1987 Detroit 671 turbo 485 HP heavy greyish smoke at start up

Hello gentleman and ladies

I have recently taken delivery of my dream boat, 1987 Ocean 48 SS with a pair of DD 671 T's 485 HP. I brought the boat back to Georgian Bay from the south end of Lake Michigan several weeks back in a total of 21 running hours over two days, she's been in fresh water her whole life.

I read that i should keep both in the 1950-2150 RPM range to get her up and over the engines step to ensure the fuel and turbos were doing their cooling job.

She ran flawlessly with consistent oil pressure and temps on both. We were running at a steady 22 knots and burning fuel at 37 gph over the 510 miles.

My question is that the starboard engine burned a gallon of oil on each 10-1/2 hour leg while the port was negligible maybe 2 quarts. During start up they both smoke but the stbd is heavy, almost embarrassingly in the marina... even when i get back into the marina after running for several hours its more pronounced than the port.

There are very few leaks if any on either. Both engines are low in hours approx 1800 hours each.

They run like freight trains for the boats wet weight...

I have no complaints, but I am concerned if the stbd may start to worsen and end up with a catastrophic failure.

On a thread i read today, in one case, it sounded like a cylinder valve guide let go which could explain or as mentioned rings and liners may be at the root.

Knowing what I have outlined would someone have a hunch or guess, and if, so what is involved in a guide replacement and would a compression test reveal that problem or worse too much ring clearance?

Also if it is rings and liners , can an old BBC engine motor head drag racer enthusiast , me... be able to navigate through the above scenarios... ?

I am aware of the interior I have to open up, but the nice thing about an inline 6 there appears to be alot more access and simplicity...

Well I appreciate your taking the time... and would greatly appreciate some thoughts

Regards

Cam Allan / Toronto Ontario / Happy Ocean SS owner... so far

Is the oil pressure the same for both engines?

The first thing I might do is pull the turbo pipes and look for oil there before worrying about engine internals.

I'm an old 6, 8 and 12v mechanic and don't have much time on in-lines other than preventive maintenance.

If the turbo passes inspection I would pull the air intake horn off the blower and examine the rotors for excessive oil contamination.

You don't mention intake air cooling. That's a bunch of hp for no air cooling and blower oil seals failing isn't uncommon even in naturally aspirated engines that don't see any boost heat.

These engines are not complex but are confusing to the uninitiated. Especially the governor control system. Hopefully your vessel documents include an applicable shop manual. If not, I recommend one before diving in and disturbing the fuel controls and injectors.

It sounds as if your engines have a great tune on them so if you know who set them up previously they could be an invaluable resource should you need some help.

Good luck

Hi JGMO

Thanks for your input and other areas to look at. Obviously these could be the cause as you point out. The oil pressure on the port engine is 8-10 PSA lower than the starboard which is the one that smokes.
I need to add that in the owners manual they are referred to as J&T motors, perhaps explaining the larger HP that you mention.

I don't seem to have a detailed engine manual, do you recommend I get DD manuals or J&T?

Can you recommend a source where I can get hardcopy manuals... I am old school , easier to read paper documents... LOL

Thanks again for you invaluable insight

Regards, Cam

Well,

The JT stands for Johnson and Towers. They were the "big dog", back when that vessel (and my youngest daughter) was born, in "marinizing" Detroit Diesel engines. Mostly to do with mounts, heat exchangers and exhaust systems but also devisiing ways to shoehorn and fit those big.babies into available engine bay space on boats. At the time, they were thoroughly familiar with those engines. At the time being the key phrase here. It's going on 40 years now....sheesh!

They might be a source for what you need. You definitely might need to consult them at some point about the custom components that they likely fabricated for your boat if you have a failure in that area. Especially when it comes to the exhaust or heat exchanger systems.

https://www.johnsontowers.com/

Other than that, contact Detroit Diesel or hit ebay to find an inline 71 service manual. I see one for $90 on there now I might jump on if I were you. I will try to include the link and hope it works here.

https://www.ebay.com/itm/3841191451...c7PxKCdEdChfFkSLV6-At9djQkbmqWsBoCnNEQAvD_BwE

Yay! It worked!

Whatever you get, keep it on the vessel at all times. It won't do you much good sitting in a drawer at home when you're 50 miles offshore and have a question.

And READ IT FIRST before ripping into something. In my formative years as a mechanic I got way better than my competition by taking those manuals into the crapper with me instead of the Sports Illustrated or other "fine" publications that they were fond of at the time.

Good luck.

Forgot to address the oil pressure difference. 10 psi difference is quite a lot but it could just be an inaccurate gauge or some gunk in a sending unit. I asked the question because the Detroits oil pressure regulators will sometimes stick. I'm not sure about the in-line but the v engines also have a pressure relief that pops around 70 psi.

I believe that these engines when all clearances are good, should be in the 40 to 50 psi range at full no load speed. But don't quote me, check the manual.

One thing you won't find in the manual though is a tutorial on just how important a clean, fresh supply of oil is to those turbos. At full boost the shaft bearing could be seeing in excess of 100,000 rpm! You need to pay particular attention to, not only the oil supply line and it's connections, but also that the oil can leave the bearing cavity and readily return to sump.

Anytime the turbos are off for maintenance, the drain passage needs to be inspected for sludge or debris. Turbocharged engines need more frequent oil changes. No sludge allowed. It's that simple.

Good luck.

I've been running and rebuilding Detroit 71s for 50+ years. Commercially and personally. Oil consumption can come from leaking turbo seal or bad rings. Keep the oil clean, maybe add a bypass filter. Clean oil is critical on turbos. Engine hours between overhauls for high hp 671s is 1000 to 3000. Run at under 80% of hp with clean oil and I have achieved 11,000 hours. Boats with hot dog captains running at full throttle is how the 1000 hour or less engines get worn out. Naturals, with the blower but no turbo, can go 30,000 hours with care. It's high exhaust gas temperatures wear cylinder parts fast.
When I learned to rebuild, I was alone with a detailed service manual and had to make a radio call to ask a question. I had aircraft and auto engine experience including machining. The original 671 engine was designed to be rebuilt in the field along with all the accessories and injectors.
The way the engine works is pressurized air enters thru the sleeve ports at the bottom of the stroke. Any oil from leaky rings collects near the ports and is forced into the cylinder with the air charge. The valves are only exhaust valves. The initial air flow forces out combustion gasses thru the valves and then charges the cylinder with fresh air.
I think a careful gas engine mechanic could rebuild a Detroit with a service manual. Sleeves have numbers on them. Sometimes original machining or repairs require a cylinder to have a different sleeve. When you overhaul, check the numbers on each and write down if different. Your engine kit supplier can mix and match sleeves. With the right sleeves you maintain the same hp as new in each cylinder. There is an adapter the fits in the injector cup to measure compression. Sometimes found used on ebay and will adapt to most compression gauges. There is a tool for removing the sleeves that is usually found on ebay. About 1"x5" pointed on the ends and screws to make longer. It goes in the cylinder at BDC into opposite ports across the piston. Rotating the engine causes the piston to push out the sleeve. You remove the sleeve and piston together.
Detroits are known for low oil pressure. They were designed shortly after pressurized oil systems came about. I have seen naturals run decades on 25 psi. My current engines are 1947 naturals. They has 10 & 15 psi at idle and 25 at 1800 and smoked worse that yours. They made a 600 mile ocean trip home. I gave them their 1st overhaul 10 years ago. I do everything but the head and injectors. Some future owner will need to do it again about 2060. I use a stand alone centrifuge and clean my oil about every 50 hours after a run. I test once a year and change the filters, but haven't actually "changed" oil since 2011. I run about 500 hours a year. My oil is transparent.