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Old 17-10-2009, 09:19   #16
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I watched the mechanic hone the bore and fit the rings. We both checked they are right way up, properly orientated, and checked the ring gap with a feeler gauge. Old rings looked good too, and remember problem was there before we stripped. My background was as a car mechanic so I know what is involved. Compression gauge is from my car dealership and has always been reliable. Engine always starts first touch and sounds very good on idle with clean exhaust. Problem begins at 3/4 throttle in neutral and at about 1/2 throttle when in gear. Prop is unchanged in 11 years I have the boat. We have been testing with air filter removed, so that is not an issue.
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Old 17-10-2009, 10:21   #17
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Try changing the fuel or at least run in a secondary line from a portable can. Black smoke usually indicates too much fuel or a bad mix.
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Old 17-10-2009, 10:41   #18
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I watched the mechanic hone the bore and fit the rings. We both checked they are right way up, properly orientated, and checked the ring gap with a feeler gauge. Old rings looked good too, and remember problem was there before we stripped. My background was as a car mechanic so I know what is involved. Compression gauge is from my car dealership and has always been reliable. Engine always starts first touch and sounds very good on idle with clean exhaust. Problem begins at 3/4 throttle in neutral and at about 1/2 throttle when in gear. Prop is unchanged in 11 years I have the boat. We have been testing with air filter removed, so that is not an issue.
Bill.
Process of elimination as you know and I'm just throwing different things out. I assume this is a recent problem and the engine worked well before? We can pretty much eliminate the top of the engine for obvious reasons. That takes care of valves, stems, cracked head etc. You're sure there is no exhaust blockage. So looking below that point would seem rather obvious. As you know compression testers for gas engines are different from diesel engines. If you're getting a true 40bar or 580psi reading that could be indicative of something as I believe the rated pressures are below that by about 100psi. Piston head is clean? Did you mic the cylinder and piston after honing for eccentric and circularity wear ? If all these checked out I'd still suspect fuel delivery. A defective fuel injection pump or incorrect fuel injection timing as others have stated. Have you changed fuel filters and run a different source of known new and clean fuel? One other wrench in the mix. You said you changed the alternator. What is the amp rating?
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Old 17-10-2009, 10:52   #19
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You said you changed the alternator. What is the amp rating?
Good thought!
Try pulling the belt off the alternator or disconnect the wires and test run. An overload can cause these symptoms.
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Old 17-10-2009, 11:34   #20
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Good thought!
Try pulling the belt off the alternator or disconnect the wires and test run. An overload can cause these symptoms.
From the original post;

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My engine throws out clouds of black smoke and oil under any kind of load and I can only get 2.5Kts (plus 1 Kt if alternator belt disconnected) instead of my customary 5Kts.
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Old 17-10-2009, 12:10   #21
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This one has me scratching my head on this blustery day on the Chesapeake.

Just a thought...with the engine in neutral and OFF...can you turn the shaft from the inside easily?

I am just trying to rule out "load" issues.
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Old 17-10-2009, 12:38   #22
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This one has me scratching my head on this blustery day on the Chesapeake.

Just a thought...with the engine in neutral and OFF...can you turn the shaft from the inside easily?

I am just trying to rule out "load" issues.
I thought about that too, seems like they checked this with this statement;

Quote:
Prop and gearbox not producing extra drag
I don't know how they would determine this other then checking the prop for growth and checking the resistance to turning by hand....

But if those things were not done (not sure what else that statement would mean) they certainly need to check.

This kind of suggests that it is not a load problem also;

Quote:
Problem begins at 3/4 throttle in neutral and at about 1/2 throttle when in gear.
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Old 17-10-2009, 12:41   #23
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Process of elimination as you know and I'm just throwing different things out. I assume this is a recent problem and the engine worked well before? ......
I think he answered this back in post #14
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Faith: Original presenting problem was 'smoke, no power' and occurred a week after I fitted a new alternator...
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Old 17-10-2009, 12:50   #24
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I think he answered this back in post #14

Should we start taking wagers?
Even though they have been checked and of course not being there, I guess fuel pump or blocked exhaust.
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Old 17-10-2009, 14:29   #25
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Tellie: Tank cleaned, fresh fuel and filters start of season (April) but will try fresh direct feed as you suggest. Drew off fuel via injector pump bleed screw - left to stand in jar and looks clean and pure.
Did not mic bore. Very light honing and inserted comp. ring in worn area and checked ring gap with feeler gauge. Bore looks good with no lip. Piston head cleaned. Compression test and slow cylinder leakage surely indicates good tight piston & rings. My gauge is designed for diesel engines. Can't see how I could have "too much compression" as engine starts so easily by hand or by starter.
Alternator is generic (190 euro v.Yanmar one at over 400!). It could be wrong amperage but all testing has been done with belt off as well as on.
Chief: Have turned engine (on half compression) with starting handle both in and out of gear to rule out excessive gearbox, shaft or prop load. My mechanic called Yanmar in the UK - they suggested excessive load, but I think I have ruled it out at this stage. Previously they were "certain" we would find a blocked exhaust....but no!
Wife says I should buy a new engine, but I said if I did I would spend the rest of my life wondering what the hell was wrong with the old one! I am not going to let this beat me!
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Old 17-10-2009, 14:38   #26
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Ah....

Quote:
Have turned engine (on half compression) with starting handle both in and out of gear to rule out excessive gearbox, shaft or prop load. My mechanic called Yanmar in the UK - they suggested excessive load, but I think I have ruled it out at this stage.

Have you dove on the prop? I know it would not affect the problem at "3/4 throttle in neutral" but a bent blade or a fouled prop WILL cause excessive loading and the exact symptoms you describe running in gear.

Good luck!
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Old 17-10-2009, 16:16   #27
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Yes, I had a diver down to check prop as my first reaction, before I started work on the engine.
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Old 17-10-2009, 16:30   #28
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Going back to the original post......

What did you do to check exhaust?

There are a number of things that can cause back pressure.
Delaminated hose Hose can look fine on the outside but I have seen hoses that had "flaps" hanging off the inside.
Obstructed Exhaust elbow (When was the last time this was changed) They do have a lifespan in salt water.
Damaged Water lift muffler
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Old 17-10-2009, 16:41   #29
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Yes, I had a diver down to check prop as my first reaction, before I started work on the engine.
Bill.
Bill,

No, you were SUPPOSED to say "Oh yea! Why did'nt I think of that!" and then report this fixed the problem..


Oh wait, the Chief has another idea... yea check that.

Good luck!
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Old 18-10-2009, 09:46   #30
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Chief: We removed exhaust hoses, looked through them (about the only light at the end of the tunnel!) blew through them and hosed water through. Removed and washed out water trap. I am not sure about the elbow - it has never been changed. I will whip it off next week, and if in doubt will test with the elbow off my friend's boat. Blocked elbow would tick all the boxes! Will let you know how I get on. Thanks again.
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