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Discussion Starter #1
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What would be the likely cause(s) this severe bearing failure? 2.0L NA Mazda MZR engine. Stock bearing. Road race application. This was a "good" rod. The "bad" rod came out in about 6 pieces with blue big end parts. I'm thinking high oil temps that caused the oil to give up, thoughts? It's not uncommon to see oil temps above 300*F in different engines in the same application. No temp gauge was on this particular engine.
 

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If they weren't running at least an accusump or dry sump setup, then there's a strong possibility that they were repeatedly losing oil pressure in the turns. I had a 944 motor that looked like that after suspension and tire upgrades without the pan or pickup baffles added in, and it lasted 3/4 of an event that way before kicking the rod out the side of the block in spectacular fashion.
 

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Sucking air in the corners and when on the brakes. Bearing welded itself on the crank after they came in the pits.
 

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Discussion Starter #6
This was a stock engine from Mazda. Oiling system upgrades (cooler, gauge, and accusump) will be added to the car before next season. I'm thinking (pure speculation) that it kicked the other rod due to oil starvation, so it only makes sense that this is also what we are seeing on this one.
 

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Agreed. The bearing did the same thing likely, but was the first to grab the crank. Once it grabs the rod breaks.
Is that in the altered?
Whoops, road race I see now. 300 degrees is a bunch. The heat probably contributed. That oil didn't have much viscosity at that temperature.
 

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Mike I'm gonna go out on a limb and say that engine was not happy at all. That bearing is crazy and belongs on a special section of the wall dedicated to it. Lol. Hate to see that but thanks for sharing.
 

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Discussion Starter #11
Any reason not to keep oil temp below 230F?
The engine had a stock Miata oiling system, so no auxiliary oil cooler was present. Coming from a drag racing background, it was eyeopening when I started working with these road racers. They are VERY hard on oil.
 

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Bearing fatigue. The higher the bearing temp...the lower the fatigue life at a given loading.

Get that oil below 250*F.....lower the better, within reason.
 

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I agree road racers are hard on engines. However I do not recall ever when I was involved with road racing (GT1, GT2, GT3) and other classes where no oil cooler was used. Most cooled everything. We had cooler on engine, cooler of gearbox, and cooler on differentials.
Glad this is being solved.
Cheers
 

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That’s an impressive wall hanger for sure!! Gnarly
That is the result of a cam sync going out of whack due to a poor design, and it was firing #8 a wee bit early on mt SBC, maybe 100* or so BTDC! It would pop, shut off, I would "fix" the sync wheel, start it up and drive it back to the trailer. Red thread lock cured nothing with the issue. It wasn't until I heard a squeaking from the engine that I tore it down and found that......... I also welded the cam sync wheel so that issue would never occur again!
 

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300F oil temp will kill pretty much anything.
Looks like you peeled the overplate and lining right off that thing
 

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Discussion Starter #19
300F oil temp will kill pretty much anything.
Looks like you peeled the overplate and lining right off that thing
I agree that 300*F is too hot, but I've seen it in more than one engine. The C7 Corvettes are BRUTAL for high temps (oil, coolant, ATF... you name it)! I have yet to have one apart after it has been abused however. I have learned that good oil is key. Hard to tell this to some owners though when the factory calls for oil that is sub-par in my experience. Some just learn the hard way.
 
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