Snapped driveshaft

[Brendann99]

So I'm breaking in the motor...still only goin max 90% throttle. Everythings goin fine when boom. Instantly not moving and the motor just seems real rough.

So I get towed back to the ramp pull it out take the jetpump off and see that my driveshaft is snapped in two. I can still move the impeller with my pinky finger no problem. So it leads me to believe it was just bad luck? But it also seems strange and makes me wonder if there is another problem. How easy should this impeller move? And anyone have any experience with snapped driveshafts?

Edit: Engine runs fine once the drive shaft was pulled out.

 

[Bills86e]

Metal fatigue. I'd go thru pump since its out, just to rule out this happening again.
I also recommend an engine alignment. A probable cause.

 

[Brendann99]

engine was just aligned 2 weeks ago when i dropped it in. i'll prolly have the local marina take a look at the pump. But other than that i'm kinda stumped. I'll prolly just replace it but hate to miss something.

 

[scooper77515]

I would guess you sucked something up. Those splines are toasted. Even if you impeller spins freely now, there was a brief period when it DIDN'T!!! Something got in there and stuck for a second, and snapped that shaft while you had some torque on it.

Those splnes look like they did their best to hold up, but failed. Well not really, the shaft snapped and the splines just got bent out of shape.

I think you can toss in a new shaft and be back on the water. Just bad luck sucking up something tough.

Check your wear ring.

 

[Brendann99]

That would make sense about maybe suckin something up.

Tho the splines seem ok to me. I don't have a new driveshaft to compare but they seemed ok. That creamy brown stuff on there is grease.

I'm just gonna get a new driveshaft and go with it.

 

[scooper77515]

Maybe the grease is making an optical illusion making it look like there is some twist there. If you have it in hand and don't see the twist I am seeing, then they are probably OK.

 

[captain scale]

Look for clues of something entering the grate and hitting the shaft or impeller. You'll see some nicks or maybe even some bent tines on the intake grate. My brother once sucked up something that hit the impeller, jammed it and it started to unscrew off the impeller shaft, then it forced the driveshaft towards the front of the ski and twisted up but did not snap! Looked like a pretzel! The crooked impeller finally dug into the fiberglass hull and locked everything up!

 

[Brendann99]

If i flick the impeller with my finger should it be easier to spin or is this normal?

http://s776.photobucket.com/albums/yy43/Brendann99/?action=view&current=VIDEO00041.flv

Obviously a motor would have no problem spinning this. Just racking my brain over what could have cause the driveshaft to snap. There's no evidence of impact or anything getting stuck on the impeller.

I am going to recheck the engine alignment. Make sure a mount didn't come loose and it shifted or something...

 

[captain scale]

A loose or broken mount could definitely cause that! More likely 2 mounts on the same side!

 

[1970_mgb]

Bill is right its a fatigue failure

I am a metallurgical engineer and I can assure you this is a classic fatigue crack. The darker clamshell appearing area on the shaft at the lower right of the picture is a dead giveaway. This did not happen quickly but over a period of time. The fatigue crack was progressing well into the shaft before it finally let go. The reason that this area is darker than the rest of the broken shaft is corrosion of the fresh crack surface as water entered the crack.
If you look closely you will see rings or "beach marks" in the crack which point back to the origin . There is also straight black line pointing to near the origin. I cant tell what it is probably just a change in plane of the crack
Look at the area on the surface at the origin. You might see deep scratches or corrosion pits which could have contributed to the failure.

Essentially fatigue is due to cyclical stress, eg vibration which can cause failure well below the well below strength of the steel

 

[Brendann99]

I am a metallurgical engineer and I can assure you this is a classic fatigue crack. The darker clamshell appearing area on the shaft at the lower right of the picture is a dead giveaway. This did not happen quickly but over a period of time. The fatigue crack was progressing well into the shaft before it finally let go. The reason that this area is darker than the rest of the broken shaft is corrosion of the fresh crack surface as water entered the crack.
If you look closely you will see rings or "beach marks" in the crack which point back to the origin . There is also straight black line pointing to near the origin. I cant tell what it is probably just a change in plane of the crack
Look at the area on the surface at the origin. You might see deep scratches or corrosion pits which could have contributed to the failure.

Essentially fatigue is due to cyclical stress, eg vibration which can cause failure well below the well below strength of the steel

Well that does make me feel alot better. Appreciate the detailed expert analysis. :cheers:

 

[1970_mgb]

Brendann
As others have said , you should still check for any cause of abnormal vibration which may have accelerated the failure in the first place and could make it happen again with time.

 

[Brendann99]

Brendann
As others have said , you should still check for any cause of abnormal vibration which may have accelerated the failure in the first place and could make it happen again with time.

I will be double checking engine alignment. Other than that is there any signs I can look for on the jet pump. Anybody take a look at that video link?

 

[seadooya]

one thing good out of this...you gotta impellor removal tool, now...:cheers:

 

[scooper77515]

Good point, dooya. Grind two edges of that shaft flat to fit a wrench, and free tool!!!

 

[Brendann99]

Haha I like the way you guys think!

 

[scooper77515]

Sooo...wanna sell it? :reddevil: :cheers: