Yanma GM20 Jammed anodes

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Horsain

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I have a Yanma GM20 which is about 16 years old and came with the boat which I purchased last year. I wish to replace the 2 engine anodes but they seem jammed and impossible to remove. I dare not use too much force for fear of cracking the engine block. Has anyone any ideas how to remove the old anodes. Many thanks
 
I too was unable to undo the large hex head nut holding the rear (gearbox side) anode on my 2GM20 so I always remove the small casting (4 small bolts) behind it. You can then unscrew and renew the anode from the inside. Then refit the casting on a new gasket. Have been doing it this way for last 20 years.

Hope this helps

SteveIOW
 
I am facing the same problem, having just inherited a 3GM30.
Does the anode just go into bare metal, or will something dribble out when I undo it? (my only previous experience of engine anodes was on a Beta, where the anode was in the heat exchanger, and changing it involved losing a bit of coolant).

Also, I seem to have a second, smaller, anode on the starboard side of the engine, just under the heat exchanger. Looks a right b*gger to get to...
 
No clever advice for the jammedness, except to eat your weetabix before trying again :). I can't imagine how failing to unscrew a bolt (which is what it amounts to) would crack the block it's screwed into.

After struggling a little with mine the first time, I used to reassemble them with a bit of white grease on the threads - came out easily the next year.

Obviously the anode pokes into the water jacket, or there would be no point having it. But the 2GM20 is raw water cooled, so you don't need to worry about "losing" anything. I used to drain ours (two plastic drain taps, check the manual for their locations as I've forgotten :) ) before taking out the anodes anyway.

Pete
 
Kelpie said:
I am facing the same problem, having just inherited a 3GM30.
[...]
Also, I seem to have a second, smaller, anode on the starboard side of the engine, just under the heat exchanger.
Click to expand...

Hold on, something weird going on here. Is it a 3GM30 (raw water) or a 3GM30F (fresh water)? The former does not have a heat exchanger, and I would not expect the latter to have anodes!

Pete
 
They really do need brute force and a correctly fitting ring spanner with some form of extension bar on it. Watch your knuckles when it does eventually give.
 
prv said:
Hold on, something weird going on here. Is it a 3GM30 (raw water) or a 3GM30F (fresh water)? The former does not have a heat exchanger, and I would not expect the latter to have anodes!

Pete
Click to expand...

Well spotted. It was a raw water cooled 3GM, but the previous owner had it converted with the addition of a heat exchanger, so does that make it a 3GM30F? Or some kind of Frankenengine?
Also, the location of the heat exchanger makes it very hard to get to the smaller anode.
Do I need to worry about the anodes at all...?
 
Kelpie said:
Well spotted. It was a raw water cooled 3GM, but the previous owner had it converted with the addition of a heat exchanger, so does that make it a 3GM30F? Or some kind of Frankenengine?
Also, the location of the heat exchanger makes it very hard to get to the smaller anode.
Do I need to worry about the anodes at all...?
Click to expand...

The anodes are to stop the dissimilar metals inside the engine from corroding in seawater. If you don't have seawater inside your engine then I don't think you need anodes. The coolant mix (aka "antifreeze", though that's not its main function) should contain corrosion inhibitors that do the same job.

Pete
 
Steve I wold like to try your idea of removing the casing but when I undid the bolts it seemed struck, I presume I just force it a bit to remove it, am I correct in thinking that coolant will leak and do you know what the casing protects. Also do you have details of the new gasket that I should buy
Many thanks
 
Warming up the motor did help and I was able to change the anode on the starboard side of the engine, but the anode at the back remains jammed. The main issue here is leverage, there is not enough space to work.
 
Horsain said:
Warming up the motor did help and I was able to change the anode on the starboard side of the engine, but the anode at the back remains jammed. The main issue here is leverage, there is not enough space to work.
Click to expand...

ditto ditto...

My Yanmar 2QM has two large (nearly an inch across) square headed plugs. I've dodged the job for two seasons but got them off this weekend. The front was quite easy and the back needed the trick to remove the whole housing.

Mine were 50% consumed, so overdue but working.

Have you freed off your housing? Sideways tapping may help if possible. Make sure you haven't missed a sneaky bolt.
 
Sam, this may depend on whether the engine is raw sea water cooled or not. My motor is cooled by sea water (ie it does NOT have a heat exchanger) and does require anodes to protect it. There are 2 one on the starboard side and one at the rear, above the gearbox.
 
SamSalter said:
My 2GM20F has no anodes.
The Yanmar parts manual shows none either.

sam :-)
Click to expand...

The "F" in the number indicates that it is fresh water cooled. Freshwater cooled engines are protected from corrosion of the cooling circuit by the inhibitors in the antifreeze. They therefore do not need anodes anymore than car engines do.

BUT

Some freshwater cooled engines will have an anode in the salt water parts of the heat exchanger. It depends on the design of the heat exchanger and in particular the materials from which it is made.

In all cases RTFM. Read the full manual.
 
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