Looking for advice on emulsified oil and engine care. We have a yanmar ysm8 in a 1979 oday 28. It has been out of the water for approx 3 years. We have found for certain that we have a cracked cylinder head and emulsified oil. We have the head off the motor and made a gasket and wood form to seal the block in order to determine if the block is also cracked. By removing the head a lot of the oil has ran out of the block but there is still enough to see it on the dip stick. We ran water into the block at the water intake point and pressurized with running water. We were checking the dipstick to see if we could see any sign of a fluid rise. We also had the oil filter cylinder off and that opening visible. We did not see any indication of water coming into the crankcase. We are working on this motor on the weekends so it is sitting as is. Should we fill the crank case with oil or some other fluid while sitting. This is the first weekend that it is sealed again by using the wood form/gasket. The head is still removed. There is some visible rust seen looking through the motor oil entry. The cylinder and oil filter cavity are clean and free of any corrosion. We are also trying to determine best method of cleaning the emulsified oil. We are thinking automatic transmission fluid to start with and then drain or I should say siphon as there is no drain plug. Then cycle some 10/40 oil a few times. Recommendation???
ysm8 emulsified oil and engine care
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Fractured head on a single cylinder motor is pretty rare. Are you sure the problem was a fractured cylinder head or was it simply a failed head gasket?
The following is obviously a guess - but typically cooling water will have escaped the head (via the crack or failed gasket) and passed into the crankcase. The expected path for this escaped cooling water would be via the oil returns. Once cooling water reaches the crankcase it will become emulsified in the oil as the water and oil are circulated through the motor.
If this were my job I would completely disassemble, clean, inspect and reassemble every single part. Doing that on this motor requires very little effort. And if you don't you are just 'putting the baby back into dirty diapers.'
Charles
The following is obviously a guess - but typically cooling water will have escaped the head (via the crack or failed gasket) and passed into the crankcase. The expected path for this escaped cooling water would be via the oil returns. Once cooling water reaches the crankcase it will become emulsified in the oil as the water and oil are circulated through the motor.
If this were my job I would completely disassemble, clean, inspect and reassemble every single part. Doing that on this motor requires very little effort. And if you don't you are just 'putting the baby back into dirty diapers.'
Charles
Hi Charles
Thank you for your response. We are certain that the head is cracked. It was pressure tested. The cracks are all near the drain screw which we did not open after pulling the boat. It set out for three winters. Generally the winters are not so bad in sc but we think the crack occurred this past winter. We had oil in the bilge. The oil became emulsified when the boat was launched in the lake and cranked. Would you disassemble because of the oil or to look for other cracks?
Thank you for your response. We are certain that the head is cracked. It was pressure tested. The cracks are all near the drain screw which we did not open after pulling the boat. It set out for three winters. Generally the winters are not so bad in sc but we think the crack occurred this past winter. We had oil in the bilge. The oil became emulsified when the boat was launched in the lake and cranked. Would you disassemble because of the oil or to look for other cracks?
I would disassemble for both reasons. However - I would want to inspect/fix any over limit wear - like sleeve taper, the condition of rod/wrist pin/piston and rings, the bearings and so forth. This is all very standard stuff - easy to do and fully explained in the YSM series manual which is immediately available online.
Oil escaping from the motor is a troublesome symptom - you need to know why oil is not staying in the motor.
The motor was last made in 1980 or thereabouts so I assume you have found a replacement head. If not then fiddling around further is pretty pointless.
Charles
Oil escaping from the motor is a troublesome symptom - you need to know why oil is not staying in the motor.
The motor was last made in 1980 or thereabouts so I assume you have found a replacement head. If not then fiddling around further is pretty pointless.
Charles
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Yes, we can get a replacement head. We checked that first to make sure we should move ahead. We assumed oil was not staying because of the cracked head. The pressure check on the block makes us think there are no cracks there. Thanks for the advice. It probably is due for a breakdown. Just wonder how difficult it is to get the motor out of the boat.
I would pour a mixture of kerosene and oil into the crankcase to clean and remove the emulsified oil and water residue. Some swear by "mystery oil". Also lubricate the cylinder wall and piston rings before turning the engine by hand. Letting the mixture sit for a few days and turning the engine periodically by hand should do the trick. Only you can tell how was the engine running when the boat was pulled 3 years ago. If it was running good and had adequate compression then a head replacement might be all that is needed. I believe your test was properly conducted and it showed no cracks in the cooling passages of the block. Do not overlook the transmission, check the oil and make sure it is turning. If it were me and the engine was running good before, I would take a gamble by just replacing the head. If you want to do a proper job and assurance of the block's condition then a complete rebuild would be in order. You may also want to replace motor mounts at that time.
Hi Benny,
The engine has always ran great and started very easily. In reality this engine probably does not have very many hours. We are in a lake and motor a little but no that much. Thanks for your thoughts!
The engine has always ran great and started very easily. In reality this engine probably does not have very many hours. We are in a lake and motor a little but no that much. Thanks for your thoughts!