Kell

Recently rebuilt motor, 7k on it.

ran mobil 1 10w-30 synthetic.

oil pressure gauge was not functioning at this time...

leaking oil from the base of the dip sic tube and the turbo seals were slowly going out. Checked oil level reguarly,

wet out for a backroad run and eventually stopped at a stop sign, then pull onto the next raid and had a deep knocking that only come in right at 3k and went away at 4kish. Took it really easy the whole way home. Wheni got to the bottom of my street all hell broke loose. Definantly sounded like a rod bearing then, metallic clacking noise. I pulled into my garage and the Check engine light finally comes on.

My oil level was way low, dropped probably 1.5-2 qts low.

dougoh

spun a bearing at the track... shenandoah track in west virginia i was in the bowl which is a left handed turn 1/2 circle to be exact...i kept the rpms up to keep the boost on and spun the bearing...i run 15/50 mobil one..the motor had 89,000 miles ..oil pressure was at 4.5 bar...i baffled the pan this time to see if this might help but for the most part i think i am going to stay away from that track

Diver944

This is a good post Tony

I'm definitely seeing a bit of a trend towards low oil levels and spun bearings

Bill

Has anyone considered pinning the bearings? I have seen a lot of high performance chevys do this to prevent the bearings from spinning.

333pg333

Hmmm...Mobil 1 Strikes again...

M758

The bearing spinning is not the real problem. The reason the bearing spins is that it contacts the crank. Then it spins. Pinning the bearing only allows the crank to rub more on the bearing thus making the results more damaging.

The way to solve the problem is to keep the crank form touching the bearings and they way you do that is to keep the oil in there.

Bill

M758,

Interesting. Your description has me thinking......

If oil pressure drops from whatever reason (oil foaming, uncovered pickup, oil staying in head, synthetic oil, etc) and the bearings "touch" the crank, why would the other bearings not spin randomly?

Could the oil starvation issue be localized at #2 bearing? Could the heavy crankshaft counterweights be causing the oil to foam from splash?

Or could it be something else? Like the crankshaft is insufficiently supported and it is flexing at the #2 bearing, thus allowing the bearing to "touch"? Could the heavy crankshaft counterweights be causing the crankshaft to flex?

I would ask the question, has anyone with a lightened and knife edged crankshaft spun a #2 bearing?

Are the bearings spinning from lack of oil, heating up, expanding and seizing to the crank and rod? or are the bearings deforming from crank flex, binding, and seizing the crank and rod? It would be interesting to take a carefull look at the bearings from a destroyed motor.

Would pinning the bearings cause more problems? When a bearing spins, excessive heat is generated on the rod side that is not lubricated. This can cause the bearing to expand and reduce oil clearances. Eventually the bearing will bind, the rod seazes to the crank, and BAM! A bearing that is pinned would greatly reduce the chances of the bearing spinning. A bearing that does not spin, greatly reduces the chance of seazing the rod to the crank. Theoreticly, unless the contact with the crank is severe, a pinned bearing should just wear more at the area of contact with the crank.

What would you gain by pinning the bearings? True it would be a band aid, and you would not eliminate the cause of the problem. Oil issue, crank flex who know? More research is needed. But I think you could possibly prevent catastrophic failure. How? By early warning. If you prevent spin from lack of oil or crank flex, the bearing would still wear unevenly. Eventually the uneven wear/clearances would allow the crank to pound the rod. In theory, you should get "rod knock" before seize, thus early warning.

What would you lose by pinning the bearings? A couple of bucks worth of machine work. Probably less than the cost of perp drilling, knife edging, or lightening the crankshaft. If my motor was apart, I just might do all of the above as preventative medicine.

A mangled crank journel is far cheaper to repair than a bent rod, bent crank, deformed piston and a hole in the block.

.........Food for Thought.

toddk911

"Could the oil starvation issue be localized at #2 bearing? Could the heavy crankshaft counterweights be causing the oil to foam from splash?"

After the rebuild from spinning my #2, the crank, PP and flywheel were all spun and balanced. Maybe that will help prevent future bearing issues.

maximus951

Before the mobil 1 bashing gets out of hand, everyone should take a few minutes or hours and read Doug Hillary's posts on oil
Link

toddk911

Can also see Ski's posts about Mobile 1 and the fact that he works IN the oil business

M758

#2 and #3 are the two weakest rod journals in terms of oil flow. So any interuption and those are first two bearings to fail #2 first then #3. Oil flow to #1 and #4 are stronger so "weak" flow impacts #2 first. I think one probelm is that the basic flow to #2 and #3 is very marginal. I believe #1 and #4 have MUCH better oil flow to them. I am not sure exactly why, but I believe I has to do with oil flow layout and galley sizes. Cross drilled cranks attept to increase the oil flow to the rod journals and therefore help out somewhat.

As for crank flex. I have never heard of that being an issue on the 944 or 928 (which has simialr issues on the #2 & #6). I did hear of an oil flow test that showed #2 & #3 journals to have much less oil flow than #1 and #4.

As for pinning... I think it would create worse failure rather than less severe ones. Rod Knock comes from the bearing spinning. Once it starts to spin you are hosed and it is only a matter of time before it all blows up. A pinned bearing would talk longer to spin and this longer to detect the knock. I would do more damage to the crank and probably seize earlier. Once sized it is all over. I had one of by failures result in seized bearing and the other was spun bearing. When it seized all hell broke loose. When it spun the damage was repairable.

J Chen

What about dry film coating the bearings for added lubrication ?
That may help somewhat during oil starvation.

UK952

I feel it may be a flex issue combined with a pressure/ supply issue as it usually happens at high revs. Not sure wether the pressure drops first and its missed or if the bearing goes and drops the pressure, how often do we keep an eye on the pressure when we are really pushing? (the road comes up pretty quick )

It certainly seems that low oil levels make it worse as to do high cornering forces.

Does the oil feed to number 4 have to follow a longer route? I am thinking it does which is why I suspect a little flex, would the torque tube create any gyroscopic force if it had any play in the bearings.

Tony

Pauerman

Does anyone think that the girdle having only one dowel pin has anything to do with these failures? Think this may have anything to do with the flexing factor?

The girdle and the block are machined on one of the forward stud holes for an extra dowel - wonder why the factory didn't install the second one.