Straight shaft runout.

[magster65]

Does anyone know how much deflection there should be on the shaft at my velvet-drive coupling? I've developed a vibration at certain rpm and I think the shaft maybe the culprit here.

 

[magster65]

Re: Straight shaft runout.

Hmmm, the dial guage shows about 2 thou. bearing movement and about 4 thou. shaft out of round at the coupling / stuffing box. When I run at the rpm to cause it to vibrate (3500) it's hard to tell where it originates. I'm pretty sure it's not the engine, it sounds and feels smooth, same with the stuffing box. What's left? I'll measure deflection at mid-shaft and at the prop taper (big and little) and check the prop for balance. Any other ideas here?

 

[Trent]

Re: Straight shaft runout.

Time to check your cutless bearing. Remove boat from the water and check at the strut.

 

[magster65]

Re: Straight shaft runout.

Thanks. I had the boat out of the water a week ago to do the bottom paint and I grabbed the shaft at the strut and tried to wiggle it. It didn't seem to have any excessive play then... I'll pay more attention this time. It didn't vibrate then either though, this is something that started since. <br />I guess I may have hit a piece of wood or something... not likely<br />I had the prop tuned up by our local prop guy, he does excellent work though so that's not likely he gave it back out of balance<br />The new motor was installed 7 years ago and I don't think it's been realigned so I'll do that too. <br />A combination of things maybe?<br />I hope.

 

[magster65]

Re: Straight shaft runout.

More often than not we never know the outcome of these things so I'll write it up for anyone who's curious. I was trying to find a vibration that was most noticeable at 3500 rpm. I was to pull the boat out today so I went to the boat this morning. I took the drive shaft coupling apart and put a dial guage on the trans flange, it was acceptable with a .002 wobble. I then put it on the drive shaft flange, it was out about .019 so I took the coupler off, it was a little crusty so I cleaned the shaft and the coupler and reassembled it. It had a .005 wobble to it so I mated the flanges as best I could to counteract each other. I took it for a test run and it's smooth as silk now. I guess a vibration uses up a bunch of horsepower. I need more prop now! Get this... 27 mph (gps) and still accelerating at 4600 rpm, I had to back off, it's not suppose to exceed 4400. That's a lot faster than I ever thought this boat would go.<br />