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  1. #11

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    In 41 years of operating my 12/71s I’ve never had a runaway even after 2 inframes and multiple injector replacements. In the last year 3 times both engines ran away due to bad fuel causing seized injectors. Thank god the emergency shutdowns worked.
    Upon disassembly all 24 injectors had a sticky black resin type goo in them. These injectors have a fine brass filter in them that was clean meaning it was not a filtration problem but the resin formed in the injectors. My injection guy says he’s seeing this same scenario more and more as the fuel oil gets worse and worse.
    "DON'T BELIEVE ANYTHING YOU READ OR HEAR AND ONLY HALF OF WHAT YOU SEE" - BEN FRANKLIN




    Endless Summer
    1967 50c 12/71n DDA 525hp
    ex Miss Betsy
    owners:
    Howard P. Miller 1967-1974
    Richard F Hull 1974-1976
    Robert J. & R.Scott Smith 1976-present

  2. #12

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    Quote Originally Posted by Briankinley2004 View Post
    I have the same questions as to how much force. I have disconnected my cables and have one of the 4 dampers on my 12-71s frozen. I have tapped with a hammer but don’t want to knock something loose inside and damage engine. Is heat an option
    pull it off and repair it. You dont want anything falling between the rotors and destroying a blower.
    Scott
    41C117 "Hattatude"
    Port Canaveral Florida.


    Marine Electronics and Electrical Products Distributor.

  3. #13

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    Quote Originally Posted by rsmith View Post
    In 41 years of operating my 12/71s I’ve never had a runaway even after 2 inframes and multiple injector replacements. In the last year 3 times both engines ran away due to bad fuel causing seized injectors. Thank god the emergency shutdowns worked.
    Upon disassembly all 24 injectors had a sticky black resin type goo in them. These injectors have a fine brass filter in them that was clean meaning it was not a filtration problem but the resin formed in the injectors. My injection guy says he’s seeing this same scenario more and more as the fuel oil gets worse and worse.
    Was there any damage to the motors after the run away? Can you explain exactly what happen and what you felt the boat doing at the time it started to run. How long did it take to shut her down once the run started and was it both motors at the same time?
    SEVEN
    1979 53' MY Hull #563
    Antioch, California

  4. #14

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    Quote Originally Posted by Boatsb View Post
    pull it off and repair it. You dont want anything falling between the rotors and destroying a blower.
    That’s my preferred route however I’m thinking the salon floor may have to come out to do so at best, possibly even a cabinet. I will investigate further. Any chance one of the two dampers on the engine operating will shut it down enough to prevent a runaway? The stuck one is the one without the reset and is connected by a linkage

  5. #15

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    Inside the air horn is a spring. Mine broke and took out the blower and bower drive shaft .

    If its stuck pull it. You only have a few thousandth of an inch between the rotors. Don't risk the blower.
    Scott
    41C117 "Hattatude"
    Port Canaveral Florida.


    Marine Electronics and Electrical Products Distributor.

  6. #16

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    The 12-71's have two boxes. One has the reset spring on it. The other is a "slave" to that one. The "slave" is the one that is stuck on mine. It may have a spring on it inside, I don't know, but it relies on the primary damper to function. It will be after Christmas before I get back to the boat but I am going to first try to remove the heavy paint and see if that will free it. The side the cable connects too is free and works fine. I assume it only shuts half the cylinders off.

  7. #17

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    Each one should have a mousetrap spring that closes the airdoor. The main has the reset spring on the outside.

    If the mousetrap spring breaks or other debris falls into the rotors you will have a mess.
    Scott
    41C117 "Hattatude"
    Port Canaveral Florida.


    Marine Electronics and Electrical Products Distributor.

  8. #18

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    Quote Originally Posted by Boatsb View Post
    Each one should have a mousetrap spring that closes the airdoor. The main has the reset spring on the outside.

    If the mousetrap spring breaks or other debris falls into the rotors you will have a mess.
    Thanks for that info. If I can figure out how to take off without removing salon floor this will be my next project. The mechanical surveyor told me if I had to rebuild them I might not be able to find parts. He only wrote up they didn't operate as it wasn't in his scope to diagnose. If I have to remove the floor to remove them I will take my chances until I get her to home port. Hopefully shutting down one of the two will slow down enough for me to get to engine room, or in a perfect world the paint is holding it open and will be easy to free.

  9. #19

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    Wound up taking mine off this afternoon. Both were corroded to the point that it took a half can of PB blaster, a pipe wrench and lots of tapping with a hammer to get the damper shafts to even move. I've taken them both apart and will rebuilding them. On one it looks like I may have to do a little metal fab to replace the damper plates. On that one, part of the mouse trap spring was missing but it looks like it had been gone for a while. The rest of the spring was still around the shaft. Luckily that was not the one that I had tried to free up while it was still on the engine.

  10. #20

    Re: 8V71TI Emergency Shut-down Air Damper Function?

    Check the blower for debris or you may find the missing piece the bad way.
    Scott
    41C117 "Hattatude"
    Port Canaveral Florida.


    Marine Electronics and Electrical Products Distributor.

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