bearing damage

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integrale Evo
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Re: bearing damage

Post by integrale Evo »

AC sports wrote: Sat Feb 17, 2018 1:23 am
integrale Evo wrote: Fri Feb 16, 2018 11:09 am I think I would be keeping the piston cooling jet holes, if the stock motor had them then certainly a modified or hard driven one will.
In a turbo application like yours I'd definitely keep them. Mine is na and they are not really needed. My pistons won't see the temps yours will. Splash and mist are adequate to lube in an na tc. I know of many na powered tcs that run flat out on ovals, full throttle in top gear for extended periods and never had pin oiling issues.
The squirters were needed when Lancia redesigned the 2l tc block for turbo in order to cool the pistons from below. At least that's what logic tells me. I know they kept that set up in their gpA wrc cars too.....I'd sure like to see what they did with the S4 though. Completely different engine I know...but still wonderfully engineered as they all were.
Sorry I disagree, your logic is flawed. They were put in to cool the pistons, you're effectively making things worse by erradicating them. A modified NA will have piston temps similar to or greater than a std road going turbo car.
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Re: bearing damage

Post by AC sports »

I don't think I was clear or maybe you misread my post. My block didn't come with squirters. The thing I'm loosing by running race rods are the oil holes in the oem rods that spray under the piston.
In an n/a application they are not really needed based on what I've seen.
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Re: bearing damage

Post by MadBill »

I've always been skeptical about how much oil can be squirted out of a cavity with less than a 0.003" high annular entry...
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Re: bearing damage

Post by integrale Evo »

AC sports wrote: Sat Feb 17, 2018 1:17 pm I don't think I was clear or maybe you misread my post. My block didn't come with squirters. The thing I'm losing by running race rods are the oil holes in the oem rods that spray under the piston.
In an n/a application they are not really needed based on what I've seen.
Yes i'm quite aware of what you are saying, they are piston cooling jets and i'd rather be with them than without. Even the later 16v N/A blocks had them.
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Re: bearing damage

Post by integrale Evo »

MadBill wrote: Sat Feb 17, 2018 4:04 pm I've always been sceptical about how much oil can be squirted out of a cavity with less than a 0.003" high annular entry...
I'm not sure how big they are, but I'd say bigger than that and can find out. It would have been a lot of expense to go to for no reason and the designer (Aurelio Lampredi) was not known for being daft - look him up, there is a lot written about him and for good reason too. These engines are lovely little pieces of work, well designed, lots of port induced swirl as cast etc and people don't even know it.
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Re: bearing damage

Post by integrale Evo »

More for completeness than anything else, but there is a pair of 1.5mm (one on each side) holes in the rod.
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Re: bearing damage

Post by peejay »

This thread came up to mind because I just pulled the engine out of my car for a refresh after almost five years of use/abuse. (maybe 50,000 miles of street driving, maybe 100 1/4mi runs, maybe 8-10 hours of competition runs at full temp load, I did not keep close track)

When I was blow drying one of the bearings, a chunk popped out of the copper underlay.

Image

I had never been too worried about the overlay being worn through, but now I am concerned.

Engine never had oil pressure problems and the journal itself looks perfect. I am thinking I need to run a thicker oil and maybe try to keep it cooler.
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Re: bearing damage

Post by pamotorman »

looks like water in the oil attacking the bearing material. that is why i always told customers to run fresh oil thru the engine before storage.
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Re: bearing damage

Post by ptuomov »

Warp Speed wrote: Tue Feb 06, 2018 1:19 pm
Barry_R wrote: Tue Feb 06, 2018 12:45 pm Its not oil pump cavitation - its bearing cavitation - similar name but a different deal.

No signs of heat or smearing on the surface - it had lube, but something pulled the material away from the bearing.
Yep, and typically more clearance aggravates it!
Greater clearance and higher oil viscosity by my logic lead to worse cavitation, smaller clearances and lower viscosity would help prevent it. Is this thinking correct?
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Re: bearing damage

Post by user-23911 »

Who's got a definition for what "cavitation" is?
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Re: bearing damage

Post by ptuomov »

joe 90 wrote: Mon May 07, 2018 3:08 am Who's got a definition for what "cavitation" is?
In this context, it's the pressure in the oil film dropping below the vapor pressure of the oil (or air-oil mixture). It happens on the low-pressure side of the minimum distance point of the journal and the bearing. As the journal slides against the bearing, the geometry on the low-pressure side of that point has an expanding cross-sectional area which means that the pressure drops. By my logic, higher the viscosity, higher the bearing speed and larger the bearing clearance, the more the pressure will drop as the oil slowly flows into the low pressure area. At some point, the absolute pressure drops below the vapor pressure of the fluid, and vacuum or near vacuum bubbles appear in the fluid. As pressure then increases again with fluid flowing in, these bubbles collapse and release their potential energy in a highly localized fashion. This local energy release causes pitting in the bearing shell, journal, propeller, etc. That's at least how I've understood it.
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Re: bearing damage

Post by Warp Speed »

ptuomov wrote: Mon May 07, 2018 8:19 am
joe 90 wrote: Mon May 07, 2018 3:08 am Who's got a definition for what "cavitation" is?
In this context, it's the pressure in the oil film dropping below the vapor pressure of the oil (or air-oil mixture). It happens on the low-pressure side of the minimum distance point of the journal and the bearing. As the journal slides against the bearing, the geometry on the low-pressure side of that point has an expanding cross-sectional area which means that the pressure drops. By my logic, higher the viscosity, higher the bearing speed and larger the bearing clearance, the more the pressure will drop as the oil slowly flows into the low pressure area. At some point, the absolute pressure drops below the vapor pressure of the fluid, and vacuum or near vacuum bubbles appear in the fluid. As pressure then increases again with fluid flowing in, these bubbles collapse and release their potential energy in a highly localized fashion. This local energy release causes pitting in the bearing shell, journal, propeller, etc. That's at least how I've understood it.
This all typically happens at TDC overlap, and is compounded by low manifold pressure, as in closed throttle decel or highly restricted intake situations.
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Re: bearing damage

Post by FC-Pilot »

Warp Speed wrote: Mon May 07, 2018 11:32 am
ptuomov wrote: Mon May 07, 2018 8:19 am
joe 90 wrote: Mon May 07, 2018 3:08 am Who's got a definition for what "cavitation" is?
In this context, it's the pressure in the oil film dropping below the vapor pressure of the oil (or air-oil mixture). It happens on the low-pressure side of the minimum distance point of the journal and the bearing. As the journal slides against the bearing, the geometry on the low-pressure side of that point has an expanding cross-sectional area which means that the pressure drops. By my logic, higher the viscosity, higher the bearing speed and larger the bearing clearance, the more the pressure will drop as the oil slowly flows into the low pressure area. At some point, the absolute pressure drops below the vapor pressure of the fluid, and vacuum or near vacuum bubbles appear in the fluid. As pressure then increases again with fluid flowing in, these bubbles collapse and release their potential energy in a highly localized fashion. This local energy release causes pitting in the bearing shell, journal, propeller, etc. That's at least how I've understood it.
This all typically happens at TDC overlap, and is compounded by low manifold pressure, as in closed throttle decel or highly restricted intake situations.
Gosh dang it. I have never had this issue in my engines, and now that I have read this and have a little bit better understanding of it I am sure it will pop up. It is all your fault guys. I was better off not knowing anything. LOL

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Re: bearing damage

Post by modok »

It's difficult to tell the difference between fatigue cracking and electrolysis corrosion, because they can accelerate eachother.
Pitting is caused by cracks in surface which go straight down, if these cracks eventually connect below a chunk falls out. Depending on the hardness VS toughness of the material it will range from micro-pitting to LARGE pits falling out, and in either case it does not necessarily indicate a fault in the material, rather shows it's mechanism of failure when overstressed

Point tho, is remember that corrosion THRIVES in cracks. I think you know what I mean. Like how once rust crawls UNDER paint it rusts faster than if it was bare. Or how magnafluxing works... two surfaces spaced slightly apart forms a battery or capacitor like action across the crack. A few methods of crack detection actually you apply an acid to make the cracks into little batteries and then look for them.

I don't know how you would look at a bearing and determine how much was corrosion and how much was fatigue, besides looking at everything else around and guessing.
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