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Old 03-01-2017, 08:03   #1
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Yanmar SB12 Burning Oil!

Hi folks! Been working on my 1978 Yanmar SB12. The engine goes through a lot of oil, approximately 1 qt per 10 engine hours. I'm getting puffs of white smoke out the exhaust.

I've replaced the fuel tank, lines, and filters. Changed the impeller and zinc. Cleaned the injector. Tightened the belt. No apparent leaks (ran the last 30 hours with oil pads underneath and no major drips....certainly not 3qt worth).

The engine starts right up, so I believe I have good compression (and thus am not leaking at the piston rings). I'm left thinking that my leak is at the valve guides. Does this make sense? Any other ideas?

If that is the case, any tips on replacing the valve guides on the SB12?

Thanks folks, and happy new year!!!

Phil
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Old 03-01-2017, 12:18   #2
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Re: Yanmar SB12 Burning Oil!

I don't know your engine, but common non ring oil use areas are valve guides, injector seal (mounted inside valve cover), and smog/crankcase collectors that vent back into the intake. A badly functioning crankcase oil collector can have an oil trap or some type of valve and vent all the collected oil into the intake instead of draining back to the sump while allowing excessive air to escape. If your rings are good, a quart in 10 hours going thru a valve guide is a lot. Is the valve stem seal good? Many engines have have a cup like seal (within the springs) that fits tightly to the stem and covers the guide. Some have o-rings.
Valve guides are usually pressed in and out or driven with a special driver. Some engines require heating the head and greatly cooling the guide to aid installation. The head goes in an oven (to expand the hole) and the guides go in a freezer (to contract the guide). Many of the heads I have done have guides .002" or so bigger than the hole they go into, hence the heat/cool.
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Old 13-01-2017, 20:04   #3
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Re: Yanmar SB12 Burning Oil!

Well, I pulled the head and had a shop clean it up, press in new valve guides and recur the seats. Everything is back together, fired up fine on a test run, and we will see how she does tomorrow!
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Old 17-01-2017, 08:04   #4
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Re: Yanmar SB12 Burning Oil!

Sometimes a different brand of oil works wonders. Rotella?
Since you are a hands on guy, try "Seafoam" to rid the inside of carbon
build up.
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Old 17-01-2017, 08:34   #5
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Re: Yanmar SB12 Burning Oil!

I second the oil idea, if like most your running 15W-40 and if your in cold weather, run straight 30W, if in warm weather, straight 40W. 1 qt in 10 hours really isn't all that excessive. I've said this 100 times, but if she starts well, makes good power and doesn't smoke up the anchorage, then there is nothing to fix.
Once an engine begins to consume oil the ring and cylinder wear rate drops significantly, meaning you may have years left in that engine, but maybe you should start planning on an eventual overhaul and start saving now.
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Old 18-01-2017, 04:56   #6
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Re: Yanmar SB12 Burning Oil!

Quote:
Originally Posted by a64pilot View Post
I second the oil idea, if like most your running 15W-40 and if your in cold weather, run straight 30W, if in warm weather, straight 40W. 1 qt in 10 hours really isn't all that excessive. I've said this 100 times, but if she starts well, makes good power and doesn't smoke up the anchorage, then there is nothing to fix.
Once an engine begins to consume oil the ring and cylinder wear rate drops significantly, meaning you may have years left in that engine, but maybe you should start planning on an eventual overhaul and start saving now.
Sounds good to me. I ran a can of Seafoam through and it seems to have reduced consumption by a bit. I will try heavier oil. I think that replacing the cylinder liner and piston rings next winter is within my abilities and budget. Heck, a set of new piston rings is only $30, and a new head gasket $24. Other than that I think it is mostly am investment in time and a few tools.
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Old 19-01-2017, 13:29   #7
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Re: Yanmar SB12 Burning Oil!

Leave some Seafoam in the new oil, to keep the process ongoing.
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Old 02-02-2018, 20:28   #8
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Re: Yanmar SB12 Burning Oil!

Update! I overhauled the engine over the last few weeks. I put in a new cylinder liner, piston, and rings. The starter was having trouble, so I replaced that as well. She runs nicely now, with no smoke, but is overheating. While I had the block all open I cleaned it thoroughly and sucked out all the junk inside but neglected the silencer (which joins the thermostat and mixing elbow). So I just dug out the fully blocked passage for cooling water through the silencer. I'll be putting it back together tomorrow with fingers crossed for cool running!
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Old 03-02-2018, 11:43   #9
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Re: Yanmar SB12 Burning Oil!

I think overheating with a newly rebuilt engine is very common.
What happens is the rebuild restores power, and with power of course comes heat. Likely she hasnít made this much power in a long time.
Your on the right track.
Itís raw after cooled? if so not much else to check if the pump is good and the block clean, thermostat of course.
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Old 03-02-2018, 12:03   #10
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Re: Yanmar SB12 Burning Oil!

Also the new liners will have been freshly honed so there will be extra heat generated via friction, that's why new cars have good heaters the first year. Then they settle down a little. As long as it's not crazy hot I wouldn't worry too much. Good luck.
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Old 03-02-2018, 14:59   #11
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Re: Yanmar SB12 Burning Oil!

Looks like those blocked passages in the silencer were the problem. She's running cool now.

Out of curiosity, where exactly do you measure the temperature of your engine? It varies wildly from spot to spot, on the block, head, exhaust silencer, mixing elbow, etc.
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Old 03-02-2018, 15:00   #12
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Re: Yanmar SB12 Burning Oil!

Quote:
Originally Posted by pmagistro View Post
Update! I overhauled the engine over the last few weeks. I put in a new cylinder liner, piston, and rings. The starter was having trouble, so I replaced that as well. She runs nicely now, with no smoke, but is overheating. While I had the block all open I cleaned it thoroughly and sucked out all the junk inside but neglected the silencer (which joins the thermostat and mixing elbow). So I just dug out the fully blocked passage for cooling water through the silencer. I'll be putting it back together tomorrow with fingers crossed for cool running!
FWIW, after owning several raw water cooled engines, I have found that a vinegar flush every few years works wonders for keeping the cooling system in top shape.

Remove the anode and thermostat and pump say 8 to 10 litres (2 gallons) though the engine for 24 hours - I use a small electric bilge pump, bucket and two hoses.

If you are in a hurry, use hydrochloric (muriatic) acid for just 30 minutes but do avoid spills

This dissolves the salt and calcium build up in the block and head etc.
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Old 03-02-2018, 15:05   #13
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Re: Yanmar SB12 Burning Oil!

Quote:
Originally Posted by pmagistro View Post
Looks like those blocked passages in the silencer were the problem. She's running cool now.

Out of curiosity, where exactly do you measure the temperature of your engine? It varies wildly from spot to spot, on the block, head, exhaust silencer, mixing elbow, etc.
Usually where the overheat alarm switch is located, although IIRC the SB doesn't have an overheat alarm.

On my 2GM20, the overheat alarm is located near the thermostat. In addition I have fitted and external temperature sensor on both the water jacket in head and the exhaust near the mixing elbow.

I plan to do similar to the YSE8 that is currently being rebuilt!
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Old 03-02-2018, 15:08   #14
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Re: Yanmar SB12 Burning Oil!

This is the external temperature alarm system I have used but there are other similar items on the web.

ENGINE WATCHDOG TM4, Audible Engine Temperature Sensor and Low Coolant Alarm
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Old 03-02-2018, 15:09   #15
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Re: Yanmar SB12 Burning Oil!

Quote:
Originally Posted by pmagistro View Post
Looks like those blocked passages in the silencer were the problem. She's running cool now.

Out of curiosity, where exactly do you measure the temperature of your engine? It varies wildly from spot to spot, on the block, head, exhaust silencer, mixing elbow, etc.
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