Engine Zincs Yanmar 6BY

[LET IT BE]

Today I was about to change the engine anodes On my Yanmar 6BY. They were replaced in the spring this year. When I applied some force the brass nut sheared off the upper anode. It was obviously corroded and the brass was weak. The threads and any remaining zinc is plugging the hole. Is this a common problem and what do,you suggest. I am thinking that the anode fits in what seems to be a casting attached to the top of the heat exchanger that is attached to the block with about 4 Allen head screws. If I remove this part then I can attempt to remove the remaining part of the anode and brass threads on a work bench and hopefully find that the threads in the casting are still able to be cleaned up and intact enough to handle a new anode. If the threads in the casting are corroded is that part available and could you give me the part number and suggest where I could buy it?
I am surprised that this part corroded so badly in 8 months. The specs call for replacement either once a year or every 250 hours so I am well within these limits . Is there anyting that I should be checking that might explain this corrosion? I had the boat hauled a couple of weeks ago and of all the other Zinks that were replaced at the same time this spring, the only ones that I found to have significant loss were the small thruster anodes and they were less than half gone so I don't think I am getting excessive galvanic corrosion in the rest of the boat. I also replaced the engine ground strap in the spring on the recommendation of a mechanic who told me the braided metal one that was original are subject to failure so the block should be well connected to the bonding system. I would appreciate input from anyone who has had similar problems.

 

[knotflying]

Here is the part number for the front heat exchanger cap - 120650-18440. You may want to get the o-ring as well - 120650-18470 Those zincs are prone to deterioration, but I am surprised at the brass plug. The bottom zinc corrodes fast. Like every three months or so. Is it possible that it was bound because of cross threading? I can't remember, but can you get an easy out in there? Perhaps spray some PB blaster on it and let it sit for a day and then try removing it. Unfortunately it does seem like you may have to remove the cap.

 

[LET IT BE]

Today I removed the four Allen head bolts after removing the various hoses that are in the way but the end cap does not want to loosen and I don't want to damage it by using too much force or harming the block by driving a screwdriver between the cap and the block. Do you know if the cap is a flush fit with the face of the block or is there a recess that would make it harder to come loose if there is some rust/corrosion. You mentioned an O ring. Where does that fit?

 

[knotflying]

The o-ring is directly behind the cap. Not sure why the cap won't just pop off.

 

[LET IT BE]

This is a follow up:
I got the cap off ok by gently driving a screw driver between cap and casting.
The zinc was only half gone.
The reason the brass hex sheared off was not due to over tightening or cross threading!
The remainder if the brass with the threads and the Zink loosened with the drill I was using to make a hole for an "easy out"
The plug broke because corrosion got between the outer end of the zinc and the inside of the brass fitting and the pressure of expansion was so great it cracked the brass metal so the hex part broke off with very little turning torque.
This part was an official Yanmar part.

It was a pain having to remove and re-install that end cap !