impeller question

[haulyard]

On the mercury forum my question dropped to the bottom of second page without any response,so i thought i would try it here where i have always had questions answered.
origonal post below:

serial number 3656641 mercury 40 single cylinder 4 hp motor,was not pumping water ,tear down of lower unit i find impeller was toast,Now how do i figure out which impeller to buy,is it sierra 18-3039 ??

And how do you get old impeller off?? i have the housing apart but i dare go no furter till i here from you guys...

THANKS

on another website i learned there may be two different shaft sizes and to be carefull on which impeller to buy.
My big question is do these impellers slide off and on or do you need to tear into the unit more than just removing top of impeller casing.
thank you

 

[tashasdaddy]

Re: impeller question

they slide off, moving you back to mercury. you have a mercury question.

 

[tredragon]

Re: impeller question

they slide right up and off of the drive shaft. look on mercruiserparts for your serial number and you should find the part numbers for everything your motor would ever need.

oh, get the kit too... might as well replace everything while you're in there.

 

[woody66912]

Re: impeller question

look at center hub of pump should see 47-#####.

 

[matt2002]

Re: impeller question

Get Mercruiser parts , not Sierra.

 

[haulyard]

Re: impeller question

Thank You

 

[haulyard]

Re: impeller question

well it sounds easy,from what you all say it slides right off....
not mine ,over the years looks like the two became one(the shaft and impeller)there must be some easier way.

how does the rest of the casing come off,the two posts for the pump housing must unscrew and i guess i will figure it out as i go.........

 

[emckelvy]

Re: impeller question

Just take a thin chisel or old sharpened screwdriver and split the brass center of the impeller. Look carefully and you'll see the flat of the driveshaft where the impeller drive key sits. Don't split in that area or you stand a good chance of driving the impeller key into the pump insert and needlessly damaging it.

Once the impeller is off, the lower pump body just pries up off the studs. You don't have to pull the studs out. But unless you have water in your gear oil there's no reason to pull the pump body.

Check the insert for wear/grooves and replace as required. Pretty much the only way to get it out without some special Mercury tool is to pry the sides inwards then pull up with pliers. The new insert will just slide down in place and at the bottom there's a 'tab' which engages into the pump body to keep the insert in place.

Scrape or otherwise clean all the rust buildup off the driveshaft, otherwise you'll have a hard time reinstalling the impeller.

If you have access to a vernier caliper, that's the easiest way to measure the diameter of the driveshaft (once cleaned). Or if you can scare up a micrometer; but the calipers are plenty accurate to tell the diff between the 2 differnet sizes of impeller/driveshaft.

BTW using the Search feature will pick up a ton of recent posts on this subject, and the procedure is pretty much the same for 3.9hp, 4hp, 4.5hp, 6hp, 7.5hp, and 9.8hp. HTH.......ed

 

[haulyard]

Re: impeller question

ok,i used a small drill then increased in size ,drilled through and along shaft,then was able to spread it open with small screwdriver,then i came in and read previous post..oh well... the impeller key went on shaft then holding shaft without moving i slid impeller down and while holding impeller and shaft i used my small screwdriver to bend the impeller tabs into housing,GOOD GRIEF WHAT A PAIN IN THE NECK...and WHO was it that said they just slide on???

ANYHOOT after setting a spell and enjoying a moment of victory over my succesfull impeller change,i assembled lower unit and had a terrible time trying to line up water tube with pump housing,tried three different times,with three different water tank runnings and have given up for the night.

anyone have insight on proper way to get that stinkin tube into the pump housing??? and exactly where do you put the rubber ring????
AGHHHHH!!!!!!!!!! Frustration

 

[emckelvy]

Re: impeller question

You'll never get the water tube back into the pump without the plastic guide tube which I'm assuming is not present on yours. It just "slip fits" into the same hole in the top of the pump where the water tube goes and "catches" the water tube while you're reinstalling the lower unit.

You can hardly see the copper water tube go into the plastic guide tube so you can imagine that trying to do it without is gonna be daunting to say the least!

Here's the part # for the tube: Water Pump Guide Tube 23-31792T $7.47

BTW the rubber ring is probably just a "slinger ring" that goes down the driveshaft and rests right at the top of the pump cover. It does as its name implies, "slings" debris away from the pump; keeps sand, silt, etc from getting drug into the pump.

You can pull up a good diagram of the lower unit at this site, it'll show you how all the parts relate to each other:

http://www.mercruiserparts.com/SelectModelType3.asp?class_id=2

HTH.........ed

 

[sunburnt]

Re: impeller question

recheck operation of impeller after a few hours of operating MOTOR. may sound like a lot of extra work ,but wont let it become toast again .PS- helps to have a buddy to reinstall lower unit, so you don't drive shift shaft to breaking point.

 

[haulyard]

Re: impeller question

removed my lower unit again,this time i attached a small hose to the pick up tube and blew air into it,should not the air exit out the **** tube,what it sounds like to me is most the air is escaping into the drive shaft housing.
is this normal?
looking at where shaft goes and where pick-up tube goes looks like they could rub,if so,is it possible i have a hole in pick-up tube,it seems to be attached firmly to what i dont know and it kinda bends out of sight,
any ideas??

 

[emckelvy]

Re: impeller question

Most of the air will come out the discharge at the bottom of the motor, into the driveshaft housing. You should be able to feel some air come out the telltale, too. If not, it needs to be blown out with compressed air.

Since you have the lower unit off, suggest hooking up water to the supply tube so you can see if you're getting a good flow thru the motor.

It's quite rare to see a water tubed "holed" by wearing against the driveshaft. While the clearances are tight in there, unless the water tube is horribly bent up it'll be held in place via its insertion into the water pump......ed

 

[haulyard]

Re: impeller question

ok,i have a better hose(better seal) on water pick-up tube ,and blowing into water tube tells me there is some blockage ,i ran a small wire into tube and tube is clear so,must be blockage where tube meets engine.(maybe old damaged impeller pieces made it into engine)

anyone ever remove powerhead from a mercury 40 year 1973???
looks like six bolts hold it to gear casing but the shift linkage looks like a handfull,in lieu of buying a manual-can someone give me the heads up on tearing into this project?

motor looks like it has been in storage for the last 30 years,very clean and runs excellent(except for no water cooling)
i paid $100 for it and thought i was stealing it,now i wish i had my $'s back

 

[tredragon]

Re: impeller question

I'm guessing you cleaned out the pee hole with wire already? hymenopterons like to get wayyy up in there and nest... that was my problem. I used old trailer light wire. weed eater line is supposed to be effective as well. hth

 

[emckelvy]

Re: impeller question

anyone ever remove powerhead from a mercury 40 year 1973???
looks like six bolts hold it to gear casing but the shift linkage looks like a handfull,in lieu of buying a manual-can someone give me the heads up on tearing into this project?

Six nuts accessed from underneath hold the powerhead down. Disconnect the fuel filter adapter at the carb and pull the entire fuel pump/filter adapter assy off the carb.

There's a throttle linkage arm to disconnect, where the plastic piece meets the flat metal arm, take the thru-bolt apart. Note it's an odd size and the nut is self-locking.

The piece of the throttle mechanism that goes to the inner throttle gear is splined, so it just pulls out when you lift the powerhead. It has a flat in one side and will only go back one way.

The shift mechanism is a non-problem-problem because that all stays with the lower cowling.

There's a flat spring attached to the front of the motor by that carb, that puts tension on the shifter mechanism detent, but that just lifts up with the powerhead.

If you have a kill switch, that'll need to be disconnected also. Take note of where the wires go.

New parts needed: powerhead base gasket, water tube rubber grommet, and the washer that goes on top of the tube/grommet. This washer is very important and must be there. Look up parts for your motor at iBoats, or the link previously posted.

Usually what happens is the motor overheats and the plastic washer squeezes shut. The new washers are made of phenolic or some other type of material that is more resistant to heat.

The other problem is with the rubber grommet itself. Corrosion products build up around the grommet and squeeze it shut.

You'll have to dig the grommet out and scrape the cavity clean where it goes. Spread a thin coat of gasket dressing (Permatex No. 3 Aviation-type) in the cavity when you install a new grommet, this'll seal it off and eliminate that problem forever.

Or maybe you'll find chunks of impeller up there! If the rubber grommet is in good shape clean everything up and be sure to replace that water tube washer anyway.

Check the bottom of the block where the discharge holes are, make sure they are clear.

I had a 4.5 with blocked holes, all the water went out the telltale and the motor got hot above idle. But it had Real Good water spray out the telltale!!!

Happy powerhead pulling!..............ed

 

[haulyard]

Re: impeller question

thanks for your time ed,and i was wondering . Is there a water jacket on this motor??something smaller i could check before motor tear-down?

 

[haulyard]

Re: impeller question

Ed, i removed the bolt for filter,and the throttle connection bolt,but i fail to see why that is neccesary,after removing the six nuts under cowling the whole thing wants to lift off. BUT it looks like only thing holding it on is the throttle gear that is(in cowling) on the other end of twist grip assembly..

it is the black gear that rests on white gear,the white gear engaged by black gear moves throttle...

it looks like the twist grip control needs to be dissasembled

am i missing something here?
thanks

 

[emckelvy]

Re: impeller question

You're right, I was thinking about the one I just did but I had things apart farther than you're taking yours. Sorry about that!

Take a look at this diagram for the throttle linkage:

http://www.mercruiserparts.com/Show...nbr=681&bnbr=9&bdesc=THROTTLE+CONTROL+LINKAGE

You'll notice assy #5, "Gear and Shaft Assembly".

Everything but the gear at the bottom should be mounted on the motor and lift off when you pull the powerhead up. The shaft goes right into the gear via splines and is keyed to go only one way.

If you're having trouble with that or your linkage is somewhat different, you could try disconnecting the bracket #6 from the block and/or driving the roll pin out of the throttle arm and pulling things apart that way.

BTW on your other question, the cover at the back of the block comes off with (4) bolts and that'll allow you to inspect the water passages inside there.

G'luck..........ed

 

[haulyard]

Re: impeller question

easily got the head off by removing six nuts under cowling and two bolts from sides of tiller arm.. withtiller arm removed the gear shaft slid right out and motor head lifted right off.

ok,all done here is what i did.
i had such a horrible time trying to line up the pick up tube with impeller housing,so i pulled tube from motor and inserted into impeller housing first and then guided tube into motor head with a small screwdriver via the water jacket opening,worked like a charm.