Twin Disk Gearbox leaking oil at coupling--is there room?

[52CMY]

My starboard gearbox has started flinging oil out of the coupling joint. it looks like the outer seal is not leaking. I suspect the inner flat rubber O-ring ("Lathe Cut Ring" M2074S) is the culprit.

Does anyone know if I have room to service this without dropping the propshaft or lifting out the gearbox? (DD8V92TAs, Twin Disk DD 5111V ge3arbox, 2 1/2:1 gearing, 2 1/2 shafts on a 1990 48MY hull (converted to 52CMY).

Any advice or tips on the service? I'm planning to pull the gearbox hydr pump for better access and painting. I have the pump gasket, Shaft seal and shaft flat rubber ring.

Hoping to slide shaft coupling aft if there's room to work to avoid haulout or lifting out the gearbox for access. Is there room to slide?

[52CMY]

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[Captain Ralph]

How much room between the rudder and propeller.
That will be your work space.

[52CMY]

Thanks Capt Ralph.
I should have measured that dimension when I had the rudders repacked JUST 8 months ago--hope to not haul it again (and drop the rudder again) to get to the gear seal.
It looks to be about 8inches based on my best photo and the drawings. Not sure if that's enough.
Does anyone know if it's been done on a 48MY/52CMY while in the water?

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[SKYCHENEY]

Don't drop the rudder. It's easier to pull a prop off.

[52CMY]

Looks like I have several decision points with my boat in the water:
1) decouple shaft and push as far aft as possible and try to repair shaft seal.
2) if there's not enough space to repair, then either:
a) jack or lift aft end of 8V92 and gearbox toward ER ceiling (there's 8-9inch headroom from turbos), to gain clearance for seal repair.
b) have diver remove prop ($350) and slide shaft further aft (assuming tapered end of shaft clears rudder post--in photos the rudders appear to be slightly outboard of the prop shafts)
c)remove gearbox from engine.

Benefit of jacking up engine off aft supports is that will also facilitate easy access for thorough repainting of an area that got trashed by a nearby HVAC pump that slung seawater under the gearbox, flywheel and aft portion of oilpan that went undetected for too long before I bought the boat.

Questions:
1) will the prop shafts clear the rudders if the prop is dropped?--(it looks like they will).
2) do I invite probably drivetrain alignment issues and added labor cost / frustration by jacking back of engine? Can a knowledgeable mech return engine to exact position after jacking or do I invite a host of issues doing this?
3) which is the least risky option?



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[SKYCHENEY]

The shaft will clear the rudder. You will want to check alignment either way you go so lifting is not a problem but most likely more difficult than pulling the shaft back.

On my 53, I was able to push the shaft back to replace a leaking output shaft seal on one of Allisons without removing the prop. Hopefully you can too.

[jim rosenthal]

I think if you raised the aft end of the engine, you would have to have an in-water realignment when you were all done with the repairs. You would not have to do it if you just undid the coupling and installed a new seal, if I understand you right.

[Captain Ralph]

Where is that oil coming from again??
Between the flange and clutch case or out of that lil hole in the coupler side?

[Captain Ralph]

Placing a pipe wrench on the shaft and using a breaker bar on the shaft nut is easy. A breaker or pull bar on the clutch flange nut is going to be difficult as it will be hard to keep the flange (out put shaft) from turning.
Here is where an air impact gun helps,, And how I serviced my TD 514 flange.

If you can get the room for an air gun, you will not need to pick up the after engine / clutch assembly.

Picking up the after engine / clutch,, That is a lot of weight. A 4 x 4 over the deck opening may not be enough to support that much weight.

You will need to re-align the shaft when re-assembling. Alignment at the flange / coupler is measured in thousands of an inch (<0.003") or better.

[52CMY]

Troubleshooting involved wrapping various cleaned parts with clean paper towels and running, then looking at oil patterns.

Leaking only seems to happen when in gear and pressurized. The rate of leakage seems to start heavy when shaft spinning but that maybe because oil is pooling with pressure in neutral and then flings more when initially engaged. Zero leaking statically with engine off.

The wrapped output drive flange just aft of the gearbox output main seal was bone dry telling me the main output seal in good.

The Twin Disk MG5111 schematic shows the aft main seal (a press in seal) and a flat O-ring inner seal inside the gearbox output drive flange (see diagram below)
6305163053


The outer seal and output drive flange is not leaking.
Oil is flinging out between between the bolted flanges of the gearbox flange and the coupler flange. So I believe the source of the leak is the rubber flat O-ring gasket inside the output flange. The Yellow highlight is where the oil is slinging onto the paper and pattern aligns with the gap between flanges.

63052

I have both the seal and the flat O-ring rubber gasket on hand to replace both if I can get to both.

My plan is to remove the 2 1/2 to 3 inch raw water hoses to get better access to the area, then carefully clean the shaft that will slide aft through the dripless seals till the prop interferes with the rudder. I'll pull the gearbox hydr pump to clean up (area got hammered by surface corrosion from the HVAC pump leak from years past) treat and repaint bottom of gearbox, etc. If I need to get more space for the shaft seals, I'll have diver pull prop.

Anything special regarding pushing shafts aft? Rotate while pushing? Other than don't get carried away and push shaft all the way out and suddenly get everything wet.

[Captain Ralph]

Oil is flinging out between between the bolted flanges of the gearbox flange and the coupler flange.

That super flat surface should be machine flat, I would not think oil would pass there.
In your pic, I see some drops in the napkin aft of that joint and tape line. Is that the oil?

If so, there may be a 1/4" hole in the coupling that the oil could be escaping from.

Then, you would be correct about that shaft O ring.
Usually do not leak on their own unless there is a flange issue.

Do you have a shaft log with packing or a PSS seal?

[52CMY]

The oil spray was in line with the gap between flanges. the big drop was slightly aft of the spray pattern and I believe it statically dripped from the bolt head on the bottom after the test run.

I have PSS seals--I know that we will have to lightly sand polish the shaft and coat with dish soap for lube. I don't know how much water will ingress as the shaft is slide aft while the carbon ring seal and stainless slip ring is out of place. I can imagine it could be breathtaking water till the stainless ring is adjusted against the belows/seal.

I read that PSS PYI commented on their YouTube video that you can uncouple transmission in the water and slide shaft as long as carbon ring and SS rotor remain in firm contact--not sure how easy that it to accomplish on heavy 2 1/2in shafts.

Is this a bad idea do in the water? Especially if I have to remove the prop to move the shaft even further aft?
I'm 12 miles from a possible haulout but would be signal engine & need a tow through tight channels in thin water.

My mech seems comfortable to do it in the water but it's my boat and my risk. I'd rather not have an emergency 12 mile tow and haulout while controlling flooding, so trying to better understand risks.

[Captain Ralph]

Make a measurement on PSS compressed hose length and a measurement between the coupler and stainless ring.
This way, while your working on the flange, the stainless ring is compressing the hose the normal amount.
When you put it all back together, yon can place the stainless ring back in it's same place.

With that big coupler, have a couple of wood blocks and wedge ready to hold up that shaft ends weight when slid back. The PSS hose and faces may not keep in that perfect dry position with out this help.

Polish the shaft and use a water based grease to slide the stainless collar up. Remember, those are double set screws in each screw hole.
When putting the stainless collar back in position, polish the shaft where the set screws were originally as the set screws are on the dry side of the O ring.

Some water will come in. less than you think. Don't let it distract you, work smooth and careful. Your pump will keep up. Ensure all debris are out of the bilges.

Interesting,, Oil making it out from the coupler / flange surface. You may want to pass a big flat file over these surfaces to ensure they are indeed flat when all apart. You may have a surface with an edge burr.
I have witnessed the aftermath from techs using a screw driver and bar to split the coupler / flange apart and induce burs in the surfaces and then not clean it up.
Paint chips and rust can contaminate that perfect machine surface connection also.
Just imagining this, leads me to understand why that O ring has failed. The flange may have been vibrating on the out shaft.
Remember, a few thousands of an inch are involved for coupler alignment.

[52CMY]

Thanks Capt Ralph for several expert tips--much appreciated!
I'll plan to use those tips for sure.
When decoupled and prior to sliding shaft aft, I'll loosen the (double) set screws, compress bellows to expose the shaft marks (from the set screws) and polish prior to sliding aft.
When away from the boat overnight I'll secure the loose shaft longitudinally to ensure constant seal compression, using blocks and bar clamps and support it from below.
For final reassembly, I'll use new set screws and Loctite on the outer screws.

I frankly still have no idea why there needs to be an inner rubber seal at all instead of a solid shaft gearbox flange. I'm looking forward to seeing what's inside the flange coupling to sort out the issue.

[Captain Ralph]

I may have said incorrectly; There are two set screws per hole, multiple holes.
The first one tightens to the shaft, the second set screw locks the first screw in place.

When final assembly of the stainless PSS collar, there could be a micro amount of play between it and the shaft. Here is where the eye/touch games come in. Try to ensure the collar is square to the shaft.
After the coupler alignment and operating at idle, if the collar wobbles or leaks, let me know. I have some tricks that worked for me in getting that collar perfect.

The flange shaft O ring is there to stop oil from seeping down the output shaft / flange spline.
It is not a common failure unless the flange is loose on the output shaft.
Just a little vibration will wear that O ring and cause a leak,, as I fear, it may have.

Oh, pump the oil out of the clutch before pulling that flange also.