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Author Topic:   Mercury 90-HP Two-stroke: Water Pump Service--Do It Yourself
Barry posted 04-19-2001 01:56 PM ET (US)   Profile for Barry   Send Email to Barry  
I bought my Montauk last summer. It has a Mercury 90-HP, a 1989 based on a recent call to Mercury with the serial number (although it was sold as a "1994"). Since I don't know when the impeller was last replaced I'm considering either having it done or doing it myself.

I called three different shops (none of which are very close by) and of course received three different quotes - $50, $75, and $150.

How tough is it to drop the lower end and do this? Exactly what steps would I follow, what tools do I need, what parts do I need, and where do I get them?

Is it worth investing in a Service Manual and would that have the info I'm looking for?

On I found just the impeller for $22.90 versus the impeller kit for $37.70.

Thanks in advance,

hauptjm posted 04-19-2001 02:30 PM ET (US)     Profile for hauptjm    
Buy the Service manual and buy the kit. If you have a reasonable aptitude towards mechanics, you'll handle it. The manual should help in regard to any "tricks".
Whalerdan posted 04-19-2001 03:05 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
I did this a couple months ago and bought the manual. The trouble was that manual covered several different years and engine sizes. It gave me a good start, but it didn't mention disconnecting the shift linkage under the cowling. I got all the bolts out like the manual said, but the lower unit wouldn't drop with the linkage still hooked up. After about an hour or so of cussing and rereading the manual still no luck. I finally got to looking at everything and figured it out. I then pulled the empeller off and it looked fine. I bought this thing three years ago and never did anything to it and I don't know how long ago the last owner touched it. I was worried when I started reading you should change it every year. Seems like that advice was overkill.
Whalerdan posted 04-19-2001 03:07 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
One more thing. Buy the kit. You'll probable need a new O-ring
Soho posted 04-19-2001 05:13 PM ET (US)     Profile for Soho  Send Email to Soho     
For what it is worth, I run 17' Nauset ( 90 hp Yamaha ) boat in salt water year round and I tend to replace the impeller every 12-14 months or so when I bring the boar out to do the bottom etc, The impeller is in good shape when I change it, but going through the exercise lets me generally check the lower unit out, change the oil and make sure that none of the bolts are seizing up, which can be an issue in a SW environment, especially as your engine gets older. Getting the manual is absolutely needed and once you have changed it once, it is no bother after that. Takes me an evening to do and I always feel somewhat righteous after I do it. The yearly exercise may indeed be a bit anal, but the impeller is important to the operation of the engine.



jimh posted 04-21-2001 05:06 AM ET (US)     Profile for jimh  Send Email to jimh     
I learned quite a bit about my engine when I pulled off the lower unit.

The first thing I learned was where the hidden bolt was that was preventing it from coming off! [Under the trim tab anode.]

Usually there is a "trick" to making the job easier. In this case I think it was the advice to leave the shift linkage in FWD.

Usually in the lower unit gear case there is a spring that wants to shift the mechanism into the FWD gear. When you are in -N- or -REV the linkage is actually compressing against the tension of this spring. So by leaving the linkage in FWD you won't have to work against the spring when re-aligning the upper and lower unit sections and their connecting control rods.

Also, if you leave the lower unit in FWD then you can rotate the drive shaft by turning the propeller. This will help you when you are installing the water pump impeller. It will also be handy when you need to realign the drive shaft to fit into the splines of the upper drive mechanism. You might have to turn it a bit to align the splines.

When I took mine apart I also found how heavy the lower unit was--heavier than I expected it to be--so be ready to hold the weight when it finally separates. It might surprise you.

Also, the drive shaft generally extends upward rather far. When separating the lower unit you will need a bit of room to pull the shaft out of the upper portion. Unless your boat is very tall on the trailer, you'll probably need to tilt the engine up to have enough room to clear the drive shaft when you remove the lower unit.

To work on the water pump you will probably need something to hold the lower unit upright while you install the new parts. I clamped mine in a vise with some soft pine to protect the skeg from the vise jaws. Be careful you don't induce a bend in the skeg, as you will have plenty of leverage on it.

When I got mine apart I found there was a small pebble that had lodged itself in place near the reverse-tilt lockout cam, eventually wearing a little dimple in the cam. It was rather amazing to find this pebble, still in place, considering all the vibration and shock that happens to an outboard. It looked like it had been there for 20 years. A outboard mechanic told me it is quite common to find small pebbles in there.

Putting the lower unit back on is harder than taking it off. There are at least four shafts to align:

--the drive shaft
--the gear case shift linkage
--the reverse lock out linkage
--the exhaust pipe shroud

Unless you are very lucky, you will probably need as assistant to help. You'll have your hands full holding the lower unit (and its considerable weight) and trying to move it upward into place, while your assistant deftly aligns the various linkages and gets them going in the right directions and holes. Then you may need to rotate the prop a bit to align that drive shaft.

When it suddenly slides back into place, then you'll need a free hand to get the nuts started. On mine, I seem to remember that a couple of the nuts must already be in place so when the stud from the lower unit pops into view the nut can be started onto the stud. Otherwise there is not enough room to fit the nut onto the stud once the lower unit is fully raised. Again, that might take a third hand to accomplish.

I like to be able to do some mechanical work on the devices I own. Being at the mercy of the service shop and its mechanics is too hard to bear. The first time you do something like this it will be a pain and a learning experience, but then you'll get better at it the next time.

Of course, I am assuming you have all the tools you need on hand--the proper wrenches and sockets and so forth--as you can't do this with just a "Tennessee Adjustable" as your only tool.

Also, don't pull the lower unit apart over grass. If you loose some little piece of hardware you'll never find it again.

Other than the pump assembly, there are not (generally) any gaskets or other parts you need to renew before reassembling, but check that factory manual for advice on this first.


triblet posted 04-21-2001 08:55 AM ET (US)     Profile for triblet  Send Email to triblet     
hauptjim, did you have the factory manual
or an aftermarket manual? The factory
manuals tend to be fairly narrowly focused
while the aftermarket manuals are broadly
focused like you described. One size fits
none. The only exception, which doesn't make
autoboard manuals, alas, is Haynes. Their
auto manuals are EXCELLENT.


hauptjm posted 04-23-2001 08:45 AM ET (US)     Profile for hauptjm    

I'll have to check on the publisher, I'm not sure. I bought it at West Marine, and it covers the V-6 OMCs from '92-'99, I believe. It definitly can be vague. I find most manuals to be written by absent-minded professors. A lot of knowledge is assumed. For years, I was the hard-head that just started taking things apart to fix them without any idea of what was around the corner. Old age and taking three times longer to fix something taught me well. Interestingly, that old method did teach me to look for certain 'tricks' and methods that I think helps to this day. Someone recently suggested that the OMC manual actually is very well written, and not as general. I'm ordering one today. In general, I'm with jimh, I would never pretend to be a mechanic, but I like to know my engine and what I'm talking about when I do need one.

andygere posted 04-23-2001 03:16 PM ET (US)     Profile for andygere  Send Email to andygere     
It almost seems like the outboard manufacturers have engineered a labor intensive maintenance requirement into the waterpump impeller. It seems to me that there could be a more elegant solution, such as an easily removed access port that would make changing these things easier and less time consuming. Of course if it were that easy, manufacturers and dealers would lose money two ways: First, fewer motors would overheat and need replacement (thus destroying the notion that outboards are disposable) and second, a major profit center would be eliminated from dealer repair shops. Kinda makes you wonder....
triblet posted 04-23-2001 05:08 PM ET (US)     Profile for triblet  Send Email to triblet     
If it covers that many years it's not an OMC
factory manual. I have the factory manual
for my '97 90 HP Evenirude. It cover's that
year only, 90-150HP (V4 and smaller V6) which
are all pretty much the same except for
having a couple more cylinders.

The downside of the factory manuals is that
they have a lot of "use service tool XYZ"
and you have to figure out that two
screwdrivers and a crescent wrench can do
the job.

What would be really trick is to have it on
CD, tell the computer what exact model you
have, and see a tailored manual. This would
be REALLY trick for cars and trucks: w-w/o
air, manual/stick, pw, etc.


where2 posted 04-23-2001 07:26 PM ET (US)     Profile for where2  Send Email to where2     
I actually flat out asked the reps at most of the outboard engine displays at the Miami International Boat Show (Da Big Show!) why they tell you to change the impeller every year. Get this: All of them conceed that it usually doesn't need a new impeller, you change it: "to keep the bolts from seizing up". That's what they said!! Hmm, ever think of anti-seize thread compound? With a little anti-seize you could probably go every other year. Maybe mine last longer in Florida where I can boat year-round. :)
Dick posted 04-23-2001 09:33 PM ET (US)     Profile for Dick  Send Email to Dick     
I have wholesaled Seloc repair manuals for years and have found them to be very good. Not as technical as the OE shop manual, but written for the average person without any factory training.

Seloc is now owned by Chilton and they do have their auto manuals on CDs. No word yet but hopefully they will do it with the marine manuals.


goshgo27 posted 08-29-2007 11:45 PM ET (US)     Profile for goshgo27  Send Email to goshgo27     

I was hoping that someone could help me. I am having a problem with my 1988 Yamaha 8HP. [Here followed a very long description of mechanical problems with the outboard motor, concluded by a request for some thoughts.]

jimh posted 08-30-2007 08:21 AM ET (US)     Profile for jimh  Send Email to jimh     
I have some thoughts:

--do not revive six year old discussions
--start new discussion when you have a different problem than the one under discussion
--obtain a service manual before beginning to perform repairs or service on your motor

You are welcome to seek advice about your outboard motor repair by beginning a new discussion.

[Thread closed]

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