25hp Nissan Lower Unit Leak?

[TwoRivers]

Hello again. (I do have a Tohatsu Manual which includes this model)
Just successfully finished repairing a 10 year old leak in my rototiller transmission now onto the Nissan.
I'm certain that the leak in my outboard won't wait that long.
Spring is right around the corner here in SWPA and I need to be ready.
I have a Nissan N25C3 that I picked up in the fall and planned to tune up this winter and put into service this spring. Over the winter I noticed gear oil leaking from the prop shaft area.
I read all the threads I could find on leaking lower units.
I read where fishing line wrapped around the prop shaft area could cause seals to be damaged.
So, I took the prop off and sure enough there was fishing line around the prop shaft and back side of the thrust holder (#28 in drawing). I removed the fishing line and reinstalled the prop. The lower unit is still leaking.
It's not perceptible (to me) where the damaged seals are located?
Could somebody point me to the location of the possibly damaged seals?
Many thanks.
Rob

 

[TwoRivers]

Re: 25hp Nissan Lower Unit Leak?

Anybody?
What am I missing here?
thanks
Rob

 

[pvanv]

Re: 25hp Nissan Lower Unit Leak?

What manual do you have?

You should use your Factory service manual (003-21035-1 SERVICE MANUAL, 1 & 2 CYL, 2-STROKE, $45.00) as a guide to replace the LU seal kit: 346873217M LOWER UNIT GASKET SET, $30.42. The faulty seal is probably the prop shaft seal (#26 in the attached diagram). Since you need to disassemble the LU to do that seal, you may as well do the whole kit -- and if you do install the kit, don't neglect to do the o-rings for the cam rod bushing, which are often overlooked. While you have the LU down, it's a good time to install a new WP kit: 361873220M WATER PUMP REPAIR KIT 25B-40C, $46.67, since you have already done the labor. These items are available from any dealer, including several forum members, even me.



If the boat can handle it, you can also convert to 30 hp at very low cost.

 

[TwoRivers]

Re: 25hp Nissan Lower Unit Leak?

Paul,
Thanks for your response. I'm using the correct manual. (got it from you)
Manual doesn't go into seal kit replacement (unless I'm missing something?)
Does the seal (#26) you mentioned need pulled and pressed back in? Any other seals need pressed?
If so I can take it to my local NAPA machine shop and have it pressed.
Do the O rings for the cam rod bushing come with the kit?
I'm not afraid to tear the lower unit apart, I'm good at that. Sometimes I have problems getting things back together
Will I need any special tools for this project? Where can I get them?
Sorry for so many questions. Figure I should get them all in before the board picks up in the Spring.
How's Buffalo? Any ice on the lake?
thanks
Rob

 

[Sea Rider]

Re: 25hp Nissan Lower Unit Leak?

Rob,

Seals dont fail just with fishing lines, if seals are oldies, that is dried, hardened will have issues and oil will drain from them too. For total peace of mind and wallet, better change a complete lower seal kit as Paul recommends.

Happy Boating

 

[TwoRivers]

Re: 25hp Nissan Lower Unit Leak?

Thanks Luis,
That's what I'm thinking too.
Just trying to figure out if this job is something I can do?
I'd hate to start working on it and find out I need a special tool that's unavailable.
Then I'd have to take it to Paul's shop in a garbage bag
Rob

 

[TOHATSU GURU]

Re: 25hp Nissan Lower Unit Leak?

You either replace all the seals in the lower unit or pressure test it and look for the leak.

 

[TwoRivers]

Re: 25hp Nissan Lower Unit Leak?

Thanks Guru,
I figure I'll replace all the seals then pressure test it.
Then re-replace the ones I screwed up

Rob

 

[pvanv]

Re: 25hp Nissan Lower Unit Leak?

Paul,
Thanks for your response. I'm using the correct manual. (got it from you)
Manual doesn't go into seal kit replacement (unless I'm missing something?)
Does the seal (#26) you mentioned need pulled and pressed back in? Any other seals need pressed?
If so I can take it to my local NAPA machine shop and have it pressed.
Do the O rings for the cam rod bushing come with the kit?
I'm not afraid to tear the lower unit apart, I'm good at that. Sometimes I have problems getting things back together
Will I need any special tools for this project? Where can I get them?
Sorry for so many questions. Figure I should get them all in before the board picks up in the Spring.
How's Buffalo? Any ice on the lake?
thanks
Rob

Rob,

See section 6 of the FSM. Page 6-17 has the exploded diagram. The manual assumes you have ordinary mechanics tools and abilities. Yes, the prop shaft seal is a press fit. You can either drive it out with a suitable punch, or use a seal puller. Installation is typically done by driving the new seal in with the appropriately-sized socket as a ram, and tapping it in with a hammer, or pressing it into place. The driveshaft seal (in the bottom of the WP housing) is also a press-fit. Yes, your local full-service shop (possibly NAPA) may be able to help, should you find that the seals seem "impossible" to remove. Experience helps a lot here.

Yes, all seals and o-rings needed come in the kit. It will require both dexterity and patience to change the small o-ring inside the cam rod bushing. We use a dental pick to pull the old ones, and a blunt drift to coax the new one into place.

Buffalo is in mid-winter (as you are). Typical temps are around 32 in the day, lower at night. Yes, lake Erie is about 1/2 frozen, so we still get a little Lake Effect precipitation. If it continues cold, and the lake freezes a bit more, the threat of LE snow will be gone soon. Last week's cold blast closed shhools and a few businesses (including mine) for a day.

If you get stuck, fee; free to drop me an email at the office; I am not there every day this time of year, but try to stay up with the emails.

HTH.

 

[TwoRivers]

Re: 25hp Nissan Lower Unit Leak?

Hope to find some time this weekend to start disassembling.
Will post progress or lack of progress to thread.
Thanks to all. Spring won't wait, better hurry.
Paul, please check your PM.
Rob

 

[TwoRivers]

Re: 25hp Nissan Lower Unit Leak?

This post is intended to report what I tentatively consider a successful lower seal kit and water pump kit installation.

Tentative in the sense that I think I put all those shims back where they came from?
I got interrupted halfway through and when I returned there were two extra shims that mystically appeared?
Anyways, since I wasn't sure where they went I figured I'd put them with the one shim that I was certain about, so it wouldn't be lonely.

After getting things back together I pressure and vac tested and the lower unit passed each test.
The cam rod moves up and down and the prop shaft rotates when I turn the drive shaft. What more can I ask for?

Thanks to all who responded.

All in all the job was not that difficult. There were a few times when an extra hand would be nice but I did it without physical assistance.
Anybody looking to do this get a manual and take your time. Especially, removing the old seals. I thought I messed up the lower water pump housing because I marked it up a bit removing the seal. I was holding my breath as I pressure and vac tested. Lucky it passed.

Got about six inches of new snow today so no tank test until temps rise above freezing but for now my leak is gone.

 

[4950cycle]

Re: 25hp Nissan Lower Unit Leak?

This post is intended to report what I tentatively consider a successful lower seal kit and water pump kit installation.

Tentative in the sense that I think I put all those shims back where they came from?
I got interrupted halfway through and when I returned there were two extra shims that mystically appeared?
Anyways, since I wasn't sure where they went I figured I'd put them with the one shim that I was certain about, so it wouldn't be lonely.

After getting things back together I pressure and vac tested and the lower unit passed each test.
The cam rod moves up and down and the prop shaft rotates when I turn the drive shaft. What more can I ask for?

Thanks to all who responded.

All in all the job was not that difficult. There were a few times when an extra hand would be nice but I did it without physical assistance.
Anybody looking to do this get a manual and take your time. Especially, removing the old seals. I thought I messed up the lower water pump housing because I marked it up a bit removing the seal. I was holding my breath as I pressure and vac tested. Lucky it passed.

Got about six inches of new snow today so no tank test until temps rise above freezing but for now my leak is gone.

I just resealed my early 80s Tahatsu "M 30 A" 30 hp lower unit. I thought the only difference between the old 25/30hp Nissan/Tahatsu and the newer lower units was one had a splined prop shaft and one (the old one) had a round shearpin shaft. I guess I was wrong ? Because I had only one big washer on my prop shaft inside the lower unit. You said you had three total. Hmmm..

 

[TwoRivers]

Re: 25hp Nissan Lower Unit Leak?

I only had one washer on the prop shaft.
I referenced that I had three shims.
The shims go between the bearing inside the driveshaft housing and the lower water pump housing.
Sorry for the confusion.
good luck and welcome to the forum.
rob

 

[4950cycle]

Re: 25hp Nissan Lower Unit Leak?

I only had one washer on the prop shaft.
I referenced that I had three shims.
The shims go between the bearing inside the driveshaft housing and the lower water pump housing.
Sorry for the confusion.
good luck and welcome to the forum.
rob

Thanks for the welcome, Are you talking about the shaft bearing race, the alloy lower housing (waterpump), and stainless steel plate with passage holes in it ?

 

[TwoRivers]

Re: 25hp Nissan Lower Unit Leak?

Thanks for the welcome, Are you talking about the shaft bearing race, the alloy lower housing (waterpump), and stainless steel plate with passage holes in it ?

I'm talking about shims.
They're listed as part # 9 on the transmission / water pump illustration.
Hope this helps?
Good luck
Rob