Mercruiser outdrive..Gasket?

orthoguy

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I just got done rebuilding the water pump in my Mercruiser lower unit. My question is, shouldn't there be some sort of body gasket between the upper and lower drives? I didn't see one, so I guess there isn't one?

BTW: Anyone purchasing a used boat or haven't replaced their water pump in a while....do it! I can't believe how bad mine was! Burnt impeller, scored pump body etc. Plus it's a good time while the lower unit is off to flush out all the calcium deposits and clean things up a bit.

Thanks,
Mike
 

180shabah

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Re: Mercruiser outdrive..Gasket?

There is no gasket, but there is an oil passage o-ring that must be replaced.
 

achris

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Re: Mercruiser outdrive..Gasket?

I'd also replace the driveshaft seal in the bottom of the top box... And plenty of grease on the studs and nuts.... so you can get it apart next time!
 

orthoguy

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Re: Mercruiser outdrive..Gasket?

I'd also replace the driveshaft seal in the bottom of the top box... And plenty of grease on the studs and nuts.... so you can get it apart next time!
OK, where do I get that part #?
 

achris

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Re: Mercruiser outdrive..Gasket?

OK, where do I get that part #?

26-96503

Same part from the first MC-1 to the last Alpha One....

And don't put the 'O' ring on the top of the driveshaft... Even if you have a groove, leave it off.

Chris.......
 

orthoguy

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Re: Mercruiser outdrive..Gasket?

26-96503

Same part from the first MC-1 to the last Alpha One....

And don't put the 'O' ring on the top of the driveshaft... Even if you have a groove, leave it off.

Chris.......

Huh? The "O" ring I just put on when I rebuilt the water pump? Why leave it off?
 

achris

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Re: Mercruiser outdrive..Gasket?

Huh? The "O" ring I just put on when I rebuilt the water pump? Why leave it off?

Service bulletin from Merc, around the late 80s... They changed the shaft so it doesn't have a groove. The 'O' ring can cause the lip of the seal (the one you're about to replace) to curl, thus allowing water into the spline cavity in the bottom of the upper driveshaft... The splines on the driveshaft (in the lower unit) are stainless, but the bottom of the upper driveshaft is cast steel... Water will corrode them out in very short order...

You have the leg off the boat... put the 'O' ring on the shaft and start assembling the two halves together... now, take a small torch (flashlight) and a dental mirror and have a CLOSE look around the seal... As you join the two halves the 'O' ring will catch the seal lip, displacing part of the 'O' ring and when the two halves are fully together the seal with be held open by the distorted 'O' ring....

Separate the two halves, remove the 'O' ring, check the seal is still ok, join up the two halves again.... have peace of mind that no water is getting in there and eating the splines away....

Chris...........
 

orthoguy

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Re: Mercruiser outdrive..Gasket?

Service bulletin from Merc, around the late 80s... They changed the shaft so it doesn't have a groove. The 'O' ring can cause the lip of the seal (the one you're about to replace) to curl, thus allowing water into the spline cavity in the bottom of the upper driveshaft... The splines on the driveshaft (in the lower unit) are stainless, but the bottom of the upper driveshaft is cast steel... Water will corrode them out in very short order...

You have the leg off the boat... put the 'O' ring on the shaft and start assembling the two halves together... now, take a small torch (flashlight) and a dental mirror and have a CLOSE look around the seal... As you join the two halves the 'O' ring will catch the seal lip, displacing part of the 'O' ring and when the two halves are fully together the seal with be held open by the distorted 'O' ring....

Separate the two halves, remove the 'O' ring, check the seal is still ok, join up the two halves again.... have peace of mind that no water is getting in there and eating the splines away....

Chris...........
You do remember that this is a FrankenStern, right? Or everyone with "O" rings should take them off?
 

achris

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Re: Mercruiser outdrive..Gasket?

You do remember that this is a FrankenStern, right? Or everyone with "O" rings should take them off?


The recommendation from Merc is to NOT install the 'O' ring at the top of the driveshaft, even if it has a groove.... Frankenmerc or not....

Chris......
 

orthoguy

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Re: Mercruiser outdrive..Gasket?

The recommendation from Merc is to NOT install the 'O' ring at the top of the driveshaft, even if it has a groove.... Frankenmerc or not....

Chris......

Alrighty then!

Thanks, Chris
 

Don S

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Re: Mercruiser outdrive..Gasket?

Chris, could you post the number of that service bulletin number, I can't find it and there is nothing in manual #6 about omitting the oring, and it was updated in 1997. I would like to post it if I can find it.
 

achris

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Re: Mercruiser outdrive..Gasket?

Arrrr, Sorry Don... It was when I was in the shop, and when we sold, I didn't keep the service bulletins file (a decision I rue to this day!!!)....

I have absolutely no way to access any of the bulletins... (apart from the really early ones in the back of some of the service manuals)

One thing that lends weight to that is the fact that after about 1995 (roughly) new driveshafts didn't have the groove. That goes for MC-1/R as well as MR/Alpha.

Chris..........
 

orthoguy

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Re: Mercruiser outdrive..Gasket?

Well, I got the new seal in, the "O" ring removed but.........I'll be darned if I can get the thing back together!

Both upper and lower drives are in forward gear but I can't get the driveshaft to engage. I come within and inch or two and that's it. The manual says to rotate the prop shaft in a counter-clockwise direction to help align the shaft splines, but I cannot get the prop shaft to turn "Counter-Clockwise" while in forward gear.

Any thoughts?
 

achris

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Re: Mercruiser outdrive..Gasket?

It will be tight... you're turning against the rotation of the water pump impeller... I usually just turn the yoke. If the top box is still on the boat, put a prop on the shaft and turn it with that.

Chris.........
 
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