tohatsu 9.8 corrosion on vertical shaft (new thread)

[J_Grove]

hello, new poster. A lot of times, people new to forums encounter "have you tried the search function" when posting questions that have come up before. This old thread https://forums.iboats.com/threads/tohatsu-9-8-corrosion-on-vertical-shaft.641202/ described my situation pretty well so I simply replied to it and then got shut down. Apparently replying to old threads is a no-no here. That must be why they keep them open instead of archiving them, so people can reply to them and get shut down and learn the rule. Got it.

I have a 2003 Tohatsu M9.8 that came on a boat I got last summer and I'd really like to keep going. It runs well and I replaced the water pump right after I got it. Unfortunately I just discovered that the steering shaft is very rusted and corroded. The motor provides aux power for my sailboat, a 27 ft trimaran and the corrosion is bad enough that I'm concerned about continuing to use it before I replace this shaft.

It looks like if ordering the part (3B2Q620100) you don't just get the shaft, you get the yoke (is that right word?) as well, in a single relatively large assembly. Unfortunately Tohatsu USA no longer carries the part. I found a marine store in Japan on e-bay that sells the part new for $200 shipped. Ouch! But I want to keep the engine bad enough that I am considering it.

What is involved in just replacing the shaft? How is the shaft connected to the yoke? If threaded, can I get a 1/2" galvanized pipe, have a machine shop thread the end and drill the holes, and just replace the shaft? Is it going to be a nasty job trying to get the old one out? Doesn't seem like it should be that easy, otherwise why does the part come as a single assembly?

Regardless of whether I find and buy the complete assembly, or just try to fabricate a new shaft, what is best way to get it apart? Sounds like from this thread you can come at it from the top (remove engine head) or the bottom (lower unit), and that coming at it from the bottom would be the easier way. I have some experience with that since I did the water pump a few months ago. So I have some basic mechanical ability but the water pump job took me a few hours so I'm definitely a novice.

Any advice or recommendations appreciated.

 

[J_Grove]

Here is a pic of the current shaft after I knocked off the large flakes of rust. I should replace this right? I only ask because the motor turns fine, which seems to be what drives a lot of these repairs. I'm just concerned about the long term structural integrity.

 

[Sea Rider]

Been there, had no idea how much corrosion had already formed there before removing the complete steering shaft from the swivel bracket assy. To access it will need to remove lots of parts, it's a time demanding job.

The steering shaft cost it's around S 190 bucks including local shipping to your address, no need to order it from Japan. In my particular case ended scraping the entire thick shaft with a metal file and hours of priest's patience. Check : https://forums.iboats.com/threads/c-19-lockdown-doing-tricks-to-motors.736675/ Posts 8-12-13 to have an idea on what will encounter.

Grease well the entire steering shaft, the swivel's bracket interior and both plastic steering bushings with marine grease whether replacing for new or not. Hope you don't break any bolt that locks both side bracket mounts in place due to salt seizure.

Happy Boating

​

 

[pvanv]

The part is about $177 retail, but out of stock in North America. It is serviced as an assembly. I would do as Luis suggests and clean the old one and see how that goes.

 

[gm280]

Not familiar with the part. Is it merely a solid shaft with nothing at either end? If so, have a machine shop turn one for you. Heck even if it is a special part with threads and/or other things attached at either end, a machine shop could reproduce one I'm sure. And maybe get a stainless steel version as well...

 

[Sea Rider]

The steering shaft it's a splined hard thick tube inlaid under the swivel bracket assy. Better file the current one to a smooth condition, won't be possible to remove existing nicks, severe pittings on the tube. Be aware that when the steering shaft is removed will find the swivel's bracket interior extremely salt crusted, pitted, you name it.

After cleaning well and greasing both assys with marine grease install 2 new upper and lower bushings, yours will definitely be found shot and with excessive side play which is normal due to use.

Once all previous removed parts are assembled back, bolt the steering shaft/swivel bracket assy at middle leg with greased bolts. If wanting the outer steering shaft and the swivel bracket interior to remain in a much healthy cond, fill the internal SW with marine grease with a grease gun.

Happy Boating​

 

[J_Grove]

Thanks for all the replies while I was away over the holiday weekend.

It sounds like I have two options. Replace it, or don't replace it.

To replace it, I have the option of getting the part new, which is not in stock in North America. I can get one from Japan, or wait for them to be in stock in NA. The other option is to just make the shaft. I have been chatting with a couple of guys who have sold these parts reconditioned on e-bay who have told me how to do it. Or have a machine shop make one. I feel like there is a lot of risk in this of taking a motor that works and turning into one that doesn't work. Seized/broken bolts, not being able to get it apart or back together with my skills (guess I should track down a factory manual), and if making one, separating the old shaft from rest of assembly and getting the new shaft in right with holes that will line up.

The other option is to not replace it. Sea Rider your description of the job about cleaning and greasing seems like it might make my current shaft last a bit longer, but the goal there is mainly about removing the play in the shaft and making it turn better. I have some play but it turns well, perhaps past owners kept did a good job keeping it greased. So if I go this route, I think I'll just leave it alone as much as possible. The risk here is that this motor is asked to push a 5000 lb boat at 5-6 knots in and out of harbors and channels, and while there isn't usually much pounding from waves, it's hard to say how far away from catastrophic failure the current shaft is.

Decisions, decisions ...

 

[J_Grove]

Well, I found the Tohatsu Service Manual and downloaded it. Unfortunately "steering shaft" doesn't turn up in a search of the document. The closest seems to be a section on removing the stern bracket. I don't have a tiller on this motor (I have rigged my own system that turns the motor when I turn the sailboat's tiller) so that may save some work, but I still don't have a clear idea or instructions on how many/what parts I will have to disassemble to change the steering shaft.

 

[pvanv]

The Tohatsu Factory service manual is copyrighted, so finding an electronic copy would be rare.
Look at the parts catalog to see how it all goes together.

 

[gm280]

Since this part is splined, a good machine shop can help in a few ways. Any quality machine shop can easily do splines. Not as difficult as one would think. However, they can also turn down the rust and then weld up material to bring it back to spec as well. So you have many options. The money is the determining factor, not lack of options... JMHO

 

[J_Grove]

thanks for the replies.

pvanv, it's an official service manual. Since it's copyrighted, I won't repeat link here.

gm280, thanks for reminding me of some of the options. However, most if not all seem to involve a large disassemble and reassemble job. Screwing that part up is what concerns me more than the money factor.

Can anyone look at the pic in the second post and say either 1) that shaft is likely to go at any minute, or 2) that may look bad on the surface but this part is overengineered and there is still plenty of life left, ?

Not looking to hold anyone liable for some opinion I got off the internet, just wondering from guys who have seen a lot of these, how bad is it?

 

[Sea Rider]

To have it clear, does the steering shaft has already been removed ? The posted pic doesn't say much to make a correct visualization, interpretation.

The steering shaft is tough steel, the wall is around 3.0 mm thick, won't break diving the motor into the deep blue anytime soon.​

The steering shaft is supported at both extremes inside the swivel bracket by two tall hard plastic bushings so there's no metal to metal rubbing at both extremes nor at middle bracket in between both mentioned parts.

Happy Boating​

 

[Sea Rider]

Assume the motor it's a tiller one ? If so to ease the tiller load, there's a nut with a spring as seen in second pic under a small red square, turn it CCW till the tiller rotates freely sideways. When the lower bushing wears too much along working with hardened grease, the lower leg will tend to lock itself in place when the prop pushes forward, quite normal to happen under such condition.

Happy Boating​

 

[J_Grove]

Assume the motor it's a tiller one ? If so to ease the tiller load, there's a nut with a spring as seen in second pic under a small red square, turn it CCW till the tiller rotates freely sideways. When the lower bushing wears too much along working with hardened grease, the lower leg will tend to lock itself in place when the prop pushes forward, quite normal to happen under such condition.

Happy Boating​

I don't have a tiller on the motor, or steering cables. I have a system rigged with a series of blocks and lines that lead to the tiller on my sailboat, so when I turn the sailboat tiller, the motor turns. Turning was difficult because the friction screw you describe was very tight, and couldn't be loosened because it seized and then I broke it off. So I had it drilled out. The motor turns easy now so I haven't had any problems related to corrosion of the steering shaft and old packed grease making it hard to turn.

The picture I posted is of the steering shaft. I have not taken anything apart so that photo is the only part that can be seen when everything is still assembled. It is very helpful when you said that the shaft is about 3 mm thick because I wasn't sure how thick it was. I have clear lost 0.5-1 mm in thickness to rust but I think the shaft still has a good bit of thickness to it. I also talked to someone on a sailboat forum who replaced the shaft when he got cracks in the clamps that hold the shaft in place at the bottom. He recommended avoiding doing this job unless the shaft actually breaks because it is a very involved job that may create new problems. And he thought it is highly unlikely that the shaft would break because even with rust it is thick and hard and the shaft under the bushings may be somewhat protected from rust.

For these reasons I have decided "if it ain't broke, don't fix it" and am just going to clean the rust offthe shaft the best I can, coat it in grease, and put the motor back on the boat. Thanks for all the replies that helped me make this decision.

 

[Sea Rider]

Wise decision as there's too much handwork involved removing many parts from the motor to access the steerig shaft in order to pull it out the swivel barcket, other related problem will be to come across many seized bolts that will eventually break in place when being removed.

If the swivel bracket still has the grease nipple installed, fill the entire bracket with marine grease using a grease gun to avoid further corrosion, pitting.​

Happy Boating

 

[J_Grove]

Got another question on the same engine that's the same kind of question.

While I've got this motor home and am trying to do all the maintenance I can to get more years out of it, I thought I would change the shaft oil, or at least check it. But both the top check/fill screw and the bottom drail screw are corroded shut. I bought a bigger screwdriver, penetrating overnight with Blaster, applying a hear gun to it, ... assuming this effort is unsuccessful.

Do I need to take it back to the machine shop and let them get these screws out so I can change this oil, or just leave well enough alone? The motor works fine and shows no signs of leaking, but I have no idea how old the shaft oil is.

 

[J_Grove]

never mind, got them free!

 

[Sea Rider]

never mind, got them free!

The lower leg oil should be replaced at each max 100 worked hours, can use any car gear oil 80-90 grade along 2 new drain plug's gaskets install.

Happy Boating​