Lower unit repair

[Rich4081]

Just wondering how hard it is to rebuild an 2000 merc 25 horse lower unit.

 

[carholme]

Re: Lower unit repair

What is the s/n of your engine?

Do you have the Mercury service manual? If not, see my PM to you in Notifications at the top of the page.

Can you say why it has to be re-built?

Gerry

 

[orbanp]

Re: Lower unit repair

Here is an on-line factory manual for your engine: Boatinfo - Mercury Service Manual for 20jet-20-25hp
Read through the gear case section, it will tell you how hard is it and what tools you would need.

Good luck, Peter

 

[Texasmark]

Re: Lower unit repair

Drive pinion to F-R gears require a dimension that requires you to reach up into the LU and make the measurement. May be able to borrow the tool required. Manual mentioned by others has the dimension. I don't know what you want to repair, but if you don't change any shims or gears you probably won't have to worry about the "mesh dimension" as nothing would have changed from the OEM setup all that much. I didn't do it and had no problems but I changed nothing to affect the dimension. Considering gear mesh was not one of your problems.

You can fish all the parts out without having to remove the drive shaft and pinion. At least I didn't have to on my Mercruiser outdrive and I went all the way to the front and replaced the shifter cam. Course it was a 4+ inch housing and I had plenty of room to get at it. On a 25 you may be cramped since the housing is much smaller.

Mark

 

[Rich4081]

Re: Lower unit repair

I hit something and ran it out of oil. Boggs motor down in gear and makes a clacking noise so I pulled it and spinning the prop by have has a bad spot in it

 

[racerone]

Re: Lower unit repair

Remove the prop shaft bearing carrier ( left hand thread ) and inspect the bits in there.----After you price the parts you may opt for a good used lower unit.

 

[oldman570]

Re: Lower unit repair

A pressure test should be done before any other work as you might have a cracked LU. If the LU has been run for sometime without oil the gears and bearings are probably shot. Your best bet is to get another complete LU and replace the one that is bad. This will get you back on the water a lot faster as rebuilding a LU can get very costly if the gears, bearings, or LU case are bad. JMO
Oldman570

 

[Texasmark]

Re: Lower unit repair

Agree with oldman. If you lost oil you have a hole somewhere.

Mark

 

[racerone]

Re: Lower unit repair

Some of these 25 HP lower units do not require any shimming work.--At least no shims are shown in the parts book.-------Take it apart if it ran without oil.

 

[Rich4081]

Re: Lower unit repair

Thank you for the input I have price some via eBay and a few others. I am a diesel mechanic so I figured I can fix it myself but I don't know if I want to spend the money now if the housing is bad. When I pulled my boat out I could clearly see the oil dripping out of the prop shaft seal but that's not to say that there is an internal crack right?

 

[racerone]

Re: Lower unit repair

Pressure test the gearcase to find the leak.

 

[Texasmark]

Re: Lower unit repair

Pressure test the gearcase to find the leak.

+1.

If you choose to pressure test it yourself, and have an air compressor with an adjustable regulated output, get an squirt bottle of soapy water (I like 50-50) and your spray head/nozzle for your compressor hose. Soap up the exterior real good and with the regulator set to about 5 psig, shove the nozzle in the drain screw hole in the casting (with the oil drained), give her a good shot and look for bubbles.

Mark

 

[Rich4081]

Re: Lower unit repair

Ran a pressure test on the motor. No good lost a cylinder... Where would be a good place to search for a good used motor?