The Elephant in the Room - #2 Rod Bearing Failures
03-05-2013, 12:26 PM
#16
Rennlist Member
Thread Starter
Good discussion... subscribing.
I know I've read a few of these threads in the past and it always seemed like the discussion came back around to RPM levels. It's one of the (few) reasons I liked my 26/6... I had no benefit to spinning the motor past 6000rpm. Just one extra little "safeguard". With the new turbo I'll probably lower the rev-limiter just to keep me from getting greedy, even if it means leaving some of the curve on the table.
I know I've read a few of these threads in the past and it always seemed like the discussion came back around to RPM levels. It's one of the (few) reasons I liked my 26/6... I had no benefit to spinning the motor past 6000rpm. Just one extra little "safeguard". With the new turbo I'll probably lower the rev-limiter just to keep me from getting greedy, even if it means leaving some of the curve on the table.
03-05-2013, 12:49 PM
#18
03-05-2013, 03:11 PM
#19
Rennlist Member
03-05-2013, 05:12 PM
#20
Rainman
Rennlist Member
Rennlist Member
Maybe this is sacrilege, but howabout looking up rough cam specs for a lot of USDM engines? Stuff like OHV V6's that redline in the 5500RPM area. GM 3800s, T-birds, etc. Torque monsters.
03-06-2013, 02:36 AM
#21
Rennlist Member
Has anyone tried Accusumps? I've heard of downsides but can't remember what they were.
03-06-2013, 09:50 AM
#22
Drifting
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Patrick:
Tony G has a thread talking Accusumps, from what I recall, it was not a viable option for our application. I have also spoken to LR about this and they have installed them on race cars. He also did not think it was a great idea, been so long ago that I don't recall the details. You have all ready installed the real cure, not a realistic option for most though, especially on the street.
Tony G has a thread talking Accusumps, from what I recall, it was not a viable option for our application. I have also spoken to LR about this and they have installed them on race cars. He also did not think it was a great idea, been so long ago that I don't recall the details. You have all ready installed the real cure, not a realistic option for most though, especially on the street.
Last edited by URG8RB8; 03-07-2013 at 10:58 AM.
03-06-2013, 02:19 PM
#23
Rennlist Member
My history is one stock 1984 junkyard N/A engine that overheated, warped the head, starting blowing coolant, and spun a rod (#2), all in 1/2 of a lap. I suspect when the head warped it let coolant get into the oil and killed the bearing.
That engine has been rebuilt (with a different used crank) and currently has over 60 hard track hours on it. My precautions to date have been: 1) I run Valvoline 20-50 Racing oil. I change the oil and filter after every other event, which is around 10 hours of run time. 2) I installed a stock oil pan with scrapers from a S2 car. 3) I have the trap door/baffle thing in this pan. I passed on the pickup ring. 4) I keep my oil between full and 1/2 qt low. I do not overfill. I have once or twice let it get almost a qt low 5) I shift around 6000 rpm except during moments of red mist behavior. 6) I do not have an external oil cooler but do have the foglight opening set up with a duct that vents air directly onto the oil/water heatexchanger. 7) I put in a new OEM oil pickup tube/assembly, out of concerns for immanent fatigue cracks/failure. I have the original stock oil pump.
There are pictures of my rod bearings after this winters replacement on my website. They didn't look great but #2 didn't look any worse than the others.
My strongest suspicion is that the #2 failures are caused by air entrainment in the oil (foaming) that is aggravated at the #2 bearing because of the configuration of the oil galleries. There is a longitudinal gallery down the axis of the engine that is fed at its entrance from the passage leading from the bypass plunger. #1 rod bearing is fed as a straight shot from the passage way i.e. no right hand turn. Conversely the branch passages to #2, #3, and #4 are all at right angles to the main passage. Thus the oil has to go around a right hand corner for each of these passages. Since air will go around a corner more willingly than a fluid, I suspect the #2 passage acts as an air/oil separator with the following passages less so. So #2 is getting the poorest quality oiling due to the high air entrainment. And eventually it gets pissed off and dies. The Valvoline racing oil says it is formulated to minimize foaming. I have no reason to doubt them. The crank scrapers also minimize foaming. Dry sump systems have their own air/oil separator as part of the system outside the engine, which is great if you can do it.
High rpms mean the forces at the rod big end are going up with the square of the piston speed. Pretty tough environment for an oil film that is a few thousands thick.
I think cross drilling the crank is a waste. From above, its not an issue of oil quantity, it is one of oil quality. If it was the uber solution, Porsche would have continued doing it instead of doing it for a while and stopping.
I love everything that Michael Mount does in his engine prep. I can only hope to understand 5% of what he has already forgotten.
That engine has been rebuilt (with a different used crank) and currently has over 60 hard track hours on it. My precautions to date have been: 1) I run Valvoline 20-50 Racing oil. I change the oil and filter after every other event, which is around 10 hours of run time. 2) I installed a stock oil pan with scrapers from a S2 car. 3) I have the trap door/baffle thing in this pan. I passed on the pickup ring. 4) I keep my oil between full and 1/2 qt low. I do not overfill. I have once or twice let it get almost a qt low 5) I shift around 6000 rpm except during moments of red mist behavior. 6) I do not have an external oil cooler but do have the foglight opening set up with a duct that vents air directly onto the oil/water heatexchanger. 7) I put in a new OEM oil pickup tube/assembly, out of concerns for immanent fatigue cracks/failure. I have the original stock oil pump.
There are pictures of my rod bearings after this winters replacement on my website. They didn't look great but #2 didn't look any worse than the others.
My strongest suspicion is that the #2 failures are caused by air entrainment in the oil (foaming) that is aggravated at the #2 bearing because of the configuration of the oil galleries. There is a longitudinal gallery down the axis of the engine that is fed at its entrance from the passage leading from the bypass plunger. #1 rod bearing is fed as a straight shot from the passage way i.e. no right hand turn. Conversely the branch passages to #2, #3, and #4 are all at right angles to the main passage. Thus the oil has to go around a right hand corner for each of these passages. Since air will go around a corner more willingly than a fluid, I suspect the #2 passage acts as an air/oil separator with the following passages less so. So #2 is getting the poorest quality oiling due to the high air entrainment. And eventually it gets pissed off and dies. The Valvoline racing oil says it is formulated to minimize foaming. I have no reason to doubt them. The crank scrapers also minimize foaming. Dry sump systems have their own air/oil separator as part of the system outside the engine, which is great if you can do it.
High rpms mean the forces at the rod big end are going up with the square of the piston speed. Pretty tough environment for an oil film that is a few thousands thick.
I think cross drilling the crank is a waste. From above, its not an issue of oil quantity, it is one of oil quality. If it was the uber solution, Porsche would have continued doing it instead of doing it for a while and stopping.
I love everything that Michael Mount does in his engine prep. I can only hope to understand 5% of what he has already forgotten.
03-06-2013, 02:22 PM
#24
Rennlist Member
Patrick:
Tony G has a thread talking Accusumps, from what I recall, it was not a viable option for our application. I have also spoken to LR about this and they have installed them on race cars. He also did not think it was a great idea, been so long ago that I don't redcall the details. You have all ready installed the real cure, not a realistic option for most though, especially on the street.
Tony G has a thread talking Accusumps, from what I recall, it was not a viable option for our application. I have also spoken to LR about this and they have installed them on race cars. He also did not think it was a great idea, been so long ago that I don't redcall the details. You have all ready installed the real cure, not a realistic option for most though, especially on the street.
03-07-2013, 09:35 AM
#30
Burning Brakes
I think I've read about a BMW using an external electric oil pump, but I can't find it anymore. I'm guessing I must have been mistaken and that electric oil pumps are simply considered too unreliable.