Yanmar 12SB

[WightSpirit14]

Hey all,

my old (1978) Ontario 28 yanmar kicks out a S-tonne of oil when first increasing throttle. then mellows out.... she never seems to lose too much oil, though.... I tried to drain reservoir cannister where the exhaust flows out but nothing seems to be in there... any thoughts?

She also seems to be "missing" a beat this year, ever once in a while,
btw changed raycor filter this year, and only in fresh water....
Any help much appreciated.

Cheers,
Mike

[Wotname]

Are you sure it's oil, it may be unburnt fuel or unburnt fuel plus carbon from the exhaust mixing elbow. The exhaust mixing elbow does clog up with carbon and the SB engines do dump unburnt fuel when the injector pump is worn and you open the throttle or otherwise overload the engine.

If it is the same injector pump as the YSB (and I think it is), they are a pretty crude affair but easy enough to rebuild. It might be due a new regulator valve by now.

[a64pilot]

If its dumping oil when the throttle is sped up, it’s also dumping a large blue oil smelling cloud. If there isn’t a lot of blue smoke, it’s not oil.
Although some call fuel, oil.

[WightSpirit14]

[QUOTE=Wotname;2695874]Are you sure it's oil, it may be unburnt fuel or unburnt fuel plus carbon from the exhaust mixing elbow.

It is black like tar , floats on top, and is accompnied by blue smoke , she always send out a small amount of thi s! ...and she does burn a bit of oil too. If it is oil, are there piston rings ? Valves ??? time to look at some diagrams online I guess, I think I have the owners manual, but will look for a decent pdf of the engine and start planning some wrench time this winter. Thanks, M

[WightSpirit14]

Originally Posted by a64pilot

If its dumping oil when the throttle is sped up, it’s also dumping a large blue oil smelling cloud. If there isn’t a lot of blue smoke, it’s not oil.
Although some call fuel, oil.

Cheers, I guess it is oil, nr\ext thing to find out why ?

Thanks, M

[Wotname]

Well I guess you have two options.
1. Try to diagnose the actual fault while you engine is still intact and running
or
2. Tear it down and look inside and rebuild everything that isn't up to spec.

I believe the first option is better .

Start at the easiest and work towards the hardest.

IMO, do the following....
Is the regular maintenance up to date?
Air filter (if fitted) clean and intact?
Fuel and fuel filter clean?

Remove and clean the exhaust mixing elbow, especially if it hasn't been done for a few years.
Measure and adjust tappets (valve lash).
Ensure prop and bottom are clean.

Now try engine again and if no improvement, then pull the injector and check /observe spray pattern - easy enough to do with your engine (i.e. a single cylinder engine that has a decompression lever and a hand crank).

If spray pattern is bad (see manual for details) either clean and rebuild injector (simple job) or take it to an injector shop for same.

If injector is OK then check compression although if engine can be started easily and especially if it can still be hand started, then compression should be good enough. However a compression test at this stage will confirm this or otherwise.

If compression is good, I would now probably look at getting the injector pump looked at. This is a simple beast on this engine so you might give it ago yourself otherwise take it to the injector pump shop. These pumps do wear and will cause over fuelling, they only have a few parts and they are still available.

If compression is bad, pull the head and check valve seats, especially the exhaust valve for wear / pitting. Check liner for wear / lip etc.

You should be able to get a good service manual on line but if not, someone here on CF will have one or use the custom google search on CF.

Disclaimer - I am not a diesel mechanic, just a DIY guy who has maintained a few small marine diesels in the past and currently doing a complete rebuild on a Yanmar YSE8 which is very similar engine to your SB12. I reckon if I can do all the above, you can.

Perhaps other real mechanics will post soon .

[Wotname]

Originally Posted by Wotname

...............
You should be able to get a good service manual on line but if not, someone here on CF will have one or use the custom google search on CF..........

Hmm perhaps not...I just had a look for one for another reason and couldn't find one quickly.

Operation manuals seem easy to get but not a full service manual - at least I couldn't find one quickly.

I do have a complete parts breakdown for the SB8 & 12 if that is any help; it's a little over 10M (pdf) if you want it emailed etc.

FWIW, the injector and injector pump is almost the same as the YSE8 and I do have a service manual for the YSE & YSM.