Mercury 2.5

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onenyala

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After fifteen years of loyal service there is water getting into the gear box and emulsifying the oil. It looks like there are two seals one at the bottom of the gear box on the final drive shaft and one on the top of the gear box where the vertical drive enters the gear box.
For the moment I am trying to replace only the bottom seal on the final drive. It seems like the ball race has to be removed before the seal can be replaced and this will require a puller.
Anyone able to give any help or advice ?
Thanks
 
At both locations, ie drive shaft and propeller shaft, there are usually two seals fitted "back to back" so that the inner one keeps the oil in and the outer one keeps the water out. (If the engine has a cluch or gears then there will be a seal, probably just an O ring, on the operating rod as well)

The one most likely to be causing your problem is the outer seal on the propshaft. Take care not to dammge the inner one or replace it anyway.

Are you saying you need a puller to remove the bearing from the shaft or from the housing after separating it from the shaft?

If the latter then a copper drift is the more likely method than a puller and the same for removing the seals. You may be able to remove the seals with a drift without removing the bearing if they press out outwards. Again if it can be removed "outwards" the outer seal may come out by drilling two holes in it and screwing in a couple of self tapping srews and using those to pull the seal out. That may be possible without any dismantling other than removing the prop.

If you do need to remove the bearing warming the whole thing up in very hot or boiling water will help as the aluminium housing will expand more than the steel bearing and so realease it easily.
 
Thanks. The seal for the prop shaft is held in the water pump back plate.
There is the gear box case onto which is fitted the water pump back plate this encloses the oil.
It looks like the seals are held in the back plate by the ball race. I will try 'carefully' to the ball race using your suggestion of boiling water and a copper drift.
 
It does sound from what you say that the bearing has to be removed first. I have THIS SITE noted as a possible soucre for downloading Mercury workshop manuals. If there is one available for your engine you should find all the info you need.

Take care with aluminium housings, they are not very strong.

Now might also be a good time to service the water pump

Sorry the above site was not much help. The iBoats forums are always a good source of advice on outboards though
 
The story so far.
I took the assembly to a well known outboard expert who for the moment shall remain nameless. Despite having the serial number of the engine he fitted a totally different seal to the original one. The drive shaft is 12mm and the seal he fitted was a 10mm. The original seal is similar to the one you described ie with two helical springs. I thought the design had been changed and tried to force the shaft through the seal. No chance. I am waiting now to see if they can obtain the correct seal and fit it without wrecking the casting !
 
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