6 HP Tohatsu 4-Stroke Driveshaft binding

[MILLSMAN]

I have a 2012 Tohatsu Long Shaft Sailboat motor that has a severe binding issue. You can't pull the start cord with the spark plug out and lower unit removed. I can turn it with a wrench on top with difficulty. Thus, I removed the power head, then cylinder head. Cylinder head and piston bore looked fine. Removed the 2 nuts holding the crankcase head (part # 47 on the cylinder and oil pan diagram) and this is where the binding is occurring. I can easily turn the driveshaft while the crankcase head is moving, but very hard to turn if I hold the crankcase head and turn the driveshaft. Trying to remove the crankcase head but it does not want to come up on the driveshaft. I could cut it off and buy a new one, but thought someone might have experience with this already and inform me on what to do???? No history on the motor, just trying to resurrect it

 

[MattFL]

Is the drive shaft binding inside part# 47 and that's why you cannot pull it off? Not knowing the history, maybe it's packed with old grease or corrosion. If you can somehow pull on part# 47 have the shaft spinning but part #47 is not spinning then that may let you slip it off. You might soak it with something like WD-40 and maybe put some heat on it to see if you can get it to free up enough to come off. Or maybe try a 3-jaw gear puller to pull it off of the shaft? Or a slide hammer, BUT be careful with the slide hammer as you don't want the shock to go through the drive shaft and damage the lower unit. Edit--> One more idea, you can hang it by part #47, from a vise or something (not clamp, just hang) and tap on the shaft with a punch or socket wrench extension and a hammer and tap the shaft out that way.

 

[Sea Rider]

If the motor is used in salt water the lower crankshaft will bind and seize against the crankcase head (47) specially if the lower leg remains sitting in salt water for long time periods without motor use.

The round portion of the internal head and the upper drive shaft as well should be well gresed with marine grease from time to time to avoid that issue, but no one does so. In 2 strokes motors will need to split open the crankcase, remove the crankshaft, soak the lower portion in penetrating oil, WD-40 to soften the salt contents and pull it out. Don't know about 4 strokes motors.

If plan cutting the head and replace it for a new one must add 2 oil seals, one spacer and a head gasket if the old one is shot. Around $ 47 in parts.

Happy Boating​

 

[MILLSMAN]

Thanks for your input. Yes, it was used it salt water. Might have been submerged at some point. Been putting a lot of WD40 on it to try to loosen. Will continue to work at it.

 

[pvanv]

The driveshaft is attached to the LU. So do you mean the crankshaft is hard to turn? I assume this is on an MFS6C.

 

[MILLSMAN]

The motor is a MFS6CS. It is a long shaft SailPro. When I received the motor the lower unit and spacer were already off the motor. The driveshaft was out of the lower unit and connected to the crankshaft. It does not want to come out of the power head???

 

[MattFL]

Here is an image with my understanding of the problem, in case it helps. @MILLSMAN please correct me if this is not correct:

 

[MILLSMAN]

That is correct. The driveshaft is stuck in part 47, and also stuck in the spline shaft of the crankshaft. Here is a pic of my predicament.

 

[MattFL]

Ahhh that helps. Will part #47 rotate independently of the shaft at all, or are they locked together? If it will, try to slide that off while spinning it to at least get that part out of the way, and that may also get you better access to the end of the crank shaft so you can get some penetrating oil and heat in there.

 

[MILLSMAN]

Yes, I can put vise grips on the shaft and rotate 47 with another pair of vice grips but it is binding a lot. If I rotate the shaft with vice grips it and part 47 turn easy along with everything else. I was only able to pry up part 47 only 1/32 of an inch or so. Shot some WD40 on the shaft hoping to help free it from the crank. The one thing I did not see in any of the diagrams is a bearing on the lower part of the crankshaft??? Thanks for all your help and your quick response.

 

[Sea Rider]

The motor must have a seizure between the drive shaft upper splines and the lower crankshaft internal splines along a salt build up seizure under the splines against the 47 internals.

Happy Boating​

 

[MILLSMAN]

Yes, I agree. What "I think" happened is that at one time the motor was submerged thus causing the salt inclusion to occur. I will continue to try to remove #47 and its contents but may end up cutting it off and buying a new #47 and all the contents, which I will have to buy anyways.

 

[MattFL]

If you cut it off, you've still got to get the top of the drive shaft out of the crank shaft, so I'm not sure if you're really in a much better position. My best suggestion would be find some guys who know metal really well, maybe some machine shop guys, especially a a shop that is familiar with marine stuff. Maybe ask them for any tips or tricks to get them apart. With any luck maybe a local shop will have dealt with that before and can separate it for a few bucks and save you some money in the long run? It would help to figure out if the shafts are stuck together due to salt getting in there and locking it up tight, or if the metal has corroded together and essentially welded itself. If it's just salt, maybe something like Rydlyme would help eat it away, if you can get it in there?

 

[Sea Rider]

Remove both lower 47 bolts, spin flywheel with hand, if nothing turns there's a huge seizure between crankshaft/drive shaft and 47. But if 47 spins freely the seizure it's between the crankshaft and the drive shaft. The upper 47 has many rubber oil seals such as 13-48 that will be difficult to bind against the crankshaft compared to the 47 against the drive shaft.

Happy Boating​

 

[MILLSMAN]

Well, finally got the driveshaft out and separated from the crankshaft. Took some prying and lots of WD40 but "got er done". Destroyed part 47 in the process but I figured that would happen anyways. Now the driveshaft goes easy in and out of the crankshaft. Crank and all connected to it spins easy. Just need to order gaskets and part 47 and all its contents. I had driveshafts seize before in the crank splines. Guess the rust expands and seizes everything. Next time I will push some HCL (hydrochloric acid) down the shaft and hopefully it will dissolve the rust.
Thanks for all your help and suggestions ............................Millsman