Odd pits found in rod bearings of 160k mile minivan motor (photo)

[Lockasiam]

Ok.

"The effect of viscosity on the cavitation characteristics of a high speed sleeve bearing is investigated theoretically and experimentally. The cavitation characteristics, the cavitation shape and the cavitation location of a spiral oil wedge hydrodynamic bearing are investigated experimentally by using the transparent bearing and the high-speed camera. The generalized Reynolds equation is established with considerations of the cavitation mechanism based on the modified Elrod method in theory, and the cavitations of different viscosity sleeve bearings are analyzed and compared. It is shown that the cavitations are strip-shaped for both the high viscosity lubricant and the low viscosity lubricant, and in the rupture region of the oil film at a high speed, the oil vapour or bubbles are produced. With the decrease of the supply pressure and the increase of the rotating speed, the rupture area of the oil film increases distinctly. The cavitation area decreases distinctly and the quality of lubrication is better for the low viscosity lubricant than for the high viscosity lubricant. The experiment results in general are consistent with the theoretical results."
https://link.springer.com/article/10.1016/S1001-6058(15)60494-2

Bonus points for running the spec instead of thicker is better.

Does this mean we should all run 0w8 in our 4.8/5.3/6.0 Vortecs? Those cavitate hardcore at 7k+. Better yet, why don’t oems like GM just ditch the 0w20 dexos gig and start developing 0w2 right now??

 

[siriusc1024]

Does this mean we should all run 0w8 in our 4.8/5.3/6.0 Vortecs? Those cavitate hardcore at 7k+. Better yet, why don’t oems like GM just ditch the 0w20 dexos gig and start developing 0w2 right now??

That was your takeaway? It means when a spec is developed things like this are tested. Deviating from the spec can deliver unexpected results.

Higher viscosity oils have higher vapor pressure and are less likely to have boundary separation. That's the assumption isn't it? The testing proves it. Sometimes the result is at odds with the assumption, and that's the interesting part.

There's a reason extensive testing is done.

 

[mattd]

That was your takeaway? It means when a spec is developed things like this are tested. Deviating from the spec can deliver unexpected results.

Higher viscosity oils have higher vapor pressure and are less likely to have boundary separation. That's the assumption isn't it? The testing proves it. Sometimes the result is at odds with the assumption, and that's the interesting part.

There's a reason extensive testing is done.

Tell that to GM and the 6.2.

 

[siriusc1024]

Tell that to GM and the 6.2.

I do believe that there were manufacturing defects. It's only certain years of L87's.

 

[MaximumMini]

The great thing about forums is that no matter what answer you feel is the "best" one, right or wrong, just wait and you'll get the one that you endorse sooner or later

 

[Trav]

Ok.

"The effect of viscosity on the cavitation characteristics of a high speed sleeve bearing is investigated theoretically and experimentally. The cavitation characteristics, the cavitation shape and the cavitation location of a spiral oil wedge hydrodynamic bearing are investigated experimentally by using the transparent bearing and the high-speed camera. The generalized Reynolds equation is established with considerations of the cavitation mechanism based on the modified Elrod method in theory, and the cavitations of different viscosity sleeve bearings are analyzed and compared. It is shown that the cavitations are strip-shaped for both the high viscosity lubricant and the low viscosity lubricant, and in the rupture region of the oil film at a high speed, the oil vapour or bubbles are produced. With the decrease of the supply pressure and the increase of the rotating speed, the rupture area of the oil film increases distinctly. The cavitation area decreases distinctly and the quality of lubrication is better for the low viscosity lubricant than for the high viscosity lubricant. The experiment results in general are consistent with the theoretical results."
https://link.springer.com/article/10.1016/S1001-6058(15)60494-2

Bonus points for running the spec instead of thicker is better.

So what is spec? LOL

 

[siriusc1024]

So what is spec? LOL

View attachment 280460

At first I thought that was from a lawn mower manual.

I see Service SE. That's old. You're going off something from the '70's? Very sensible. What used to apply no longer necessarily does. Even during the time of that it didn't apply globally.

Does this in your mind somehow refute the paper I linked?

 

[Sam_Julier]

I’m learning a lot here. Let’s not let this become a thick vs thin debate. Thanks.

Sam

 

[Trav]

At first I thought that was from a lawn mower manual.

I see Service SE. That's old. You're going off something from the '70's? Very sensible. What used to apply no longer necessarily does. Even during the time of that it didn't apply globally.

Does this in your mind somehow refute the paper I linked?

No, it refutes your statement!

It means when a spec is developed things like this are tested. Deviating from the spec can deliver unexpected results. Bonus points for running the spec instead of thicker is better

This is VW/Audi 502.00 spec, a good oil spec and not 1970's and definitely a global spec, what part of that spec should I adhere to 0w30 or 10w40?
There are many wide ranging specs from low viscosity oils to higher viscosity oils.

Possible viscosity classes for VW 502 00 are SAE 0w30, SAE 5w30, SAE 10w30, SAE 0w40, SAE 5w40 and SAE 10w40. The VW standard 502 00 also applies to gasoline engines of the affiliates Audi, Skoda and Seat.

When was the last time you saw cavitation damage to a pressurized shell bearing?

 

[MaximumMini]

I think the biggest take away from this thread is the bearings themselves.
I found that the bearings in the OP photo were non-chamfered around the oil hole and all the pitting occurred there.
The replacement bearings are all chamfered. (sp?)
My best WAG is that these chamfered replacement bearings probably will not show this type of erosion after 150k miles.

in addition, I'd take another WAG that some of that bearing damage and small particles came from those pieces of the rod bearing as they flecked off. A bit surprised the factory would make such a poor call. I have no reason to believe the motor has ever been touched internally before.

Anyone agree or disagree?

 

[MaximumMini]

If I knew that my motors all came with non-chamfered rod bearings I would change them for chamfered bearings just to preclude this.

Why on Earth would a car manufacturer use non-chamfered bearings?
Isn't it pretty obvious a straight drilled oil hole in a rod bearing is prone to fatigue failure along the circumference of that hole?

 

[siriusc1024]

No, it refutes your statement!

This is VW/Audi 502.00 spec, a good oil spec and not 1970's and definitely a global spec, what part of that spec should I adhere to 0w30 or 10w40?
There are many wide ranging specs from low viscosity oils to higher viscosity oils.


When was the last time you saw cavitation damage to a pressurized shell bearing?

I don't think so. Viscosity recommendations for an air cooled engine don't apply to temperature regulated liquid cooled.

 

[Trav]

What gives you the idea 502.00 is for air cooled engines (it is not), it is still a modern spec for many liquid cooled engines still in service globally.

 

[Trav]

If I knew that my motors all came with non-chamfered rod bearings I would change them for chamfered bearings just to preclude this.

Why on Earth would a car manufacturer use non-chamfered bearings?
Isn't it pretty obvious a straight drilled oil hole in a rod bearing is prone to fatigue failure along the circumference of that hole?

Look up chamfering oil holes on crankshaft, crankshaft radius and you will find it is not as simple as just chamfering a bearing shell. Most stock engines don't have or need this.

 

[MaximumMini]

Look up chamfering oil holes on crankshaft, crankshaft radius and you will find it is not as simple as just chamfering a bearing shell. Most stock engines don't have or need this.

Ok. Thanks.
For a minute I thought Dodge had gone cheap on engines.
That said, it is precisely where the erosion occurred so there's that.

 

[Oliveoil2]

I don’t think I’ve ever seen a rod bearing that didn’t have some sort of chamfer. It also looks like improper metallurgy with the bearings. The bearing scar starts at the edge of the oil hole and goes up. They all do. Always replace bearings once you’ve done the work to get in there.

 

[MaximumMini]

I don’t think I’ve ever seen a rod bearing that didn’t have some sort of chamfer. It also looks like improper metallurgy with the bearings. The bearing scar starts at the edge of the oil hole and goes up. They all do. Always replace bearings once you’ve done the work to get in there.

I learned that crankshafts must be ground in the direction of rotation...then polished in the opposite direction of rotation. Never knew that. Is that what you mean when you refer to Metallurgy?

 

[Trav]

I learned that crankshafts must be ground in the direction of rotation...then polished in the opposite direction of rotation. Never knew that. Is that what you mean when you refer to Metallurgy?

I would go and talk to an engine machinist if you can find a good one which is becoming increasingly rare these days, not many new guys are getting into this field. This guy does nice work.

 

[Jetronic]

Ok.

"The effect of viscosity on the cavitation characteristics of a high speed sleeve bearing is investigated theoretically and experimentally. The cavitation characteristics, the cavitation shape and the cavitation location of a spiral oil wedge hydrodynamic bearing are investigated experimentally by using the transparent bearing and the high-speed camera. The generalized Reynolds equation is established with considerations of the cavitation mechanism based on the modified Elrod method in theory, and the cavitations of different viscosity sleeve bearings are analyzed and compared. It is shown that the cavitations are strip-shaped for both the high viscosity lubricant and the low viscosity lubricant, and in the rupture region of the oil film at a high speed, the oil vapour or bubbles are produced. With the decrease of the supply pressure and the increase of the rotating speed, the rupture area of the oil film increases distinctly. The cavitation area decreases distinctly and the quality of lubrication is better for the low viscosity lubricant than for the high viscosity lubricant. The experiment results in general are consistent with the theoretical results."
https://link.springer.com/article/10.1016/S1001-6058(15)60494-2

Bonus points for running the spec instead of thicker is better.

what viscosities are they comparing? Need a bit more than an abstract.

seems like we all need oil pan heaters, so we don't start the engine with cold oil, ever.

 

[MaximumMini]

I had a thought regarding the pitting.
Could it be the pitting was caused by stresses and vibrations that were induced along the crankshaft during that time the vehicle was driven with one cylinder (the one I replaced the piston in due to no compression)?

I do not know how long the previous owner drove the vehicle like that. I do know I drove it home from the purchase point (200 miles) with cyl No 2 misfiring.

Maybe correcting the damaged piston and no compression problem would eliminate the originating source of the pitting I encountered?