Removing lower unit

[MSC]

Hi, I am new to this forum, came here to ask a question & learn what I can. I have a 2000 mercury 40HP, 3 cylinder outboard, in the past I have always paid someone to remove lower unit & change water pump housing & impeller, but this time I decided that I should be able to do this myself. I have found web sites that show you how to do it on other mercurys. So I go outside & loosen the 4 bolts ( 2 on each side ) but the unit won't come off, I tap it with a dead blow hammer, still won't come off. I begin to think that there must be other bolts that I don't know about, went to my local dealer but they wouldn't let me ask one of the mechanics. So can someone tell me how many bolts there are & where they are located? Do I have to disconnect the shifting linkage to remove lower unit? Thanks

 

[Texasmark]

Re: Removing lower unit

Don't know about your engine. I have the 90 hp range and in that range and 25 or so hp larger, there is an additional bolt at the rear. On some engines with a zinc sacrificial anode which also serves as a torque reducer (trim tab) it is under the tab requiring you to remove the tab then from underneath look up into the hole 1.5" roughly that the tab covered and there will be a socket head screw there. On later model engines they moved that screw/nut forward of the trim tab and it is easily visable. Some smaller engines have no tab and no bolt/nut/screw at the rear.

Check it out and get back.

Mark

 

[MSC]

Re: Removing lower unit

Thanks Texasmark, but what about the linkage? should the LU drop off once I get all the bolts out? Should it be in forward or reverse when LU is removed?

 

[crem1]

Re: Removing lower unit

Gear usually is in forward, but reverse also works

 

[Texasmark]

Re: Removing lower unit

Merc uses a twisting shifter, at least on their 90's. the shift rod coming out of the top of the lower unit (adjacent to the water pump) has a splined shaft male which mates to a splined shift shaft female that goes up to the shift lever. As long as corrosion doesn't impede the process, this should slide apart.

Any gear will allow you to physically separate, but F is recommended by some and as Crem 1 said R works too. Just make sure when you go back together, the shift shaft and the lower unit are set up for the same gear. Otherwise you will have some funny shifter operation.....like you put it in N but it takes off in F.

One reason a drive gear is preferred over N is that upon mating the drive shaft to the powerhead, with the shifter in gear, the prop can be used to move the drive shaft spline into alignment with the power head and things go together that "last inch".

Mark

 

[MSC]

Re: Removing lower unit

OK, I was outside working on it when you made your last post, found the 5th bolt & removed it, the LU droped about an inch, the only thing holding it on is a rod about 1/4" OD, maybe larger. If I understand you right this is on a spline & should seperate with a little pressure. The rod has a rubber boot on it so I can't really see it.

 

[MSC]

Re: Removing lower unit

The 1/4" rod runs from right behind water pump housing ( covered by rubber boot going up about 2" ) thru the top of Lu where it screws into a nut ( about 1" long ) from there it continues into engine housing. The boot is held on by a small cable tie, I am thinking about cutting the tie to remove boot, maybe there is a pin or something that needs to be removed

Where is the spline located?

 

[saumon]

Re: Removing lower unit

Please post your serial number; we love them here!

Seriously, with your serial number, we can have access to the related parts diagram and better help you.

There's so many setup. Only for the shif shaft, it could be splined midway, or sometimes there's an access (rubber plug) on the driveshaft housing where you can loosen a bolt, or even, on other model, you have to disconnect it from the top, right under the carbs.

 

[MSC]

Re: Removing lower unit

Thanks, serial # 0T082384 it's a 2000 mercury 40HP, 3 cylinder, model 40ML

 

[saumon]

Re: Removing lower unit

Thanks, serial # 0T082384 it's a 2000 mercury 40HP, 3 cylinder, model 40ML

If you look at this page:

http://www.ishopmarine.com/ishop/js...cCatFilter=MM&eCatSupFldr=supplier-050-025-MM

and you click on ?Gear housing - Driveshaft? and ?Driveshaft Housing/Exhaust Plate? you'll see both the upper and lower parts of the shift shaft. Is the boot you were talking about right at the bottom of the shaft? If so, don't bother with it, cause the splined part is located approx. in the middle of the shaft lenght. Sometimes it's a retainer, like a nut, that you can accees through an opening in the midsection.

 

[MSC]

Re: Removing lower unit

I got it, really simple once you know how. For anyone else that might have this engine here is how it works, there is no spline or locking mechanism. The shifting rod (1/4") runs from inside the LU thru the upper housing, once it exits the housing there is a nut that is about 1" long that the rod screws into, you simply back off of that nut until the lower section of rod comes loose, you can then remove Lu to make repairs.I also think that this nut is for adjustment if necessary.

A question about rotation of shaft, when I install the new impeller how do I make sure that the rotation is right?

 

[crem1]

Re: Removing lower unit

Grease lightly the interior(impeller housing), then it doesn't matter which way you will turn the shaft it will self-aclimate

 

[MSC]

Re: Removing lower unit

Thanks guys I couldn't have done this without you, all that I have to do now is install the LU & bolt up, I hope that this part goes smoothly. Now that I've done it I don't think that I'll have any problems in a year or so when it will need to be done again.

 

[saumon]

Re: Removing lower unit

Grease lightly the interior(impeller housing), then it doesn't matter which way you will turn the shaft it will self-aclimate

I've always been told to turn the driveshaft clockwise while putting the impeller in to prevent the blades to be bent backward...

 

[crem1]

Re: Removing lower unit

It does not matter which way you turn the driveshaft, at such a low velocity it does not do any kind of harm

 

[Texasmark]

Re: Removing lower unit

It does not matter which way you turn the driveshaft, at such a low velocity it does not do any kind of harm

I have never been inside a water pump when the engine was running 5000 rpm. One would think that since the pump changes from a displacement pump at low speeds to a centrifugal pump at high speeds, having the blades in backwards wouldn't matter as the first time you had the boat out it would straighten it'self out.

Well that makes for good shop talk, but I never put an impeller in with the blades oriented in any direction other than the way they will be oriented when the engine is running.

Mark

 

[MSC]

Re: Removing lower unit

So which way should I turn shaft before installing? What direction does shaft turn when running?

 

[saumon]

Re: Removing lower unit

So which way should I turn shaft before installing? What direction does shaft turn when running?

Clockwise when viewed from the top

 

[Texasmark]

Re: Removing lower unit

I've always been told to turn the driveshaft clockwise while putting the impeller in to prevent the blades to be bent backward...

Me too and I just read it again yesterday in my Merc (brand) service manual. I never proved otherwise, and I know the blades bend back at high speeds becoming a centrifugal pump. It is possible that once centrifugal, when the blades go by the outlet where the radius of the pump housing expands to take on new water, they could assume the correct direction there.

Really a moot point with me however, as I always rotate the shaft cw and don't have to worry about it.

Mark