Not a good day for my 6-71s

So it started out as a pm. Replace the heat blankets on the turbos as they were looking a little crispy. 9 years old,OK let's replace them. Take them off which is not an easy task I might add and discover the coupling between the turbo and the wet elbow is leaking. (Which we now figure is why the blankets looked crispy). So now the whole ass'y comes out turbos and all. Upon inspection we discover that one of the veins on the exhaust blower is missing. Things are really looking good now. Off both turbos go to the "facility" get them back this week. But being the prudent individual I am we need to find out if the turbo was damaged from the engine or did it just self destruct. The above took place over the last 3 weeks. I'm not worried though because the boating season on the Great Lakes is so long. (Sarcasm intended)

So I !just got off the phone with the yard, they spent the morning looking into the actual engine. Did a compression test

#1- 400#
#2- 420#
#3- 300#
#4- 300#
#5- 300#
#6- 395#

So we still don't know if the engine spit something through the exhaust, but we do know I have a serious problem on my hands.

Oh and just to add some salt, this engine has 325 hrs SMOH
There is no warranty since I was done 7 years ago.
I'm really hoping it's just the head. Someone tell me. Don't worry "it's just the head"

I drove an 85 Suburban w X? miles on it. Took a compression check as it didn't idle great .. had a slight lope. One cyl was 40psi. Drove it 3 or 4 years more. Seemed to have good power. You've got 3 cylinders down but not out. If it won't do anymore damage to itself your Jimmies could possibly run for years.

Normally I would take my chances and just monitor over the next year but we're scheduled to start the Loop the first week of August.
Have to decide shortly whether to mention this little hiccup to the Admiral.

Greetings,
Mr. mb. Hmmm....Tough call but if you don't at least have a look at the head, you might be worrying yourself into a tizzy 24/7 wondering when the "penny will drop" and not fully enjoying your adventure. I know nothing about engine internals but is there any way the cylinders can be inspected with a boroscope perhaps? Just my $.02.

RT Firefly said:

Greetings,
Mr. mb. Hmmm....Tough call but if you don't at least have a look at the head, you might be worrying yourself into a tizzy 24/7 wondering when the "penny will drop" and not fully enjoying your adventure. I know nothing about engine internals but is there any way the cylinders can be inspected with a boroscope perhaps? Just my $.02.

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Yes the great thing about Detroit's is they have inspection plates.
But I suspect that in order to confirm the valves they'll have to pull the head. I'll find out tomorrow.

You are correct though RT, there is no way I'm leaving like this. I'll spend the entire time waiting, as you say, for the penny to drop.

Eight years ago we were up in the North Channel of Lk Huron when we dropped a valve in this engine. It was day three of our 3week summer vacation with the Kids. Had to turn around and spend 40hours running time at 5knts limping home. Fortunately we had just dropped them off at camp for a week so they missed that fun part. I have no intention of repeating that again.

Post photos of the damage on the turbo.

Also, if compression is below about 400# on any cylinder, that cylinder will not fire on start. So if you have a bunch of holes at 300 that thing would not start.

Was it smoky on start or hard to start? If not I pull into question those comp readings.

Ski in NC said:

Post photos of the damage on the turbo.

Also, if compression is below about 400# on any cylinder, that cylinder will not fire on start. So if you have a bunch of holes at 300 that thing would not start.

Was it smoky on start or hard to start? If not I pull into question those comp readings.

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That's rather interesting. What should the compression be on this engine?
Yes it has been abnormally smokey, but no real issue starting that's what started this whole mess, I assumed I had a sticky injector, the turbo blankets were going to be a while we're at fix.

Ski in NC said:

Post photos of the damage on the turbo.

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Unfortunately I haven't any.

Is your "yard" expert on DD's? If not, get someone who is. Just my $.02.

Good luck.

hmason said:

Is your "yard" expert on DD's? If not, get someone who is. Just my $.02.

Good luck.

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He is. In fact he owns 10 of them (6-71's) in ferries he owns.
They have their own rebuild shop.

A T or TA engine with 17:1 compression ratio will be 500psi healthy engine idling about 500-600 rpm. 450psi mininimum spec. At 450psi and below, it is usually top ring busted or glazed liner. 400psi and below won't fire at cold start. Makes for heavy smoke on start, if it starts at all.

Ski in NC said:

A T or TA engine with 17:1 compression ratio will be 500psi healthy engine idling about 500-600 rpm. 450psi mininimum spec. At 450psi and below, it is usually top ring busted or glazed liner. 400psi and below won't fire at cold start. Makes for heavy smoke on start, if it starts at all.

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Ski....I know the engine was not running when they took the readings. The boat is in the shed and the turbo is not installed. So I suspect based upon the numbers you just provided that the compression is probably lower than if the engine was actually running. If this is true then would you agree we still have a problem based on the 100psi deviation between the cylinders?
It's times like this that I wish I knew more about these engines.

Compression on a DD is normally done by putting a dummy injector in the hole, and running engine on the cylinders with remaining injectors. Done with engine idling at normal rpm, but that rpm will be a touch lower due to only five firing. Done at full operating temp.

Do it some other way, and pressures will be who knows what. If done with cold engine and on the starter, the numbers will be lower.

How bad was the smoke at idle? Gone at warm idle or still there? Cold idle smoke can be tolerated if it goes away with warm up. Smoke issue almost never an injector, most common is compression issue.

What you describe is what the yard said last week. They were looking for deviation between the cylinders as they thought maybe a piece of valve broke away and went through the turbo. They figured if that was the case ONE cylinder would be low. They sure weren't counting on three being low.
I guess I'm going to have more conversation to find out what's next.

As to the smoking, it suddenly started smoking heavy at start and wouldn't go away then the next time I started the engine it was fine.
It happened a couple of times over the last season, which was why I asked to have it looked at during the winter.

Ski/Eric: does the OP need to re-fit the turbos to take a proper compression test? If yes, maybe that should be done with tests performed by someone who doesn't have a vested interest in doing a re-build....?

Turbo and exhaust needs to be intact to do it right. Otherwise smoke all over and turbo oil line will pump oil out.

DD's can have sticky rings that tend to loosen up as engine gets to temp. Part of the reason some have cold start smoke, and also why test is done hot.

MB- Go into detail about the smoke. Engine hot, cold? Idle? Color of smoke? You mention it did it a few times, but not always. Any unsual sounds? When it did it was it temp dependent?

Smoke from low compression will fit a consistent pattern based on engine temp and load. It won't come and go randomly.

A DD with poor sealing rings will be hard to start cold, and will smoke white/blue. As engine warms, smoke will reduce or even go away. Putting it under a load helps too. If smoke is gone at warm idle after running under a load, compression is "good enough" for continued use. If smoke comes back at idle after removing load, then it's time to do something.

Injectors can fail and cause smoke issues, but once broken in, they are pretty reliable.

The first time it did this was on a cold start. Smoked as usually does at beginning, starboard engine calmed down after usual minute or so. Port just kept up at same level, after 15 minutes it was still smoking. Ran her home for 1/2 hour by the time we got there it was still the same. The next time it started I believe it was normal again. This happened a couple of times. I can't really say that the smoke color was a heavy blue but it was slightly darker than normal starting white.
As you said the compression numbers are definitely lower than they would be if the engine was running, that was expected. It is the 100psi deviation between them that has me concerned, why would it be the three rear cylinders? The next step was to pull the inspection covers and have a look at the rings.

Yep, check rings and liners through airbox covers. Cheap and easy. And messy.

I am coming way out of left field on this one. But have you checked the fuel coolers??? A ruptured fuel cooler can cause smoke(of a different variety). I only say this because I went through all of this. Are your filter bowls clear of water???

A good air hose can be connected via a scrapped & modified injector.With a pressure gauge blow down times can be compared .

Then a bad valve can be heard as the air leaks past at TDC.

If you have done a compression test the injector timing will need to be reset (run the rack) so the extra work of yanking the head is no bother , just a gasket or two.

Looking in my Navy 6-71 book the recommended procedure to check compression is running at 1000RPM , with one cylinder at a time checked . 510psi seems the high reading .

There is a Caution NOT to attempt a test on just the starter.

A 25lb difference is cause to remove the head and examine the valves, valve seats , valve stems for sticking and the head gasket.

Remember this as for the Navy , cheap abundant labor at almost no cost.

Plan B. could be to assemble the engine and when idling warm , pop the injectors one at a time and see if there is huge RPM drop on one cylinder .

If its not bad , next cold start observe the exhaust clean up as the engine warms.

If its normal , just a bit of smoke below 140F , DO run the loop , then have it looked at next time you are in the Gulf area..

There are still loads of shops in the Gulf with great DD skills , and the loop is only 1000 hours or so , no big deal on 5 cylinders and one weak one.

Good hunting.

When you pulled the turbos was there lots of carbon on the vanes? I'd call the turbo shop and ask them for some input as well. What rpm do you typically run at? I had an injector tip go through a turbo once, but that resulted in a whole different set of symptoms. Darn thing still got us home though.


Via iPhone.

cafesport said:

When you pulled the turbos was there lots of carbon on the vanes? I'd call the turbo shop and ask them for some input as well. What rpm do you typically run at? I had an injector tip go through a turbo once, but that resulted in a whole different set of symptoms. Darn thing still got us home though.

Via iPhone.

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That's what started this whole mess
When we pulled the turbo the veins were damaged. So we needed to find the cause. Did it self destruct or did it suffer from external damage.

If only one of the vanes is missing, it might be prudent to do a LPI (dye penetrant test) on the turbine (exhaust side) wheels to see if there is cracking evident. Might just be fatigue stress at end of life or due to overheating.

Generally speaking, when something goes through a turbo, it wipes out more than one vane, Indeed, it usually takes them all.

You may be looking for a cause that is non-existent.

Post a photo of the turbo damage.

Northern Spy said:

If only one of the vanes is missing, it might be prudent to do a LPI (dye penetrant test) on the turbine (exhaust side) wheels to see if there is cracking evident. Might just be fatigue stress at end of life or due to overheating.

Generally speaking, when something goes through a turbo, it wipes out more than one vane, Indeed, it usually takes them all.

You may be looking for a cause that is non-existent.

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I think rebuilding a turbo is relatively cheap?? At least in my neck of the woods it is.

Yup. Usually is. Not a lot of moving parts...

Not much to add other then I wish you a speedy repair!

At 100,000 plus rpm little things matter. Doesn't take much to throw the whole turbo out of balance. What causes this, could also be causing your other symptoms especially considering only 350 hrs smoh. Rebuild both turbos, bolt them back on and run the hell out of the engines for 10 hours and see what happens.


Via iPhone.

I don't have a picture of the turbo damage. Best I could do is ask the rebuild house what was the extent of the damage. The turbos have already been rebuilt, that is done. It's just this issue of cause and effect. We hate like hell to pit this thing back together only to take it apart again.
I'll see if I can get a report from the turbo people but it still doesn't address the deviation in compression between cylinders.

So we're going to reassemble the whole mess, drop it back in the water and then recheck the compression. Since I'm in Cincinnati and the boats in Detroit it'll take the yard about a week to have it ready to launch.
I'll report back once I find answers.