Strange crankshaft wear pattern

[Kiggly]

The mains are cross drilled and the top bearing shells are grooved. The bottom mains are full face bearings, although I have run grooved lowers in the past.

I can’t find anything good here with a search for crank oiling timing, any pointers?

Also, I’m running about 85-90psi after the filter and the theoretical centrifugal pressure to the center of the 57mm mains at 10.4k is 62psi. I figured it was probably enough, but I can certainly run a bit more. If the consensus points toward it being likely an oil flow issue, I can easily change that with more pressure.

[naukkis79]

They're NOT nitrided.

They are nitrided. Highest performing japanese engines don't have induction hardened cranks as they are prone to crack. Nissan, Subaru, Mitsu, all used some kind of stainless steel in high performance engine cranks - and they aren't induction hardened as that ruins stainless steel flex properties. Newer cranks have probably plasma nitrided trows so they don't have traditional nitriding marks on counterweights.

[Warp Speed]

Cross drilling and high rpms do not go together very well! Lol

[naukkis79]

Also, I’m running about 85-90psi after the filter and the theoretical centrifugal pressure to the center of the 57mm mains at 10.4k is 62psi. I figured it was probably enough, but I can certainly run a bit more. If the consensus points toward it being likely an oil flow issue, I can easily change that with more pressure.

Problem with cross drilled main bearings is that pressure can go directly to unpressurized side of main bearing. With only one feeding hole you have much, much more pressure to feed con rod than just engine oil pressure as main bearing crushes oil and pressure multiplies.

90 psi is only about 6 bar. Old saying was that you want about 1 bar of oil pressure for every 1000 rpm so you probably could up oil pressure a bit.

[MadBill]

I think if we did a poll, we'd find the vast majority of SpeedTalkers would say: "10# per 1,000 RPM."

[pamotorman]

Also, I’m running about 85-90psi after the filter and the theoretical centrifugal pressure to the center of the 57mm mains at 10.4k is 62psi. I figured it was probably enough, but I can certainly run a bit more. If the consensus points toward it being likely an oil flow issue, I can easily change that with more pressure.

Problem with cross drilled main bearings is that pressure can go directly to unpressurized side of main bearing. With only one feeding hole you have much, much more pressure to feed con rod than just engine oil pressure as main bearing crushes oil and pressure multiplies.

90 psi is only about 6 bar. Old saying was that you want about 1 bar of oil pressure for every 1000 rpm so you probably could up oil pressure a bit.

i have run BBC with the stock cross drilled mains cranks at places like Daytona, Trenton and Poconos turning 7000+ rpms with no problems.

[Warp Speed]

Also, I’m running about 85-90psi after the filter and the theoretical centrifugal pressure to the center of the 57mm mains at 10.4k is 62psi. I figured it was probably enough, but I can certainly run a bit more. If the consensus points toward it being likely an oil flow issue, I can easily change that with more pressure.

Problem with cross drilled main bearings is that pressure can go directly to unpressurized side of main bearing. With only one feeding hole you have much, much more pressure to feed con rod than just engine oil pressure as main bearing crushes oil and pressure multiplies.

90 psi is only about 6 bar. Old saying was that you want about 1 bar of oil pressure for every 1000 rpm so you probably could up oil pressure a bit.

i have run BBC with the stock cross drilled mains cranks at places like Daytona, Trenton and Poconos turning 7000+ rpms with no problems.

Just not 10,000 rpm and 70psi boost huh?!? Lol

That's not a real good case to defend a cross drill strategy!

[pamotorman]

Problem with cross drilled main bearings is that pressure can go directly to unpressurized side of main bearing. With only one feeding hole you have much, much more pressure to feed con rod than just engine oil pressure as main bearing crushes oil and pressure multiplies.

90 psi is only about 6 bar. Old saying was that you want about 1 bar of oil pressure for every 1000 rpm so you probably could up oil pressure a bit.

i have run BBC with the stock cross drilled mains cranks at places like Daytona, Trenton and Poconos turning 7000+ rpms with no problems.

Just not 10,000 rpm and 70psi boost huh?!? Lol

That's not a real good case to defend a cross drill strategy!

oil flow not pressure is the answer to keeping the bearing healthy. i had a customer call and say they smashed in the wet sump oil pan in practice and they now only have 35 PDSI oil pressure instead of 65 and wanted to know what to do. i told them to run it as oil flow is more important than pressure. it was a 100 mile race and they won. took the engine apart when they got back and everything was perfect. new pan and they were on the way. plain bearing turbochargers run at many 1000s of rpms on 60 PSI of oil pressure.

[Warp Speed]

K

[hoffman900]

Problem with cross drilled main bearings is that pressure can go directly to unpressurized side of main bearing. With only one feeding hole you have much, much more pressure to feed con rod than just engine oil pressure as main bearing crushes oil and pressure multiplies.

90 psi is only about 6 bar. Old saying was that you want about 1 bar of oil pressure for every 1000 rpm so you probably could up oil pressure a bit.

i have run BBC with the stock cross drilled mains cranks at places like Daytona, Trenton and Poconos turning 7000+ rpms with no problems.

Just not 10,000 rpm and 70psi boost huh?!? Lol

That's not a real good case to defend a cross drill strategy!

Talking about dating oneself! I don't doubt it worked for him then, but I think we've learned a lot in the last 40-50 years!

We've talked about cross-drilling ad nauseam here.

[Kiggly]

The google search function is 100x better than the board's internal search and I found some good stuff. I do know this engine has some pretty bad oil aeration issues. Sounds like the cross-drilling can collect small bubbles into big bubbles and do bad stuff. If that is the cause, my next move going to a dry sump system will be a big step in the right direction. Between this and a bit more oil pressure, I'll hopefully see some improved results. I'm definitely still open to any input, but since the wear is agreed by a few as potential starvation and both of these moves will help, I think I'm on the right track. Thanks for all the input folks.

[swampbuggy]

WARPSPEED------------How much oil pressure do you guys like to see at a track like Michigan, or Fontana where the engines are at 7to 9000rpm's a lot? Thanks OCD Mark H.

[pamotorman]

i have run BBC with the stock cross drilled mains cranks at places like Daytona, Trenton and Poconos turning 7000+ rpms with no problems.

Just not 10,000 rpm and 70psi boost huh?!? Lol

That's not a real good case to defend a cross drill strategy!

Talking about dating oneself! I don't doubt it worked for him then, but I think we've learned a lot in the last 40-50 years!

We've talked about cross-drilling ad nauseam here.

please explain why it worked back then but would not work now. what laws of physics have changed in 40 years ?? i have read the R&M article but has anyone else documented the same problem ???

[tuffxf]

Gday Kiggly,
Are all the rod bearings and all the journals showing the same on a repeat basis?
Cheers

[Kiggly]

Yes, they pretty much all look the same over all 4 journals and the last 2 crankshafts. There are subtle differences, but the same basic theme.