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Old 02-06-2019, 06:27   #16
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Re: Yanmar yse8 black soot

Have you checked the oil level and its look?. It happens to me once, long time ago. The cause was a blown head gasket that let oil to be ejected with the exhaust.
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Old 02-06-2019, 07:34   #17
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Re: Yanmar yse8 black soot

I had exactly the same issue yesterday. I wondered how a dirty prop can create this problem, can anyone explain this please?
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Old 02-06-2019, 07:48   #18
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Re: Yanmar yse8 black soot

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Originally Posted by Dsmnswan View Post
I had exactly the same issue yesterday. I wondered how a dirty prop can create this problem, can anyone explain this please?


A dirty prop is harder to spin than a clean one. This places more load on the engine. Diesel engines, when at 100% or greater load will expel black smoke from a condition called over fueling.

Essentially you’re providing fuel that should result is 3000 rpm, but the engine is only spinning at 2000.
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Old 02-06-2019, 11:57   #19
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Re: Yanmar yse8 black soot

Had exactly the same issue as in the video even when in neutral with my YSE8. A few months later the engine died to where it just wouldn’t pull revs and certainly couldn’t move the boat. (As an aside that transom looks like a Raven 26).

I spent many many hours and a significant stack of cash trying to solve. Eventually I figured the problem out and fixing it cost nothing. The exhaust was a typical boat exhaust with a wet muffler/water lock. When purchased it offered two options for entry. Both horizontal or vertical. I’ve dropped in a picture to illustrate; the inlet options are at the back. Made of hard plastic, when fitting you select which of the two entry points you’re going to use. And you cut a hole in the desired one.

You can see in the picture that both the inlet ends are solid.

With my wet box, whoever had fitted the unit had just drilled a tiny hole in the inlet being used. The engine had been working its guts off for years trying to pump water through. I don’t how big the hole needs to be but check if it’s your problem, as by the time I discovered this fault the motor was pretty well dead.

The other problem that many people suggested would cause the problem was a blown head gasket. Both the 8s and 12s blow head gaskets regularly (every 2-3 years) because of retained sea water in the lower water jacket opening when the motor is off. Raw water cooling has its issues when combined with a horizontal cylinder.

Also I hate to be glum but that’s a really old engine. I spent a great deal of money and time trying to get my motor to run correctly. That included recondition/rebuild. All I learnt was you can’t make a 50+ year old engine run like a new motor. For several years I just used a 5hp Tohatsu long shaft. Worked well too. Eventually saved up enough to replace the old Yanmar. Would have had a new engine much sooner if I’d just accepted my old Yanmar had died some years before. And of course pasts for those little engines are now off the planet. I remember spending $800 on a new set of engine mounts. And exhaust elbow was about $500 or something ridiculous.
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Old 02-06-2019, 12:36   #20
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Re: Yanmar yse8 black soot

Something further that occurs to me. I replaced the engine with another little marine diesel 5 years ago. The new motor was second hand and had been in a genset.

If I were faced with the same problem today I would install an electric motor.

Would be half the cost and of course the number of through holes reduces to one. And I know I’ll get a few nay sayers here on the forum, but replacing the YSE also required new:
- changes to engine bed and new mounts,
- morse controls (gear lever/accelerator),
- water inlet and filter,
- new exhaust system, and
- new fuel system.

And of course YSE8s have their own fuel tank on top (as standard). So means building a new fuel tank somewhere (I just used a 10 litre plastic tote tank).
Plus significant changes to electrical for new engine gauges and switches.

Oh and by the way YSEs have left turning props; most engines have right turning props. Eek new prop needed too, another $1,200 and the sky is the limit with props.

All that extra stuff adds up real fast. Plus hard stand fees ($500), crane hire (to lift motor) another $150, paint for engine bay, hose clamps etc. Man it adds up. And of course it doesn’t alter the value of the boat one iota. These days electric is much cheaper, clean, quiet and reliable. And so much less to go wrong.

My use of the vessel is such that I mostly only need to exit/enter marina. Sure I go for longer trips occasionally but can easily take a small $500 genset.
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Old 02-06-2019, 23:09   #21
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Re: Yanmar yse8 black soot

I would say " it depends" about rebuilding the yse8. IF you can do the work yourself & source aftermarket parts it's ok. E.g. we rebuilt ours YSM8 ( nearly the same) for US $650 including new piston,rings,exhaust v/v, used crankshaft,new big -end & main bearings, rebuilt injection pump, rebuilt injector. But there isn't a price on my labour in that. Now it runs a good as new I imagine never having had a new YSM8. Electric power would not work for us
However if you bought the parts alone from the NZ Yanmar agent it would be somewhere in the vicinity of US $3000 so it would not be worth doing. The head gasket problem is easily cured if you use Loctite 518 or Heldite on the head gasket
I'm a little biased as i sell aftermarket parts for these engines locally but I freely admit if I could buy a new multi-cylinder kubota based engine I would.
The O.P.s engine may only have an injection pump problem or exhaust blockage which could be easily cured. They are simple easy to work on engines that last a long time IF maintained properly. The important part is to diagnose correctly the cause of OP's problem before deciding wether to junk the motor.
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Old 03-06-2019, 00:16   #22
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Re: Yanmar yse8 black soot

Quote:
Originally Posted by Sailmonkey View Post
A dirty prop is harder to spin than a clean one. This places more load on the engine. Diesel engines, when at 100% or greater load will expel black smoke from a condition called over fueling.

Essentially you’re providing fuel that should result is 3000 rpm, but the engine is only spinning at 2000.
Many thanks for the explanation much appreciated

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Old 03-06-2019, 20:47   #23
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Re: Yanmar yse8 black soot

Rethinking on the OP's issue, it seems to me that any wear in the Injector Pump (IP) could NOT cause over-fuelling. Any wear in the plunger (and it's housing) or the regulator valve would cause less fuel being delivered.

Possibly the governor or the governor linkages might cause over-fuelling but IMO, this would be unlikely (unless the linkage has been maladjusted recently).

FWIW...
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Old 04-06-2019, 14:30   #24
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Re: Yanmar yse8 black soot

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Originally Posted by Wotname View Post
Rethinking on the OP's issue, it seems to me that any wear in the Injector Pump (IP) could NOT cause over-fueling. Any wear in the plunger (and it's housing) or the regulator valve would cause less fuel being delivered.

Possibly the governor or the governor linkages might cause over-fueling but IMO, this would be unlikely (unless the linkage has been maladjusted recently).

FWIW...
That's the route I followed with my motor too. It's obviously a fueling issue so let's tick off all the components along the way. I even replaced the fuel tank as I was suspicious it had a case of diesel bug. All the way to getting the injector checked; perfect. Even an injector check requires new shims and they cost. What's next pull the head? Now we need a gasket set at $150 odd. Yanmar parts for these old engines are ridiculously expensive.

And no matter what the OP does, it's still a 50+ year old engine that's worked hard, and is now worn and tired. It's likely it hasn't pulled its rated 8hp in years, most likely its down to 6hp on a good day. I wonder how many times previous owners have overheated it.

I really don't mean to be negative, but I kept throwing money at my old motor YSE8 (including a rebuild) and each time I parted with the cash the motor would run for a few more months. Then something else breaks. If I'd realised (actually a better word is accepted) when I bought the boat the motor needs replacing (as I was told by both the surveyor and the mechanic the previous owner used), I would have saved more than $3,000. But more importantly I would not have to have spent countless hours crawling about in the engine bay, stressing about money, and worried the old girl would break down at the worst possible moment (which it had a tendency to do).

I wanted to be able to take my family out in safety. Replacing the motor was the best thing I did in terms of enjoying my boat.
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Old 04-06-2019, 18:09   #25
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Re: Yanmar yse8 black soot

For the record, some of the main wearing parts of the YSE8 (valves, rings, piston, sleeve, IP bits etc) are common to other small Yanmar industrial engines (some of which are still being manufactured) and aftermarket parts can be sourced for way less cost than the Yanmar branded items.

While you can buy an expensive Yanmar gasket set as posted above, you don't need to. Really all that is needed is a new head gasket ($50 for the Yanmar one and around $30 for an aftermarket one - AU prices). Maybe an exhaust gasket; $25 for a Yanmar one but less it you make your own. All other gaskets can be made for next to nothing and the O'rings (if needed) are dirt cheap.

The only part I had to bend over for was the main crank bearing on the flywheel end. It was $500 from Yanmar and that HURT. It could have been customed machined for way less IF I had been able to source the same Kelmet (IIRC) metal that Yanmar uses. Others have machined this bearing from LG2 bronze and as I understand, this is a sort of suitable path in order to prevent the Yanmar reaming of one's fundamental ...

IMO, the biggest issue with rebuilding the YSE8 is ensuring the oil pump is in tip top condition. While it is repairable, there is no easy fix. Mine took many many hours and a fair bit of machining to before it was better than new.

However this is not the focus of this thread and I hope the OP reposts if (when?) he sorts his over-fuelling issue.
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Old 06-06-2019, 17:34   #26
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Re: Yanmar yse8 black soot

One more possibility. There is no restriction on the air intake is there? An uncle had a lotta trouble with his Bukh until he found the rag that had gone down the air intake Though as another poster pointed out it sounds more like a strangled exhaust on the vid but u say you checked that. I'd try it without the waterbox muffler, just run straight hose as well if you say the elbow is clear.
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