Prop shaft seal...Can I do this???

[kozman01]

I'm looking to replace the seal on the prop shaft of my 1969 Merc 800 engine. Is this a job that can be done by someone with some mechanical ability? Or is it wiser to take it in to the stealer and have the shop do it. I'm selling the boat come spring but I don't want to leave someone with the small leak I have in my lower unit. Thanks for any help.

 

[Hooty]

Re: Prop shaft seal...Can I do this???

First, are you sure it's the prop shaft seal? Are you sure it's not something as simple as the gaskets/orings on the fill and drain plugs? If you're sure it's the shaft seal, get a shop manual and go for it. It's not that difficult.<br /><br />c/6<br />Hooty

 

[coosarunner]

Re: Prop shaft seal...Can I do this???

I have a '74 Bomber bass boat with a 650 Mercury. I replaced the two prop seals and it was simple. I have a manual but it's very general in instruction. The critical aspect is trying to mount the seals straight. I had a pipe that I slid over the driveshaft to put the seals on evenly. Filled it back up and it's holding pretty well.

 

[kozman01]

Re: Prop shaft seal...Can I do this???

I'm just going down the list of things. I cleaned out the area where the drain/fill screws go and put new seals in each time I go out and each time I go out, I get water in my oil. I tightened up all the bolts on the lower unit and am still getting water intrusion. I figured the prop shaft seal would be the next logical step. If I'm incorrect or not on the right track, please advise me, thanks. I have a Clymer manual from like the late 70's. It's not real descriptive on how to take the thing apart, is there a better manual for this?

 

[BF]

Re: Prop shaft seal...Can I do this???

I think you should pressure test it. It might not be the prop shaft seal at all. Maybe it's the driveshaft seal under the water pump (?). I made up my own pressure testing device using a small rubber stopper, some small tubing, a stopcock (medical kind), syringe and a pressure guage. I drilled a hole through the stopper, and slipped fine, stiff tubing through the hole, used silicone to seal/stick it in there. attached other end to stopcock, and attached the pressure gauge (via a pice of tubing) and the syringe also to the stopcock. Reality is you probably don't need a pressure guage. You just wanna be able to pressurize the LU a bit to see where the air leaks out.<br /><br />Take LU off, drain the oil, put stopper in drain hole, and inject air into it with syringe. Should hold 10 psi. Yours won't (air will leak somewhere). Lay LU in a kiddie pool and see where bubbles come out. On mine it was from the driveshaft/water pump. Removing the pump base, I saw the driveshaft seal had separated. Replaced pump base (& seal) and re-tested. Held pressure no problem. Reinstalled, refilled with oil, got no water in all season.<br /><br />HTH,<br /><br />Brent

 

[kozman01]

Re: Prop shaft seal...Can I do this???

Is that a difficult seal to replace? The driveshaft/waterpump seal.

 

[BF]

Re: Prop shaft seal...Can I do this???

nope, it's easy. You have to have the LU off, you take the upper water pump housing & impeller off. What you'll see next is the water pump base. That slides up over the driveshaft (sometimes it takes some prying to get it loose). The seals are pressed into the plastic water pump base. You can get new seals by themselves and press them in (locktite to keep in place), but more commonly, you just buy the new pump base for ~$20 with the new seals already pressed in.<br /><br />When I did mine (in a V150), I put a completely new water pump in (new upper housing, impeller, all new seals & gaskets, new base with seals) cost ~$90. I could've just done the base, since I didn't even have a season on the impeller. When you put the new base in, don't forget to lube the inside of the seals prior to installing them (that goes for prop shaft seals too).<br /><br />Anyway, it's not hard... but to re-state... IMHO you'd be wise to make sure that whatever seal you replace is leaky. Particularly if you goal is just to fix the leak, not to redo all the seals in the LU. <br /><br />HTH,<br /><br />Brent