Oil Film & GM's Spun Beariings: What Went Wrong?

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FetchFar

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On the recent GM 2.0L Turbo 4 and 2.5L 4 engines, the spun bearings that occasionally popped up, was it that the bearing clearance was too high, too low, out-of-round, flat spot, surface roughness, metallurgy or heat-treating? Does anybody know? Big-end bearings. Oil film "disrupted", meaning protrusion or too much clearance, or too little???

"The failures, according to GM, are caused by bad connecting-rod bearings that slipped past quality control at an unidentified supplier in June 2013. The flawed bearings can disrupt the oil film between the bearing and the crankshaft, leading to catastrophic metal-on-metal contact. “All engines now are designed to microns [0.00004 inch],” said Pawlik. “If the oil film isn’t consistent, bad things can happen.” -- from Car and Driver Article link
 
Originally Posted By: gregk24
Wait, these are current GM engines? What vehicles are they in?


Yes, current, new cars. All 2.5L fours and 2.0L turbo 4's in GM cars are possibly affected, at the rate of a fraction of a percent, they think so far. Not all are bad, and GM is not recalling anything, just waiting to see who fails and brings it in under warranty.

Its hard to get the inside story of whats going on. GM thinks the engines are "hyper-sensitive" to oil film thickness. What does that mean?
 
It just seems to get worse and worse for GM, I feel kinda bad for them. Providing new engines to the owners affected by this problem will show that GM is sticking up for there customers.
 
Originally Posted By: gregk24
It just seems to get worse and worse for GM, I feel kinda bad for them. Providing new engines to the owners affected by this problem will show that GM is sticking up for there customers.
Warranty. If I had one of these engines, I might consider using a xw-30 (where the xw-20 is used in the 2.5L) and a 0w-40 in the turbo 2.0L which specs a 30, with all this talk about "hypersensitive to oil film thickness" talk.
 
Originally Posted By: FetchFar
Originally Posted By: gregk24
It just seems to get worse and worse for GM, I feel kinda bad for them. Providing new engines to the owners affected by this problem will show that GM is sticking up for there customers.
Warranty. If I had one of these engines, I might consider using a xw-30 (where the xw-20 is used in the 2.5L) and a 0w-40 in the turbo 2.0L which specs a 30, with all this talk about "hypersensitive to oil film thickness" talk.


"Hypersensitive to oil film thickness"...this sounds like an excuse for poorly manufactured bearings, or admitting to using too thin an oil.
 
Originally Posted By: gregk24
"Hypersensitive to oil film thickness"...this sounds like an excuse for poorly manufactured bearings, or admitting to using too thin an oil.


Their "fix" on future production is to decrease the rev-limiter RPMs a bit. I thought oil film was thinnest at low-RPM high torque points, not max revs.
 
Originally Posted By: FetchFar
Originally Posted By: gregk24
"Hypersensitive to oil film thickness"...this sounds like an excuse for poorly manufactured bearings, or admitting to using too thin an oil.


Their "fix" on future production is to decrease the rev-limiter RPMs a bit. I thought oil film was thinnest at low-RPM high torque points, not max revs.



My guess is that they are limiting max revs in order to lower the oil temp spike which will be thinner when elevated.
Perhaps an oil cooler of some sort would be a prudent addition if one was to purchase one of these.
 
Originally Posted By: Clevy
My guess is that they are limiting max revs in order to lower the oil temp spike which will be thinner when elevated.
Perhaps an oil cooler of some sort would be a prudent addition if one was to purchase one of these.

Originally Posted By: Nate1979
Does increases rpm's always mean higher oil temps?


My understanding is temperature does elevate at high RPMs, reducing viscosity, lowering oil film thickness from that, although high RPMs itself raises oil film thickness. In other words, you get thicker oil films from Viscosity*RPM/Load, and at near redline RPMs, Load is down from its peak a bit, viscosity could be thin (hot), yet RPMs itself keeps oil film there. Somewhere along the torque curve at a high-torque, lowish-RPM point is where the oil film is at its thinnest (lugging). So I don't get GM's "fix" to lower max RPM obtainable.
 
I have yet to have the dynamics of a spun bearing explained to me in a manner than makes sense...the interference fit between bearings and iron mean that the bearing metal should shear well before the bond breaks from bearing to cap.

Smokey's theory was that the pounding of detonation pulls the sides in, and wipes the oil film clean off, causing a weld/spun bearing...works on a superficial level, as the tangs then just help to drive the steel shell into the gap between crank and rod/block.

I'm not convinced totally, as cam bearings spin too...which is where I will start my thoughts.

Best I can guess is that at prolonged high revs/load, bearings heat up, blocks caps and rods heat up, and expand...bearing shells expand quicker, as they have lower thermal mass, but that makes them tighter.

On rapid cooling, shells cool quicker, and shrink faster than either the crank, or the rod/block, making them looser in the block, and tighter on the journal...get the wrong tolerance stack-up, incorrect alignment, and I can get to a spun cam bearing state.

With mains/rods, maybe high revs, traffic light stop/idle, knocking on moving off gives the right perfect storm for a change in bearing details, and a reduction in max RPM to make the problem go away in a bandaid like fashion rather than an engineered out fix.
 
Quote:
I have yet to have the dynamics of a spun bearing explained to me in a manner than makes sense
The oil film fails and the bearing wipes. Now the shell is welded to the journal and the shell spins with the journal. Calling it a spun bearing is looking at the damage after the fact. Calling it a wiped bearing would be more accurate.

There are dynamic actions taking place in the bearing. At higher rpms the centrifugal forces increase which can change the rate of the oil being thrown out of the bearing. If the oil supply isn't adequate to keep the bearing fully flooded, you'll have failures. There might be other problems that happen at these rpms.
 
Originally Posted By: Ken2
Quote:
I have yet to have the dynamics of a spun bearing explained to me in a manner than makes sense
The oil film fails and the bearing wipes. Now the shell is welded to the journal and the shell spins with the journal. Calling it a spun bearing is looking at the damage after the fact. Calling it a wiped bearing would be more accurate.

There are dynamic actions taking place in the bearing. At higher rpms the centrifugal forces increase which can change the rate of the oil being thrown out of the bearing. If the oil supply isn't adequate to keep the bearing fully flooded, you'll have failures. There might be other problems that happen at these rpms.


Thats why it would be good if an insider at GM could tell us what the flaw was that makes Pawlik, the chief engineer for those engines, say "hypersensitive to oil film" etc. Certainly you want to really nail the clearance, as they do in F1 racing for example.
 
Originally Posted By: Ken2
The oil film fails and the bearing wipes. Now the shell is welded to the journal and the shell spins with the journal. Calling it a spun bearing is looking at the damage after the fact. Calling it a wiped bearing would be more accurate.

There are dynamic actions taking place in the bearing. At higher rpms the centrifugal forces increase which can change the rate of the oil being thrown out of the bearing. If the oil supply isn't adequate to keep the bearing fully flooded, you'll have failures. There might be other problems that happen at these rpms.


Wouldn't that be called oil starvation and not oil film failure?
 
Shannow may be you can shed some light on my theory.
I believe GM has gone to an all aluminum bearing shell.
Given the expansion of the aluminum is double that of forged cast iron its going to expand right into the crank effectively eliminating the oil film clearance and blocking the oil feed hole.

The hotter it gets the tighter it gets then begins to shear aluminum off the bearing to the point the tangs holding it tear off and then it spins.
I suppose you could apply this to steel shell bearing as well as the expansion is still greater than the forged or sintered iron even if the shell were 100% steel.
Add lead and copper and the expansion increases even further.

I suspect the bearing were just too tight when assembled.
I am just a simple mechanic not an engineer so my theory is probably full of holes but thats okay, i don't mind posting my stupidity.
lol.gif
 
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