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Old 08-04-2013, 13:02   #1
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Replace rear main seal in the water?

Hi all,

I am just beginning the task of replacing my rear
Main seal on my Perkins 4154. To do this I have to slide my prop shaft rearward, remove the tranny, adapter plate, bell housing, etc. Well, i have a PSS shaft seal, would you attempt this job with boat in the water? That's what I had planned, but now I am nervous about a possible steady trickle of water into the boat for a day or two. I hate to have the boat hauled for this, but I would also hate to sink at the dock. The PSS does not support the forward shaft like a traditional shaft packing. I can probably shim the forward end of the shaft to keep it relatively dry. Has anyone else done this?

Your advice is much appreciated, as always.

Bill
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Old 08-04-2013, 18:58   #2
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Well, I got tired of waiting and worrying, so I slid the shaft aft and propped it up with no leaks. Tomorrow I will remove the tranny and get to the heart of the matter. As always, progress is slowed by access, frozen bolts, etc.

Cheers, Bill
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Old 08-04-2013, 19:20   #3
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Re: Replace rear main seal in the water?

If your going to leave it overnight w/o being on board, I would wedge something against the coupler to keep the PSS ring tight against the carbon ring, just for safety sake.

I've changed out PSS and packing boxes both while in the water. It's no big thing! The water pressure is very low. It doesn't take much to seal off a leak around a shaft.

If you had to leave it for a long time you can dive down and seal off the stern tube with plumbers putty. Then dig it back out once your done.
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Old 08-04-2013, 20:27   #4
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Re: Replace rear main seal in the water?

Well OK here is a warning. The trans may not come out. The splined shaft sticks in the drive plate on the flywheel. Mung , corrosion etc on the splines prevents it from sliding out. I don't know what big time mechanics would do but I just kept prying and driving in wedges until the drive plate broke apart. Springs and everything came out. This was a major rip and tear project to get the transmission off. Good luck.
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Old 08-04-2013, 20:49   #5
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Re: Replace rear main seal in the water?

I've changed stuffing box for a PSS seal when my boat was in the water and naturally there was a leak during changeover which the bilge pump handled no problem. I've since changed a clutch drive plate. First check the shaft and clean off any burrs with a file (they cut the rubber 'O' ring inside the PSS rotor). Coat the shaft with washing up liquid and the shaft will slide back easily.
There is a bolt below the g/box, many people overlook it and then try and wedge it apart. If you have a 'frozen' seized bolt try a sharp tap with a hammer on the bolt head while the bolt is under tension with a spanner to undo it. During rebuild I exchanged the allen key clutch plate retaining set screws for bolts to make future drive plate changes easier. I also fitted a heavy duty type drive plate to last longer. On reassembly coat the bolts with copper grease and it makes any future repairs much easier.
I hope this helps.
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Old 08-04-2013, 22:46   #6
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Re: Replace rear main seal in the water?

different engine, but I did it on my Westerbeke W30. Once I had slid the shaft back, I dove and stuck a zinc outboard against the cutlass bearing to keep pressure against the bellows. No leak and peace of mind.
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Old 13-05-2013, 12:01   #7
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Re: Replace rear main seal in the water?

I just bought a Ericson 39. Owner told me the motor was rebuilt less than a year ago. New paint. Looked like it. Went for a sea trial yesterday. The motor oil poured out, by the looks of it, out the end of the tranny. Felt like the tranny was slipping had very little forward propulsion. Had to sail to get back home. 3 hours of motoring. Does this sound like rear main seal. If so how many man hours would you think to replace it. Plus should something be done about the slipping tranny or was that do to all the oil. Thank for input.
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Old 13-05-2013, 17:28   #8
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Re: Replace rear main seal in the water?

Hi, which end of the tranny did the oil come out of? If it was the prop side, it is probably transmission fluid. If that is the case, you can remove the transmission and bring it to a repair shop. If the oil was coming from the rear main seal of the engine, it should be dripping down from somewhere around the bell housing, where it attaches to the engine. What is the oil level like for both the engine and tranny? One of them should show low due to losing the mentioned fluid.

As a side note, after changing out my rear main seal, the motor continued to gush oil. After reading this forum and others, I suspected the mechanical lift pump. Changed that and no more leaks! However, my oil analysis showed 50% fuel contamination!!!! Which explains A) why there was no drop in my oil level, and B) why it was leaking to begin with. The oil was so diluted that normal oil seals could not contain it. Changed the oil today and ran it for a while with no drips. I will change it again soon to try to eliminate the fuel in the crankcase. Good luck.

Cheers, Bill
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Old 14-05-2013, 06:30   #9
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Re: Replace rear main seal in the water?

Racquin, if you've just bought the boat you should be covered under the 'Sale of Goods' act so go straight back to the owner and get him rectify the problem and foot the bill. it's probably a rear shaft seal and as it's a hydraulic g/box you would start to lose drive with low oil level, the g/box is best left to a specialist to overhaul, don't forget to fit a new drive plate to the flywheel before reassembling, if you use copper grease(anti seize compound) it will fit together easier and importantly be easier to disassemble should you need to in the future, keep a record of all part numbers of pieces fitted for future reference.
I hop this helps.

montenido, I guess you've now learned that it was the fuel pump diaphragm ?, ford diesels were prone to that fault, just as a precaution I periodically feel the oil between my fingertips for viscosity and smell it when I dip my engine, it can be a good early warning system.
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