Yanmar YSM12 Oil Pressure

[Rick2413]

I had posted a question last summer looking for opinions about what would cause low oil pressure on my fully rebuilt YSM 12. All advice from the seasoned diesel mechanics on here pointed towards bad bearings. With less than 150 hours on the engine....... I pulled the engine apart on the weekend and, to my dismay, they were right. Not sure what happened but it destroyed the crank on both ends beyond the possibility of machining to .50mm for oversize bearing. The connecting rod bearing was unaffected.......
So....any opinions on possible causes(I assume something got into the oil path)????

Also, Can anyone point me to someone who might have a crankshaft????
toyroom@ns.sympatico.ca
1-902-434-7824
Rick

 

[Hermit Scott]

When you posted that I had just rebuilt my YSM12. Also I am very distrusting of people that are making money from me and helping me at the same time. Like a mechanic for instance. The main bearings are $150 for your engine. Polishing the crank is probably another $40 or $50. So a mechaninc can make another $200 just by not replacing your main bearings. After all they are bearings that have oil circulating through them constantly and in all likelyhood will last a very long time.
This isn't like something like not replacing a piston, where all a customer would have to do is take the head off and see they have an old piston, you have to split the case to look at the bearings as you know.
As far as I know, there are no other parts you can buy like oversized bearings for that engine. The design is just too old. Have you found someone who has oversized bearings for that engine?
My business partner owns a number of ar repair shops in town. I have seen the most unbelieveable things happen. One shop sells at least one alignment per day, they don't even have an alignment machine. They just rotate the tires until it drives straight. When someone comes in for an oil change, if it's exotic and will take too long to get the filter, it doesn't get a new filter. How would any one ever know? If someone comes in with a dead battery, they automatically need a new one and it ruined the alternator, every time. This is standard for the repair industry. There are mechanics I trust, I barely know them personally but I have seen how they do business and trust them. It amazes me how people don't take me seriously, and take their cars to whatever shop to get it fixed. I live in a warehouse attached to a repair shop, believe me I know what goes on.
I have not looked at your engine. I don't know for sure. I am justrying to instill a little of the distrust that is in me into you. If I had someone else build an engine for me, I would watch them at critical steps and always get the old parts.

 

[Hermit Scott]

One thing you can do, if you can't find a crank is have a good shop weld it and grind it to repair it. I would have to say that is going to be cheaper for this engine than buying a new one, if you even can. You may be able to find a used one, but it may be worn beyond the tolerance anyway.
Also whoever does it, the bearings have to be 'matched' to the crank. Also, ask them how they turn it to grind it; they should center off of the oil seal part of the crank not the area where the bearing rides. If they aren't doing it that way they don't know what they are doing. The bearing will say not to machine them at all, but they have to match the crank for the tolerance to be right. It's ok to just "kiss" them with a hone but nothing more.

 

[kloudie1]

Rick, Hermit is right .. You can have the crank welded up and re-machined .. A real automotive machine shop that does cranks should be sought out to do the work. They can get it back to standard size. going to cost some, but not like a new crank.. You may be able to cross reference back to the tractor motor that this was made out of and get a crank there.

 

[Rick2413]

Scott....here is a site with oversize part #'s http://www.yanmarspareparts.com/qrg/ysm-12.pdf

 

[sailaway78]

Main Bearings

I would think that since the rod bearing is OK, there was a problem with the mains to begin with. Wrong size bearings would be my first guess. Would be pretty slim chances of some little piece of trash stopping the passages to the mains, and not the rod bearings. Hermit is correct in that you can have the shaft welded up, and turned back to standard. This is a very common practice among hot rodders, and is the way many stroker cranks are made. Take it to an automotive machine shop that does cranks, and if there is one in your area that caters to a lot of hot rodders, thats the place to go. Will be MUCH MUCH cheaper than buying a new, or even a used crank. I would see if it is possible to match up the bearings with automotive bearings, particularly the Clevite 77s, which are as good as it gets. Bearings shouldn't be many dollars. Then be sure the clearances are correct, before you put her back together. Plasti guage will give you a pretty accurate reading on the bearing clearances, without a set of expensive mics.

 

[Hermit Scott]

I would have done the oversized bearings had I known it was available.
Easy-I don't think you can plastigage these because the bearing is one piece.

 

[sailaway78]

Hmmmmmmmmmm

Sure learning lots the past few days. A one piece main bearing. Thats certainly a new one on me. What kind of set up do they have to keep it from spinning. First thing I would do with that is make a trip to the local bearing supply, and see if there was possible a roller bearing that would replace it. And of course Blitz has the three pole main breaker in his AC panel. New things never quit coming. Specially when you mess round with bolts.

 

[Bill Roosa]

Lube, lube, lube

You HAVE to lube the bearings BEFORE you install them. This keeps them form scoring during the initial start up when everything is dry. There is a special tube you can get from re-build shops that is designed for this or use STP oil treatment. Pack the oil pump, supply tube, and discharge line with lube so it primes immediately
I suspect that who ever replaced the crank before either did not lube the main journals or sized the bearings wrong.
Pretty classic stuff, get the connecting rods right but forget about the main journals.

 

[Rick2413]

Re: Lube, lube, lube

I did the rebuild myself and bought all the specialty calipers/micrometers, wash tank etc. and things were triple checked and substantially pre-lubed. All bearings and machine work was done at the local engine builders. This is why I was totally at a loss to see this crank. After receiving all your responses, I went to pick up the crank at the shop and queried them about welding/re-machining. They send it to Quebec to be done with a cost of about $650. Apparently it's a special hard chrome process. An option I'll consider if I can't locate a used one.
After being ultra careful, this problem has definitely shaken my confidence. I rebuild a 3GM30F over the winter and have ran it on a test bed for about 5 hours and 3 oil changes. This afternoon I disasssemled the bottom end, inspected the bearings, plastiguaged and re-lubed. All was okay. Paranoid!!!! Although I'll never be certain what happened, I guess my biggest lesson learnt was to have an actual oil pressure gauge in addition to an alarm. If over time you notice pressure is dropping, you can correct the problem before it's to late. I'm not certain when the alarm sounds but I believe it is well below 20PSI which is way to late to be alerted to a problem

 

[phoneman]

Sounds to me like there was a problem with the thrust bearing that may have spun and wore out very quick allowing back and forth movement in the crank.

 

[sailaway78]

Something else going on

Rick, from what you have posted, seems like you did things right, and you have the expertise to accomplish this job with no problems. So, I would suspect there is something else wrong in there, that is slipping past. So, a couple more questions. Did you replace the oil pump, or make sure it was putting out enough. And, I once saw a cracked tube between the pump and the pickup, that was very difficult to find, and spun a bearing before it was discovered. Last thing I can think of is the oil filter. Some have a check valve that prevents the oil from draining out, so as to prevent a dry condition on start up, while the filter fills back up. Assuming that you did all you did right, almost all that is left is some kind of oiling failure.

 

[Hermit Scott]

engine

If you look in the top left of the exploded engine you will see one of the main bearings in the center of the aluminum case. The other is the engine block that has one pressed in it. I couldn't budge it with a 5 ton press. It takes an incredible amount of force to get them in and out.
Rick- there is a pressure release ball-spring valve right after the pump, did you check to make sure that is not hemoraging for any reason or loose or missing the spring? It's designed to dump oil back into the case/pan if the filter is clogged.
$650 sounds rediculous. That must be in boat dollars. You should take it to a engine building car shop like Easy said. It will be more like $150 or $200.

 

[Rick2413]

Re: engine

Thanks to all again. Although oil pump, check valve, thrust washers etc were new, a Club member who I showed the crank to last night suggested that something initially started the damage and it started to self chew itself and the tolerances on the bearings became so great that the oil pump could no longer keep adequate pressure to lube and continued to create further wear.(hence the need for a oil pressure gauge to warn of a declining pressure status before it is too late) Sounds good.....Any how, I'll spend the day trying to source out another place that can weld/re-machine the crank now that I have a basic idea of cost.

 

[kloudie1]

Man, Rick, sorry to hear the story. I understand the confidence thing, having that happen to me with a VW engine that was getting power modifications. More on oil pressure.. The pressure control valve can get bits stuck in it and dump oil back to the sump.. It doesn’t take much to unseat or jam that little ball open. It is strange to have no damage to the rod bearing, since it is lubricated through the crank drillings of the output side main bearing. Interesting to note that if something plugged the case drilling for the oil passage to the front main bearing of the engine, (misaligned holes, gasket bits, etc) you would not get a low oil pressure alarm. The front bearing might fail , but oil would still be going to the back bearing normally through the external oil pipe. This would feed the rod bearing and the rear main .. After the front main really gets bad, the shaft wobble would fail the rear main and then you’d get a low pressure alarm (just under 10 psi, if I remember?).. Just thinking out loud this morning over coffee.. a little early for Merlot!