removing lower gear case from merc 120

ron21647

Recruit
Joined
Jul 8, 2003
Messages
1
1986 Mercruiser 120 hp, Alpha 1 engine s/n 0B400***<br /><br />I am trying to open the lower unit to replace the water pump impeller. I have all the bolts loosened - 1 in the front, 2 on the sides, trim tab and under the trim tab. I can not get the case separated. any suggestions on what to do next?<br /><br />thanks,<br />Ron
 

shakespear

Seaman Apprentice
Joined
Jul 11, 2001
Messages
40
Re: removing lower gear case from merc 120

is there a hex bolt in the hole at the very back of drive?
 

KiLer

Cadet
Joined
Jul 20, 2003
Messages
22
Re: removing lower gear case from merc 120

I feel your pain.....my 88' 120 mercruiser alpha 1 gave me a headache too..... there's 2 on the sides,one under the trim tab and 1 in the back as well....it'll seem like it's stuck. your gonna need to pry it apart....the splines on the shaft tend to get stuck. are you doing this cause it's not pumping water ? if so (and I'd do it anyway) check ALL water ways for debris....pull the thermostat out as well and check for blockage. might want to replace that as well....mine was only $12.<br /><br />Hope this helps.
 

Skinsk

Petty Officer 2nd Class
Joined
Aug 31, 2003
Messages
128
Re: removing lower gear case from merc 120

If it's stuck, it may be due to salt corrosion on the studs going through the front and the four on the sides. <br /><br />It's easier to remover the whole drive, and then fight the halves apart. You will probably have to heat the areas around the studs, and pry on the seam with screw divers. Try driving a screw driver in the seam at the very rear of the drive. <br /><br />you may have to heat a lot. Sometimes even heating, then driving in screwdrivers, and then letting the whole thing cool and contract.<br /><br />It can be a pain if the drive hasn't been separated in a long time.<br /><br />I do my impeller every other year, so I don't usually have any problem splitting the halves.<br /><br />Scott.
 

luisito

Seaman Apprentice
Joined
Sep 5, 2003
Messages
35
Re: removing lower gear case from merc 120

to remove lower unit you have 6 bplts<br />1 front 2 front sides 2 rear underside<br />1 under trim
 

twin485

Cadet
Joined
Sep 3, 2003
Messages
11
Re: removing lower gear case from merc 120

Careful with the heat Ron that alum. reacts funny under intense heat. A couple of soaks with Rostoff may prove just as effective. Don't pry along the right side(viewed from the back) you may damage the seal seat for the oil passage to the top section. Soak it and let it sit,saok and let it sit. Be patient with that alum. Ron.<br /> You way have to pick up some fine thread nuts the same as your ss nylocks screw them onto the studs and after you drive(lighty tap) a thin blade scrwedriver in the seam at front and rear hit the nuts that you have screwed 3/4 the way on the studs.<br /><br />BE PATIENT WITH THAT ALUMINNUM Ron.
 

KiLer

Cadet
Joined
Jul 20, 2003
Messages
22
Re: removing lower gear case from merc 120

I used a good stiff putty knife to get mine started...after that a thin flat blade screwdriver...once i got it about an 1/8" apart i used a larger one and it popped right off....I'd avoid the Heat at all costs....like mentioned above...it's alum. not a good idea to heat it up.<br /> It'll break free just take your time and don't get flustered.
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: removing lower gear case from merc 120

hello<br /> sometimes the corrosin gods dont smile. usually indicates the maintenence schedule needs to be shortened. I have had some sucess using the two side nuts as jacking nuts. if you carefully run the nuts up until the top of the nut comes into contact with the upper case then give it some pressure sometimes it will break free. on saltwater corrosion I have found chlorox bleach to be effective. watch out for runbber parts clothes and eyes if using bleach. I also dont like heat but it is a nessasary evil in this business<br /> oxy/acetylene is my friend and a must with saltwater engines. good luck and be patient. it did not corrode overnight so it may not come loose as fast either :)
 
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