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  1. #1

    ZF Gear: No Oil Pressure

    I'm stumped. Please help if you can.

    Portside ZF BW250 marine gear (behind 12V71tic) has operated normally throughout ownership. Three weeks ago, the oil line from the gear to the mechanical ER gauge sprang a leak. I shut it down and removed the hose. There was some oil flowing freely from the top of the gear out the open flair fitting. Not having a cap, I cut the hose and reattached a foot or so of hose standing straight up to contain the oil; I wrapped the end of the hose, but not air tight.

    IMG_8689.JPG

    I had two new lines made up, one for each engine, and installed. Cranked both motors today. Starboard warmed up as per normal. The port gear will not make pressure. The oil level is to the top mark. I loosened the flair on the mechanical ER gauge at the gauge; no oil was reaching the gauge. The electric oil pressure gauge on the bridge checks out OK.

    My scientific wild-ass guess is I've lost prime to the oil pump while the hose was off for about a week. As I said, I changed the starboard oil pressure gauge line, but that was on and off in a very few minutes. A brief shot of port side RPM had no effect. The ER temp is around 60 degrees and the oil is 40 wt. I've run the shifter through the gears with no effect. I've manually turned the prop shaft and it's free.

    Anyone have any suggestions?
    Semper Siesta
    Robert Clarkson
    ASLAN, 1983 55C #343
    Charleston, SC

  2. #2

    Re: ZF Gear: No Oil Pressure

    Perhaps you need to unscrew the hose and fill with oil. The mechanical gauge may not be reading because of air pressure in the hose or there is a blockage. If you unscrew the fitting from the gearbox does oil squirt out when engine is started? Could the pinhole in the bottom of the gauge be somehow blocked when they made up the new hose?

  3. #3

    Re: ZF Gear: No Oil Pressure

    Thanks. Done that. I cross connected sender lines from both engines. Good motor/gear generated oil pressure in bad gear. That also verified electric sender is working. Also verified torsional coupling is intact, so it's spinning inside. Filter screen assembly is now off and it's clean. It's a complete mystery. Do oil pumps on these gears go bad? Very odd since all was good until I changed that hose.
    Semper Siesta
    Robert Clarkson
    ASLAN, 1983 55C #343
    Charleston, SC

  4. #4

    Re: ZF Gear: No Oil Pressure

    If the remote gauge and sender are working I don't think you have an issue with the pump. Did you say you swapped the hoses between the two mechanical gauges? If the transmission is shifting I don't see how the pump could be bad.
    Last edited by Dan Mapes; 12-23-2017 at 11:31 AM.
    Regards
    Dan

  5. #5

    Re: ZF Gear: No Oil Pressure

    I'm confused too, does the gear that sprung the leak go into gear spinning the prop, forward and reverse?
    CRICKET
    1966 HAT50C101
    Purchased 1985 12v71Ns
    Repowered 1989 with 8v92TI
    Repowered 2001 with 3406E

  6. #6

    Re: ZF Gear: No Oil Pressure

    It most likely is something very very simple. Retrace steps.
    FTFD... i drive a slow 1968 41c381

  7. #7

    Re: ZF Gear: No Oil Pressure

    Quote Originally Posted by Cricket View Post
    I'm confused too, does the gear that sprung the leak go into gear spinning the prop, forward and reverse?
    Not as much as me!

    Does not go into gear. Zero oil pressure. Pulled the filter screen and it was spotless. I pumped the oil out of the chamber as if I was cleaning the screen. Reassembled and cranked engine, no pressure and screen chamber remained empty.

    As I said earlier, torsional coupler fine.

    The way I know gauges are OK is that I cross connected the sending hose from the stbd. gear to the port gear. In other words, the starboard gear sent oil through the line into the port gear and made pressure. The stbd. engine produced over 100 psi indicated on the port electric helm gauge. Obviously not enough volume to shift. Gauges are OK, not making pressure.

    Pulled the top cover from both gears and cranked each with fuel off. Can't see any differences when I rotate the prop shaft manually.

    There is so little out there on these gears. Starting to wonder if oil pump is bad with maybe a snapped shaft or shear pin (if it has one). There was/is no thump, no grinding, no nothing. It just woke up one day and decided to not make pressure after I changed one four foot 1/4" hose to the mechanical gauge in the ER.

    I'm listening.
    Semper Siesta
    Robert Clarkson
    ASLAN, 1983 55C #343
    Charleston, SC

  8. #8

    Re: ZF Gear: No Oil Pressure

    When you sprung the leak how much oil did you lose?

    If a high percentage of the oil was lost, pull the pump. The pump may suffered damage, no pressure maybe a sheered shaft.

    If there is no pressure with ambient oil the pump has a problem or the pressure relief valve has problem.

    I would start with the pump.

    Good luck.
    GLORY Hull # 365
    Northport, NY

  9. #9

    Re: ZF Gear: No Oil Pressure

    Quote Originally Posted by Glory View Post
    When you sprung the leak how much oil did you lose?

    If a high percentage of the oil was lost, pull the pump. The pump may suffered damage, no pressure maybe a sheered shaft.

    If there is no pressure with ambient oil the pump has a problem or the pressure relief valve has problem.

    I would start with the pump.

    Good luck.
    Loss was in ounces, like two or three. Leaning heavily toward the pump. The coincidence is just hanging me up.

    But I do have a plan that might prove it out. The gear has two oil pumps. One driven by the motor and one prop shaft driven. On one engine, the off power shaft will free wheel. At 5-7 knots, it will easily produce the standard operating pressure of 175 psi. Both pumps feed a common oil system.

    It's worth a try especially since I'm due to change slips anyway. Should be able to try it late next week. Going to be about impossible to get anyone over here by then anyway. In the meantime, keep those cards and letters coming. I still feel it could be something stupid simple.
    Semper Siesta
    Robert Clarkson
    ASLAN, 1983 55C #343
    Charleston, SC

  10. #10

    Re: ZF Gear: No Oil Pressure

    I’m not familiar with Covington’s or ZF gears. Do they have gear coolers on the front of the engine? Breaking the vacuume to the gauge may have let all the oil drain back to the sump. I’m betting that the pump lost it’s prime. Can you get oil to the pump from the cooler lines?

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