950+ hours and conflicting advice on PM

[RobnBern]

Good Morning All:

My 1995 370DA has 7.4L Bluewaters with V-drives and runs fairly nicely. Recently, the starboard engine put out a fair amount of blue smoke on start up (after it had not been run in about 3.5 weeks). Once warmed up, the smoke went away. There was no rough idling or any indication (beyond the smoke) of a problem. A dock mate, who runs a single diesel, said that I've got problems coming. He recommended that I have the manifolds removed for inspection and the valves adjusted or repaired. (I may be confusing a bit of what he said because he suddenly got very mechanical and over my head). After he left, another guy on the dock who has a 340 Dancer stopped over. He said the smoke was not an indication of imminent failure. He felt that since the boat had been sitting so long and the age, model etc of the engines, the cold causes the valves to shrink a bit and the oil on the top of the engine to leak down. His recommendation was to just run the boat and if I wanted to put an oil additive in, that would stop the smoking on start.

When I run the boat a lot, I never have this issue. Now, I was down on the dock yesterday and fired the boat up and she did fine. No excessive smoking or anything. (This time the boat had only been dormant for 2 weeks) So, to my question. Who do I believe? Is it throwing away good money to have the exhaust manifolds taken off and inspected?? Or is it a huge risk to leave it as is? I don't object to doing PM, in fact, I'm all for it. I'm just confused on this one since each of those guys have a TON more boating and mechanical experience than I do but they have vastly different opinions.

Thanks CSR....Robin

 

[Quint4]

The biggest killer of marine engines is probably water entering the engine from leaky exhaust components. It is important to have the exhaust inspected and gaskets replaced (common failure point).

So......if you do not know when it was last done, establish a baseline and have exhaust looked at by a competent marine mechanic.

 

[bahamabreisus]

Blue smoke upon start up, is most likely nothing more than a weak valve seal. When sitting unused oil is passing into the cylinder and burning off when starting. Could possibly be fixed with a good additive. I dont think you have any major issues. Valve job maybe. 950 hours is not a lot for a well maintained 454. Good luck

 

[sr330daguy]

Blue smoke is an indication of oil burning.You say it only happens after the engine hasn't been run for several days. Are you consuming any oil? Correct viscosity of oil? Then I would look at the valve stem seals.They can be replaced in the boat with an air compressor,spark plug adapter,and valve spring compressor. Hope this helps

 

[fwebster]

I won't argue the point about checking your risers and riser gaskets, but I don't think that has anything to do with the blue smoke.

You are into a several of my rules of boat ownership, which, incidentally, I learned the hard way. First, don't fix stuff that isn't broken. Second, when something happens that is not normal for your boat, don't try to repair it until it happens enough for you to properly diagnose the problem. Blue smoke on one start-up isn't a pattern. So, I think the guy with the diesel boat that says your engine is going to die a future death and your boat will sink at the dock is full of crap. Third rule:...unless his clothes are on fire, ignore the guy down the dock who has proven he is full of crap.

What I think has happened is that you had a valve seal stuck (normal for 7.4 Mercs) and the engine turned over enough before starting that one cylinder got a little oil in it, and when it did start firing, the oil on top of the piston burned out of the cylinder and you saw some smoke. Wait until this gets to be a regular repeating event before getting worried, and even then, check the compression first. If the engine is still holding compression, I wouldn't pull a head off to fix a valve seal. I would just watch the oil level and put up with it until there was some other reason for pulling the heads. Back in the old days, I ran a drag car with a 427Ford engine in it. We didn't even put seals on the valve guides because a little extra oil on start up prevented valve wear. The motor was clearanced anyway, so a little more smoke didn't make any difference.

So, pick guy no 2 and go boating.......... after you have the risers checked.

 

[RobnBern]

WOW!! Great and quick responses. Sounds like guy #2, who by the way, is about to make his 7th great loop trip (2nd on his 340) really knows what he's talking about. Frank, I just had a compression test done over the summer and the report back was no problems at all. So, I'm thinking that I'll call a good mechanic and have him check the risers for me, especially since the boat lived in the Chesapeake Bay for a number of years.

As far as ignoring the diesel guy if he was on fire, it would be in my best interest to put him out since his boat is parked right next to With Benefits.

 

[OldSkool]

Great advise Frank. Too many engines have been condemned due to blue smoke start ups. Valve guides/stem seals/seats are usually the culprit and the symptoms Robin is experiencing is classic for this issue. Once the engine is warmed up the excess oil is burnt off and the engine runs clean. I've had more than one GM engine do this with a few hours on them.

If the engine begins to use excessive oil or blow blue continually then more action will be needed. Otherwise, check the manifolds and risers and go boating.

 

[Burp]

Agree with #3 and #4. Blue smoke upon start up, is most likely nothing more than a weak valve seal. You don't have to pull head to replace them but probably can't do it yourself. Here a impression how to replace them.

[video=youtube;ob_4-F-m1FI]http://www.youtube.com/watch?v=ob_4-F-m1FI[/video]

 

[Captain Allen]

Great thread. I have the same thing going on with my starboard engine. Only smokes when it's cold and I have to turn the engine over a lot to fire it up. My engines are carbed, so it takes a little cranking when they haven't been run in a while. Once the engines warm up, all is well, no smoke and they run great. BTW, I have 968 hours on mine.