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Obie 02-19-2017 09:37 PM

New to me 50, Steel full displacement, engine questions
I hope I get this correct. First I am very dislexic so please bear with me a bit.

I have had many boats, and have loved a few thousand open ocean miles single handing. Mostly on sailboats but have had a 48 foot uniflight, and a 42 foot Giles. I have just picked up a 50 foot steel boat, waterline is reported at 45.8 feet, beam is 15' 8". She was built in 1964 as a pilot boat an used in Alaska. She has an original single gray marine 6-71 natural. The wheel is around 36" with a 3" shaft. She holds over 3,000 gallons of fuel
My question here is I am thinking of re powering her. I was thinking a 5.9 cummins would be to small at 210 hp. Maybe a 8.3 cummins. Or I might have an option of obtaining a big cam 4 cummins just rebuilt for around 10k, no transmission. It is just a truck engine. I would keel cool, and dry stack?
I think the 5.9 cummins would stall when you engage? Also I need a hydraulic clutch pump to run bow thruster, and there is a large hydraulic windless for and aft, and a hydraulic crane on the deck.

This is a lot, any help would be great. Realy not sure we're I am going.
Thank you

Lepke 02-19-2017 09:49 PM

You'd have a tough time finding a more reliable engine than the 671 you have now. What is the issue? The engine is easy to overhaul, parts are everywhere, no electricity need beyond the starter. Many used PTOs are available for the engine front. I recently rebuilt 2 671s for under $5000 including having the heads professionally rebuilt.

RT Firefly 02-19-2017 09:49 PM

Welcome aboard. If she's running now, why repower? Save the 10K+ for filling that 3000 gal tank.

Nomad Willy 02-19-2017 09:50 PM

What's her displacement?
Welcome to the forum.

BandB 02-19-2017 09:53 PM

That's my question as well, WHY repower? What's your reason. That may also play a role in determining the best choice for a repower if you do so.

Xsbank 02-19-2017 10:04 PM

I have a 6CTA 8.3, M1 (250 hp) it is keel cooled, dry stacked and throws a 36" wheel on a 2 1/2" shaft. She also has a pto hydraulic pump and a belt-driven fire pump. She never stalls when I put her in gear and she's happy (but very noisy) at wot, 2100 rpm.

The 6CTA would be just fine, but like the other posters, why do you need to re-engine? Any chance of a picture of your boat?

healhustler 02-19-2017 10:05 PM

Have to agree on keeping the 671. There's a few boats out there that I may change out for a 4 cycle option, but you've got one that a singing Detroit just seems appropriate.

swampu 02-19-2017 10:16 PM

My vote is to keep the jimmy's, I love mine

O C Diver 02-19-2017 10:47 PM

Had a Grey Marine in one of my charter boats. The engine was built in 1944. For as big as it is, it's only 168 HP, but lots of torque. My recollection is that the head configuration limited the injector size, so not really possible to increase the HP. Not sure when they changed the head design to increase the HP.


O C Diver 02-19-2017 10:52 PM

To turn a 36" wheel, she must have a really big gear ratio, maybe 4:1 or better.


T4Liberty 02-19-2017 10:59 PM

Unless there is something major damaged beyond repair (block), I can't endorse trading a DD671N for any of the very fine motors you mention. My vote is every engine should be a Detroit.

O C Diver 02-19-2017 11:06 PM


Originally Posted by T4Liberty (Post 525341)
Unless there is something major damaged beyond repair (block), I can't endorse trading a DD671N for any of the very fine motors you mention. My vote is every engine should be a Detroit.

They also make fine mooring blocks because of their weight. :rolleyes:


Obie 02-20-2017 12:18 AM

That's a lot of votes for keeping her. I want to say thanks first of all for your responses.
So I just picked her up. The previous owner passed suddenly, he owned a diesel truck shop. He was in the process of undoing the motor to pull it. Suposubly she ran great 2 years ago befor she went on the hard. But she had an oil Annalise's that showed some metal in the sample. I had another JT 6-71, it had to be rebuilt at tacoma diesel, bill was $25k. I was thinking I did not want to put any money into that old of technology. I can see in the log books were she has been rebuilt twice already. I am a fan of the 5.9 cummins, I like the idea of a non merinized motor I can get parts for anywhere. But with that said I am not against looking into keeping the 6-71. It seams parts are getting a bit hard to find, who know what kinda shape the heat exchangers are in, transmission and so on. She is a single diesel so it's kinda important LOL.
Pictures to come. I am in Mexico right now, so it will be a bit.

Again thanks

Mako 02-20-2017 02:25 AM

Obie it sounds like a nice workboat.

I had problems with my previous pair of Grays also before I overhauled them, but it's incredible how durable they are (mine were 50+ years old). As long as you can rebuild in-frame and don't need to haul the block then there is little advantage to repowering. You're an experienced boater and must have an idea of the amount of effort required just in creating new engine mounts alone.

You stated that your Gray was natural, which is a totally different animal than the hyper-charged J&Ts. Parts are NOT getting hard to find (just open up Boats&Harbors), they are quite readily available anywhere in the western hemisphere (not here in Qatar), and a rebuild shouldn't be too expensive. You may wish to consider switching out the 2 valve head for a 4 valve.

Save the money of a repower and just add some modern sound absorbing material. Except for the noise, they are such impressive engines that I seriously considered installing one in a new construction trawler, although the fuel efficiency isn't that great either.

sunchaser 02-20-2017 06:57 AM

A newer engine design is well worth considering. As previously mentioned, exhaust system, mounts, driveline etc all carry time and costs to replace if your new engine is not a 6-71. This money and labor stuff can all be calculated and suitable contingencies applied.

But, it is an older steel vessel. Is the basic structure, tanks, interior re-fit etc worth the money and effort? If so, a repower with a newer 6-71 vs the Cummins is worth considering too. DD made many positive changes to the 6-71 over its many years, even the lower HP versions. Nothing magic about the Graymarine other than nostalgia for those of us that have no skin in the game.

Many interesting options for what could well be a very stout vessel. Sounds like a fun project. Enjoy.

FF 02-20-2017 07:31 AM

". But she had an oil Annalise's that showed some metal in the sample. I had another JT 6-71, it had to be rebuilt at tacoma diesel, bill was $25k."

Engines are built of metal, there is ALWAYS some metal in the oil.Read the paperwork to see what it was.

Most JT engines I have seen were for sport fish , very high power ,high RPM and turbo, perhaps for 1000 hours then rebuild.

No comparison to a 20-30,000 hour NA engine run at 1500 - 1800 RPM.

Ours is a 6-71 from 1954 War Reserve with TD 3-1 tranny .

IF you can find the fuel consumption log at cruise you can easily decide if a different engine will be strong enough.

I would go to the JD farm folks and get a completer factory rebuilt and put your old tranny on it.
JD has farm sales with no core charge at times.

If you can do a real low buck conversion the International DT 360 and DT 466 are fantastic sturdy engines with SAE tranny mounting .Mechanical or electric injection , probably $3,000 or less for either.

Obie 02-20-2017 10:37 AM

3 Attachment(s)

Obie 02-20-2017 10:49 AM

Just a few pics, I think she is around 50 ton.

RT Firefly 02-20-2017 11:00 AM

Mr. O. Holy crap! She looks GREAT.

Pack Mule 02-20-2017 11:05 AM

This boat looks familiar. Wasn't the previous owner here on TF ?

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