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Old 27 March 2009, 08:24   #1
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Country: Other
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Boat name: Meu Menino
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Length: 4m +
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How to tell an engine is in trouble?

Hello,
I bought a 2nd hand rib with a Mariner 30EFI. It had 11 hours so the burn-in is allready made.
The question is, how can I know if the engine is in good shape? Let me explain...
From reading this article - http://boatpoint.ninemsn.com.au/engi...om-2530hp-8296
- regarding several engines, and the Mariner among them, I realized that on my first day out, with aproximately the same load (517Kg rib included), my rib's performance was under average as top speed was 36km at 5500rpm. The boat used on the test in this article reached 46Km. The voyage was up-river with no wind.
Sometimes when I stopped, blue smoke would come out but not always...
The guy that delivered it said he checked oil and sparkplugs. Besides, here in Portugal, when changing owners any boat must go thru a flotation and mechanical inspection.
Can anyone give some insight on this?

thanks
Hugo
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Old 27 March 2009, 08:46   #2
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The boat on test must have been different in some way, maybe the prop was a different pitch? or must have had a lot less weight on board?
That said, assuming a reasonable amount of prop slip, for your boat to reach 46kmh you would need to be reving over 7000RPM with it as its set up now. Maybe you should try a pitch coarser on the prop? you could be at the rev limiter at 5500rpm,
I am assuming the engine is a 4 stroke in which case Blue smoke isnt a good sign, its is burning oil, it shouldnt do that even if its not run in, of course blue smoke from a 2st is OK. I would get a compression test done and change the oil incase the wrong grade has been,added, or its contaminated with petrol. if its been overfilled, or laid down the wrong way for transport and oil gotten on top of the pistons then run its not unheared of for a piston ring to break.
also worth trying fresh petrol incase some 2 stroke found its way in the tank!
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Old 27 March 2009, 09:29   #3
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If you have an EFI, there will be electonic "vmax" (spark & fuelling controlled by the computer to limit it) unlike an old carburetted engine that will just keep revving until it explodes under low load. As Doggy days, might be worth trying a higher pitch prop. Does it take off like a rocket? - if yes, another good indication of low pitch!

If it's any help as a comparison, I managed 21Knots (approx 38KpH) from a 4m rib / 25Hp. Your 36Kph is about 19 knots, so not too far out. I would try an inch or so bigger pitch & see what happens.

And, no, blue smoke is not good on an EFI!
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Old 27 March 2009, 13:02   #4
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if you say its had 11 hours running in ,,burn ,,time its still going to be tight for a while yet .
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Old 27 March 2009, 15:56   #5
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Quote:
Originally Posted by m chappelow View Post
if you say its had 11 hours running in ,,burn ,,time its still going to be tight for a while yet .
It may still be tight, but shouldnt blue smoke. he is getting 5500RPM too.
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