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Oddjob

In the middle of a routine rod bearing replacement. Found an interesting pattern on the top side bearing halves. Shows up on all 4. Have not seen this before. Have a couple differing opinions of what this is from a couple people I have shown this to. Back side of the bearing appears normal, no unusual contact or non-contact marks on the backside.

Anyone seen this before?

LUCKY DAVE

That is surface fatigue failure. I have dealt with that same exact problem on a nitrous land speed engine, caused by minutely too much spark lead.
Google it, there are many pictures and discussions on the subject.

Oddjob

Potentially overlay fatigue? Close ups:

Oddjob

Dave or others,

I thought the close-ups above were pretty interesting - can you confirm that this is similar to the surface fatigue you have seen previously?

refresh951

What oil are you using?

Oddjob

In the race engines, Ive been using Brad Penn 20-50 last few years, Amsoil 20-50 prior to that.

refresh951

Looks like overlay fatigue which is generally the result of low oil film thickness. May want to run 25w-60, add bigger oil cooler, and have the new rod bearings coated.

LUCKY DAVE

The pics are similar to what we have seen, but a much more advanced case. Ours had just a few "flakes" missing. Still, a huge problem in a 380hp/liter engine.
We sent ours to Carrillo to see if they agreed with our analysis (they made the rods) and they confirmed it was bearing overlay fatigue, and they felt it was caused by too much spark lead in a nitrous engine. They have tons of experience in this area.
What we learned in the process of developing this engine (and setting a world record) is that nitrous setups are VERY intolerant of too much lead, two degrees more than the optimum power setting results in near instant lower end death.

gruhsy

Can you explain that one a little more? just asking not 100% on what you are saying is happening. extra forces due to the nitrous?

thks

LUCKY DAVE

In a nutshell, yes.
Our engine has a very efficient (fast) burning head. Combine that with 13 psi of boost and a 150 shot of nitrous, and the burn is almost instantaneous.
Exact ignition timing is critical to making the power required to go fast while not hammering the bearings out of the rods.
As you might imagine, the ignition/nitrous/boost/fuel mapping gets complicated with the need to be able to program in rising rate power as the bike goes through the gears in order to hold a steady 15% wheelspin from the start to the finish line. We're using a custom made ECU based on Microsquirt.

KSira

Did you run a larger oil cooler, and what oil temperatures did you see during a race?

gruhsy

Thks. Thought that was what you were getting at

Oddjob

Not sure a low friction coating (swain or other) protects from fatigue damage? I would have expected metal to metal contact due to lack of or reduced oil film to look somewhat different than this.

Currently running two mocal coolers in series, 13 row and 19 row. Have seen oil temps above 260F when running the straight KISS cooler setup. Engine got very hot during this past year's local club race, which is why I pulled the pan to replace the bearings. But again, this damage is not what I would have expected to see from high oil/engine temps (?).

LUCKY DAVE

The way I understand it, overlay fatigue is caused by abrupt peak loading being too high (such as from detonation), not by metal-to-metal contact. The (too high) loads are conveyed by hydraulic pressure through the oil film, micro flexing the bearing shell itself.
I believe the process is somewhat similar to the cavitation fatigue seen in the low pressure side of highly loaded boat props, where the shock wave from collapsing micro bubbles hammers at the metal.