8V71TI Emergency Shut-down Air Damper Function?

[Play'N Hooky Too]

I have a 1976 46C Hatteras with 8V71TI engines that I bought about a year ago and have been doing a few repairs during that time. One of the things I noticed early on was that the cables from the emergency shut-down t-handles on the flybridge were corroded to the point that neither of them would even budge when I tried to test them. I finally got around to tracing the cables to the damper valves on the top of the engines. The first thing I noticed was that both of them had been disconnected from the actuator levers at some point. The second thing was that when I manually tripped the levers....nothing happened. I thought the dampers might be stuck from the multiple coats of paint that had been applied over the years so I tried gently tapping on the shaft cams to see if I could free them up. Still nothing. Without knowing exactly how they functioned I decided I didn't want to risk damaging them so I just re-seated the levers into the groves on the cams and moved on to something else. I've since ordered new cables and had planned to replace the old ones this weekend. In doing that I would like to make sure the dampers are functional.

So my questions are...when the t-handles are pulled/ levers are tripped what should happen as far as the dampers? Are they spring-loaded or do they just fall closed? And second, is there some reason the cables would have been disconnected other than the fact that they were just too corroded to work? Maybe it's common knowledge to everyone except me that never in the history of the world has a marine Detroit Diesel engine ever ran away to the point of having to be shut-down with the damper valves?

Any direction y'all could provide would be greatly appreciated.

Thanks

-Alan

[brico]

While it is highly unlikely that the engines will run away needing the emergency stop, you may end up in a situation that your throttle cable gets stuck and you cannot lower the RPM or as happened to me engine stop relay quit so the only way I could think of stopping the engine (at idle rpm alongside the dock) was to use the emergency damper shutdown. Mine are naturally aspirated and have those rotoblowers so dampers are spring loaded and once cable pulled from the flybridge, it would shut the dampers and starve the engine of air and stop them pretty quickly. Simple mechanism easy to reset after it has been used. My only problem is that the securing knobs that secures the "T" handle are cracked and do not "look" good or reliable so I hope that next time I need to pull the handle it will not be in vain. Those are 37 years old and may need replacement. I should not procrastinate with safety items.....

[Play'N Hooky Too]

Thanks for the reply.

10-4 on the safety items. If they are there I want them to be functional.

I guess what I'm really wondering is if the dampers don't move once the levers have been released, what degree of effort/ force should I apply to get them to move? I don't see any external springs on the damper shafts so if there are any they would have to be internal.

[kingsley_oasis]

Get them fixed. A runaway due to stuck fuel rack, motor burning oil due to failed blower or turbo seals is often a death sentence for engine without them operational.

[Walter P]

While it is highly unlikely that the engines will run away needing the emergency stop, you may end up in a situation that your throttle cable gets stuck and you cannot lower the RPM or as happened to me engine stop relay quit so the only way I could think of stopping the engine (at idle rpm alongside the dock) was to use the emergency damper shutdown. Mine are naturally aspirated and have those rotoblowers so dampers are spring loaded and once cable pulled from the flybridge, it would shut the dampers and starve the engine of air and stop them pretty quickly. Simple mechanism easy to reset after it has been used. My only problem is that the securing knobs that secures the "T" handle are cracked and do not "look" good or reliable so I hope that next time I need to pull the handle it will not be in vain. Those are 37 years old and may need replacement. I should not procrastinate with safety items.....

I was told many years ago by DD to avoid using the emergency shut down air dampers except in a true
emergency. It could cause damage to the engine. Now, I have no knowledge that this will happen and
since I am not an expert on them, I never used them except to make sure they worked with the engine
off at the dock. If your regular shut down fails to work, you can always go down to the ER and manually
hold the linkage to shut off the fuel. If that is the case, then you either need to replace the celenoid or
adjust the linkage. I have also heard of runaway detroit's but I'd bet that it's rare.

Walt

[Scarlett]

From surveys I do, other boat brands, like Defevers, do not even install the manual air shut offs on Detroit’s and I asked our local Detroit guru about not having them and he did not think they were that important and apparently neither do some of the other boat manufacturers. All I know is I have them and I make sure they work. John

[dottieshusband]

The T handles and cables may be corroded and inop, but the catch notch on the spring loaded intake air flaps can be manually tripped. The flaps can easily be tripped and reset and with the engine off, it's a good thing to become familiar with.

[Briankinley2004]

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

[brico]

The T handles and cables may be corroded and inop, but the catch notch on the spring loaded intake air flaps can be manually tripped. The flaps can easily be tripped and reset and with the engine off, it's a good thing to become familiar with.

That is very true, however I mainly operate my engines from the flybridge, so in order to come down, remove the hatch and jump between engines and trip the flap takes considerable time, so having them operational and functional on the flybridge in case of emergency need to stop an engine (and I am not only thinking of unlikely run away engine but stuck throttle cable) it makes sense the tripping handles and cables are functioning well. I haven't tried shutting the engine with solenoid at higher than idle RPM after I am at the dock or anchored. It may work. Perhaps I should try it out.

[racclarkson@gmail.com]

That is very true, however I mainly operate my engines from the flybridge, so in order to come down, remove the hatch and jump between engines and trip the flap takes considerable time, so having them operational and functional on the flybridge in case of emergency need to stop an engine (and I am not only thinking of unlikely run away engine but stuck throttle cable) it makes sense the tripping handles and cables are functioning well. I haven't tried shutting the engine with solenoid at higher than idle RPM after I am at the dock or anchored. It may work. Perhaps I should try it out.

Learn how to shut down your non runaway motor at the fuel shutoff solenoid/rod. There is no guarantee that an engine will shut down after tripping the dampers. It may well still operate near idle speed.