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Old 26-01-2009, 21:31   #16
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Originally Posted by No Survivors View Post
Are these typically sleeved engines?
If by "sleeve" you mean removable cylinder liners ("wet liners"), some (but not all) small marine diesels have them and they are good candidates for a rebuild. I don't believe the small Yanmars have wet liners, however.
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Old 26-01-2009, 21:41   #17
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(Tooting my own horn, if I may be allowed)

I have followed a number of yard "mechanics" who have told people there engine is shot

It's gonna blow at the worst time

Ya can't get parts for it

The cost of rebuilding is the same almost the same as a new one.

Like doctors....it IS OK to get a second opinion

What you want is a guy who is going to troubleshoot and diagnose like me "toot-toot"

Who will give you a written report and not to exceed estimate 'tooty-toot-toot'

Who will have a reference or three and pictures of past work "TOOOOOOOOT-TOOOOT"

BTW I have just completed two Yanmar Engines this year with blown headgaskets
one was due to a freeze cracked head and one due to over cranking.

BTW Black smoke is a fuel problem
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Old 26-01-2009, 22:03   #18
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My yanmar smoked like crazy when the prop was fouled. I would check that first. I would point blank ask him what the compression is. It is a number, not just "low". You should at least be able to check the oil, if it was accidentally left low it would almost certainly fail in short time as his prediction. was this black smoke a sudden change? other symptoms?
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Old 27-01-2009, 01:50   #19
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Welcome jibs up!

It is the nature of this place that when you ask a question you often get 50 questions in response and few answers.

Engines generally fail or wear out. Accessories (attached to engines) usually fail.

Wear out - the oil and bearings are designed to keep the parts in the engine separated and reduce the amount of wear. Wear still happens all throughout the engine. Eventually wear causes all sorts of signals to appear. Oil consumption increases, smoke can increase at times, temperatures shift, compression reduces. clearances increase. The engine relies on compression to run. Compression demands a well sealed cylinder. The cylinder needs openings to allow fuel in, to allow exhaust out (valve and valve train system) and to allow the gas to compress and expand (the piston and cylinder itself).

Wear out is slow and predictable.

Failure - Sometimes the parts are stressed due to lack of lube, overheating, or sometimes just bad assembly. In this case parts can work loose. You may have a sign in advance such as a loud tapping, or knocking or engine shaking. These are very bad signs and must be investigated immediately.

How to tell? - If the engine starts easily, runs well and seems to produce good power then the engine is probably ok. Marine (yacht) diesels get very little use and will last a very long time. They handle abuse well and so it is very strange to hear someone say, "It is about to fail in 20 hours."

I would ask, "What specifically is about to fail?" I don't doubt he is a decent mechanic but if you are new to the boat and he has been maintaining it 2 years he might have some insight. I would question him more. As to his motive of money - he advised you to find someone (else?) to rebuild the engine. If he is not making anything on the deal he might be sincere.

It bears questioning hiim more about his opinion. Why will it fail? What will fail? How has this condition changed over the last 2 years?

What is the oil consumption? What is normal?
What are the temps (oil and water) trending? How has this changed?
What is the compression in each cylinder? How has this changed?
What are the valve train clearances? How have they changed?

Finally - How do you use the boat? Daysailing? How do you use the engine? Into slip, out of slip? Motor saiing 8 hours per day? Full time? Weekends year round? Weekends summer only?

If the usage of the engine is low and you could tolerate a tow someday and there are no grinding, tapping, slamming, pounding, knocking noises, I would keep on driving. You amy get 2-3 more years out of it.
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Old 27-01-2009, 02:03   #20
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Don't diesels normally blow white smoke when suffering from lack of compression?

From Nigel Calder's "Marine Diesel Engines" black smoke is likely to be caused by:
-Obstruction in the airflow
-Excessive high ambient temperature
-Overload
-Defective fuel injection

As the Chief says its probably a fuel problem - you're seeing unburnt carbon particles in the exhaust.
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Old 27-01-2009, 17:04   #21
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One common thing on the yanmar GM is the exhaust elbow. It is considered a ware item and needs to be replaced every few years about $80 plus gaskets. The water rusts it and reduces the exhaust water hole. I took mine off, I could not see anything because of the rust and junk. I would check the exhaust elbow then the prop for barnacles
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Old 28-01-2009, 09:15   #22
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Thanks all. End of thread.

Thanks everyone for your posts. It is clear that I need more information about this engine before giving up on it. End of thread.
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Old 28-01-2009, 10:12   #23
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Just curious, where are you located?
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Old 28-01-2009, 10:22   #24
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I pretty much agree with what's been laid down here. A couple of addn'l points. 1)Check the endplay of the crankshaft by pulling back and forth on the front pulley. 2) Have the mechanic perform a leakdown test. If he is a reliable diesel mechanic he will have the capability to install an air line in the injector hole and pressurize the cylinder at TDC. One should then be able to ID where the air is excaping from. Better test equipment will even give a % reading of excaping gases. There will be some leakdown but if it is not significant have the injectors serviced, the valves adjusted and the pump timing set and drive on. Oh I did forget another basic. You need at least 10psi of oil pressure for every 1000 RPM.
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Old 03-02-2009, 19:59   #25
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If the mechanic says the engine is on it's last legs he may have detected a bad bearing knock. This could be the reason he predicted a catastrophic failure. If this is the case then I have to agree with the mechanic. If the rod goes it can do a lot of damage. You don't mention His reason for his prediction so it would be hard for anyone to give an informed opinion with such limited information.
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Old 03-02-2009, 21:18   #26
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Chief Engineer, we are located in Ithaca NY. Our "mechanic" owns the boat in the neighbouring dock and has only charged minimally for the work he has done to date. He has no financial interest in our engine replacement. We will take the information we have gathered from this thread and try to figure out our next step.

Thanks so much, everyone!
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Old 03-02-2009, 21:28   #27
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Originally Posted by jibs up View Post
Chief Engineer, we are located in Ithaca NY. Our "mechanic" owns the boat in the neighbouring dock and has only charged minimally for the work he has done to date. He has no financial interest in our engine replacement. We will take the information we have gathered from this thread and try to figure out our next step.

Thanks so much, everyone!
Personally my next step would be to run it, and make it work. Worst case scenario, you blow it up, your already thinking of replacing it anyways. Best case scenario you find out he was wrong and you have a pretty good motor on your hands but a mechanic that is making predictions that he has no business making.

I don;t mean this to sound as harsh as it does but you really only have two choices, trust the guy and rebuild it or replace it, or run it and see what happens, yes there is always a third option of taking it to another mechanic but he WILL have financial interest in replacing it so your basically screwed all the way around anyways.
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Old 03-02-2009, 22:45   #28
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First of all there is no way to predict the amount of time before something will fail, it is impossible, red flag number 1. Secondly all diesels emit black smoke, some more than others, This is not true..Go buy a new injector and through it in..I bet your black smoke goes away..black smoke is an over fueling issue period..rather thats from lugging it while poring the Cole's to it or a bad injector. etc...red flag number 2. it is a catastrophic event as in it will probably no longer runbut not catastrophic as in its going to blow up,(not sure if a diesel will run down a cylinder or not, anyone?)Not true either and yes they can..just like any other motor..and a cracked ring... burnt valve ..hole in piston..can become catastrophic....none of which will produce black smoke..but all can be catastrophic and blow your engine destroying your block in the process.. destroy the block etc. red flag 2.5. and finally red flag number three, if he used the actual term marginal when referring to the compression level does he know exactly what marginal for that motor actually is(you would be surprised as to the number of mechanics that don't).

Read up on your exact engine find out what the specs are and then go back to him and get actual numbers. From there you are better able to make a sound decision.
Other wise good advice
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Old 03-02-2009, 23:33   #29
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Other wise good advice
No combustion reaction is ever perfect there will always be residual carbon and other elements and compounds released during the reaction. Where do they go? Some make it out the exhaust valve resulting in the black smoke you see at start up and under load, the rest ends up in the "carbon build up" you see when you tear down the motor. Yes if it is heavy there could be a fuel to air ratio issue. But he mentioned a down cylinder which means that it is not going to burn correctly, which has nothing to do with an injector issue, and will result in black smoke due to lack of proper compression for "complete" combustion, but a marginal compression level and smoke does not mean the engine is going to fail. If that was the case I would have junked my 1 ton pickup 100k miles ago.

The reason why you see black smoke when a house burns incomplete combustion because something do not get hot enough to burn, same idea with diesels. Diesels ignite the fuel by increasing pressures in cylinders 16-20 times normal atmospheric pressure, it gets so hot from the compression that it explodes.

Catastrophic as in not run, not as in blow up like go poof in a ball of flames. In other words your going to be replacing the block but not the boat. A catastrophic ENGINE failure event and a catastrophic event are two completely different things and given jibs experience level with motors that needed to be made clear, guess I didn't make it clear enough though.
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Old 04-02-2009, 00:52   #30
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Your eloquent but still wrong..

Incomplete combustion in a diesel is white smoke not black..black smoke is developed from inadequate air to the combustion chamber irregardless of its temperature...and as a mater of fact over fueling will result in higher cylinder head temperatures all the while poring out belches of black smoke ...prolonged and unchecked leading to the point of temperatures risking burning holes in the tops of your pistons...

The "down cylinder" dumb term... was not his prognoses but rather in my opinion a well meaning guess at best by an unqualified auto mechanic..did they pull a compression test?..perform a leak down test?..punch test the injectors?

Buy an injector and through it in..their cheap... we'll see if I'm right.. I bet I am.
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