Dying Diesel

[inspiration]

My 24 year old yanmar 12hp single cylinder inboard has developed a problem, it runs ( very noisily ! ) and starts on the button every time, however it has a habit of very suddenly running VERY smokey, the engine revs out of control, the choke handel will not stop the engine. This has happened 3 times this season, the engine settles down and runs as if nothing ever happened. However yesterday afternoon it happened again only this time the smoke was very bad ( almost reaching land ! ) and the only way I could gain control of the situation was to turn off the fuel valve and pray the engine didnt destroy itself before the fuel in the system ran out.

Any suggestions as to what may be causing this? The first time was on a flat calm day and the other 2 were in rough weather.

Also any suggestions as to a good value ( ie cheap.......i am a scotsman afterall !!!) replacement engine.


I have to admit having your engine pack up really gives your sailing skills a brush up as this turned an afternoon jolly into a night sail in winds varying from 20+kts to flat calm. arriving home 10hrs later than planned. The last 0.75 miles towing with our dinghy. Expect the unexpected !!!

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[sailorman]

it sounds as though it "picking-up " oil from the crankcase & burning it, therefore revs raising + smoke.
it could be catastrophic if the engine "races" out of control.
it could be piston rings, valve stem guides.
suggest u dont use the engine untill its checked-out
asume its a YSE 12
good luck

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[jimboaw]

only .75 miles? Had to drag my 40 footer 6miles with only a 5hp Mariner on the dink. Still, that's another topic. Sounds to me to be injector pump problem. If it was rings she would not start so readily, valve stems, then it would not be intermitant and I asume you check the oil in the sump? The smoke being the result of to much fuel being injected and not burnt. Black I presume?. Have the pump overhauled before anything more drastic.

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[inspiration]

I have heard that the YSE 12 does not like being motorsailed which could bring oil up into the cylinder head as it is a horizontal cylinder. The smoke is white which suggests oil rather than fuel i presume?

I did once have to tow an elan 36 2 miles in the dinghy because the factory fitted the fuel guage backwards.... and the sailing school did not supply the boat with an outboard..........not a happy bunny !!!

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[waverider]

Yes it does read if it could be a injector nozzle injecting too much fuel, a worn pump...or may not be timed correctly (black smoke and a heavy firing knock = advanced, whitish blue smoke = retarded pump timing) ......worn rings = very poor starting due to low compression and if the oil level is not dropping, it does appear be a 'top end' problem.

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[inspiration]

If it was an injector/pump problem would the problem not be there all the time instead of occasionally ? The engine usually runs smoke free and started first time after being layed up for 8 months this winter.... Could it be worn or sticking rings?

Any suggestions as to a good value reliable replacement?

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[waverider]

Depends as it could be down to oil seals in the pump as I take it that the pump is driven by an auxillary shaft. Oil seals do wear over time......As for rings it could possibly be a stuck oil ring but then the engine would be burning oil continuously. as for the compression rings the engine would be a pig to start.

Does the engine have any harsh noises such as a loud firing knock when it starts emitting the smoke?


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[nickjaxe]

There is one of the older landrovers that when it gets worn it puts out oil mist via the breater to the air fillter which when it get enough oil on it let the oil be drawn into the engine to run on it and it then runs out of control, what type of air fillter have you?

Nick.

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[TheBoatman]

If the smoke is black then it's unburnt diesel if it's white or blue it's oil. Unfortunately what ever it is the engine probably needs a major re-build therefore it's make your mind up time, either get the engine rebuilt or buy a new engine. If a new engine is the prefered option then buy another yanmar ther'e great engines<s>.

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[oldharry]

Blowby. When it runs away engine oil is getting in to the cylinder and the engine is running on that. If it was the pump at fault then there would be black smoke if anything. Also the stop control would work.

Scary and not a little dangerous when it happens, as the engine can run to destruction.

Remedy: Rebore, new pistons and rings. Or: New engine!

IF the crankcase breather vents in to the air intake, check the inlet manifold - it will be very oily inside. To prevent it running on, take the breather pipe to a container (to catch the oil!), and wear a gas mask because of the fumes the engine will give off.

Further confirmation of blowby: Block the breather off. Take the oil filler cap off, run up the engine, and place a rag firmly over the filler orifice to block it off. Release it after 20/ 30 seconds. If there is a whoosh of pressure, you have excess crankcase pressure due to worn bores/damaged rings. Do not do this for any longer as you will blow the seals out of the engine and do a lot more damage.

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[steve28]

I think that your problem is down to the rings being worn, Try running the engine with the oil level on the minimum level and see what happens.
Or try putting a post on the message board of: www.yanmarhelp.com


steve

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[Trevor_swfyc]

It sounds more like a fuel problem to me, as you say turning off the fuel supply stops it. Something is sticking somewhere could be an injector is not shutting or as previously stated a fuel pump control problem.
Guess you have not altered anything like the overrun control nut, that is factory set.

Trevor

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[andy_wilson]

If the stop control doesn't stop it, it's almost certainly burning engine oil, or something sticking in the govenor.

I notice she's been laid up for a while.

Check the crank-case vent / breather is clear first, back pressure could be forcing the oil through somehow.

Then...

Find a diesel mechanic (auto) and ask him what he uses to get smoky diesel cars throught the MOT. Fuel additive will almost certainly contain detergents to clean the fuel system and top end, and oil additive will have something to condition (soften / swell) rubber seals within the engine.

For the fuel treatment, fill the engine filter half full of the stuff before re-fitting it and bleeding. Then give her a run feed it through the system, probably 1/2 hour minimum under load.

Don't know about the noisy bit, is that a new symptom?

Try getting a stethoscope on it. Tool factors sell these for engines etc., or just press your ear against a long screwdriver pressed against various parts of the engine. Very difficult with any diesel though, 'specially a single cylinder.

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[l'escargot]

If it is a Y(SB,SE or SM) series, the most common cause is too much oil in the crankcase. This is then sucked into the breather which vents to the air intake.

If it has been dismantled recently, it is also very easy to put the breather back in upside down so that it sucks oil out of the sump at the slightest angle on starboard tack.

It is a common problem with the Yanmar horizontal single cylinders.

If you go backthrough the posts <A target="_blank" HREF=http://www.yanmarhelp.com/msgboard.mv>here</A>, you will see it comes up quite often.

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[Evadne]

I think you'll find that the old mechanic's way of getting a smokey diesel through its MOT was to add a slug of paraffin to the fuel. Not recommended for general running!

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[supermalc]

I have a YSE12 and have learnt a little about these old engines. Yes they do suffer from running on the sump oil, caused by blowby from too much crankcase compression. Also the breather can be assembled upside down as has already been said.

Because the engine is horizontal, the situation is made worse by the fact of heeling on a yacht. Try this telephone. Firm specalise in these engine, and have all the parts. Requires new piston, rings and liner (don't think they can be rebored, but may be wrong) 01326280214

<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://geocities.com/malcsworld/>http://geocities.com/malcsworld/</A>
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