71c 1:1 problems need help

Discussion in 'Inboards' started by mudman, Mar 9, 2009.

  1. mudman
    Joined: Mar 2007
    Posts: 88
    Likes: 5, Points: 0, Legacy Rep: 72
    Location: Madisonville, LA

    mudman Junior Member

    I have not put this boat in the water yet, due to the fact that the tranny is freaking me out.

    It makes a pulsing whine when in forward neutral, or reverse. Oil level is high, in fact, I filled it up as far as I could until it started coming out of the vent while I was running it in the yard. While i was trying to figure out what the whine was, the oil line blew (exiting line from tranny) right at the transmission case.

    The oil was not hot, since I was running the boat for about 3 minuites. I'm using flex loc hose with a 250 psi rating. The setup is a 1:1 Borg Warner and an 80 hp subaru gasoline engine. Pressure could not have exceeded 250 psi?

    Is the whining noise a problem, or the pump cavitating and pulsing? How do I stop it? Why would the tranny line blow out? Air in the line, restriction at the cooler? Any help is greatly appreciated.
  2. mudman
    Joined: Mar 2007
    Posts: 88
    Likes: 5, Points: 0, Legacy Rep: 72
    Location: Madisonville, LA

    mudman Junior Member

    Well I calculated my pressure drops and figured out the problem. I'm using 1/4" ID hose for the cooler lines. My cooler is 4 feet away therefore 8 feet of hose. The max ammount of liquid is 10.5 gpm at 180 psi.

    Using the given numbers I had a pressure drop of 200 psi, which is no flow at all. If the ID of the hose is upped to 3/8", the pressure drop is roughly 50 lbs. Using 1/2" line, the drop is next to zero.

    The 1/4" hose was choking the flowrate of the oil. The hose kept busting directly at the outlet of the tranny, which is where the pressure would have been the greatest.

    I don't know whether to get 3/8" line or 1/2". I think that the cooler guts have 3/8" since the cooler has 3/8" NPT fittings. If I use 1/2" , I'll get a drop across the cooler and possibly bust it, but If I use 3/8", the drop will only be 50 lbs across the entire cooling system. What is everybody else using?
  3. Jango
    Joined: Aug 2005
    Posts: 519
    Likes: 7, Points: 0, Legacy Rep: 63
    Location: Mid Atlantic

    Jango Senior Enthusiast

    Both my stock 71C and 72C with beefed up clutches use High pressure reinforced rubber 3/8 lines and are working fine.

  4. thudpucker
    Joined: Jul 2007
    Posts: 885
    Likes: 31, Points: 0, Legacy Rep: 453
    Location: Al.

    thudpucker Senior Member

    Whatever kind of line you get, make it expensive and reliable. You'll never be looking when a line gives way and it's gonna be way too late when you finally notice.

    A pulsating whine would be someting that's supposed to rotate on a shaft, but is oscillating instead.
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