New Lower Unit Seals a DIY Job?

[Hydro Mark]

I have a 1968 Mercury 1250 125 hp outboard. It hadn't ran in almost 25 years. I changed the water pump and got it running. Runs very strong and shifting is fine.

At least the prop seal leaks and maybe others. Is this something I should attempt?

I'm mechanically inclined and I have rebuilt automotive and motorcycle motors and transmissions when I was younger, however the most I've done on an outboard is link n sync and water pump replacement.

Thanks,

Mark

 

[carholme]

Re: New Lower Unit Seals a DIY Job?

Mark;

Here is the parts list for your engine which is a model 1125108, if it is a '68. Do you have the engine s/n?

MERC 1250 - Mercury, Mercruiser, Force, etc. Parts Lookup

The service manual you require is p/n 90-68647:

90-68647 in Books | eBay

Until you get the OEM manual, here is a link to the condensed version of the Clymer manual to give you an idea of the job.

Small Engine Repair Reference Center Home: MERCURY - MERCURY 6 CYLINDER MODELS (1966-1968).

Download it soonest to your computer as the link is short lived. See R&R and Overhaul of the Lower Unit, beginning on page 141.

Gerry

 

[Chris1956]

Re: New Lower Unit Seals a DIY Job?

Mark, Disassembly of the gearcase is the hard part of changing the seals. I would make sure the prop seal leaks, before attempting it. The seal in the base of the waterpump is easy to change.

 

[Hydro Mark]

Re: New Lower Unit Seals a DIY Job?

Mark;

Here is the parts list for your engine which is a model 1125108, if it is a '68. Do you have the engine s/n?

MERC 1250 - Mercury, Mercruiser, Force, etc. Parts Lookup

The service manual you require is p/n 90-68647:

90-68647 in Books | eBay

Until you get the OEM manual, here is a link to the condensed version of the Clymer manual to give you an idea of the job.

Small Engine Repair Reference Center Home: MERCURY - MERCURY 6 CYLINDER MODELS (1966-1968).

Download it soonest to your computer as the link is short lived. See R&R and Overhaul of the Lower Unit, beginning on page 141.

Gerry

Thanks Gerry. The serial number is 2397059. I'll order up an OEM manual.

Thanks again,
Mark

 

[Hydro Mark]

Re: New Lower Unit Seals a DIY Job?

Mark, Disassembly of the gearcase is the hard part of changing the seals. I would make sure the prop seal leaks, before attempting it. The seal in the base of the waterpump is easy to change.

Thanks Chris. There's milky lube coming out of the hub and I just assumed it was coming from the prop shaft. I guess it could be coming from the water pump seal and out the exhaust. There is no exhaust tube and I was told that's how this motor is - hope that's right.

Can I change the seals without rebuilding the lower unit? I didn't really want to get into clearances, shimming etc..

Thanks,
Mark

 

[carholme]

Re: New Lower Unit Seals a DIY Job?

One way to tell if it is a waterpump or shift shaft seal is to drop the LU again and see if there is oil in the waterpump area or forward in the shift shaft area.

Your s/n is a 1968 as you indicated:

125 1250 6-cyl 2314956 2536209 1968 USA

From here:

Mercury 2-takt, R6, 6-cyl, 80 - 150 hp, produktions?r, modellguide

AS Chris has suggested, I think it would be wise for you to drop the LU and see if you have oil there. Could make life a lot easier for you if it is just a w/p or shift shaft seal.

Gerry

 

[coolbri70]

Re: New Lower Unit Seals a DIY Job?

are you sure its not oil from the fuel mix? was it run on muffs last? I thought I needed seals only to find it was normal. is there water in the lower unit?

 

[GA_Boater]

Re: New Lower Unit Seals a DIY Job?

are you sure its not oil from the fuel mix? was it run on muffs last? I thought I needed seals only to find it was normal. is there water in the lower unit?

I think that's the key question, is there water in the L/U? Also, I'm pretty sure you have or should have an exhaust tube.

 

[Hydro Mark]

Re: New Lower Unit Seals a DIY Job?

One way to tell if it is a waterpump or shift shaft seal is to drop the LU again and see if there is oil in the waterpump area or forward in the shift shaft area.

Your s/n is a 1968 as you indicated:

125 1250 6-cyl 2314956 2536209 1968 USA

From here:

Mercury 2-takt, R6, 6-cyl, 80 - 150 hp, produktions?r, modellguide

AS Chris has suggested, I think it would be wise for you to drop the LU and see if you have oil there. Could make life a lot easier for you if it is just a w/p or shift shaft seal.

Gerry

Agree. I think I'll drop it this weekend. Thanks.

 

[Hydro Mark]

Re: New Lower Unit Seals a DIY Job?

are you sure its not oil from the fuel mix? was it run on muffs last? I thought I needed seals only to find it was normal. is there water in the lower unit?

I'm pretty sure. It smells like gear oil. That crap stinks. Thanks Brian.
Mark

 

[Hydro Mark]

Re: New Lower Unit Seals a DIY Job?

I think that's the key question, is there water in the L/U? Also, I'm pretty sure you have or should have an exhaust tube.

There was water in there one time but not the next. I hope I'm not supposed to have an exhaust tube, because I definitely don't have one. Can anyone tell me for sure whether or not I'm supposed to have one?

Thanks,
Mark

 

[carholme]

Re: New Lower Unit Seals a DIY Job?

From the parts list I sent you in post #2, Look at item 13 under DRIVE SHAFT HOUSING ASSEMBLY.

Gerry

 

[bgc]

Re: New Lower Unit Seals a DIY Job?

Mark,
I would test the seals in the lower first. Take a threaded adapter, for filling the lower unit, and attach it to a hand vacuum/pressure pump via a hose and clamp. I found mine at Harbor Freight.
Buy Mityvac Selectline Dual Vacuum / Pressure Pump MITMV8255 at Advance Auto Parts

Fill a container of water and submerge the lower, bring to 15 P.S.I. and look for bubbles. If no bubbles are found let it sit overnight and see if the pressure drops. Conduct the same check pulling vacuum, sans the water submersion.

 

[GA_Boater]

Re: New Lower Unit Seals a DIY Job?

Yes, you should have one. It stays in place when the lower unit is dropped - Look up inside the drive shaft housing, Mark.

 

[Hydro Mark]

Re: New Lower Unit Seals a DIY Job?

Thanks guys. I'll drop the LU this weekend. I have a MityVac somewhere, I'll look for it too. How long should the LU hold pressure/vac?

Thanks,
Mark

 

[Hydro Mark]

Re: New Lower Unit Seals a DIY Job?

I could not stand the suspense any longer and just dropped the LU. It looks like there is NO Exhaust Tube. Ugh...


And is probably the reason the water tube sleeve looks like this...


Thanks,
Mark

 

[Hydro Mark]

Re: New Lower Unit Seals a DIY Job?

I just ordered this tube from ebay. It looks likes there's bolts that hold it in? And some other holes. Is this going to be possible to install without taking the drive shaft housing off?

Thanks again,
Mark

 

[JDusza]

Re: New Lower Unit Seals a DIY Job?

What's an easy way to pull the old seals?