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Old 08-23-2019, 08:07 AM   #1
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Twin disk transmission, in gear or neutral for single engine?

I've got a 1990 twin disk model MG-507
Wondering if the event of an engine failure, is it better to leave the inoperative engine transmission in forward or neutral?
I'm sure it says in the manual, but I don't have them for these transmissions
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Old 08-23-2019, 08:49 AM   #2
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I'm pretty certain that transmission is hydraulically operated from an internal oil pump. This means no pressure when the engine isn't running so the position of the shift lever will have no effect at all. It will be in neutral no matter the position of the lever. (No pressure, no clutch engagement)

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Old 08-23-2019, 09:00 AM   #3
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Quote:
Originally Posted by Nopistn View Post
I've got a 1990 twin disk model MG-507
Wondering if the event of an engine failure, is it better to leave the inoperative engine transmission in forward or neutral?
I'm sure it says in the manual, but I don't have them for these transmissions
There are specific warnings against freewheeling in my MG-509 manual, so I assume the same would apply to yours. Absent hydraulic pressure, it will free wheel regardless of shifter position unless locked, which you can do with a bit of line.
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Old 08-23-2019, 08:33 PM   #4
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I have the MG506 and the manual specifically cautions that the shaft must be prevented from free wheeling. I suspect your 507 is the same.

Just a note that ONLY mechanical gear boxes can be locked like you ask about. These are hydraulic gearboxes and as pointed out when the engine is not running the gear box has no pressure so NOTHING can be locked.

Typically only very small gearboxes can be locked as they are mechanical, not hydraulic.

Figure out how to secure that shaft. You must also KNOW which direction the shaft will spin when towed. Many single engine boats have a L.H. shaft rotation so when viewed from behind the engine, looking forward, the shaft will rotate CCW. Mine is like this.

Often a large pipe wrench can be used. It must be oriented so the teeth grab the shaft or the coupling as the shaft tries to rotate. There is a direction for it to work. The wrong way and the wrench will simply slip.
The teeth will leave marks but they can be filed off later. The marks are not heavy.

I have done this on two occasions. I also use a piece of 3/4 plywood , about 6" x 6", between the wrench handle and the hull to spread the load. I carry large Tyraps and use several of them to ensure the wrench stays on the shaft or it may fall off. In my case the shaft rotates in a direction, CCW as above, that the wrench MUST hang upside down to grab and that means its natural tendency is to fall off.

You could also use a heavy rope wound around the coupling several times for grip and then tied off. But you must sort out where to secure the rope ends to develop that grip.


Go to Twin disc and ask if they can supply a manual or try Ebay as they do appear from time to time. Be patient. It is worth trying to get one and from what I've seen they are not a lot of money especially compared to the cost of doing something wrong.
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Old 08-23-2019, 09:47 PM   #5
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Looks like service manuals for download freely available

https://www.google.com/search?q=mg50...obile&ie=UTF-8
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