Mercury 250 optimax breaking driveshafts.

[Chaz]

Did you let my kid drive it .. ?

With the instructions .... go have fun ...

[Fishinmymission]

What powerabout said makes sense if it's possible to bend the mid. No idea what it would take to bend the mid.

[flabum1017]

What powerabout said makes sense if it's possible to bend the mid. No idea what it would take to bend the mid.

or a loose powerhead.............. NCGNick.... check the torque on the powerhead bolts and nuts.....

[David Borg]

Once had a customer with the same issue, turned out to be a bad lower crank bearing . Not saying yours has a bad crank bearing as it could be alignment as others suggested but stating from experience

[Fishinmymission]

I have a hard time believing a rough trip could bend a mid. Nuts torqued to factory specs also shouldn't come loose. Crank bearing failure sounds most logical so far as long as the lower unit is all new. Especially if it's the exact same failure position and mode the worn bearing could be the source of misalingment. Might be worth it to pic up a used fishing lower unit on ebay this will rule out anything getting bent in your lowercase if you break another shaft. If you break another it will be under 10 hours and it might be worth checking out the powerhead. If you got the time to take the power head off and check the bearing you can do that but it's alot of work if that ends up not being the issue.

[Capt.Insane-o]

If anything was bent it would be wearing the drive shaft splines.

[flabum1017]

Nuts torqued to factory specs also shouldn't come loose.

Guess you don't remember or weren't around when Merc had a bunch of powerheads coming loose, so common in fact, they had a service bulletin addressing the issue. If memory serves right, it was due to the thick gaskets compressing. Just because it's "factory torqued" does not mean someone didn't screw up at the factory..... Remember the Lemmonrude loopers and the loose reed boxes due to the Mexicans dipping the screws into the permatex and creating a hydrolock that prevented the screws from being able to go in far enough?

[flabum1017]

If anything was bent it would be wearing the drive shaft splines.

Agreed, but he also has not been able to put a whole lot of time on a shaft before it breaks......

[Fishinmymission]

Design screw up such as gasket compression could be it if that was a known issue for the motor. I wasn't aware of that and always good to think outside the box. I'll commonly see a taper in the spline wear when I'm documenting failed drive shafts at work. If you see it and the splines/shaft are designed properly and the steel is the right strength it's a dead giveaway to misalignment. Problem is there are other times where I suspected misalgnment for other reasons yet spline wear was more uniform.