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Oh Reely!
10-14-2009, 02:51 PM
I am looking at a boat that has 1984 detroit 671's in it and they have 4000hrs on them. what sould i do. Should I not even consider buying the boat with out expecting to overhaul them. Any advice is appreciated

Thanks in Advance

Phill


adventuris
10-14-2009, 03:03 PM
what model 671

doughnut
10-14-2009, 03:04 PM
Are they 6-71N's? (normally aspirated)if so, I have seen them with 10000 hours, are they JT's? The higher the power rating, the fewer the hours of reliable performance. I have heard some downright scary TBO times on the high horsepower models.


Sleeper
10-14-2009, 03:04 PM
Most Detroit guys will tell you that 4000 hours is past re-build time if they are high HP models. There are so many variables that go into that equation though that it truly can't be exactly predicted. The HP is the biggest factor as already stated, a 6-71 NA may last longer than you but a 450HP model, not so long. One thing for sure though, understand the cost and account for it in your offer.

Oh Reely!
10-14-2009, 03:07 PM
It is the 450hp version

Battlewagon
10-14-2009, 03:33 PM
Any high HP diesel is due for a rebuild at 4000 hours. If the hour meters are mechanical tachometers/hour meters the hours are probably even higher. These meters count hours at 1800 rpm. That means every 3 minutes at idle counts as one minute on the hour meter. Chances are they may have already been rebuilt. If so at how many hours and how much was done. Also find out the "marine age" of the heat exchangers. These (again on any diesel) are usually only good for 7-10 years in salt water. Also mixers. If you are looking to buy and then rebuild find out if they are Johnson & Towers. They sell long blocks for around $9,000. Still have to use all your marine gear. If you get the serial numbers you can call them and get exact numbers for your engines. All that said two quick things to check. 1) Start the engines cold and time how long it takes for the smoke to stop. 2) Run the boat up on plane and verify no black smoke and RPM 2500+ If it passes these tests the engines are probably ok. I'm on my fourth year with mine.

PS. if you are coming from gas engines the first oil change at 24 quarts per side will be a bit of a shock. CF-2 only. NOT Delo-400

Oh Reely!
10-14-2009, 03:56 PM
How long should it take for the blk smoke to go away. Wouldnt be cheaper just to do an overhaul on the engines

doughnut
10-14-2009, 04:04 PM
How long should it take for the blk smoke to go away. Wouldnt be cheaper just to do an overhaul on the engines



What type of boat? Depends on what they need. Might be able to do an in boat rebuild. But, if they have to come out, exchange for the JT's may be the way. As stated above, you need more info. How old is all the marine gear? Time since overhaul (cuz I can almost guarantee they've been majored, if they have'nt, you will know when you run them) Aslo, there is wealth of info at boat diesel dot com. With that said, the 6-71 is an ancient reliable design. Big and heavy. The naturals were just bomb proof. I saw some 871 N's that the operator swore had 20K plus hours on them. Sounded like bolts in a saucepan, but running. 2 stroke power !!!

And like Battlewagon said, 6 GALLONS of oil. LOL, I forgot all that fun!

Oh Reely!
10-14-2009, 04:07 PM
Just talked to the original owner it is a 38 topaz and he says all the gear is up to date but the motors have not been overhauled at all.

ladyjane
10-14-2009, 04:12 PM
had a friend with 12-71 nat. that engine sounded like a p51 fighter plane

Oh Reely!
10-14-2009, 04:43 PM
So are you guys suggesting I stay clear

gradyguy2956
10-14-2009, 04:53 PM
I don't know about you guys, but I just love the sound of a 671! Classic Detroit Iron!

49erJim
10-14-2009, 04:57 PM
one of the best engines ever made.

Johnboy
10-14-2009, 05:15 PM
Everything is a trade off. I'm like my engines (671TIB'S @485HP). I've had 4 years with only normal maintanence. My engines don't leak as much oil as some people say and I have never had to clean soot off the transom. However I do maintain them on a regular schedule (oil, filters, zincs, cleaning heat exchanger,etc). I installed block heaters. I don't baby them but I never abuse them either. At cruise (2000 rpms for me) I burn approx 22 gals per hour and get about 22 knots with full fuel and crew.

I'm happy with mine. The best advice I can give you is to find a really good DD mechanic and do a complete engine survey. It's money well spent. If you like the boat, get a through survey and factor any work needed into your offer.

John

thataway
10-14-2009, 05:21 PM
There are a couple of small car ferries on the Sacramento Delta with 6-71 N on a Z drive. They run constant 1200 RPM (I believe) for 2 years, without shut down. (oil refiners and regular oil top off) Then they are majored. They claim to never have a failure--2 years night and day is somewhere about 17,500 hours. Much different service than on a fishing boat.

Oh Reely!
10-14-2009, 05:22 PM
Everything is a trade off. I'm like my engines (671TIB'S @485HP). I've had 4 years with only normal maintanence. My engines don't leak as much oil as some people say and I have never had to clean soot off the transom. However I do maintain them on a regular schedule (oil, filters, zincs, cleaning heat exchanger,etc). I installed block heaters. I don't baby them but I never abuse them either. At cruise (2000 rpms for me) I burn approx 22 gals per hour and get about 22 knots with full fuel and crew.



I'm happy with mine. The best advice I can give you is to find a really good DD mechanic and do a complete engine survey. It's money well spent. If you like the boat, get a through survey and factor any work needed into your offer.

John

Thanks for the advice

Moby1
10-14-2009, 06:05 PM
How long should it take for the blk smoke to go away. Wouldnt be cheaper just to do an overhaul on the engines

Make sure you do a cold start/ no block heaters and cool to touch. If they white smoke for more then 30 secs to a minute they are probably getting tired (low compression). Air box inspections are relatively easy to do on the 6-71's. As stated above have a good Detroit guy survey them.

Buoy Scout
10-14-2009, 06:51 PM
Get an engine survey. Hire a competent DD mechanic, do compression checks, look at air box leakage, etc. That is the only way to assess the engine's condition.

38Blackfin
10-14-2009, 07:02 PM
So are you guys suggesting I stay clear

naw, just do your research, www.boatdiesel.com (http://www.boatdiesel.com), several DD vets over there. At 4000 hrs, it's probably due an overhaul, but parts aren't expensive(relatively), and readily available. A problem with exhaust manifolds sticks in my head, but may be a different model.

one of the best engines ever made.

Yep. (sorry:grin:). What he said; rock solid, well-known, millions of them out there.

good luck!

Randy

38Blackfin
10-14-2009, 07:05 PM
How long should it take for the blk smoke to go away. Wouldnt be cheaper just to do an overhaul on the engines

Black smoke is typically a load issue: too much prop, too much fuel, too little air, etc.

Randy

54bullwinkle
10-14-2009, 07:44 PM
The 450 hp version are good motors. 6-71 TI are turbocharged and intercooled. Excellent motor. Very simple. Never had any trouble. They will smoke when older, burn a little oil and leak a little oil.

4000 hrs is time to major them. I had TI's and did mine at 2800, easily could have waited another 1000, but they were smoking more than I liked. After rebuild, ran great, smoked less. 10 years later boat is still running on the same rebuild.

If you can drop the oil pan, the whole rebuild can be done in the boat. Manifolds come off and the heads are pulled. Pan is dropped to access the crank and pistons and sleeves come out.

Will run 1200 - 1500 per cyl. Great motors

Negatives: Connection from exhaust manifold to turbo very hot and always rusts. Heat shields are a pia. Leak oil around bolts, but copper washers and a set of Airseps will help the leaks.

Butch Davis
10-15-2009, 07:46 AM
The 71s are very simple engines. That's a very good thing because an owner can learn to rebuild one with about forty hours of training. If there is room to remove the heads aboard the boat they can be overhauled in the engine mounts.

Owner maintenace is also pretty easy with a little training

c_mccann
10-15-2009, 07:54 AM
up to 485 hp and they will get you about 3000-4000 hours, the key is to start them regurally and use block heaters. Good motors, they really raise fish, nice rumble, easy to maintain. There are many versions of 'majored' in the detriot world when assessing a used boat- have a DD mechanic look at them.

JAGSARE1
10-15-2009, 01:06 PM
I have someone in Jax that is a good DD guy and can look for you if need be. Let me know.

reefhunter2
10-15-2009, 01:19 PM
I am looking at a boat that has 1984 detroit 671's in it and they have 4000hrs on them. what sould i do.

Buy it and run it to death. Overhaul in place and run it for another 4000 hrs! That's what I'd do.

cantfish
10-15-2009, 01:57 PM
I had a pile of them in concrete trucks. Wonderful engine!!! Wish they still made it.

49erJim
10-15-2009, 02:13 PM
and they don't shake and drink fuel as much as the V8's or others.

Oh Reely!
10-16-2009, 07:30 PM
So I cant plan on getting another season (200hrs) out of them befor the overhaul

Moby1
10-16-2009, 08:08 PM
My oppinion is if you can get them started there is no reason you shouldn't be able to get a couple of hundred hours out of them. However, they may smoke like hell when they are cold! My 6-92's had stuck rings and a broken piston ring gland and still ran perfect prior to overhaul. Where is this boat located?

Oh Reely!
10-17-2009, 04:34 AM
The boat is in southport N.C.

chrisjb
10-17-2009, 04:53 AM
Just a story on a friend's 671N...charter captain and noticed reduced power from one engine when coming back from canyon. Upon investigation, he was surprised to see crank cracked apart between cyl 3 & 4. It got him back - pretty impressive.

As others said, ck out that diesel site, well worth it, and definitely have local dd dealership do a complete engine survey. No first hand experience on a rebuild, but those who have done it tell me it's pretty simple and relatively cheap (in diesel dollar terms).

Mackey
10-17-2009, 07:21 AM
I am looking at a boat that has 1984 detroit 671's in it and they have 4000hrs on them. what sould i do. Should I not even consider buying the boat with out expecting to overhaul them. Any advice is appreciated

Thanks in Advance

Phill

450hp 671ti are due for an overhaul at 4000hrs. If you really like the boat, adjust your offer price to include the overhaul of the engines. Get quotes from several Detriot dealers on the overhaul price and don't forget the transmissions. Its a buyer market, don't cut yourself short on this deal. There is always another boat out there. If the seller does not like the offer, walk away.

54bullwinkle
10-17-2009, 09:32 AM
Biggest prob you will have with that boat (38 Topaz FB) is a very tight engine room.

prober
10-17-2009, 10:33 AM
Most of the commercial salmon boats I ran in Alaska had them because of the reliability and ease of rebuild. Great motor but you will want to line the engine room in lead sheet for soundproofing. They are pretty loud.

Moby1
10-17-2009, 07:32 PM
The boat is in southport N.C.

If you were in the northeast I would have given you the name of my Detroit guy. Good luck!



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