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casey1999 01-13-2011 01:36 PM

Yanmar 3GMD Rebuild
I have a Yanmar 3 3GMD engine that is close to 30 years old. The engine runs and fits the boat well. Being direct sea water cooled I could see in the future it may give me problems. Could the engine be rebuilt with a new block and other required parts economically and be good for another 20 or so years? I have heard these old engines are built heavy than the newer Yanmars. I like the fact it is direct sea water cooled as it is very simple and has fewer parts to break or maintain than a freshwater cooled engine. Seeing the engine has lasted 30 years so far seems to indicate direct sea water cooled was not so bad.
Thanks, Casey

Ilenart 01-14-2011 01:50 AM

Maybe, maybe not. The only way to find out is pull it apart and find out. I just had a 22yo Yanmar 20hp pulled out for a rebuild and in soon became apparant that a rebuild was not worth it and I went for a new engine.

The seawater Yanmar's has anode's that need to be replaced often. If they have not been done regularly (mine were not serviced for 5 years) there is a good chance the engine is a writeoff. However if the anode's have been inspected yearly and replaced often a rebuild could be worthwhile.


tommays 01-14-2011 04:34 AM

Opening up a 30 year old saltwater cooled motor that still runs well is Pandora's BOX defined

bljones 01-14-2011 07:47 AM

If it ain't broke.....
Run it until it is. Then worry about it.

casey1999 01-14-2011 10:30 AM

Replacing the Anode
Thanks for all the advice. I recently bought the boat and have been doing the engine maintenance. One item was the anodes. I do not think they had been serviced in over 5 years. I removed the one on the head and installed anode (the original was totally gone). I tried to get one off the block but ended up rounding off the anode plug- looks like I will have to drill it out without damaging the block threads. I have not had a chance to try to remove the 2nd anode in block. I have heard maybe holding dry ice to the plug then put a wrench to it. I did use a laser cut socket on the plug and it still rounded- I think there is major corrosion between plug and block.

Any advice for trying to remove the anode plugs?

tommays 01-14-2011 02:10 PM

Your into the don't fix it if your not prepared for the repercussions stage of the motors life as even a skilled drill and tap person can have one run off the tracks when trying to hand drill out something in a confined area.

Any good shop is going to have a corrosion damage wavier as when matiance gets let go to long all kinds of things get broken trying to take them apart no matter the level of caution

casey1999 01-14-2011 04:39 PM

Should I even try to drill out the old anode plug or just leave it as it is knowing there is no anode protection?

I still have the other anode plug I can hopefully get out to offer some corrosion protection- if I can get it out.

sirenamary 07-12-2011 06:52 AM

Hi Casey, I am facing the same issue - did you get your anode out OK?

casey1999 07-25-2011 04:32 PM

Sorry for late reply. I did get the anode plugs out- Not such a bad job with the right tool.
Bolt Extractors - Tools - IRWIN TOOLS

Since the bolt head was not in good shape, used the Irwin model #53917 24 mm bolt extractor. It worked great. Before using I heated the anode plug up with a plumbing type propane torch. Estimate heated to 180 deg F. I had a lot of fire extingishers available and i took a wet rag and put it on the surrounding parts to keep them cool. I also removed to diesel fuel pump off the engine and the fuel lines as the plugs are close to these items and did not want to damage or set on fire. I did use some PB Blaster before and after heat cycling to try to make removal easier- because the plugs are sealed I do not think the PB Blaster did any good as it had no way to get into the threads. I used a 4 foot pipe on the socket wrech with the Irwin bolt extractor. I had almost my full weight of 185 lbs on the 4 foot extension before the anode plug began to very slowly turn. At first I thought I was tearing the plug apart but I was lucky and it came out. Did same procedure on 2nd plug and it worked. I did try to use dry ice prior to heating (I was afraid of a fire) but ice did not work. I am told you can mix alchol with the ice to make a slurry which will allow the ice to cool the bolt better but I did not do this. I installed new anode plugs as the originals were in bad shape. I used anti sieze on the new plugs and hopefully will allow easy removal. I will inspect anodes annually.

PS- keep the PB Blaster away from engine seals (transmission seals) and gaskets and fuel pump. I have heard the fluid can destroy these parts. Use a Q-tip to apply- not spray.
good luck

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