Internal Zinc on a Yanmar 2 GM

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Nelsonhow

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Jan 4, 2007
406
Hunter 30 Centerport
I just found out that my 1983 Yanmar 2 GM has 2 internal zincs. One in the rear and one on the starboard side behind the diesel oil filter and above the manual lift pump. The starboard zinc needs to be changed. It's attached to a big plug on the block. The PO rounded off the plug but I can still grip it with a socket. The space is limited but I couldn't budge it. I 'm afraid that I'll crack the engine block if I force it.

Any suggestions would be appreciated....
 
rardiH36

rardiH36

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Jun 21, 2007
2,117
Hunter Cherubini 36_80-82 Sausalito / San Francisco Bay
Just in the off-chance it might pertain -- your 2GM20 is the sea water cooled variety? I ask because my 2QM20 is seawater cooled design but was retrofitted to self-contained anti-freeze coolant going through the engine. It has engine zincs, but they don't need changing anymore because sea-water no more.

The PO of my boat thought he had a 2GM20, so I inherited a GM series manual. It says the zincs need to be replaced every 500 hours of operation, but recommends more frequently. Why has only one of the two zincs attracted your attention for changing?
 
rardiH36

rardiH36

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Jun 21, 2007
2,117
Hunter Cherubini 36_80-82 Sausalito / San Francisco Bay
garyc said:
does replacing zinc's require a gasket?
Click to expand
Looking at the service manual pages pertaining to engine zincs, no mention is made of gaskets. The illustrations don't indicate them either. However, if they exist, my guess is they would be the copper washer type like on oil drain plugs? One illustration shows a "packing" at the interface of the zinc and the iron plug housing. But nothing between the plug housing and the engine. Best talk to a Yanmar dealer for advice.

Once when I drained my anti-freeze coolant from my converted 2QM20, I removed a zinc plug just to see what the zinc looked like. I later just screwed it back in. I don't remember if a copper gasket was fitted, but I wouldn't have fitted a new one. No leaks afterward. But my engine wouldn't have had corrosion pitting in the area due to seawater cooling.

An exception might be for the 1GM10 model. This has only one zinc. By the illustration is threaded into a flange plate. The plate is then fastened against the engine with two bolts. A gasket isn't shown, but likely one is needed.
 
kloudie1

kloudie1

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Nov 6, 2006
10,052
Hunter 34 Mandeville Louisiana
I recently changed some in a 2 QM 20 and the new zinc came with the new gasket in the package; a copper gasket,..
Looking at the parts manual for the 2 GM (not 2 GMF) the copper gasket is shown as part number 23414-250000.
The plug in the head is 122780-09320. The one (2 ?) in the block is 128270-09300
I think the zincs are 27210-200300. I think that Yanmar packages the whole thing together including the o-ring for the zinc.. and I don't have a number for that ..but your friendly Yanmar parts guy should be able to help.
It looks like that zinc in the head is in a cover which bolts to the rear of the cylinder head. An option to get the zinc out would be to remove the cover and work on it outside..
The gasket for that cover to the cylinder head is 121450-11680
These are for a 2 GM.. not a GMF nor a QM (although the QM's may use the same zinc, and copper gasket)
 
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Nelsonhow

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Jan 4, 2007
406
Hunter 30 Centerport
Rardi,

I bought both zincs intending to replace them both but could only remove the rear zinc. I did this by removing the access plate that the zinc is screwed into and clamping it in a a bench vice and removing it. The I reassembled the plate and new zinc.

I couldn't get the second one on the side of the motor out. I figured replacing one is better than none and am now puzzeling how to get the second one out without destroying the block....
 
rardiH36

rardiH36

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Jun 21, 2007
2,117
Hunter Cherubini 36_80-82 Sausalito / San Francisco Bay
Hi Nelsonhow:

Previously mentioned was PB Blaster. Worth a try. But give it lots of time to work. I've sometimes had success with seemingly hopelessly frozen stuff eventually freeing. Spray on. Forget for a few days or a week. Spray again. Wait, etc.

How did the zinc you did remove look? Just curious. I've always thought it amazing that engines can be cooled with salt water and if maintained correctly can last decades just like the self contained/heat exchanger types. Any idea how long the engine has been used since the previous change-out?
 
kloudie1

kloudie1

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Nov 6, 2006
10,052
Hunter 34 Mandeville Louisiana
I don't think you can torque the plug enough to hurt the block.. As previously noted, put PB blaster on the threads, being careful to not get any of that stuff on the fuel lines or the lift pump edge where it can get to the diaphragm.. Ya might try one of those socket things that have a bunch of octagonal, hardened steel pins inside. They are advertised to grab something like the rounded head of that zinc holder .. Like this http://www.google.com/products/cata...=wo9zTuboMYKKsQKyhMWLBQ&sqi=2&ved=0CEQQ8wIwAA#
only maybe the next larger size.. Measure to find out.. I thibnk they can be found at some auto parts places and home stoores and places like Ace Hardware.. but give the PB a week or more to work and tap it with a hammer some before trying to unscrew... Worst case is to pull the pump and filter to get some working room .. if the universal socket or small pipe wrench or vice grips can't get it, then it is time to get a drill (probably going to need a "close quarters" drill) and start drilling it out.. (No fun at all) If ya have some gear heads for buddies, the promise of a cold beverage after the plug is out sometimes will loosen things! Good Luck..
 
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