1984 Caterpillar 3208NA OEM Alternator

[Skagit Song]

Greetings, My 1984 GB 36 Sedan has a single Cat 3208NA. A previous owner installed a larger frame size alternator that does not allow swing room for belt tensioning. I have since installed a genset and would like to go back to the OEM spec alternator (Cat p/n 2N7759, 51 amps). Is this a good idea? Where can I get said part? Cheers, belt slipping Bill

 

[Portage_Bay]

I'm curious. What alternator did the PO install and what is the interference? I have Cat 3208 naturals with the OEM alternator. I would like to upgrade to higher output alternators to reduce gen set run time.

 

[Skagit Song]

It's 81 amps and one of the mounting holes got drilled out to fit. The alternator case hits the engine block if you try to swing it in either direction. The belt has to fit perfectly and if it stretches you can't tighten it.

 

[Comodave]

Maybe you guys should swap alternators... Seriously I would look at different bracketing for the alternator. I would also want more than 81 amps for a high output alternator, maybe that was the most that would fit?

 

[Portage_Bay]

I had thought to offer to trade. But since his alternator is a bigger frame and hits the block it's not what I need.

I've talked to Marine HowTo. He sells a higher output alternator that will fit the 3208. Barely.
https://shop.marinehowto.com/produc...leece-neville-externally-regulated-alternator

There are two issues. A single V belt can only provide so much power and the 3208 has only a single V. The back of the OEM alt nearly touches the manifold. So a bigger frame is not an option. 90 amps is about it.

There are work arounds. Convert the 3208's single V to double V or serpentine with after market kit then build a bracket to hang the alt way outboard of the block and manifold. Seems like a lot of trouble and potential failure points.

When I upgrade it will be to two of the above alts, one per engine. Then tie the two together with either the Balmar Centerfielder or the Wakespeed WS50O into the house bank. Charge the start bank from the house bank.

Right now one alt charges the house bank the other the start bank. The internally regulated truck alts while rated at 50 amps put out about 25 amps.

For me another issue, simple to solve, is my engines are "energize to run" the solenoid is a constant 7 amp draw per engine. That's 14 amps wasted.

25 amps out of the alt, 14 consumed by solenoids. Doesn't leave much for charging. So the gen runs whenever we're underway

 

[Alaskan Sea-Duction]

Give these folks a call. I have 3208 T/A which has Motorola 51amp alternators.

https://www.dbelectrical.com/produc...ines-3196-3208-3406-3408-3412-3176-3176b.html

 

[Southern Boater]

I had thought to offer to trade. But since his alternator is a bigger frame and hits the block it's not what I need.

I've talked to Marine HowTo. He sells a higher output alternator that will fit the 3208. Barely.
https://shop.marinehowto.com/produc...leece-neville-externally-regulated-alternator

There are two issues. A single V belt can only provide so much power and the 3208 has only a single V. The back of the OEM alt nearly touches the manifold. So a bigger frame is not an option. 90 amps is about it.

There are work arounds. Convert the 3208's single V to double V or serpentine with after market kit then build a bracket to hang the alt way outboard of the block and manifold. Seems like a lot of trouble and potential failure points.

When I upgrade it will be to two of the above alts, one per engine. Then tie the two together with either the Balmar Centerfielder or the Wakespeed WS50O into the house bank. Charge the start bank from the house bank.

Right now one alt charges the house bank the other the start bank. The internally regulated truck alts while rated at 50 amps put out about 25 amps.

For me another issue, simple to solve, is my engines are "energize to run" the solenoid is a constant 7 amp draw per engine. That's 14 amps wasted.

25 amps out of the alt, 14 consumed by solenoids. Doesn't leave much for charging. So the gen runs whenever we're underway

I've got the same engines, appreciate the comments, it's making me think about my own system

 

[Capitaine R]

I don't know if this is in anyway possible, but I will throw it out there. Is there any way to install a tensioner pulley to the set up you already have so you can leave the alt hard mounted but still tighten your belt?

 

[Portage_Bay]

I don't know if this is in anyway possible, but I will throw it out there. Is there any way to install a tensioner pulley to the set up you already have so you can leave the alt hard mounted but still tighten your belt?

I do like the idea. Without staring at the front of the engines I can't be sure I can squeeze one in. It's a pretty tight fit.

 

[Portage_Bay]

Greetings, My 1984 GB 36 Sedan has a single Cat 3208NA. A previous owner installed a larger frame size alternator that does not allow swing room for belt tensioning. I have since installed a genset and would like to go back to the OEM spec alternator (Cat p/n 2N7759, 51 amps). Is this a good idea? Where can I get said part? Cheers, belt slipping Bill

I dragged the thread off from where you started. For an OEM alternator I'd try Tri-County diesel They're up your way. Or Hatton Marine in Seattle. It's been quite a while since I dealt with them but their parts department used to be able to do great things for out of production engine parts. A quick Google search turns up Riverside Alternators and Starters. They have an aftermarket that may work 2N7759 Caterepillar Alternator New Aftermarket. I have no experience with Riverside.

As for it being a good idea? I'm of the opinion it is not a good idea unless you want to run your gen full time, which is what I do. I've found the OEM alternator gets too hot at sustained high output. Pulling just 25 AMPS out of the OEM alternator for hours is working it pretty hard. It was designed to quickly charge a start battery in a truck.

Calculate or measure your cruising DC load, estimate the required start and house bank charge after being anchored overnight and see what you come up with. I don't know what your DC demands are but for me it's quite a list, especially in cold weather.

DC loads full time
Inverter
Two VHF sets
AIS
Sounder at inside helm
Laptop running Coastal Explorer at inside helm running off inverter
Garmin plotter / sounder on fly bridge
Radar on standby, transmit in fog
Autopilot
Energize to run solenoids

In cold weather

Hurricane heater

Intermittent and variable loads
Refer
Vaccuflush head
Lighting, the heads are pretty dark, we keep the aft cabin curtained so it's dark too.


Night or low vis
House lighting.
Running lights at night or in low vis
Radar usually on transmit at night always in restricted vis. i'm old skool.
Various short term AC loads off the inverter.

It all adds up quickly. If I run the gen for the first couple of hours after anchoring then bulk charge is handled by the charger. Shut the gen down and let the alternator charging the house bank take over and it runs very hot. I haven't measured the temp but it's painfully hot to the touch.

 

[jungpeter]

Hi Skagit Song,

The OEM alternators on my 78-vintage Tolly with CAT 3208NA engines are long gone, and since replaced by Leece-Neville 8MR 105A alternators, modified for external voltage regulation. The 8MRs are a tight fit, but DO fit in the OEM locations, and DO allow proper belt tightening of the single belts used to drive them. Due to the design of the front end of the 3208s, using multiple drive belts (or a serpentine belt) to power a large-frame high-output alternator is very difficult. And, 100 amps is about the limit for a single drive belt.

However, reverting to the OEM CAT alternator(s) seems like a poor choice to me. 51 amps is (in my opinion) undersized for modern DC power requirements. And unless you wish to go to the extraordinary effort of manufacturing bracketry and a multi-groove drive pulley to mount a large-frame alternator, possibly below the engine on centerline, I'm pretty sure you're stuck with about a 100 amp alternator, in the OEM location, such as the 8MRs or one of Balmar's choices. But you certainly don't have to live with CAT's OEM version.

And lastly, as I believe a previous poster recommended, I suggest you take a long look at Rod Collin's excellent website (https://marinehowto.com/), where he discusses alternators and regulators at length.

Regards,

Pete

 

[Comodave]

Hi Skagit Song,

The OEM alternators on my 78-vintage Tolly with CAT 3208NA engines are long gone, and since replaced by Leece-Neville 8MR 105A alternators, modified for external voltage regulation. The 8MRs are a tight fit, but DO fit in the OEM locations, and DO allow proper belt tightening of the single belts used to drive them. Due to the design of the front end of the 3208s, using multiple drive belts (or a serpentine belt) to power a large-frame high-output alternator is very difficult. And, 100 amps is about the limit for a single drive belt.

However, reverting to the OEM CAT alternator(s) seems like a poor choice to me. 51 amps is (in my opinion) undersized for modern DC power requirements. And unless you wish to go to the extraordinary effort of manufacturing bracketry and a multi-groove drive pulley to mount a large-frame alternator, possibly below the engine on centerline, I'm pretty sure you're stuck with about a 100 amp alternator, in the OEM location, such as the 8MRs or one of Balmar's choices. But you certainly don't have to live with CAT's OEM version.

And lastly, as I believe a previous poster recommended, I suggest you take a long look at Rod Collin's excellent website (https://marinehowto.com/), where he discusses alternators and regulators at length.

Regards,

Pete

+1 on Marinehowto.com. Very good website. If you can fit a 105 amp alternator and be able to tension it properly then that should fix the OPs problem. And you are right that a single belt can run a 100 amp alternator. Good post.

 

[Sax]

I replaced my Cat 3208 TA 51 amp alternator with a small case 105 amp alternator. Although the cases looked identical, there was a slight difference in the mounting holes. When I attempted to install the new alternator, the case contacted the exhaust manifold before I could adequately tension the stock Cat belt. I went to a slightly small diameter belt and was able to make the 105 amp alternator work without additional modification to the mountings. I sourced the 105 amp locally at an alternator repair shop.

 

[ghost]

Replaced mine with 100 amp Balmar on the single v belt. Then I used a centerfielder between both engines so I effectively see close to 200 amps between them. Went to a single large house bank and another dc charge controller to charge the starting batts.

Balmar no longer makes an alternator that will fit, so I’d use the Leece Nevil mentioned above. Once you have what works, just have them rebuilt not replaced.

 

[sunchaser]

Prestolite, the owners of Leece Neville, make many alternators for virtually any diesel. Many are rebadged to OEM specs. Each alternator that has been named by previous posters will have a dimensional drawing so you can match it up with current workable setup.

 

[Mike Negley]

power generation on the Cat 3208.

Most Cat engines have output drives for hydraulic pumps. I had a boat with Cats (twin 3126s) that had two pumps and the hydraulic system ran a generator, the windlass, stabilizers and the motor for the dinghy lift. Hydraulic power is very efficient and can be divided into components for better space managent.

 

[Portage_Bay]

I'm not aware of any block mounted PTO for the 3208. I've searched so I could easily add a hydraulic system. As far as I can tell it would need to be a pump mounted external to the engine either shaft or belt driven. Having had such systems built for work boats I know they're possible. But not really a good option for a pleasure boat.

 

[Mike Negley]

PTO on Cat 3208

You may find it on or near the transmission. it will be some what hidden. These engines are used on earth moving equipment which has accessories powered with hydraulics.

 

[BajaCruiser]

I am evaluating the purchase of a 1984 Grand Banks 42 with twin Caterpillar 3208s. I have been told by the broker representing the seller that these are 350HP diesels. The engine "Vin Numbers" that I have been provided are:
Engine vin #s
Port 01z03416
Starboard 01z03411

My Google searching has not led me to a site where these numbers yield any specifications. Can anyone guide me to a good info source, and/or provide me with any information on these specific engines? Thanks!!

 

[High Wire]

I am evaluating the purchase of a 1984 Grand Banks 42 with twin Caterpillar 3208s. I have been told by the broker representing the seller that these are 350HP diesels. The engine "Vin Numbers" that I have been provided are:
Engine vin #s
Port 01z03416
Starboard 01z03411

My Google searching has not led me to a site where these numbers yield any specifications. Can anyone guide me to a good info source, and/or provide me with any information on these specific engines? Thanks!!

You would be better off making this it’s own topic than tying this to an alternator thread.

 

[fgarriso]

This my help.

 

[tiltrider1]

Take your serial numbers, call a CAT dealer’s parts department and they can tell you what configuration the engines were in when they left the factory. They can also tell you if they were sold as a matched pair.

 

[BajaCruiser]

OK. Will do. Thanks for that guidance.

 

[BajaCruiser]

..... and - thank you for the specific guidance. I didn't see them until after I posted the comment above. I will try both avenues!!

 

[Southern Boater]

I am evaluating the purchase of a 1984 Grand Banks 42 with twin Caterpillar 3208s. I have been told by the broker representing the seller that these are 350HP diesels. The engine "Vin Numbers" that I have been provided are:
Engine vin #s
Port 01z03416
Starboard 01z03411

My Google searching has not led me to a site where these numbers yield any specifications. Can anyone guide me to a good info source, and/or provide me with any information on these specific engines? Thanks!!

The best site for Cat (or other marine diesels) related info is boatdiesel.com. You do need to pay a small basic subscription, but lots of good engine/transmission specific info.