2001 Yamaha F115 4 stroke- main bearings failed

[Bigearl]

I bought this motor used with 176 hours on the clock. Compression was good 140 to 143 psi, the motor was very quiet running with the cowl off and generally sounded very good. Likewise performance in the water seemed perfect ran up to 5600rpm at WOT. Oil looked reasonable, a little bit dark but nothing to really concern me.
Once I bought the boat I changed the lower unit oil and engine oil and filter. I filled it with 10w-30 synthetic oil (Pennzoil automotive). After putting about 10 hours on the motor it developed a serious oil leak at the upper crankshaft oil seal under the flywheel. I downloaded the shop manual, bought a new oil seal and stripped the flywheel etc. to get to the oil seal but before even trying to get the seal out I could see that I could move the crankshaft fore and aft (back and forward) by about .010". There was no point in putting in the new oil seal so I pulled the powerhead off and opened the crankcase (cylinder head etc. left in place). The upper main bearing and the next main down had both failed and had metal to metal contact with the crank shaft. The next three bearings got progressively better and the bottom bearing looked OK.
The crankshaft is showing scoring of the upper journal and this becomes progressively less so that by the center bearing the crank looks good. I am going to check journal diameters with a micrometer but I don't believe any are worn down, just lightly scored.
The big end bearings and journals look perfect and I tested #1 and #2 with plastigage and it reads .001" clearance. I can't see problem with the cam bearings but have not stripped them, just no radial movement that I can see. I cut the oil filter open and could find no metal on the filter pleats and the motor interior is perfectly clean. (I believe the motor had never been pulled apart before I did so, everything looked original). Also no scoring of the cylinders in the lower section I can see.
NOW MY QUESTIONS:
1)Has anyone any theory on why this type of failure would occur?
2)If the motor was run without oil or very low oil for a short period does it seem logical that only the top main bearings would fail?
3)I am going to order new bearings but what should I do about the crankshaft scoring, should I lightly polish it with fine carborundum paper?

Any suggestions and guidance would be appreciated.
Bigearl

[Bigearl]

I forgot to add that I had checked the oil pressure before starting to disasemble the motor and it checked out at 60 psi aqt about 1000 rpm.
Bigearl

[robert graham]

Sorry to hear about your problems. The bearings are oil pressure lubricated so maybe an obstruction in oil passages? This has to be a fairly rare thing to happen, and hopefully somebody like Rodbolt may offer his thoughts on the possible causes. Keep us posted with your findings and progress.

[Bigearl]

Thanks for your response, I have checked the passages for any obstruction by hooking up a compressor to the oil pressure sensor port. when I blow air into this I can feel the flow of air coming out of the oil passages that feed the mains, so I don't believe there was any obstruction. I am thinking that the motor may have been run without oil for a short period by the previous owner.
Bigearl

[99yam40]

Did you put in a Yamaha oil filter or just one you found that would fit?
Not sure if automotive parts and oil should be used in a marine motor.
The filter will drain oil out if there is not a check valve in it to keep that from happening and that means no oil pressure for a little will every time you start it up

[Bigearl]

I used a Wix filter listed specifically for the Yamaha motor. I know it did not have any check valve as I cut it open to inspect. It looks identical to the Yamaha filter I removed, but I don't know if Yamaha filters have a check valve inside, I thought it was normal for all motors to rely on the residual oil in the bearings to lubricate them until the pressure rises on startup.
Thanks for your suggestion, I will use a Yamaha filter after this.
Bigearl

[ausnoelm]

I can't say I have ever seen a valve inside an oil filter, and most do rely on left over oil to supply lubrication at start up, I guess it is possible that one of the bearings was somehow faulty (though it would be rare) more than likely just plain old bad luck.

[200090tlry]

I have seen lots of valves in oil filters

You need to look at more expensive ones. The italian filter on my diesel jeep has funky spin on filter you can not pour oil in can $15 filter from Mopar. Alot of nicer German filters have vehicle specific valves inside. If it was my Yamaha I would use there filter.

[robert graham]

If Rodbolt would come back I'm sure he could shed some light on this bearing failure, otherwise maybe call around a few Yamaha dealers and just ask if they've ever experienced this type of bearing failure? Just curious, are those upper main bearings balls, rollers, plain? If the seal went bad first would the drop in oil pressure cause the bearing failure? I'm not that familiar with these 4 stroke motors.

[seahorse5]

The 4 cylinder 115 series and the 150 drain back the oil filters after shutting the motor off. When you restart, they are basically dry and have to fill up before generating oil pressure. If someone started the motor with the throttle open quite a bit, the motor would race when started and may have spun a bearing before the oil pressure came up.

With 4 strokes, it is very common to see them started up without oil installed in them when new.

[Bigearl]

Thanks to all for the input. Firstly these are plain bearings pressure lubricated. I agree with Seahorse5 that the motor should never be started up with throttle, it should idle until oil pressure builds up. Synthetic oils have an excellent film strength and the short amount of time it takes for pressure to build it should normally be well protected .
I have now ordered all the bearings, seals, gaskets, bolts etc to rebuild the bottom end and will report my progress.
I am still wondering about lightly polishing the scored crank with carborundum paper backed by a square block. I will test clearances with plastigage once I install the new bearings and hopefully it will be in spec.
Bigearl

[Bigearl]

I am interested in Seahorse5's comment about the 4 strokes being started up when new with no oil. I presume these motors are shipped without oil and when installed on a boat someone starts it without realising it has not been filled yet. If this occurred does Seahorse5 know what the result is, the motor has a low pressure indicator but no alarm.
Bigearl.

[robert graham]

My guess is that all modern motors, automotive and marine have some type of check valve system in the oiling circuit to give almost instant pressure on start-up. Some of our vehicles with oil pressure guages show pressure almost instantly when ignition key is turned. It would be intersting to know exactly what caused your bearing failure, but good luck with your rebuild!

[marinermikes]

I would be very leary about using that crankshaft. If you would decide to use it I would take it to a professional machine shop and have it cleaned up and then check to see if it's still within spec.

Check your specs on the journals. It may be out and could be what caused the problem in the first place.

Another problem other than being undersized is losing the case hardening on the journal.

[marinermikes]

When I say check all the journals you should look in the manual and see what they should be and put a micrometer on them.