replacement schedule is annually, that will leave you without protection for most of the coming year. Add to that the restriction of water flow in the HE from the big lump of zinc and you wonder why they bother with an anode at that location. I have pulled my HEs (on several engines) apart to clean them out and never seen any evidence of electrolysis, so the lack of an engine zinc periodically hasn't made a huge impact.
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Old 03-13-2013, 06:38 PM   #3
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Greetings,
Mr. k. "never seen any evidence of electrolysis" Could it be that the wayward stub of the zinc is still in electrical contact with the body of the HE thus providing protection?
A problem I've run into the last couple of zinc service sessions is I've been unable to buy replacement zincs with the same threads as the existing brass plug. Likewise, my local zinc source does not have the replacements with the brass plug. "Nude" zincs only. My solution has been to re-tap the brass plugs. VERY easy. Same diameter, different TPI.
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Old 03-13-2013, 06:54 PM   #4
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I have the stbd engine and generator to do next but if the rest look like this I might try a spring-fall schedule. My boat in in the water all winter.
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Old 03-13-2013, 06:56 PM   #5
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Mr. RT I think I will try the drill and tap next time. the anode without the brass is 1/2 the price.


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Greetings,
Mr. k. "never seen any evidence of electrolysis" Could it be that the wayward stub of the zinc is still in electrical contact with the body of the HE thus providing protection?
A problem I've run into the last couple of zinc service sessions is I've been unable to buy replacement zincs with the same threads as the existing brass plug. Likewise, my local zinc source does not have the replacements with the brass plug. "Nude" zincs only. My solution has been to re-tap the brass plugs. VERY easy. Same diameter, different TPI.
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Old 03-13-2013, 07:26 PM   #6
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Greetings,
Mr. 36. I don't even remember drilling other than to get the remains of the zinc out of the brass plug. As I said, the diameter of the threaded recess in the plug is the same just the # of threads per inch is different. You're basically ruining the existing thread by cross threading with the tap BUT it dies appear to work. Could be the existing thread was 1/4-28 and I simply bastardized it with a 1/4-20 tap or vice-a-versa. Come to think of it I may have re-threaded the zinc instead. Good Grief!!! Don't ever get old. The memory isn't the FIRST to go....I also may have soaked the brass in something to dissolve the zinc???.....OK. I'll give up now.
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Old 03-13-2013, 08:37 PM   #7
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Yanmar brass zinc heads have a slightly different thread on the OD of the brass plug- BSP vs NPT and a very different thread on the zinc. The brass plug OD thread is close enough that I just buy new NPT brass plugs, screw them in and from that point forward I can use NPT pencil zincs.

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Old 03-13-2013, 09:57 PM   #8
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Long story short: I burned through two heat exchangers at $700 a pop on my old Onan generator before an educated tech figured out it really DID need an engine zinc and that it had the wrong heat exchanger case on it. So we ordered a new case that accommodates a zinc and wow those heat exchangers on Onans really can last a long time rather than the measly two or three thousand hours we were getting before!!
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Old 03-14-2013, 12:22 AM   #9
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RTF:
If the wayward stub was doing anything, it would be reduced in size. Mostly I see lumps that are not much reduced in size, just broken off.
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Old 03-14-2013, 07:31 AM   #10
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This zinc anode was in-service exactly 12 months. Look how it was chewed off at the base but the anode looks mostly intact. This is a Perkins 4.236. I would hope it would have wore down all over.
What is chewing the anode off? I too would have expected it to disolve fairly evenly.
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Old 03-14-2013, 08:48 AM   #11
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Greetings,
Mr. k. Good point.
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Old 03-14-2013, 11:28 AM   #12
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What is chewing the anode off?
Maybe this with carbide teeth?
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Old 09-17-2014, 01:16 PM   #13
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Onan 4 kw Generator Zinc

My 4 kw Onan generator is located aft in the engine room & sufficient access to the heat exchanger side is not possible. i can only quess the addition of an aftermarket Sen-Dure remote unit will be the recommended fix. Any other ideas?
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Old 09-17-2014, 03:34 PM   #14
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A couple things for you guys:

You can just cover the the bronze plugs with muratic acid in a small container and in a minute or two the zinc is gone and the plug is ready for a new zinc.

Galvanic activity is like a plating process. Realize that the zinc anode is sacrificing into the seawater to be deposited on the bronze internals. This zinc is keeping your bronze internals from sacrificing some other less active metal such as an exchanger housing material that has made contact with the bronze through the sea water somehow.
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Old 09-17-2014, 09:27 PM   #15
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Quote:
Originally Posted by Gulfstar 36 View Post
This zinc anode was in-service exactly 12 months. Look how it was chewed off at the base but the anode looks mostly intact. This is a Perkins 4.236. I would hope it would have wore down all over.
The anodes in my Perkins 6.354's heat exchangers only last about six months. Any longer and you get the results you are getting. You're protecting the bronze tubes in the heat exchanger on the saltwater side and not the fresh water (coolant) filled cast iron engine block. That's why there is no zinc in the engine block.

I cast my own zinc's and change them out twice a year. In the case where one breaks off, I melt it out of the bronze cap with a propane torch. When heating the cap, face the zinc side of the cap toward the ground or away from you in case there is any water under the zinc which may cause it to pop molten zinc when super heated.
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Old 09-21-2014, 06:38 PM   #16
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I have found that the zinc on my port engine lasts 2 times as long as on the port. I have added the stbd zinc to a 5 month check and replace.
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Old 09-21-2014, 07:03 PM   #17
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Check them every three months. If they are starting to go, they will unthread easily and no damage to the expensive parts.
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Old 09-21-2014, 07:40 PM   #18
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You may have a little stray current running around on that one engine...give it a good cleaning, replace all terminal blocks and wire ends,,,

Before all that I guess you could disconnect all grounds and see if there's any current between the block and a ground wire....
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Old 09-21-2014, 07:55 PM   #19
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If I left the same zincs in my genset for a year, it would not start. That's because the sound shield would be empty!
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Old 09-22-2014, 12:04 AM   #20
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I don't think I have ever had a zinc corrode evenly. Sometimes more evenly than other times but never evenly. Often if they are actually poked at when out a lot of metal will simply flake or slough off. It has done its job, just hasn't fallen away yet.

If you are leaving your engine zincs for a year that is far too long.

You should be checking them far more often, more likely every 2-3 months.
If they are ok then change them regardless but lengthen the interval a bit. When they look like they are half gone , it is definitely change time., but they may need to be poked or brushed a bit to really see how much is left.

But don;t just leave them, ever, with some predetermined idea of how long they will last.

Just in case you are thinking that the big hull mounted zinc will help, then NO, it won't. The engine , gear and any other internal equipment zincs are protecting closed, almost totally isolated systems, that have different requirments than the external metals.
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