YSM12 Oil Pressure Problem

[Rick2413]

I'm hoping there is still a few knowledgeable YSM12 people around because I'm stumped!!!! My engine was totally rebuilt two winters ago and a rough guess is it has about 100 hours on it. All bushings and bearings and every part imagined was replaced. After runnung for around and hour at around 2200RPMs(4.5-5kts)my oil pressure is down around 10 psi. If I reduce throttle to 800RPMS(idle) my pressure drops significantly and my alarm begins to chirp. I removed the connecting rod bearings and plasti guaged it and it was well within specs and the bearing surface was perfect. Today I installed a new oil pump gears, oil pump cover plate and O ring. I had the machine shop install a bushing for the oil pump shaft in the aluminum cover which was just a bit out of tolerance. Installed new W30 oil and took my Hunter30 for a run. Same problem!!!!! Once the oil gets hot and thinned out, pressure drops. I installed a new raw water impeller and ensured the raw water filter was not clogged(engine not overheating)
What are the symptoms if the crank case ventilation cover plates are installed wrong(I seen mention of it in the archives)
What about using a thicker oil (20W40)??????

Any thoughts would be greatly appreciated....Thanks

 

[Alan]

Did you replace the oil filter?

I would install a mechanical oil pressure gauge where the oil sender is for your on-board gauge. This will verify the true oil pressure. I would also replace the oil filter.
Checking rod bearing clearance is a good thing but how about main bearings? If all this checks out you might have a crack in the casting to an oil gallery which would explain the drop in oil pressure after heat-up. If you can pressure feed oil to the system you will find the source of the leak.

 

[porsche]

main bearings

Have you plastic gauge the mains? That is another reason to lose O/P.

 

[Rick2413]

Keep the suggestions coming

Rad....the oil pump gears were only $48Can. I did install another new Oil Pressure Sender and I also installed a "Tee" and added a mechanical guage which confirmed my pressures. The end crank shaft buskings/bearings are not accessible unless the engine is dismantled but am guessing with only approx 100 hours on them they are okay??? The oil filter on this beast is a mechanical one and I did remove it and rinsed it out as well as the journals on the front cover.

 

[Patrick S/V Shangra-La]

Try replacing the pressure senser

If every thing else is new the senser might be bad.

 

[porsche]

rebuild

When they rebuilt the motor did they use the original crank shaft? did they tell you what the clearence of the mains were at that time. I realize that the motor needs to be torn down to check them but if the crank was just with in the specs at the time of rebuild then maybe after 100 or so hours the crank is to worn? I assume this problem didn't happen overnite. So if it had press. problems that were getting worse over time, then I feel something has worn out. If it never had good press. then I would say something during the rebuild was not right. Alan

 

[Rick2413]

Specs

Thanks again for your response Alan. I did the rebuild and had my clearances re-verified at the local engine shop(who also pressed in the new bearings). I agree with your thoughts, the obvious problem or assumption would be the crank end bearings but with so few hours of use I hoping for another solution. Wish I had installed a mechanical guage on day 1 so I would have a reference. I'm trying to avoid yanking the engine.
No obvious oil being burnt in the exhaust output or loss of oil level. The book calls for 3 liters. Because of the engine angle, I've read in the archives, not to add oil to the full mark but just below, which I do. That requires about another 1/3 liter. With that much more oil laying back in the crank case be too much and the crank beating it even thinner with extra heat which is why my question on the crank case ventilation and it's purpose.

 

[Eddie7045]

Rick, you have been using crankcase oil that

is rated for use in diesel engines, I trust?

 

[Rob19574]

Crank Case Ventilation

Rick -

The crank case ventilation cover was an issue I had experience with after a rebuild on my YSM12. That caused a runaway situation though and I was burning about a quart of oil an hour until I figured it out. My mechanic that rebuit the engine installed a breather vent cover backwards and the oil was being blown through the blow-by tube and into the intake manifold. Supposedly a common mistake Yanmar-trained mechanics make as told to me from Mac Boring (the right way it goes together looks like the wrong way it should...). That does not sound like your problem.

There is an oil pressure regulator valve that is accessible under the cylinder side cover. Did you replace / check that? Aside from that, the only thing not covered are the rings, piston and liner - are they leaking any gas into the crankcase?

Let us know how you are making out.

- Rob

 

[sailaway78]

A wild a$% guess

There is something in there, or should be, that controls oil pressure. It is usually called a relief valve, which keeps you from having too much oil pressure, and blowing seals out. Since you have rebuilt it, I am assuming you have a manual which should give you this info. I would certainly look in this direction.

 

[Rick2413]

Response

Rob and Eddie,Rob I think it was your archive I read and brought about the question and I also replaced the pressure relief spring and ball yesterday as well. Eddie..Just read the specs on the oil I used and it is definitely diesel(API CF-4) SAE 30, but you had me wondering. I took it for granted that if I bought it at the Parts For Trucks diesel shop it must be right(and it is). Rings, piston and liner were all new. Possibly the break-in period was not appropriate so it is a possibility, as are the crank end main bearings. Everything being relatively new still, it's hard to suspect them on a Yanmar that is reputed for being indestructable. Hence, I'm leaning towards engine oil getting to warm although no engine temperature alarm comes on. I'm wandering if my 1/2" raw water line is providing enough supply volume???????

 

[porsche]

clearance

Rick, I am an auto,truck mechanic and have been for 30 years and this sounds like a oil clearance problem to me. Either a gasket,preasure relief system as noted earlier or bearings. Since the presure is dropping off after warm up I do not believe it to be an oil burning problem [rings,pistons]. I would lean more to a gasket in the oil presure system to maybe pushed out or as stated before maybe a crack in the oil press. system as well. Alan

 

[Hermit Scott]

Question for you

Rick,
I am getting ready to undertake some repairs on a ysm12. It is currently not running but will crank. I wanted to ask you a few questions. Did you have the cylinder liner replaced during the rebuild? How do you check the compression on these engines since there in no spark plug hole? Where is the glow plug that I hear diesels have? I have looked all through the manual and I do not see it. I am going to drive down to my boat, 2.5 hours away and I want to get something useful done. I'd like to check the compression and the fuel system for operability, by checking the spray from the injector.
Scott

 

[TT23844]

YSM oil pressure

Rick - Liftow on Acadia St in Dartmouth have a factory service manual for the YSM 8-12 : it may be useful to have a look at it ( I borrowed & photocopied it a few years ago and it's been pretty useful. I have a YSB 8, an earlier & smaller version of the YSM, but essentially the same engine)
I'd get a good quality mechanical pressure gauge and hook it up in place of the present sender, then note the pressure cold & hot etc. I had this problem in my truck : the factory (electrical gauge & sender) was showing some very low readings and I was getting worried, but the mechanical gauge showed there was adequate pressure ( 20 PSI at idle; 40 PSI at c. 2500-300 RPM, hot ) so I reconnected the old electrical gauge and stopped worrying abt. it. That was 3 yrs & many miles ago and I've had no problems since.
Unless someone has retro-fitted a FWC system on your engine, the Y series engines were all raw water cooled and ran around 125°F, so the engine should be running cool enough to minimize heat build-up causing the SAE 30 oil to thin out and show a marked pressure drop. For what it's worth, I was considering converting my raw-water cooling to a FWC system and increasing the operating temp to c. 180°F as diesels run better & are more efficient when hot, but a very experienced diesel mechanic suggested that the Yanmar lube system may not be capable of providing adequate lubrication at the higher temps I was aiming for.

 

[Rick2413]

Scott

Scott...I did replace the piston liner and new piston and rings.With the head,top of cooling compartment and piston removed, the liner can be pushed out in the direction of the head. There is an "O" ring around it that keeps it snug for obvious reasons. YSM12 does not have a glow plug. To check the compression you need a diesel compression tester and adapters and you remove the fuel injector and insert it there. First place to start is bleeding the fuel system and ensure all fittings are tight. There is lots of info in the archive.Hope the info helps a bit.

 

[Rick2413]

Response

Alan, the more I run the scenerio, the more convinced I am with you....As I look through the parts catalogue, there really isn't anything else but the bearing clearance. The engine has exterior feed lines to the journals which are snug and not leaking. Monday, I'm going to try Rotella 10W40 and only put in the 3 liters that the manual calls for to see if there is any improvement. If not....the engine will have to be disassembled.Thanks again for a professional input(I'm just a backyard guy who loves to get his hands dirty and learn)

 

[porsche]

dirty hands

You don't need to tell me about dirty hands. But I get paid for it LOL. A crank shaft journal may measure up in one spot but not in another as in [out of round] this could cause premature wearing of the bearing either mains or rod or both and this will cause loss of presure. It doesn't take much at all to loose alot. Good luck Alan

 

[Hermit Scott]

crank shaft

Porsche,Is it possible to grind the crank shaft and install oversized journal bearings? Or would he just have to replace the crank?

Rick,Thanks for answering my questions. I thought glow plugs were integral parts to all diesels (so my mechanic friend says, not a diesel mechanic obviously).

The last owner had a can of starting fluid by the engine and said "you'll live on this stuff", I heard that starting fluid can ruin something in a diesel and shouldn't be used, like it could burn a valve or something of that nature.

 

[Rick2413]

Scott

Scott....Another reminder I forgot to mention. If you are cranking the engine and it is not starting, it is advised by many on this site to close your raw water intake shut off valve and remember to open it quickly once the engine is started. With the impeller still providing cooling water, it is highly likely that water with back fill into your engine.

 

[Rick2413]

Scott

Scott....Another reminder I forgot to mention. If you are cranking the engine and it is not starting, it is advised by many on this site to close your raw water intake shut off valve and remember to open it quickly once the engine is started. With the impeller still providing cooling water, it is highly likely that water with back fill into your engine.