Yanmar 2GMF to 3GMD swap??

Jan 24, 2021
19
Hunter 31 Nashua
Hi All,

Just picked up my first sail project (85 hunter 31) and I was planning on pulling and rebuilding the current 16hp 2GMF engine but have an opportunity to instead get a newer (and in much better shape) 20hp 3GMD, the 3GMD includes a 2.6 km3-A and the wiring harness for an irresistible price. Curious to know if this swap has been done already. There's little for peripherals on the old one that would be salvageable after years of sitting. This project is going to be somewhat of a total refit, so all would have been coming out anyways, just curious to know if there's any pros/cons I should consider based on others experience with these 2 motors.. Thanks!
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Motor mount alignment and transmission mating would be my guess. Probably less work than a rebuild if the newer engine is in good condition. How many hours on it? I have the 2GM in Bella.
 
Jan 24, 2021
19
Hunter 31 Nashua
The person selling doesn't know how many hours, I basically have little to go off other than the fact that it's incredibly clean, and my current one looks like it's been sitting at the bottom of the ocean since it was taken out of the water 5-6 years ago. Little bit of a gamble, but again, the price is irresistible. The current mounts in mine are not even close to salvagable to would all be coming out anyways
 
Nov 6, 2006
9,884
Hunter 34 Mandeville Louisiana
Check that the GMD has a heat exchanger on it for "fresh water cooling" .. Kind of confusing in your neck of the woods since your sailing water is fresh.. but it should have a heat exchanger .. Not super important if you sail on fresh water, but if the engine is "sea water cooled" (no heat exchanger) and came from a salt water boat, I'd want to inspect very carefully.
 
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Jul 7, 2004
8,402
Hunter 30T Cheney, KS
These are just my opinions. I've swapped a few car engines but never a boat. I even rebuild the diesel in my old Mercedes:
Anyone can power wash and even paint an engine for show. Best guarantee is to hear it and do a compression test. The nice thing about rebuilding one is now you have a "new" engine to rely on. And everything will go back with no headaches. It could be that the swap would work great but it's a gamble since you know nothing of its internal condition.
 
Jan 24, 2021
19
Hunter 31 Nashua
Ok well, I've basically going back and forth with the guy, story goes, he got it with a bunch of other stuff in trade or something, doesn't know much about it or it's history. After hemming and hawing about all that, he basically just told me to come get it all out of his way for $150!!! I really can't go wrong with that!!!
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
It's a great price if it's in good shape. Otherwise you may be back at square one with an engine that you had to make fit. Let us know how it works out :thumbup:
 
Jan 24, 2021
19
Hunter 31 Nashua
Thanks for the dimensions! They look extremely close surprisingly. I already planned on a rebuild of the old so worst case, I can rebuild the new if needed. I've literally rebuild 100s of gas engines, diesel is all new to me though so it will be a learning experience, luckily the father-in law is an old school diesel heavy equipment guy who's rather excited to get involved :)

Pics of the 3GM attached!!
 

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Dec 14, 2003
1,393
Hunter 34 Lake of Two Mountains, QC, Can
Pictures show that the 3 GMD is not fresh-water cooled. We do not see the heat exhanger on it. Not as important as Kloudie said in freshwater lakes or rivers although it does insure more constant engine temps.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Does not having the heat exchanger mean the water heater, if there is one onboard, will have to rely on electrical power?
 
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Dec 14, 2003
1,393
Hunter 34 Lake of Two Mountains, QC, Can
Does not having the heat exchanger mean the water heater, if there is one onboard, will have to rely on electrical power?
Yes ! Although I have seen some jury-rigged installations but they never seemed to work properly.
 
Jan 24, 2021
19
Hunter 31 Nashua
So I'm clear, we're talking about a closed loop cooling system, right? So I could just add the missing heat exchanger??
 

HMT2

.
Mar 20, 2014
899
Hunter 31 828 Shoreacres, TX
Yanmar has two styles of engines one is directly cooled only by the flow of seawater, the second has a closed loop cooling system. For instance in my ,83 H31 I have a 2GM you have. In yours a 2GMF which indicates it has a closed loop fresh water cooling system where as my 2GM is only cooled by seawater. Not sure about your new three banger though. You can take a look at your old engine and it should have the sort of cooling system they are talking about.
 
May 17, 2004
5,031
Beneteau Oceanis 37 Havre de Grace
So I'm clear, we're talking about a closed loop cooling system, right? So I could just add the missing heat exchanger??
More than that if you want a closed loop system. All of the diagrams I can find for a 3GMD show it as raw water cooled. To convert from raw water to fresh water (closed loop) cooling you’d need to add a heat exchanger and also a water pump for the closed side. You could keep it as raw water cooled, which in fresh water won’t be too bad, although as others said you won’t be able to use it for heating water, and if you want to bring the boat (or sell it) in a salt water environment it won’t be as good.

For $150 it might still be worth a shot, depending on how bad your current engine is. When you say it was “taken out of the water 5-6 years ago” do you mean the engine was in water, or just the boat?
 
Oct 29, 2005
2,355
Hunter Marine 326 303 Singapore
Ok well, I've basically going back and forth with the guy, story goes, he got it with a bunch of other stuff in trade or something, doesn't know much about it or it's history. After hemming and hawing about all that, he basically just told me to come get it all out of his way for $150!!! I really can't go wrong with that!!!
Let me guess your hemming and hawing is a tactic to press the price down? ;) :clap: That I gonna learn :biggrin:
 
Nov 26, 2014
51
HUNTER h31 Northport L.I.
I think length of the 3 cylinder motor would mean cabinet work. I know my 2gm30f dampner is close enough to front cover that it wore a hole in insulation. and I don't think there is that much room to go back, exhaust elbow as well as room for shaft seal could be more work than worth not to mention new shaft , and new prop as the old one wont be right for application. rebuild 2 cylinder and resell 3 cylinder for money to do it.
 
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Jan 24, 2021
19
Hunter 31 Nashua
Thanks for all the input! I will exclusively use this in saltwater. width and height are almost the same, the depth difference (front to back) looks like 5", i'd plan on building a new front cover as I wouldn't want to try and reposition the tranny back at all.. I'll be picking up the 3gm thursday either way and pull the 2gm when it's a little warmer here. I'm pretty much gutting everything in this boat so will just have to weigh out the swap once I get a better feel for what's involved.. I'll probably rebuild both either way and sell whichever doesn't make the cut
 
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Aug 10, 2020
511
Catalina C25 3559 Rocky Mount
run it on the floor before you start getting too excited. odds are it's fine, but I wouldn't start swapping it until you verify it is good.
 

Blitz

.
Jul 10, 2007
672
Seidelmann 34 Atlantic Highlands, NJ
Just to clarify, the 3GMD is raw water cooled.

you can still route it through the water heater's heat exchanger to create pretty warm water, not hot.

Just because you use a raw water cooled Yanmar in Salt water, it won't be a loss. you'll gain the HP you might want, and with proper maintenance it will be fine. My 3GMD is about to start it's 37th season.