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Old 16-09-2019, 16:19   #1
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Yanmar SB 8 black exhaust

Thé marina I was visiting requested that I Change berth at low tide and I got stuck in mud.They towed me and said to give full power.I believe black exhaust means rings replacement.Can this be done with engine in the boat?And is it worth the repairs?Thanks for comments.
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Old 16-09-2019, 17:20   #2
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Re: Yanmar SB 8 black exhaust

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Originally Posted by copaco View Post
Thé marina I was visiting requested that I Change berth at low tide and I got stuck in mud.They towed me and said to give full power.I believe black exhaust means rings replacement.Can this be done with engine in the boat?And is it worth the repairs?Thanks for comments.
No, black smoke usually indicates over-fuelling and this is usually caused by over-loading the engine - presumably in this case by having a WOT and no boat speed (i.e. stuck in mud).

Not surprising for this engine due to it's rather simple injector pump and governor arrangements.

Do you get the same amount of smoke if you run the engine at WOT while tried to the dock?

As for the rings, if the engine starts OK when cold and oil consumption is no too high, then the rings are fine.
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Old 16-09-2019, 17:30   #3
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Re: Yanmar SB 8 black exhaust

What Wotname said +
What revs can you reach at WOT in gear in flat water?
Make sure your exhaust elbow is not partially blocked as well.
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Old 17-09-2019, 04:38   #4
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Re: Yanmar SB 8 black exhaust

I changed the oil and ran the engine at the dock.Black oil spits out the exhaust.The exhaust elbow is new this spring.
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Old 17-09-2019, 09:14   #5
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Re: Yanmar SB 8 black exhaust

Have the injectors checked.
Same thing happened to my Yanmar and the new tips cleaned up the exhaust that had been spitting black since day 1.
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Old 17-09-2019, 09:39   #6
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Re: Yanmar SB 8 black exhaust

Could be a clogged or dirty air filter. Injector problems cause grey exhaust not black
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Old 17-09-2019, 10:00   #7
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Re: Yanmar SB 8 black exhaust

The injector is new.I’m going to have a look at exhaust hoses and elbow.Thanks everyone.Will let you know.Learned a new abbreviation.Wide Open Throttle!
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Old 17-09-2019, 10:14   #8
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Re: Yanmar SB 8 black exhaust

Presume when you state it is an SB8 you mean YSB8 and so the motor has a single horizontally mounted piston More likely to be a worn head gasket. It's salt water cooled, and slowly but surely sea water causes corrosion to the lower edge of the head gasket. Simple job to replace with the motor in place. Many people replace head gaskets every 2 or 3 years as maintenance; such a common problem.

I'd try this first before deciding to spend serious coin with new liner, rings etc. Also it's a really old motor and may be at the end of its life.
So it blows a bit of smoke with spots of oil (actually that's a good wholesome mix of water/diesel/oil and carbon and built up crud from the water trap). Who cares! As long as it starts and gives some power (it will be well down on the rated 8 hp after all these years) and gets you in and out of the marina it's doing its job. But be warned the end is nigh.
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Old 17-09-2019, 14:16   #9
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Re: Yanmar SB 8 black exhaust

The piston is vertical.I only see clear water after the waterlock and cooling water comes out fine.With à blown heat gasket would I not see fuel leaks?
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Old 17-09-2019, 16:02   #10
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Re: Yanmar SB 8 black exhaust

Grantmc doesn't realise the earlier 8hp Yanmar before the yse8 & ysb8 was the vertical cylinder SB8. It caught me earlier that trap as well
I'm trying to find out if you are overpropped as that causes black smoke too. So again please answer question as to what revs your engine can attain Not tied to the dock in flat water.
I can't remember from yr thread about the injection pump if you ever had a compression test done.
Those engines can be rebuilt good as new with new liner, piston, rings & valves.
Head gasket problem is an easy fix. Just use gasket cement, my favourite is Loctite 518 but there are others like Hylomar & Heldite.
I first tried putting head gasket on dry & it did leak after a few months. I've learnt my lesson & tell all my customers to use gasket cement ( I sell aftermarket parts for them )
Has the black smoke problem come on suddenly or has it always done that?
Did you ever check the tappet clearance?
IF the problem has come on suddenly I'd start with tappet clearance, then check injector spray pattern, then compression test or head gasket.
Please answer question re what revs you can attain, tied to the dock is better than none,as that will help with diagnosis
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Old 17-09-2019, 16:18   #11
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Re: Yanmar SB 8 black exhaust

I do not have an rpm gauge but the rpm does not sound as if it changed.I did not have anything black in the exhaust before getting stuck in the mud and using full throttle to try to move.A mechanic toll me compression was fine.I cannot turn the engine with the cranking handle.
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Old 17-09-2019, 16:45   #12
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Re: Yanmar SB 8 black exhaust

Ok so compression fine, you have new injector & newish exhaust elbow. Good knowing it did not blow black smoke before as that rules out prop UNLESS you have something caught on it. I'm assuming you have used WOT before this incident?
Does it blow black smoke at WOT whilst in neutral?
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Old 17-09-2019, 17:20   #13
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Re: Yanmar SB 8 black exhaust

FWIW to anyone who cares - In North America,Yanmar sold the SB8 from 1976 to 1980 and the YSB8 from 1976 to 1977.

The earlier series were the SVE8 and the YSE8, both sold from 1974 to 1976.

Only the Y series were horizontal.
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Old 17-09-2019, 17:37   #14
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Re: Yanmar SB 8 black exhaust

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Originally Posted by Wotname View Post
FWIW to anyone who cares - In North America,Yanmar sold the SB8 from 1976 to 1980 and the YSB8 from 1976 to 1977.

The earlier series were the SVE8 and the YSE8, both sold from 1974 to 1976.

Only the Y series were horizontal.
Thanks for the good oil Wotname
I'll get it right next time
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Old 17-09-2019, 18:37   #15
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Re: Yanmar SB 8 black exhaust

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Could be a clogged or dirty air filter. Injector problems cause grey exhaust not black
CaptVR here, your absolutely wrong. Gray smoke is an oil burning problem, nothing to do with injectors. If your throwing black smoke, it is a fuel issue. If it's been doing it since day one, especially under heavy power, you could be over propped. Most times it is injector problems. If this has come about over a period of time, it normally means you need injectors cleaned and spray patterns set. Also check to insure your air filter is clean and free flowing, this does not normally lead to heavy black smoke, but can cause smoking at higher speeds. 9 times out of 10, black smoke from exhaust with a warm engine is a fuel injector problem... Capt. Vince Rakstis, Retired marine surveyor
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