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

[MaximumMini]

Anyone know what causes this type of pitting in rod bearings. When measured, they were all only .0015 inch from standard size.
But all of them had this area of missing metal right around the oil hole. Same place on each bearing.
I believe these to be the Original, Chrysler installed bearings.
These marks are not on the other bearing halves.
Bearing No 1 was at the front of the engine nearest to the crankshaft pulley.

I would imagine someone very knowledgeable would be able to decipher what these marks mean, the cause and more.

The motor now has all new rod bearings.

 

[Tman220]

That pitting reminds me of the type of erosion caused by cavitation. Never seen it on rod bearings but I suppose it's possible.

 

[mattd]

Looks like fatigue

 

[CarbonToast]

Why did you decide to change the rod bearings?

 

[MaximumMini]

That pitting reminds me of the type of erosion caused by cavitation. Never seen it on rod bearings but I suppose it's possible.

Didn't think of that but that is a superb thought and makes perfect sense to me.

 

[MaximumMini]

Why did you decide to change the rod bearings?

Because I had them and figured why not.
After seeing the one I had removed with the little pit I was just more comfortable doing it.
Very easy job that only took about an hour. Now I know exactly what I have for rod bearings.

The engine is running fantastic and I'm about to take it on a road trip. Compression is coming up nicely.
Oil pressures meet or exceed factory specifications.
About 150 miles since the piston replace.

 

[Cujet]

That pitting reminds me of the type of erosion caused by cavitation. Never seen it on rod bearings but I suppose it's possible.

That is what I think also. We've seen that on engines that detonate/ping or on diesels that have too much advance on the injection timing. As an impact related failure. In other words, the 'impact' of pinging/detonation caused the oil to cavitate, or more accurately, the collapse of vapor bubbles. As always, higher viscosity is more resistant to vapor bubble collapse.

However, typical cavitation damage is often more wide spread on the upper rod bearing shell. Not limited to one location.

Use good fuel, and adequate viscosity.

 

[MaximumMini]

That is what I think also. We've seen that on engines that detonate/ping or on diesels that have too much advance on the injection timing. As an impact related failure. In other words, the 'impact' of pinging/detonation caused the oil to cavitate, or more accurately, the collapse of vapor bubbles. As always, higher viscosity is more resistant to vapor bubble collapse.

However, typical cavitation damage is often more wide spread on the upper rod bearing shell. Not limited to one location.

Use good fuel, and adequate viscosity.

Good post cujet

I suspect the broken ring lands on the piston with no compression that I ended up replacing was damaged by detonation / knocking.
So the info in your post and Tmann220 seem to tie everything together best to me at this point.

What about failed / failing injectors making the mixture too lean? It appears some work was done on the injectors (some were replaced).
So using a higher viscosity oil would be more likely to cause cavitation like this than low viscosity (thinner) oils?

Important to know since the motor is from 1999 and I was considering going to Delo XSP 15w-40

 

[ripcord]

Non functioning knock sensor?

 

[Cujet]

Good post cujet


So using a higher viscosity oil would be more likely to cause cavitation like this than low viscosity (thinner) oils?

Thanks. Maybe the right way to view the situation is to simply say that adequate viscosity helps prevent cavitation damage. Fuel diluted oil increases the risk. As does oil that is too thin. Switching to 20W-50 is not the solution, a healthy, well tuned engine is.

But going 10,000 miles on oil that loses viscosity (shears) and gets diluted with fuel, is a risk factor.

What you've found is not uncommon.

 

[MaximumMini]

Non functioning knock sensor?

And another good one!
It does have a knock sensor, but is it working? I haven't tested it yet.
One would think if it was working then the piston should not have been damaged. The timing should have been retarded most of the time. I definitely need to make sure.

I've cleared all codes and in 150 miles there are no DTC's. Bad knock sensor is supposed to set a DTC.
Maybe it is bad and no codes are being set? I def need to investigate / test the knock sensor.
If I just replace it without doing tests, it might not solve anything if one of the leads is bad for example.

Thanks

 

[MaximumMini]

Thanks. Maybe the right way to view the situation is to simply say that adequate viscosity helps prevent cavitation damage. Fuel diluted oil increases the risk. As does oil that is too thin. Switching to 20W-50 is not the solution, a well tuned engine is.

But going 10,000 miles on oil that loses viscosity (shears) and gets diluted with fuel, is a risk factor.

What you've found is not uncommon.

How do you feel about using Delo XSP 15w-40 (SN ratings) in a 1999 low rev motor?
I think it "might" hit 3,500 rpm if I floor it to pass.

 

[DougR]

According to Motor Service, there are 3 potential causes of cavitation...

(1) High temperatures and low-boiling impurities may advance cavitation: • Impurities in the oil: water, fuel or deposits from abrasion and dirt • Oil pressure that is too low: unforeseen loss of pressure (for example due to defective oil pump) is present or the oil pressure is set too low • The vapor pressure of the oil used is too low • Increase in temperature in the bearing (for example due to a lack of oil) • Oils with low viscosity increase the risk of cavitation.

(2) Vibration or suction cavitation: • Lubrication gap is too large, causing the hydrodynamic pressure in the bearing gap to fall • Crankshaft vibration: journal movement causes a reduction in pressure on one side due to resulting suction effect • Vibration in the bearing bore (generally for connecting rod eyes) due to deformation or bending – resulting in a reduction in pressure in the oil film.

(3) Flow cavitation: • Breaks in the surface (oil bores, oil grooves) and diversion of the oil flow may cause a reduction in pressure.

Cavitation can definitely occur at a sharp edge. I'm wondering if the oil hole chamfer is more like a sharp edge. Do you have a means to take magnified images of the chamfer at the oil hole edges including areas with and without erosion?

 

[siriusc1024]

That's cavitation caused by the sharp edge of the oil hole. Should be chamfered.

Any chance someone went up a few viscosity grades like Rotella T4? That'll exacerbate the problem.

 

[TomYoung]

I am equally concerned about the wear in cylinders 3 through 6. It’s rough. And ,00015 wear is not nothing. Best wishes on your mini rebuild. Consider shorter OCI s

 

[Jetronic]

Good post cujet

I suspect the broken ring lands on the piston with no compression that I ended up replacing was damaged by detonation / knocking.
So the info in your post and Tmann220 seem to tie everything together best to me at this point.

What about failed / failing injectors making the mixture too lean? It appears some work was done on the injectors (some were replaced).
So using a higher viscosity oil would be more likely to cause cavitation like this than low viscosity (thinner) oils?

Important to know since the motor is from 1999 and I was considering going to Delo XSP 15w-40

No, a higher viscosity oil is less likely to cavitate, also it will slow down the flow to the rod bearing if the cavitation is flow related (as it looks to be)

 

[PontiacHO]

Piston replace? Busted with pieces inside the engine hence rod bearings with the obvious pitting…

 

[Pablo]

Much truth above but one cannot rule out metallurgy.

 

[MaximumMini]

According to Motor Service, there are 3 potential causes of cavitation...

(1) High temperatures and low-boiling impurities may advance cavitation: • Impurities in the oil: water, fuel or deposits from abrasion and dirt • Oil pressure that is too low: unforeseen loss of pressure (for example due to defective oil pump) is present or the oil pressure is set too low • The vapor pressure of the oil used is too low • Increase in temperature in the bearing (for example due to a lack of oil) • Oils with low viscosity increase the risk of cavitation.

(2) Vibration or suction cavitation: • Lubrication gap is too large, causing the hydrodynamic pressure in the bearing gap to fall • Crankshaft vibration: journal movement causes a reduction in pressure on one side due to resulting suction effect • Vibration in the bearing bore (generally for connecting rod eyes) due to deformation or bending – resulting in a reduction in pressure in the oil film.

(3) Flow cavitation: • Breaks in the surface (oil bores, oil grooves) and diversion of the oil flow may cause a reduction in pressure.

Cavitation can definitely occur at a sharp edge. I'm wondering if the oil hole chamfer is more like a sharp edge. Do you have a means to take magnified images of the chamfer at the oil hole edges including areas with and without erosion?

Great information. Thanks
Meanwhile, I just used a jewelers loupe to examine the edges and they are not chamfered at all. Apparently a straight drilled hole.

The replacement rod bearings are chamfered.

 

[Lockasiam]

How do you feel about using Delo XSP 15w-40 (SN ratings) in a 1999 low rev motor?
I think it "might" hit 3,500 rpm if I floor it to pass.

The 3.8 doesn't really care. Go for it