snapped driveshaft Mercury 2011 150 Optimax

[the_dude]

So this is the second driveshaft I've snapped. This time I was 42 miles offshore so it was rather inconvenient. My last driveshaft was 2 years ago and I put over 1000 miles on this one. Any ideas as to why my motor is eating driveshafts? I put a brand new lower on this time and it still broke.

 

[alldodge]

What was the boat doing when it happened?
If the prop came out of the water and rev'ed high it will break things when it comes back in the water

 

[racerone]

Exhaust housing might be bent.-----Which means engine block and lower unit are not aligned.-----Driveshaft is flexing and eventually breaking due to fatigue.

 

[Faztbullet]

Where is it breaking at? Pinion or upper DS bearing?

 

[the_dude]

It's breaking right inside the water pump. I did hear the motor come out of the water on our way out, maybe twice for just a fraction of a second. We pushed straight into some steep chop for a while.

 

[alldodge]

The coming out of the water is what's doing it.

The offshore racers has a dedicated throttle man, he pulls the throttles back every time a prop rev's increase above spec. Even those guys will break things when the props rev up and then hit the water again

 

[Scott Danforth]

They have hard-cut rev limiters that will kill or significantly stumble the motor until you return to neutral to keep from breaking things.

Cryo-treating the shaft will help, however you may start taking out gears

 

[QBhoy]

What kind of prop pitch you loading her up with ? Is she on a fast hull that might have shock loaded a high pitch prop when in a state that the prop came out, then reentered the water ?

 

[Faztbullet]

That has the non ratcheting lower so it is a lil less forgiving than the ratcheting models.

 

[tphoyt]

We used rev limiters back in the day.
May be worth looking into.

 

[the_dude]

Prop is 3 blade 15x17 black max. Hull is Bayliner 21 center console. I don't think it's particularly fast. It appears that SEI is going to warranty the lower as it has only been 2 years.

 

[tphoyt]

That’s great news

 

[tphoyt]

I’m not sure what rev limiter are running these days when I was using them it was back in the 80’s on Johnson 235’s and they weren’t terribly expensive then. We were running off shore races a lot and they worked well by bringing the rpm’s down before hitting the water again. Man I miss those days.

 

[QBhoy]

I’m not sure what rev limiter are running these days when I was using them it was back in the 80’s on Johnson 235’s and they weren’t terribly expensive then. We were running off shore races a lot and they worked well by bringing the rpm’s down before hitting the water again. Man I miss those days.

Sounds like a great experience there…
These optimax engines have a rpm limiter built in. Usually around 100-150 rpm above the max rpm range figure.

 

[Chris1956]

I have heard of Johnnyrude V4 engines snapping their driveshafts, but never a Merc.

Hopefully there is some underlying misalignment of the driveshaft or bearing issue. If not, I consider the design of the DS to be poor engineering, if the OP's boat/motor combo would snap a driveshaft. They could make them 1/8" thicker and eliminate the issue for us recreational boaters.

My speedboat (Merc V6) gets launched all the time, and I have never had a failure. I have run aluminum and SS props of 21 or 23" pitch w/o issue.

 

[Faztbullet]

Just a matter of time and right condition Chris...they all snap. Yours will be at the pinion. Stock 3L break under water pump, Torquemasters at pinion

 

[Chris1956]

Fazt, I guess I am naive, but I do not think the driveshaft should be made so close to power output tolerance that it would ever snap. It is a big dumb piece of SS. Make it a bit stronger and eliminate that issue,

 

[Faztbullet]

Tis combination of stainless and nickel and is heat hardened at pinion bearing. They snap right above heat treat, just take right rpm and shock to gearing

 

[the_dude]

The service tech said it would take 5 days for a rebuild. Well they didn't rebuild it, they sent me a brand new lower. Pretty stoked on SEI.