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ejlindahl 08-01-2016 20:30

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
1 Attachment(s)

The top of the bearing is at the level of the bottom of the vent hole. So, normally, if you fill the lower unit until oil is dribbling out of the top vent hole then this bearing is totally submerged in the gear oil. The rubber seal is just above the bearing and may get a little splash of lube as well.

However, in my lower unit, as I've explained in my other posts, the seal and bearing are sitting tightly against each other and thus completely block the vent hole.

I took the parts pictured in my previous post to the local Merc shop. The mechanic didn’t remember the intimate details of this model. Doubtless he’s worked on many of them over the years, though. He thought that the rubber seal had slipped down the driveshaft an 1/8" or so from its proper seated position and that is why it sits tightly against the bearing and thus blocks the vent passage. I think the seal was never pressed into its seat all the way to the stop and when the bearing was pressed in behind it, it snugged up tight against seal resulting in the blockage.

Now I have to decide if I want to try and get the drive shaft off of the bearing and then get a special (inside) puller to remove the bearing and then dig out the seal to see if the mechanic’s theory is correct. The other option is to throw it all back together with a new impeller and fill it as much as possible with warmed gear oil from the prop shaft end and just run with it for a season or forever….. I’ll let you know what I do, though I am leaning away from any more disassembly.

PS: In the middle paragraph of my post #12 I mentioned a mysterious squiggly figure, #16 in the exploded diagram of the assembly, (look at the first post to see the diagram). The mechanic said that is a section view of the seal. He explained that these ring-like seals are of the cup variety. I have seen similar seals in wheel bearings so the light immediately went off in my head as to what this seal looks like. This type of seal has a metal channel that forms a cup shape. Imagine you cut a slice out of an o-ring lay it on the table……you’d have just a small round disc. A similar slice out of this ring-like bearing is like an upside down “u”. The “u’” is steel and the inside and part of the outside of it is lined with rubber to form the seal against the spinning drive shaft. The squiggle in the diagram is this slice (section view) of this seal. The taller white part to the right of the squiggle represents the vertical drive shaft. The mechanic explained that the diagram simply is showing that the cup or “u” of the seal must face down when you install it in the water pump housing. I guess thats what being a pro means, he’s been there, seen that……… I’ll try and post a cut-away image of a similar seal from the internet but just google wheel bearing seal and you will see many or maybe this link will work.

PS#2. Ggray, good idea to see what the gear ratio is. Seems like many are interested in this. I gotta remember to do that as it should be easy with the lower unit removed.

Man this is turning into an epic for a small $250 motor, but it runs well and I love everything else about it.


tinkrman69 08-01-2016 22:34

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
if you fill the oil till it comes out of the hole at the top of the lower the pump'll blow the seals. lower units are designed to be filled to just above the pinion gear on the drive shaft, hence the upper screw on the housing. forget the assumed problem and put it back together and go boating.

as the shaft and gears turn the oil is forced uo that shaft log and saturate that bearing. that seal your are talking is a double seal sealing the water from one side and the oil on the other. if you are seeing a "squiggly thing in a drawing it's probably the spring that is in the inner side of the seal. also I have never seen a bearing pressed onto the drive shaft and any lower unit. no mater what size. even on High performance/racing outboards.

Sounds like your just looking for a problem. if it aint broke don't fix it.

ejlindahl 09-01-2016 00:34

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
2 Attachment(s)

Thank you for taking the time to help me out. Below is a thumbnail of the Merc Shop Manual. Although I understand about blowing a seal, I am inclined to follow its directions regarding how much oil to put in the lower unit.

The problem I have is real and it is that the oil level hole, (vent hole), you see in the attached thumbnail is plugged by a presumably improperly positioned upper drive shaft bearing and seal. This means I can not fill the lower unit in the normal way nor can I tell when it reaches the proper level. The need for special tools and the extra hassle to remove the bearing and seal (to truly find out and hopefully correct the problem) is a big deterrent. Its probably been this way for 20 years.

I’m pretty much to the point of doing as you suggest: Put it back together, Tipping it upside down and filling it with around 2.5 ounces of gear lube and call it good. (The manual says to put 3 fluid ounces in the non shifting lower unit and for the shiftable engine it says 2.5.)

Regarding the bearing being pressed onto the drive shaft: The lower bearing is obviously not because the drive shaft just slid out of it. The second attached thumbnail picture shows the upper bearing being hammered down onto the drive shaft. Not sure if this means “pressed on” but it sure is stuck on mine.

Thanks all for the help I think I have my game plan and it does not include fixing the problem,…. maybe later.

ejlindahl 09-01-2016 10:04

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
Can't edit the above post but when I said my solution/gameplan is to tip the lower unit upside down and fill it with 2.5 oz of gear oil I meant filling it with warmed oil in a large syringe thru the lower fill hole leaving space around the tip of the syringe so that air can vent out the hole. The normal way is as described in the thumbnail picture in my previous post.

Regarding someones question about the gear ratio. The shop manual says the 2.2 hp is 1.85:1 and the 2.5, 3.0 & 3.3 hp is 2.18:1.

Unless I disassemble the whole mess in the future to find the problem I think we're pretty much done with this issue. Hope it helps others.

donradcliffe 09-01-2016 11:12

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
Rather than trying to dribble warmed oil in through the lower plug, put the oil in a squeeze bottle with a tube or straw on the end. Invert the engine and get the tube down as far as you can and then squeeze.

I agree that the shaft bearing is out of place, but as long as it isn't rubbing on anything I'd fill with oil and use the motor.

tinkrman69 10-01-2016 08:35

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
Hi ejlindahl

It appears I haven't worked on this particular model. But with the blow up it looks quite simple.

is the lower bearing #2 seated in the bottom of the shaft log? is the spacer No. 11 installed alt he way and is it clean with no burrs? do you have the drift tool to set the upper bearing? it will also put the bearing in the proper place on the shatf, so it will rest on the spacer and not allow the shaft do set too deep into the pinion gear No 10 at the bottom. if you don't have the tool then install the lower bearing into the housing and install the shaft with the spacer and and pinion gear in place,making sure the shaft doesn't stick too far through the gear, it should just be visible from the gearbox side. measure or mark the shaft at the top of the spacer. then remove them and use a pipe bigger than the shaft and small enough to rest on the inner race of the bearing No 13 and tap it onto the shaft using lubricant on the shaft, till you've reached the mark on the appropriate side of the inner race of the bearing. place it in the housing and align the gear at the bottom, put the seal No. 16 in the pump housing No 17 making sure to seat it all the way in and that it is in the right direction. you can use the old seal to drive it in. install the housing, install the water punp and fill the lower unit with oil in the upright position. sense the need for a special tool to set the bearing there probably won't be a shoulder on the shaft to seat the bearing. this being said placement of the bearing during assembly is critical. the method above should get you where you need to be. during the measurement stage in the beginning make sure the shaft doesn't stick past the gear. it shouldn't stick past more than 1/32 of an inch. you should see wear marks on the splines to indicate where the pinion rides.

ejlindahl 10-01-2016 10:46

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
Hi Tinkrman,

Thanks for all the details. You've mentioned some nuggets in there that are not covered in the shop manual. Maybe I'll get around to fixing it right as you've described but since its been this way for 20 years I am just going to put it all back together and fill with the specified amount of gear oil as described in one of my previous posts. It's just too much hassle to figure out how to get my hands on the special gear puller for bearing #13 and everything else to do the job. Remember there was no problem with this motor until I went to drain and install new gear oil then I thought I'd post to see if other people had the same problem and what was the fix

In case you were wondering: There is no shoulder in the shaft log for the lower bearing #2 to be seated against. The shop manual says to hammer it down til about 1/8" above the bore of the prop shaft, then it says to test for drift with the pinion on the shaft by rocking the drive shaft back and forth while listing for the click of the gears contacting. Kind of hoky. If the drift is not right you have to pound the bearing thru the bottom of the log and try again. It must be seated correctly as it has worked just fine and I have not touched or measured it, ( I am at least the 3rd owner). The spacer #11 is just a sleeve and loosely fits on the drive shaft and the diameter of the bore it is in is ~1/4" larger than the spacer itself. So unless the upper bearing and lower bearing are set just right and pinch the spacer tightly, (no way to know that) it really looks like it just spins around in the bore and the shaft spins around inside the spacer. I imagine its all whirling around in there, (but maybe not if it is pinched just right by the upper and lower bearings). There are no burrs or wear marks that would indicate that this is anything but as designed.

Hears the shop manual I'm using that should shed more light on this:

Thank you for taking the time to help out. I have a plan of action now. Fair winds.

tinkrman69 10-01-2016 19:37

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude

no special puller needed for bearing 13. get a pice of pipe the same size or close as the spacer that can fit over the shaft and is as long as the shaft or longer and tap it down the shaft. make your measurements as described before and reinstall it to the specified location on the shaft. simple!

tinkrman69 10-01-2016 19:42

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
most special tools aren't as necessary as the manufacturer would have you believe. altho they may make a job a little easier, it's also a source of revenue, for them.

HappyMdRSailor 15-01-2016 05:17

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude

Originally Posted by ejlindahl (Post 2010401)

Man this is turning into an epic for a small $250 motor, but it runs well and I love everything else about it.


No kidding huh???

I think it would be eye opening if we actually calculated the amount of time spent thinking on projects like this...

Of course it doesn't count if you are relaxing with a beverage simultaneously...

ggray 29-01-2016 09:13

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
Have you gotten everything back to your satisfaction?

I may try to find the time to replace the impeller--after all, it is about 25 years old-- so maybe I'll have a better understanding of what you found inside.

I'm remembering something else about this motor. The tendency to snap shear pins when shifting into gear unless the motor is at a very, very low rpm. Lower than you would expect.

Have you had this problem? Many times, after warming up in neutral, I would shut off, put in gear, and then start again.

donradcliffe 29-01-2016 10:28

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
I had two of the Tohatsu 3.5 engines. The first one (bought in 1994) had no gear shift and went through shear pins until I switched to homemade SS pins. The second one was bought in 2008 with a F-N shifter, and still had the original shear pin when I sold it last year. However, the shift lever had to be replaced when it got caked with salt and had to be destructively removed. These motors were used over 200 days a year as my primary dinghy power source.

I never did figure out why the newer motor didn't break shear pins.

ejlindahl 30-01-2016 16:09

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
The saga continues:

Strange coincidence; I'd put this aside for the last 20 days (took awhile to get the parts), and only just this morning decided to put it all back together and lo and behold there are a couple new posts from yesterday. Here’s some feedback.

(The part reference numbers below refer to the thumbnail in my original post. They are different than what some parts sellers use! i.e. Iboats bearing part reference number may be 13 but Mercury Marine may have it as 11. Same picture, different number. So if you are following this closely you should use my thumbnail in the original post.)

On the 10th you described how to get the top bearing, #13, off the drive shaft. That is not the problem. My issue is that the bearing is stuck in the carrier portion of the water pump base, #17. I think (and the shop manual says) that I will likely destroy the bearing and or seal when this bearing and seal are removed. The manual says this even with their assumption that one uses the special tools.

Once out of the carrier, I'm sure I would have gotten the bearing off the shaft in the manner you describe. However, upon a second look at the shop manual with fresh eyes, and seeing how the sketches of the procedures are portrayed I now realize that they expect that the bearing just comes/pulls/drops out of the carrier easily with out having to hammer on it. No way on mine! On my unit I think corrosion has siezed the two together where the bearing is seated into the female bearing carrier area of the water pump base, (#17). The bearing is stainless steel and pump base is aluminum. This was the same problem for me getting the water pump base out of the lower unit casting. Took me several hours of carefully warming, wd40, tapping, cajoling, cussing to get it out, and yes there was just a small amount of that white aluminum oxide & corrosion in that interface too. (you don't need to do this to change the impeller or gear oil. I just wanted to see and fix why my gear oil vent hole was plugged.)

One cannot hammer the bearing, #13, out of the carrier with a correct size socket (or what ever mandrel you can devise). The diameter of the hole in the water pump base that the drive shaft goes through is only a few 64ths" larger than the actual shaft diameter. There is no visible lip of the bearing to hammer on. It needs a special "expanding shaft" puller from below to pull (or slide hammer) it out. You might be able to hammer it out with a screw driver at an angle thru the drive shaft hole but you will definitely ruin the bearing and seal doing that, (and run the risk of breaking the $85 cast aluminum pump base). Ages ago I removed a few bad wheel bearings and seals in this manner so I have an idea how it goes.


I found changing the impeller pretty obvious. The big caveat is to not completely unscrew the shift link clamp (and lose it) in the little hole in the exhaust housing. And though I haven’t got there yet I read that its a pain to get the shift linkage, drive shaft and water pump tube lined up to reinstall. A trick was to use some small wire to hold stuff as you slid it together. I found some threads or posts that discussed this, sorry no link though. If you need it here is a shop manual I found online. Boatinfo - Mercury Service Manual for 2,2-2,5-3,0-3,3 hp I don’t think you can download it or print from it but I have it on my laptop next to me in my shop. And I have printed some pages as screen shots but the illustrations and text are hardly useful. Maybe someone more techy can do this but that ain’t me

My impeller was really shot, just stub arms where the vanes used to be, and there was a thin layer of black rubber goo smeared inside the stainless steel cup insert that the impeller spins in. I took all the parts to the merc mechanic to answer a few questions, (he was very nice). He commented that when impellers look that burned up it is likely that the stainless steel cup insert (#23) that the impeller spins in has also, itself, spun inside the upper water pump housing (#24). There is a tang protruding from the bottom of this cup insert and it keys into the upper water pump housing. The tang normally prevents the insert from spinning inside the housing. But the friction of the melting impeller against the insert cup heats up the cup and housing and eventually the tang starts plowing its way thru that area of the melting/gooey plastic housing thus allowing the insert cup to spin, or at least rotate out of alignment. This creates a misalignment of the impeller/cup insert/housing assembly with the drive shaft. They are mounted a bit out of line in that the hole for the drive shaft through the cup insert is not exactly in the center of the cup itself. This is what makes the pump pump; the impeller kind of wobbles around in there in an eccentric motion as it spins with the drive shaft. (remember this is a new used motor to me, I never run my motors dry) So if they are out of alignment then it won’t pump as well and may create excessive heat and wear in a newly replaced impeller. It may also crack the plastic housing itself or put a side ways pressure on the drive shaft. It looks like mine might be ok, the mechanic said when they look like mine he not only installs a new impeller but replaces the whole pump housing. Of course we all understand why; a half hour of his labor is more than the cost of a complete rebuild kit and pump housing. Me, my labor is free and I like “taking apart stuff” and parts cost retail $$$ to me. I will use it as is and monitor the water pump flow. Having done this disassemble once I know i can do it again in less than an hour.

Shear Pin:

I heard/read somewhere of a guy that had an aluminum prop and was always breaking shear pins. A plastic prop solved the problem. I think he said there was an improvement in performance as the prop blades flexed to give more bite out of the hole and then as top end was reached it seemed to go faster, but don’t hold me to this. My prop is plastic but i’ve only run it 15 minutes before deciding to do some preventative maintenance and change the gear oil,,……. leading to this thread. Another guy with the same problem wrote, (maybe it was Donradcliffe) that he made SS ones to solve his shear pin breakage. I have a plastic prop and brass pins but just in case I made some extras out of same diameter brass bolts I had lying around. I’d be a bit nervous about subbing ss for brass pins. They are there for a reason…… but if it works……

I’ve spent so much time writing that I don’t know if I can finish the reassembly today. But will report back when I do.


ggray 30-01-2016 17:39

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
Yes, you have done a lot of writing!
Actually, I have the plastic prop, so that won't be a solution for me!
I'll just be careful.

karl m 24-11-2016 18:07

Re: Unable to fill the lower unit with gear lube on my 3.3 Mercury Tohatsu, Evinrude
Hi Ejlindahl,
Am joining this conversation very late, but am having the exact same problem as you. I noticed this thread as I was browsing for info.
Have you solved your problem, given up or other?

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