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Old 02-13-2019, 05:21 PM   #1
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Zinc for Tran?

I have a Twin Disk hydraulic transmission MG 5050A. It works fine, but I'd like to change the oil. The manual tells me that there is a pencil zinc somewhere close to the heat exchanger. I think the heat exchanger is not included with the unit, because I cannot find it. The main engine has a pencil zinc in the sea water pipe, which is easy to replace. I wonder, if that is the only zinc for this purpose, or the transmission must have one, as well?
I attach photos, where you can see the hydraulic hoses come into the transmission, but I do not see any cooling hoses. Is it possible that the hydraulic oil cools the transmission?
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Old 02-13-2019, 07:23 PM   #2
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The hydraulic lines go to and from the cooler. Find the other ends of the lines.
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Old 02-13-2019, 07:33 PM   #3
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Quote:
Originally Posted by High Wire View Post
The hydraulic lines go to and from the cooler. Find the other ends of the lines.
I did. The lines go to the hydraulic pump, which is driven by belt from the engine. From the pump, the line goes under the main engine into a tank. See photos.
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Old 02-13-2019, 07:53 PM   #4
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I see 2 separate systems. In the fist set of pictures is the transmission oil lines to the oil cooler. Just about every boat has them. Somewhere in the seawater flowpath is a heat exchanger that cools the transmission that the first lines are connected to. Maybe 350 psi max on the oil side.

The second set of pictures shows a hydraulic pump and tank system that drives a windlass or hoist of some type with hydraulic fluid pressures up to 3000 psi. It uses hydraulic fluid, not transmission oil. It should not be connected to the first unless it shares a common seawater line for cooling.
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Old 02-13-2019, 08:01 PM   #5
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I see 2 separate systems. In the fist set of pictures is the transmission oil lines to the oil cooler. Just about every boat has them. Somewhere in the seawater flowpath is a heat exchanger that cools the transmission that the first lines are connected to. Maybe 350 psi max on the oil side.

The second set of pictures shows a hydraulic pump and tank system that drives a windlass or hoist of some type with hydraulic fluid pressures up to 3000 psi. It used hydraulic fluid, not transmission oil. It is not connected to the first unless it shares a common seawater line for cooling.

The boat has hydraulic steering. So, the other lines go to the PH and back to the rudder.
I only see one oil line go in and out from the transmission. I thought that was the hydraulic line.
I will open the floor this weekend and look for more lines. I'll take more photos.
Do you see anything related to the pencil zinc, the manual talks about?
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Old 02-13-2019, 08:09 PM   #6
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The boat has hydraulic steering. So, the other lines go to the PH and back to the rudder.
I only see one oil line go in and out from the transmission. I thought that was the hydraulic line.
I will open the floor this weekend and look for more lines. I'll take more photos.
Do you see anything related to the pencil zinc, the manual talks about?
Follow the seawater path from the sea strainer to the engine exhaust. That is where any zincs would be.
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Old 02-13-2019, 08:26 PM   #7
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Follow the seawater path from the sea strainer to the engine exhaust. That is where any zincs would be.

I know one of them. Right after the sea chest where the water comes in. There is a pencil zinc. I replaced it today, because it was completely gone. Since it was not long time ago when this pencil was replaced, I thought there was more somewhere. I just put new zincs on the hull in December. I also have a stray current isolator installed. I don't know why the pencil zinc was gone so fast?
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Old 02-13-2019, 11:05 PM   #8
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In your photos is one picture of the schematic of the gearbox and the gearbox pump/control valve setup.

THe dwg. clearly shows the output port TO the heat exchanger and the return port FROM the heat exchanger.

THose are the two 1/2" ID lines seen in the photos of the gearbox pump and the control valve.

Those lines should go ONLY to the gearbox oil cooler likely mounted on the side of the engine block near the stringers. THey will have NOTHING to do with anything else. They are strictly for cooling the gearbox.

They will disappear below or near to the engine underside. The seawater will also run through that heat exchanger/oil cooler to cool the gearbox oil so also follow the seawater circuit as suggested. Your system is VERY similar to mine although a different engine and a similar gearbox, mine a MG506. TD followed very similar designs.

THe zinc you are looking for is for the gear oil cooler, not the gearbox itself.
There will be ONE zinc in that gear box oil cooler on the end cap. It's a small one and if like mine be very carefull about the length of the zinc when you replace it or you will damage the cooling tubes. If the cooler is anything like mine it is expensive to replace and is basically not available any longer. Cut it 9/16", no longer, from the shoulder where the zinc pencil screws into the cap. Check the zinc often, every 50 hr or so untill you determine the needed interval.

When you find the gear cooler post a photo and I will tell you if it is like mine.
The gearbox AND the gear cooler are under about 300 -400 PSI when operating which is why the hoses are actual hydraulic hoses with hydraulic fittings..

THe other hoses, the tank and the other pump driven off front of the engine by the belt[s] should have nothing to do with the gear box. Those hoses also look larger so maybe supply several items. Steering, bow and or stern thruster, fin stabilizers, hydraulic anchor windlass, lifting boom or dinghy lift? ?? THis system maybe or should also have an oil cooler but NOT tied to the geabox cooler oil circuit at all.

The steering is maybe less likely to be operated from this system. It can be hydraulic but not powered.

I could be wrong of course but you need to carefully trace the hoses to be sure. Make a dwg. but be carefull tracing as it can be quite easy to mistake one line for another if they are in close proximity.

But I seriously doubt that the gear box and the other hydraulic system are tied together in any manner except that they each have an oil cooler for their own, individual needs, with the only connection between is the seawater supply line.
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