Warped Prop ??

[jrs151]

Getting a really bad wobble or warped shake coming from the IO while at idle speed or faster. The feedback is really noticeable through the steering wheel and shakes the whole boat. The wobble slows and increases with RPMs, and is to the point where I had to idle power back to the ramp and not dare open up the throttle or get back on plane!

What happened just before was I inadvertently (of course) I skimmed over a sand dune yesterday while on plane. Enough so as to drop RPM's significantly and quickly , but didn't get stuck. Powered back up and there it was, I quickly noticed a bad shimmy/wobble coming from the drive unit and decide to limp home. At first, I thought I chipped or broke one blade off my prop. So I got the diving mask out and looked - no issues, prop and drive looked okay. Now I'm leaning towards the U-joints due to the amount of feedback coming back through the steering wheel (especially when turning side-to-side). I haven't had a chance to pull the drive yet, but based on these symptoms what might I look for or expect to find?

 

[mylesm260]

Re: Warped Prop ??

I don't have the answer, but I do have a thought.....

Your U-joints are spinning even in neutral. Have you tried revving the motor in neutral a little bit?

Granted, they will react differently when not under load, but it should give you some indication if something is wrong with them.

 

[180shabah]

Re: Warped Prop ??

Why didn't you put on your spare prop for the trip home?

Take the prop off, fire it (don't forget the water supply, or the pump willbe toast) up and put it in gear, does it shake?

 

[TilliamWe]

Re: Warped Prop ??

Most likely culprit is the prop or the propshaft. U-joints are possible, but they are quite a way away from your impact point. The two closest things to your impact point are the prop (which hit the bottom) and the shaft that the prop is bolted to (propshaft). Keep it simple and start with those two items.

 

[jrs151]

Re: Warped Prop ??

Thanks! Normally I would agree - the prop too... but now that I got it out of the water, the prop is fine. In neutral it spins free and clean by hand. And what you might find very surprising is that there is a "Pro Pulse" composite prop on my drive! So I gotta say 'thumbs up' on the Pro Pulse folks, because I was 100% sure I had broke a blade or two at first. { BTW, I always carry a spare prop on board, but since the prop looked fine I didn?t swap it out. } We can all agree that the plastic prop should of have sheared or broke a blade or two if the impact was that bad, right? Well, the prop is fine, lower leg is fine, skeg is fine (minus some paint). No impact from rocks etc...

My theory is that the prop hit the sand pretty deep which immediately increased the torque which subsequently dropped the engine RPMs too quickly. That amount of force might have broke something that was on it's way out anyways (like the gimbal bearing or U-joints). I was just curious if someone recognized what it means when a noticeable shimmy/wobble is coming back up the steering wheel and as if the something is majorly "out of balance" in the rear?

 

[mylesm260]

Re: Warped Prop ??

I don't know...

Those U-joints are pretty similar to what you would find on a car / truck.

If you think about it, a u-joint on a car is seeing much much more torque because of the multiplication of 1st gear in a transmission.

If you can take a pickup truck with a V8, Rev it to 5000 RPMS, and dump the clutch, and create enough torque to cause your rear tires to break free Multiple times without harming your U-joints, I have a very hard time believing that they could fail under a circumstance like that.

I think you are grossly underestimating how beefy the power-train is in a boat. I would suspect damage to the lower unit (bent prop shaft) way before I would suspect damage to a U-joint from something like that.

Something else to remember: There is a gear reduction in the upper half of the drive. Meaning that there is more torque on the prop shaft than on the U-joints.

If your gear ratio is 1.84, than 1500 ft/lbs of torque shock at the prop (Impact vs rotating inertia of engine/flywheel) would only result in 815 ft/lbs of torque shock on the U-joints.

Automotive U-joints see 1000 ft/lbs of torque on a regular basis, so I can't see it being the problem.

And if you made a 1500 ft/lbs impact on your prop, it would grenade, I'm sure.

 

[boatguya1]

Re: Warped Prop ??

Sart in on the hose with the prop off, does it shake?

James

 

[TilliamWe]

Re: Warped Prop ??

Sart in on the hose with the prop off, does it shake?

James

Good idea. Also...

How about hooking up dial indicator to check the run out on it?


"Something else to remember: There is a gear reduction in the upper half of the drive. Meaning that there is more torque on the prop shaft than on the U-joints. "

Thanks, I couldn't figure out how to explain that, so I used my "u-joints are farther away" statement.

 

[180shabah]

Re: Warped Prop ??

Good idea.

That's why I suggested it

 

[jrs151]

Re: Warped Prop ??

Thanks for the explanations, I do follow what you all are saying about torque, etc... If I read what I'm hearing I should be mostly concerned about the lower unit?? If I pull it apart, what obvious signs could I expect (metal shavings, binding, etc...).

Perhaps a little more perspective on the drive history... I had the drive off last year to replace my shift cable and noticed a puddle of drive gear oil in the bellows area. I know I needed the upper drive oil seal replaced but figured I'd have time this year to get to it. So I cleaned and greased it all back up at the time and kept my gear oil topper topped off with oil. My fear is that a significant amount of drive oil has since made its way back in there and "washed" the grease away from the u-joint bearings. So my question is/was this a recipe for disaster and is the viscosity of gear oil too thin for gimbal and u-joint bearings?

 

[Bondo]

Re: Warped Prop ??

My fear is that a significant amount of drive oil has since made its way back in there and "washed" the grease away from the u-joint bearings. So my question is/was this a recipe for disaster and is the viscosity of gear oil too thin for gimbal and u-joint bearings?

Nope....

Change the prop,+ Try it....

Whatever it is,... I Really Doubt it's the U-joints or Gimbel Bearing...

 

[jrs151]

Re: Warped Prop ?? - possibly fixed

Re: Warped Prop ?? - possibly fixed

All, a good call on checking the prop! With the boat out of water and running I watched the engine shaft spinning inboard and the rate of spin was way faster than the "wobble" I felt in the steering wheel during the transit back to the ramp. So I totally understand the ratio point that was made earlier. Therefor the wobble has to be coming from the prop. However, with a composite (aka plastic) prop it just doesn't register there would be any alignment issues, or be so-called bent... These props don't bend - they rather crack and/or break.

With that said, here's one for the mechanic journals:
As I mentioned earlier, this is a Pro Pulse adjustable prop. What had happened is the adjustment tab on one of the blades sheared causing the affected blade to go into 'full pitch' position (see attached). This is two inches more than the other three blades. One can deduct this would simulate a "warped" prop. I cannot test the boat in water until the weekend, so I'll update this thread with a final confirmation when I can. Thanks to all who contributed and kept me from chasing a ghost.

Needless to say, this prop has always been my 'test prop', so I'll need to stop procrastinating and get a real prop.

 

[180shabah]

Re: Warped Prop ?? - possibly fixed

Re: Warped Prop ?? - possibly fixed

Would this be the wrong time to suggest a Hustler or Legacy from Turning Point? IMHO these are the best aluminum props on the market. Although, before we go too far down this path it would be best to start a new thread in the prop forum.