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Thread: Engine Failure - Dry Sump Lubrication

  1. #1

    Engine Failure - Dry Sump Lubrication

    Hello everyone,

    I am Rabsimran Gulati from Formula Manipal, a team from India. We recently participated in the Formula Student Germany and Formula Student Czech Republic events. We faced issues with the engine’s lubrication system in both the events.
    Before I describe the events, I will explain the system we are using.

    We are currently using a Honda CBR 600RR PC37 (2005 - 2006 model) engine and running a dry-sump lubrication system with it. The previous year was the first time we had implemented the dry sump system. Also, we currently use a Motec M400 ECU, which was also implemented in the previous year. We have designed the intake, exhaust and cooling systems with internals being stock.
    The lubrication system includes -
    Honda CBR 600RR PC 37 engine with a Dailey Engineering scavenge pump , 2 stage pre ’07 model (04-99-2220), without an air-oil separator and 2 scavenge ports, externally mounted reservoir with a running capacity of 3l (Oil being used, Motul fully synthetic 4T 300V 10w40).
    Lubrication Plumbing:
    AN -10 scavenge lines (from dry sump to scavenge pump inlet). Scavenge ports oriented transversely w.r.t the car, one of either side.
    AN -12 scavenge line (from scavenge pump outlet to reservoir inlet)
    AN -6 line pressure feed line (from reservoir outlet to engine pressure pick-up port).

    Before running in the event, we had the engine running on this setup for almost 50km on a rolling road dynamometer, and about a 150 km of testing. We were always logging data such as the engine coolant temperatures and oil pressures. We made sure that these values never crossed their limits, knowing the desired oil pressures for various RPM ranges.
    However, during our pre-competition testing phase in Germany, the engine started making an abnormal ‘tick-tick’ noise that we had never heard before. Soon after the engine stopped cranking, kind of getting locked internally. Assuming this was a block-related internal issue, we switched to our spare block and continued with the testing.
    At FS Czech Republic, in the dynamic test area before the Autocross event, the engine started making screeching sound and we went directly to autocross. During the Autocross, the engine failed with the oil cooler flange separating away from the block. The connecting rod of the 2nd cylinder broke and flew out of the block leaving a hole behind. Also, smoke was observed, probably because of the oil burning up by coming in contact with the hot exhaust pipes. Due to this failure we could not compete in the rest of the competition. Upon checking the logged data we observed that the oil pressure values dropped severely below the desired value during failure.
    It was suspected that choked flow rate due to the small ID of the -6 line (from reservoir outlet to engine pressure pick-up port) caused loss of oil pressure at high revolutions causing the failure. We then replaced the pressure feed line from a -6 to -12 size and the tested the system. The overall pressure values were higher than that obtained previously, with occasional momentary unexpected pressure drops still occurring.
    We managed to fix the issue before the start of the Acceleration event at FSG and competed in the Acceleration and Autocross events. Could not complete the endurance event due to a leak in the fuel tank (not related to the issue being discussed)
    Once we were back home we opened up the engine which was making the noise (which was replaced with the spare engine during testing) and we noticed that the journal bearings of cylinder 2&3 were severely damaged. Find the attached pics.
    Pic 1: Bearing of 2nd piston. 1.JPG
    Pic 2: Bearing of 3rd piston. 3.JPG
    Pic 3: Crankshaft journal of 3rd cylinder. 4.JPG
    We are confused as to why this sound (tick) and failure was observed at the competition and not when we were in India, during our 3 months of testing with the system. The only variable being, the change of oil brand from Motul to Repsol fully synthetic 10W40 (which has a higher viscosity at 100oC).
    We believe that this was due to insufficient supply of oil to the crank journals due to the -6 line. We continued testing with the new system and we ran the engine for about 170 kms. The oil pressure values were within the desired range.
    But the engine recently failed with the exact same symptoms. There was a rattling noise heard during testing and the engine was immediately shutdown. Very fine metal powder was found in the sump and at flywheel. Unfortunately, we did not have the oil pressure values this time as the sensor was faulty and did not log any values. We immediately opened the engine and observed a similar failure. The journal bearings of the third cylinder failed in a similar fashion. Find the attached pics.
    Pic 4: Metal powder in sump. 5.jpg
    Pic 5: Overlapped bearings of 3rd piston. 6.jpg

    Since we observed a similar failure, we understood that our engine issues have not been solved by changing the size of the feed line from-6 to -12.
    I hope that the experts in this forum can help solve our issue or at least give us a lead on where we might have gone wrong.

    Please feel free to ask any questions if I have missed out on any essential information.

  2. #2
    Sounds like a typical loss of oil pressure due to G's moving the oil away from the pickup.

    Perform a G approximation test by tilting your engine assembly and observe if the oil pickup remains covered in oil. If not, well theres is your problem.
    Jay Swift
    Combustion Powertrain
    Global Formula Racing 2013-2014

  3. #3
    If you're willing Rabsimran, I think seeing what your oil pan looks like may also paint a picture. I would be sure to see if your scavenge pump is okay as well since you had the fine metal powder. Were there any large bearing pieces?
    Wayne State University Formula SAE [Warrior Racing]

    2015 - Technical Advisor (Engine - Calibration Lead) "Old Man Jenkins"
    2013-2015 - Powertrain Director (Engine - Calibration /Electrical Lead)
    2012-2013 - Engineering Captain (All the things)
    2011-2012 - Cooling/Exhaust Lead

  4. #4
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    Rabsimran,

    Your photos show that you have spent much money on a "racing dry-sump system", ... and got the same result as an off-the-shelf wet-sump.

    My guess is that your problem is in the design of your oil-tank (ie. what you call "externally mounted reservoir"). Photos or drawings of this tank and its associated plumbing would help pin down the problem.

    Z

  5. #5
    The designs of reservoir and sump are shown in the images below:

    Sump:
    sump.JPG

    Plumbing on sump:
    Lubrication plumbing.jpg

    Reservoir side view:
    reservoir2.jpg

    Reservoir rear view:
    reservoir1.jpg

    The scavenge pump was dismantled at the event and was found to be okay. The inline mesh filters at the ports of scavenge pump blocked the large metal chips of journal bearings.

  6. #6
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    Rabsimran,

    Firstly, your photos show that it is fairly certain that your failures are due to lack of reliable supply of high-pressure oil to the crank-bearings. For these types of "slipper/shell/plain-bearings" the oil-supply MUST ALWAYS BE AT PRESSURE and have NO AIR-BUBBLES. So no pressure drops, and no "foaming" of the oil is allowed. (In contrast, all-roller-bearing engines do fine with only a fog of oil to keep things slippery.)

    So the problem lies somewhere between the crank-bearings and whatever is supposed to be pumping oil to the bearings. Note that the "scavenge section", in itself, is not a problem here. It is there simply to keep the bottom of the crankcase mostly empty (for less power-sapping drag), and to send most of the oil to the external-reservoir, preferably with the minimum addition of air-bubbles in the oil.

    But now I need a clarification. In your first post you say,

    Lubrication Plumbing:
    AN -10 scavenge lines ...
    AN -12 scavenge line ...
    AN -6 line pressure feed line (from reservoir outlet to engine pressure pick-up port).
    This last "pressure feed line" should go (MUST GO!!!) to the INLET of the main-oil-pressure-pump of the engine. This line must have minimal obstructions and supply pure, clean, bubble-free oil from the external-tank to the main-pressure-pump. From this main-pump it then goes under pressure (at ~2++ bar) to the crank-bearings.

    So I hope you are not feeding the oil from the external-tank to an oil-gallery AFTER the main-pressure-pump???

    To repeat, the pressure-feed-line from external-tank MUST GO to the SUCTION-SIDE of the main-pressure-pump.

    Do you have an oil-flow schematic of your system? Such a schematic is usually the first step of the engineering design process.

    Z
    Last edited by Z; 01-08-2017 at 06:55 PM.

  7. #7
    Z,

    The pressure feed line goes directly from oil tank to the pressure pump inlet through a -12 line and not to a gallery after the pressure pump.

    The oil-flow schematic of the current design is shown below:
    Oil flow schematic.JPG

    While going through the ECU logs it was found that the oil pressure at gallery just after the pressure pump (where the oil pressure switch sits in the CBR600RR) showed signs of inadequate oil pressure when the car comes out of slalom. Screenshots of rpm, oil pressure and lateral G's are attached below:
    f3.JPG

    f5.jpg

    fail 2.JPG

    falure 1.jpg

    We do not have an air-oil separator but the oil tank has baffles installed parallel to the axis of the tank at the peripheries with tangential oil entry to give a swirl action to the incoming oil for air separation.

  8. #8
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    The lack of air-oil separator/cyclone is probably the biggest problem here, if air/foam gets into the oil, you will have pretty ordinary oil pressure/flow. That and baffle design allowing starvation under accelerations. The German track could well have had better grip that your home test venue meaning you never saw the same G numbers in testing vs at comp..
    ex-UWA Motorsport

    General team member 2013-15, Vehicle Dynamics Team Lead 2012
    Project Manager 2011, Powertrain minion 2009/10

  9. #9
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    Have you got data from the skidpad event? Or some cornering with relatively steady throttle?
    ex-UWA Motorsport

    General team member 2013-15, Vehicle Dynamics Team Lead 2012
    Project Manager 2011, Powertrain minion 2009/10

  10. #10
    Nick Favazzo,

    Thank you for your response. I'll look into our design for deaeration and if needed, will buy an AOS.

    I'm afraid we don't have a proper data for the skidpad event. I have data from FSG '16 Autocross, if you'd like to see.

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