tohatsu 3.5 outboard fault

[CliveG]

On Friday evening I was about to remove the outboard from the tender prior to leaving the mooring.
I shut off the fuel with the engine running to allow the carb to empty.
As the fuel ran out the engine revved up and then stopped suddenly followed by a rumbling noise.
On pulling the starter cord the engine did not turn over and there was the rumbling noise again.
Carried on with the weekend plan as we where heading for a marina and would not need the outboard.
Had to row ashore on our return to the mooring.

Investigated the fault last night.
Having removed the engine covers and the recoil starter box i found that the not holding the flywheel on to the top of the crankshaft had come lose.
the woodruff key between the flywheel and the crank had sheered.
i suspect that the nut had been lose for some while as the part of the key left in the crank appeared to be necked in.

I you have on of these motors I would advise that you check that this nut is tight.
I believe that there are quite a few outboards of the same design with different names on them.

 

[sailorman]

thanks Clive good engines Eh

 

[cliff]

That is the first one I have heard of with that problem. I have run Mercurys (same engine) for years and not had any problems such as you describe.

Has the engine ever been serviced? flywheel off?
--------------------

"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[hollandd]

i had the same problem when mine was 6 months old it was fixed under warranty, iwas told it was a known fault

 

[CliveG]

The engine has not been serviced whilst I have owned it.
Got it this time last year.

I think that I will put a star washer under the nut when I put it back together.

 

[Lakesailor]

Don't do that. You should tighten the nut with a torque-wrench to the specified torque. That stretches the threads just enough to lock them. A star washer will interfere with that process and the flywheel will come off at some later stage.

 

[VicS]

[ QUOTE ]
Don't do that.

[/ QUOTE ] Put some Loctite on the thread maybe?

 

[Lakesailor]

That would be a good back-up. The theory is that the taper on the crank and in the flywheel form an immovable interference fit.
That's why it's so difficult to remove flywheels.
It may just be worth using some valve lapping paste on the joint and grinding the flywheel (less the woodruff key) to the crank before fitting.

 

[CliveG]

Thank you for the advice.
Any idea on the torque needed?

 

[Lakesailor]

In short, no.
It depends on the thread size and pitch and the material of the crank. I'd risk it at 80-100 lbs/ft if it were my engine. You really need to find out from a manual. A dealer may tell you, perhaps?
If you have much engine building experience and us a ring spanner or decent socket strong arm, you should be able to judge when the threads are starting to pull. It's unlikely you could overtighten it as it's pretty hefty and holding the flywheel to create resistance is likely to be the limiting factor. Like Vic says some Nutlock would help keep it on.

 

[CliveG]

Thank you Phil

I have got a replacement Woodruff key and some locktight.
I have built a few mini engines in my time so I have a feel for tight and too tight.
I won't try to go as tight as a Mini Flywheel!