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28-11-2023, 15:53
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#1
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Registered User
Join Date: Feb 2019
Location: Ashfield, MA
Boat: Morgan 323
Posts: 83
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Yanmar 3GM-D with freshwater conversion to serpentine belt?
I have a 3GM-D that is now freshwater cooled. At some point before my ownership a heat exchanger and additional water pump were added in order to do this conversion. The top water pump and rearmost belt are the add-ons.
I am interested in changing to a higher output alternator and a serpentine belt. I do have a message in to Balmar, but I thought I’d ask here to see if anyone has done this already. Thanks!
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28-11-2023, 16:55
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#2
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Registered User
Join Date: Jun 2009
Location: Annapolis, MD
Boat: Sabre 34-1 (sold) and Saga 43
Posts: 2,609
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
With that small engine and small boat, what is meant by "high output?" If you are looking for less than about 120A, you might be able to get by with a single poly-v that goes from crank to water pump to alternator and back. That makes it fairly easy.
Unless you go big with Balmar, the crank pulley is the real challenge. It was for me on my 1998 4JH2E.
One belt requires the water pump to slide back a bit to align.
I know, not much of an answer. Hopefully some of the thoughts help.
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28-11-2023, 17:22
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#3
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Moderator
Join Date: Feb 2010
Location: Australia
Posts: 3,764
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Thats not a job I’d want to tackle, not because its technically difficult, I just think the labour cost might be high. Sometimes the juice isn’t worth the squeeze. Thats an interesting conversion to fresh water cooling, I did a similar thing to repower an old “ life of Pi” lifeboat with a 3T yanmar.
I’ll be interested to see how your high output alternator works out, the catamaran I’m working on now has twin 3GM30 F’s and very large alternator on the Stbd engine that only charges the lithium chemistry house bank, driven by a single gates green stripe vee belt…. it sure sheds a lot of belt dust but can’t go any tighter for fear of overloading the circulating pump pulley and bearings….. the perfect situation for either a toothed belt or a multi micro vee.
Ok, I just had a look at that stbd engine alternator and its not as I described. It has a dedicated extra pulley on the crankshaft and can be adjusted by rotating the alternator…… the coolant circ pump is driven by the original pulley but has an idler to adjust the belt tension.
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29-11-2023, 08:02
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#4
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Registered User
Join Date: Feb 2019
Location: Ashfield, MA
Boat: Morgan 323
Posts: 83
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Quote:
Originally Posted by sailingharry
With that small engine and small boat, what is meant by "high output?" If you are looking for less than about 120A, you might be able to get by with a single poly-v that goes from crank to water pump to alternator and back. That makes it fairly easy.
Unless you go big with Balmar, the crank pulley is the real challenge. It was for me on my 1998 4JH2E.
One belt requires the water pump to slide back a bit to align.
I know, not much of an answer. Hopefully some of the thoughts help.
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Yes, it's helpful. The additional water pump on this one does make it a bit more challenging.
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29-11-2023, 08:33
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#5
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Registered User
Join Date: Feb 2019
Location: Ashfield, MA
Boat: Morgan 323
Posts: 83
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Quote:
Originally Posted by skipperpete
Thats not a job I’d want to tackle, not because its technically difficult, I just think the labour cost might be high. Sometimes the juice isn’t worth the squeeze. Thats an interesting conversion to fresh water cooling, I did a similar thing to repower an old “ life of Pi” lifeboat with a 3T yanmar.
I’ll be interested to see how your high output alternator works out, the catamaran I’m working on now has twin 3GM30 F’s and very large alternator on the Stbd engine that only charges the lithium chemistry house bank, driven by a single gates green stripe vee belt…. it sure sheds a lot of belt dust but can’t go any tighter for fear of overloading the circulating pump pulley and bearings….. the perfect situation for either a toothed belt or a multi micro vee.
Ok, I just had a look at that stbd engine alternator and its not as I described. It has a dedicated extra pulley on the crankshaft and can be adjusted by rotating the alternator…… the coolant circ pump is driven by the original pulley but has an idler to adjust the belt tension.
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I'm not too concerned about the labor since I'd be doing it, and if machining is required my brother is a retired toolmaker/machinist with a full shop at his house. So we could get it done. I was wondering if the Balmar kit would bolt right up, but after some email exchanges, it sounds like some custom work would have to be done in order to run the serpentine belt. Possible new water pump mounting, etc. I'm concerned that upgrading to a 100 amp alternator would smoke the v-belt under heavy load. Right now it's a small 35 amp; I'd really like to get more charging there since we're on the boat over 4 months during the warm season in Maine. Usually sailing, but we get 45 min minimum runtime between leaving the anchorage and getting into the next one.
Good deal on finding your adjustment on the stbd engine!
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29-11-2023, 08:36
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#6
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Registered User
Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,815
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
What size V belt is on there currently? Is it 3/8" or 1/2"? If it's 1/2" (or can be upgraded to 1/2") then you'll probably be fine with a 100 amp alternator and a good quality belt. A 5/8" V belt or a serpentine belt would be better, but not strictly necessary at that level.
If you can add an idler pulley for better belt wrap and get appropriate pulleys for the crank, coolant pump, and alternator, it would be possible to convert to a single serpentine belt that runs everything.
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29-11-2023, 08:55
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#7
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Marine Service Provider
Join Date: Jan 2013
Location: Kimberton,Pa.
Boat: Cabo Rico 34
Posts: 1,097
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Suggest posting your guestion over on the Yanmar Marine Engine Owner's Google Group
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29-11-2023, 08:56
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#8
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Registered User
Join Date: Feb 2019
Location: Ashfield, MA
Boat: Morgan 323
Posts: 83
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Quote:
Originally Posted by rslifkin
What size V belt is on there currently? Is it 3/8" or 1/2"? If it's 1/2" (or can be upgraded to 1/2") then you'll probably be fine with a 100 amp alternator and a good quality belt. A 5/8" V belt or a serpentine belt would be better, but not strictly necessary at that level.
If you can add an idler pulley for better belt wrap and get appropriate pulleys for the crank, coolant pump, and alternator, it would be possible to convert to a single serpentine belt that runs everything.
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I just found some better photos; looking at them, I think the water pump belts are 3/8” and the alternator is 1/2”. Maybe I’ll go that route first and see if the V-belt will do it without slipping. It would save some boat bucks and labor on my end. The boat is also 5 hours away, so that makes these projects a hassle when they get involved.
I do have some belt dust, but I think it’s because the mount for the second water pump was poorly done; it’s actually almost 1/4” out of line. I brought it home to make a new one this winter.
Thanks for your thoughts!
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29-11-2023, 08:58
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#9
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Registered User
Join Date: Feb 2019
Location: Ashfield, MA
Boat: Morgan 323
Posts: 83
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Quote:
Originally Posted by AA3JY
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I'll check it out. Thanks!
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29-11-2023, 09:33
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#10
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Registered User
Join Date: Sep 2019
Location: Bellingham, WA
Boat: Gulfstar 50 ketch
Posts: 344
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Since you're already making a new mount for the raw water pump, It looks to me like there might be room to move it further aft and run both water pumps with one belt, freeing up the front pulley(s) to be whatever you want them to be. I'm a big fan of serpentine belts for alternators - less tension means less side-loading on alternator and crankshaft bearings, and lack of belt dust is really nice!
I machined a bolt-on serpentine belt pulley for a 2nd alternator that mounts below the engine, the idea being to balance (i.e. cancel) the side-loads on the crank pulley - not hard to do if you've got access to a lathe, but a lot easier when the engine is sitting in my shop in a mockup of my bilge rather than 5 hours away!
You also might consider moving the raw water pump elsewhere (below or beside the engine) - dripping salt water on top of the expensive bits of an engine is a bummer! It looks like you could pretty easily modify (or remake) the mount for the lower pump to carry both pumps and drive them off the same belt. Easy to unbolt, bring home with both pumps, modify so both pulleys are in same plane, then bolt back up and measure for the correct belt length.
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29-11-2023, 09:59
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#11
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Registered User
Join Date: Jun 2009
Location: Annapolis, MD
Boat: Sabre 34-1 (sold) and Saga 43
Posts: 2,609
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Two comments:
1) If you are looking at a 100A alternator, your V-belt should be good. I'm running a 130A on a V, and I've only got about 100 degrees of wrap, compared to your 180.
2) Access to a lathe is HUGE. I have one, and it made all the difference (in addition to my 130 on the V, I added a 140 on a poly-V). I dug around and around and around, and found a poly-V from a Mac Truck that met my needs. Bought a chunk of aluminum, and machined an adapter between my crank pulley and the new poly-V. All in, well under $100. In your case, you might well be able to run it all on one belt. Alternator pulleys are a dime a dozen, either new or junkyard or in your parts bin. The water pump might present an issue.
Note, if you go all on one poly-V, you'll need to get a much larger water pump pulley to keep the same rotation ratio.
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29-11-2023, 13:38
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#12
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Registered User
Join Date: Feb 2019
Location: Ashfield, MA
Boat: Morgan 323
Posts: 83
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Quote:
Originally Posted by Bellinghamster
Since you're already making a new mount for the raw water pump, It looks to me like there might be room to move it further aft and run both water pumps with one belt, freeing up the front pulley(s) to be whatever you want them to be. I'm a big fan of serpentine belts for alternators - less tension means less side-loading on alternator and crankshaft bearings, and lack of belt dust is really nice!
I machined a bolt-on serpentine belt pulley for a 2nd alternator that mounts below the engine, the idea being to balance (i.e. cancel) the side-loads on the crank pulley - not hard to do if you've got access to a lathe, but a lot easier when the engine is sitting in my shop in a mockup of my bilge rather than 5 hours away!
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Nice work on your setup! And that's good food for thought. I'm going to spend some time looking at my photos and maybe do some brainstorming with my brother. We might have to take a ride to Maine with some measuring tools and get more photos. Thanks!
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29-11-2023, 13:40
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#13
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Registered User
Join Date: Feb 2019
Location: Ashfield, MA
Boat: Morgan 323
Posts: 83
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
Quote:
Originally Posted by sailingharry
Two comments:
1) If you are looking at a 100A alternator, your V-belt should be good. I'm running a 130A on a V, and I've only got about 100 degrees of wrap, compared to your 180.
2) Access to a lathe is HUGE. I have one, and it made all the difference (in addition to my 130 on the V, I added a 140 on a poly-V). I dug around and around and around, and found a poly-V from a Mac Truck that met my needs. Bought a chunk of aluminum, and machined an adapter between my crank pulley and the new poly-V. All in, well under $100. In your case, you might well be able to run it all on one belt. Alternator pulleys are a dime a dozen, either new or junkyard or in your parts bin. The water pump might present an issue.
Note, if you go all on one poly-V, you'll need to get a much larger water pump pulley to keep the same rotation ratio.
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That's a lot more good info; thanks! I've got a lot to think about now.
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29-11-2023, 21:48
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#14
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Registered User
Join Date: Mar 2016
Location: North of San Francisco, Bodega Bay
Boat: 44' Custom Aluminum Cutter, & Pearson 30
Posts: 826
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Re: Yanmar 3GM-D with freshwater conversion to serpentine belt?
My Pearson 30 has a Yanmar 3GM30F. I am running a 85 amp alternator on a 1/2" V belt for 2 years with no problems. I did get the better Napa belt for it.
I would love a lathe
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