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9.9 Lower unit rebuild

Posted: Wed Nov 30, 2011 10:01 am
by Magic Time
I am about to conduct the rebuild of one of my 9.9 lower end units

This unit has had water leaking into the oil chamber and consequently water and then beige colored oil draining out when I change the oil from the lower unit. So I would like to replace all the seals.
I have reviewed the manuals that Phenix kindly posted. Unfortunately there is little guidance on the “ how to” in these manuals.

Please see photo a
Question 1
Is the ring with the two bolt holes the outside portion of the bearing housing or is it a separate ring holding the bearing housing in place.
Question 2
Regardless of whether this is part of the bearing housing or a separate ring retaining the bearing housing.
What is the best way to remove this or these parts from the main lower end casting?

If any one is aware of a posting describing this procedure please tell me how to find that post.

Re: 9.9 Lower unit rebuild

Posted: Thu Dec 01, 2011 7:00 pm
by amytom
Have a look at They have a pretty good series of exploded parts diagrams. The ring your talking about is part of the frame work.
Good luck getting it to come apart, I've tried on a couple and haven't been able to get them to budge. Keep us posted.

Keep in mind that a whole new lower unit is $725.00, how much is your labor worth to you? Then again if it's become a personal challenge I can completely understand.


Re: 9.9 Lower unit rebuild

Posted: Fri Dec 02, 2011 9:47 am
by duetto
that link that amytom put out on this is great!


Re: 9.9 Lower unit rebuild

Posted: Sat Dec 03, 2011 10:05 am
by thinwater
A factory manual (, never a 3rd party manual) is also worth its weight. The factory manuals are MUCH better. And after all, you have 2 of these engines.

I have found it very helpful.

Re: 9.9 Lower unit rebuild

Posted: Wed Mar 21, 2012 8:50 pm
by Magic Time
Ok so I am finally getting back to this repair.

Regarding the propeller shaft oil seal (in the Bering housing at the propeller end).
I have looked at two manuals, a Yamaha manual and a Seloc manual.
Both indicate the use of a puller to extract the Bering Housing out of the lower end housing.
For this to happen the Bering Housing will have to slide along the propeller shaft as it is pulled out of the lower end unit.
See photo A. Can any one confirm this process.
Regarding the oil seals below the water pump.
It appears that you must use a screw driver and pry the oil seal housing up the drive shaft by levering under the oil seal housing, up against the edge of the lower end housing.There seams to be only one spot on each side of the oil seal housing where you can get a screw driver under the housing edge to lift the housing.
See photo B. Can any one comment on this process.

Would be nice to hear from someone who has done a complete seal rebuild on a lower end unit but any comments are welcome.
Thanks for any assistance.

Re: 9.9 Lower unit rebuild

Posted: Thu Mar 22, 2012 10:33 am
by Allezcat

No,no,no! Don't try to pry this housing out. You must remove the pinon gear at the lower end of the driveshaft (inside the lower unit gearcase) and extract the driveshaft BEFORE you can remove this part containing the seal. I will try to get a photo for you. I have a lighly used lower unit I could sell you reasonably if you don't want to get into all this.


Re: 9.9 Lower unit rebuild

Posted: Wed May 23, 2012 10:21 am
by Magic Time
Lower End Oil seal rebuild continued

Ok so with a little help from a valued contributor, Chet thanks so much.
I will slowly continue the threads in this post. I hope that if someone else
attempts this repair these notes and photos will be of use. Note These notes photos are offered as a suggestion only. I make no guarantee that if the procedure is followed there will not be breakage. The amount of corrosion will be different on each motor that the repair is conducted upon. I had to repair two T9.9 lower ends This first one had about 6 seasons use and the next about 12 seasons on it. One was harder to disassemble than the other because of different degrees of corrosion.
You will see a good example of this later in the thread.

The Lower unit oil chamber is sealed around the drive shaft by two seals that are installed in the oil seal housing.
And around the propeller shaft by two seals that are installed in the bearing housing. There are also two orings on the bearing housing.
See the following link and look up the schematic of your motor ... s=outboard

Contrary to the last photograph you do not try to pry the oil seal housing out
until you remove the drive shaft.
To do this you must first extract the Bearing Housing.

I soaked the lower 10” of the lower end in a bucket of Double Strenght vinegar
for 3 days. I wanted to loosen as much corrosion or growth as I could because
I presumed that the inside flange of the Bering Housing would be scraping up
against the inside wall of the lower end casting
as it was extracted. If you have barnacles or other growth in that cavity
( the area open to the water) you need to get them out first. It turns out that there are
4 steps or levels machined into the inside of the lower end where the bearing housing resides so as you extract the bearing housing there is more space for it to slide out.
It is still best to have that water filled cavity as clean as possible before you attempt to take out the Bearing Housing.

Note remove all parts particularly the propeller nut from the propeller shaft
before you soak the lower unit in vinegar. The nut that was on my motor is brass.
It could be ruined by the electrolytic action of the vinegar.

I used a generic flywheel puller. It did not come with the 3 hooks,
I made them from 3/8 – 16 x 8” bolts. I bent, shaped and cut each hook. I heated and bent the bolt, holding it in a vice and hammered it over to make a sharp bend. About 92 degrees from straight ( so the finished hook is smaller that 90 degrees). I then squired off the inside angle of the hook with a file and them measured and cut the short end of the hook making sure it was just under ½ “ long. At this length the end of the hook should not scratch the inside of the casting as the hooks pull the bearing housing out. Make sure that the inside of the bend is squared off so that there is no fillet remaining in the bend.
You want to be as sure as you can that the hook is pulling up onto the thickest part of the housing (close to the wall of the casting and not on the thinner edge that is close to the inside of the housing where the hooks are sitting. On the second lower end I cracked that thin edge because the hook was pulling onto it. In inspecting the hook I found I had not squared the inside of the bend in one of the hook.

These three hooks need to be as Identical as possible.
The 3 hooks and center bolt on the puller, that is turned to extract the Bearing Housing must be kept in alignment with the prop shaft.
Photo 1 Extracting Bearing Housing

Re: 9.9 Lower unit rebuild

Posted: Wed May 23, 2012 10:24 am
by Magic Time
The amount of ft lb necessary to extract this part was significant.
The Bearing Housing will slide out of the cavity leaving the drive shaft stationary.
I heated the outside of the lower end casting with a propane torch in an exempt to make it expand. I then turned on the puller a little. Then tapped hard onto the top of the puller bolt with a steel mallet. I did this until I saw a gap between the lower end casting and the Bering Housing. I applied a good penetrating oil all around and let it soak into that gap for a half hour.
I did not want to brake any parts so I took as may precautions as possible.
I continued with the same process as above until the Bearing housing felt like it could be lifted by hand ( This should be when the red oring is visible ). Remove the wheel puller and gently extract the entire assembly by pulling the propeller shaft straight out of the casing.
Photo 2 Bearing Housing extracted.

Re: 9.9 Lower unit rebuild

Posted: Wed May 23, 2012 10:28 am
by Magic Time
Note the Reverse gear may fall out of the bearing housing if you lift it alone. There is a very thin shim that goes on the reverse gear. It could be lost or damaged or the gear damaged if it falls out of the housing. My reveres gear was loose. Luckily it only fell into the in side of the casting back down the prop shaft.
Photo 3 prop shaft with reveres gear.

Re: 9.9 Lower unit rebuild

Posted: Wed May 23, 2012 10:32 am
by Magic Time
Photo 4 of the Prop shaft with it components in order of assembly.

Re: 9.9 Lower unit rebuild

Posted: Wed May 23, 2012 10:35 am
by Magic Time
At this stage I will set this aside and concentrate on removing the drive shaft so I can remove the oil seal housing that is under the water pump.

Here are a few preliminary photos.
Photo 5 Lifting the water pump housing.

Re: 9.9 Lower unit rebuild

Posted: Wed May 23, 2012 10:50 am
by Magic Time
Photo 6 Below is the housing gasket on top of the stainless steel (Outer Plate) plate that sits under the impeller.
6 outer plate.JPG
6 outer plate.JPG (152.64 KiB) Viewed 13758 times
Photo 7 Below is a photo of one of the lower end Oil Seal Housing after I removed the stainless steel ( Outer Plate ) plate from under the impeller.
Clearly you should remove and clean under this plate when replacing the impeller.
Clean area before you remove the Drive Shaft
7  dirty pump chamber.JPG
7 dirty pump chamber.JPG (110.26 KiB) Viewed 13751 times
Removing the Drive Shaft
Note in the photo below ( Pinion nut photo) in the middle of the large gear you can see the end of the “shift plunger” . This part may be where shown or it could be in the end of the propeller shaft It is loose and can fall out and be lost. Also in reassembly the square end goes into the end of the drive shaft the round end towards the shift leaver.
Photo 8 Below is a photo of the Pinion gear nut that is at the bottom of the drive shaft.
8 Pinion gear nut.JPG
8 Pinion gear nut.JPG (141.69 KiB) Viewed 13746 times

Re: 9.9 Lower unit rebuild

Posted: Wed May 23, 2012 10:58 am
by Magic Time
To Remove the nut.
I tried unsuccessfully to find a tool that Yamaha calls a “drive shaft holder”. Yamaha part number YB-6228 . The dealer that I spoke to could not find one of these for me. He suggested I us a vice. I used one with no teeth and wrapped the shaft with a rubber bike tub to stop it from slipping or the vice from scoring the shaft.
This worked but I recommend finding the correct tool. If anyone has this tool and is willing to lend rent or sell it please contact me. I would use this when it comes time to torque the pinion nut back on.
After loosening the Pinion nut I carefully feed the nut, gear, and all the associated washer, bearings, shims over a long twist tie as they came off the drive shaft. This way I was sure to remove all parts in there correct order.
Now you can pull out the drive shaft from the oil seal housing.
Remove the oil seal housing by using two screw drivers and simultaneously leaver the oil seal housing upward. Place a small 1/8” thick shim between the screw driver and the edge of the lower end casting before you pry. This is so that you are applying force with the screw driver inline with the casting and not at an angle to the edge. If you do not us a shim you may collapse the edge of the casting. Tape a shim to each screwdriver if needed

Photo 9 Removing Oil Seal Housing.
9  Removing oil seal housing.JPG
9 Removing oil seal housing.JPG (137.48 KiB) Viewed 13738 times
Photo 10 Oil Seal Housing Removed
10 Oil seal housing removed..JPG
10 Oil seal housing removed..JPG (148.61 KiB) Viewed 13727 times
Clean all old gasket material and corrosion from the oil seal housing and from the lower end casting. I used a large xacto knife then 320 wet dry. Make sure you keep the matting surfaces parallel and flat.

Note The photo below shows the Drive shaft Tube (oil stained plastic tube) that is in the lower unit, under the oil seal housing. It is loose and can fall out. If it does make sure that you reinstall it the same way it came out. On my motor the little tab on the edge of the flange ( on left side of flange in this photo ) is facing back towards propeller.
Photo 11 Drive Shaft Sleeve
11 Drive shaft sleave.JPG
11 Drive shaft sleave.JPG (142.49 KiB) Viewed 13735 times

Re: 9.9 Lower unit rebuild

Posted: Wed May 23, 2012 11:00 am
by Magic Time
A question to forum readers who may be versed in the details of marine engine repair.

In photo below, of top of oil seal housing.
The water channel in this housing has some damage. It is rather deep but the basic shape of the circular chamber is intact.
If I can replace the two seals with out further damage, can I use this part or should I replace it. I intend to paint it with Zinc Chromate primer. To help protect the aluminum.
Is there a paint that I can spray on top of the Zinc Chromate to further protect the surface.
Photo 12 Damage to top of Oil Seal Housing.
12 Damage to top of oil seal housing.JPG
12 Damage to top of oil seal housing.JPG (146.17 KiB) Viewed 13730 times
Any opinions regarding the above questions would be appreciated.
Or if anyone has some tips that would help make the disassembly process easier please add them to the post

Re: 9.9 Lower unit rebuild

Posted: Tue Jun 12, 2012 9:49 am
by Allezcat
Magic Time,
What a great posting! Thanks for all the photos and comments. As to the housing (casting), I would replace it after all the effort to get to it.
I also would add a freshwater flush fitting to the exhaust cover plate on reassembly, but thats another whole project.