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.
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Re: 8V71TI Emergency Shut-down Air Damper Function?
"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
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12-02-2017 09:16 AM #12
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Re: 8V71TI Emergency Shut-down Air Damper Function?
SEVEN
1979 53' MY Hull #563
Antioch, California
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12-02-2017 10:05 AM #14
Re: 8V71TI Emergency Shut-down Air Damper Function?
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
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12-02-2017 10:19 AM #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.
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12-02-2017 09:10 PM #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.
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12-02-2017 10:29 PM #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.
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12-02-2017 11:30 PM #18
Re: 8V71TI Emergency Shut-down Air Damper Function?
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.
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12-03-2017 09:25 PM #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.
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12-03-2017 09:28 PM #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.