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Old 10-05-2022, 00:08   #1
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Detroit 671 oil leaks

I have a pair of freshly rebuilt 671TIBīs that I am chasing down oil leaks on and repairing.

What sealant materials work well when replacing gaskets, and what material works for sealing oil leaks at bolts?
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Old 10-05-2022, 00:22   #2
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Re: Detroit 671 oil leaks

I'm not sure that the gasket goo or sealant which will prevent all the leafs on a GM 671 has ever been developed.
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Old 10-05-2022, 01:40   #3
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Re: Detroit 671 oil leaks

I spent years off-an-on working on a boat with twin 8-71s, 1961 vintage but with very low hours.
The owner calls me one morning.

He: "There's oil in several places on the engines".
Me: "Good, that means they have oil in them"
He: "That's a joke, right?"

It is kind of a running joke about Jimmys, that they just seep/weep in all kinds of places.
I don't have a foolproof answer except that there have been better gasket kits for those engines.
Perhaps at some level we have to smile at a design from the 1930s and appreciate them as still being one of the best marine engines ever produced.
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Old 10-05-2022, 11:01   #4
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Re: Detroit 671 oil leaks

Oil leaks are a feature on Detroit 71's.
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Old 10-05-2022, 11:06   #5
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Re: Detroit 671 oil leaks

Detroit Diesels are like Harleys, if the dont have oil under them, there's something wrong.
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Old 10-05-2022, 13:08   #6
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Re: Detroit 671 oil leaks

Some of these answers may seem glib. But the two stroke Detroit diesels are well known for leaking oil, and I've seldom seen a dry one.

I'd be working hard to get it dry too, so give it a shot. Permatex silicone Blue "Gasket maker", is what I tend to use for that sort of thing.

Good luck.
Paul.
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Old 10-05-2022, 14:18   #7
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Re: Detroit 671 oil leaks

Quote:
Originally Posted by Bowdrie View Post
I spent years off-an-on working on a boat with twin 8-71s, 1961 vintage but with very low hours.
The owner calls me one morning.

He: "There's oil in several places on the engines".
Me: "Good, that means they have oil in them"
He: "That's a joke, right?"

It is kind of a running joke about Jimmys, that they just seep/weep in all kinds of places.
I don't have a foolproof answer except that there have been better gasket kits for those engines.
Perhaps at some level we have to smile at a design from the 1930s and appreciate them as still being one of the best marine engines ever produced.
The 671 that I owned over 40 years ago, fondly referred to as the "slobbering Jimmy", is still running for a friend...and still slobbering.
Buy lots of diapers.
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Old 10-05-2022, 15:26   #8
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Re: Detroit 671 oil leaks

Plus one on the permatex Good product but you will still probably have some leaks. Don’t stress out too much and try to devise a simple catch system
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Old 10-05-2022, 20:09   #9
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Re: Detroit 671 oil leaks

Years ago on our '93 FP Antigua 37 w/ Yanmar 2QM-20's, oil leaking around the HP injector pump developed in the port engine on the way from Seattle to Baja. A mechanic in San Diego found a gasket defect around a bolt hole, and replaced it to the tune of $500.

A year or so later, in the middle of nowhere in Central America, same thing on the other engine. I "cured" this with a bead of thickened epoxy around the pump join after good acetone prep and sanding a bit. This also worked on the banjo nut fittings in the fuel returns, I believe, which kept loosening - steel into aluminum. All held through the next 1500 hrs when we sold the boat.
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Old 10-05-2022, 20:27   #10
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Re: Detroit 671 oil leaks

Quote:
Originally Posted by JohnSlattery View Post
I have a pair of freshly rebuilt 671TIBīs that I am chasing down oil leaks on and repairing.

What sealant materials work well when replacing gaskets, and what material works for sealing oil leaks at bolts?
Loctite 242 or permatex equiv for bolts or thread tape, you can wind a bit under the head of the bolt to make like a soft washer. Loctite 518 or permatex equiv for gaskets, also another tick for silicone being a lot cheaper.
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Old 10-05-2022, 21:23   #11
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Re: Detroit 671 oil leaks

RTV blue is pretty good, however, remember 71's crank cases are pressurized, so it needs time to kick before you power it up or it just blows it out.
Like everyone says, it is just a fact of life with 71s. Good engines though.

M
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Old 11-05-2022, 11:51   #12
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Re: Detroit 671 oil leaks

I've rebuilt many DDs, especially 71 series. They don't have to leak. Careful inspection of surfaces before the gasket is placed and an oil fee surface eliminates most leaks. Also shafts that have seals need to be inspected for wear. Because Detroits run for many decades, often you'll find grooves in the front crank pulley hub, accessory shaft and water pump">raw water pump. If worn, they need to be replaced, sleeved or hard chromed and resurfaced. Left as is, they just ruin the new seal. You do get oil vapor from breathers and some of those will drip oil depending on the engine model and especially bad in worn engines. All engines with ports in the sleeve burn some oil. Some much worse than Detroits.

That said, most DDs have a catch pan under the oil pan. But when they were designed, oil was cheap and the EPA didn't exist. The good old days.
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Old 14-03-2024, 14:04   #13
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Re: Detroit 671 oil leaks

Hello.
I have a question.
Maybe someone can help me:

I own a Hatteras 38 with 2 Detroit 6-71 Turbos.
They are Covington Marine Engines.

One of the Engines starts perfect, runs perfect. No Smoke, everything fine.
But when i Stop the Engine, Oil comes out of the to Pipes on the Side of the Engine. About 0.5 Liter.
When is running, no Oil, only gases. But when i Stop the engine, Oil.
There is no Pressure in the Sump.

��*♂️��*♂️

Sorry for my bad english. I am from the Canary Islands.
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Old 14-03-2024, 14:20   #14
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Re: Detroit 671 oil leaks

G’dayRonny Kipar….welcome to the forum…...Excellent engines and it’s normal to have oil leaks out of the air box drain pipes…..JUST NOT A HALF LITRE. Usually only a small amount and often collected in a catch can. If you’re mechanically inclined, it’s time to take off the air box covers and inspect the piston rings and liner ports, broken rings could be the problem, liner ports also, but more likely is a piston pin retainer plug, you’ll know as soon as you get the covers off. Easy engine to rebuild, liners just slide out.
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Old 22-06-2024, 16:41   #15
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Re: Detroit 671 oil leaks

Hello.
Sorry for my delay. But i didnt see your Thread.

I checked my piston rings and port liners. I didnt see nothing broken.

I put some pictures if i can.

I didnt understand what you mean with " Piston Pin Retainer Plug".
How can i check this? Must i take off the big screw under the gallery?

Thank you
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