Darn Vibration! Need some help here please!

[CruiserSHO]

All,

I just finished repowering a 1974 Fiberform with a VP280 out drive and a Chevy 350 attached to it. Had it out on the water for the first time on Mothers Day and the motor ran fine. Went through all RPM bands without a problem when not in gear. When in gear, it's fine until you hit about 1700 RPMs and then a very strong vibration occurs all the way to 3000 RPM's. I am not in any way a boat expert so I need your help. I read a few of the other topics on vibrations on this forum, but I will ask these questions: Can the prop cause this? It's slightly bent in a few locations and has a small chip out of it on one blade which is no bigger than a penny. I read things about possible UJoint issues. When I had the upper assembly out, the Ujoints weren't tight like if they were new, but they weren't in too bad of shape based on first look. Last question: Could a harmonic balancer on the motor be the issue? I removed the old one from the previous 1974 307 V8 and placed it on the new motor. It's not damaged, and doesn't vibrate when out of gear. Should I even consider this an option? Fellas, your the only help I can get with this. A trip to Colorado is only 2 weeks away and I need her fixed. Thank you all in advance....Best regards, Dave.

 

[QC]

Re: Darn Vibration! Need some help here please!

it's fine until you hit about 1700 RPMs and then a very strong vibration occurs all the way to 3000 RPM's

What about above 3000 RPM?

Can the prop cause this? It's slightly bent in a few locations and has a small chip out of it on one blade which is no bigger than a penny.

Absolutely and it may in fact clear up at higher RPM. I wouldn't mess with anything until I had a good prop on it. Even a rebuilt one can have vibration issues, but a bent one with chips can for sure.

I read things about possible UJoint issues . . . Could a harmonic balancer on the motor be the issue?

The balancer should cause an issue out of gear as you noted. U-joints, coupler, gimbal bearing, driveshat, propshaft could all be the cause, but start with the prop. It's the easiest and cheapest and will definitely cause a vibration with sometimes very little, or no, visible damage even. Yours showing damage would be where I started. Prop vibrations are not necessarily about weight variances, it is hydrodynamic differences between the blades . . .

 

[steelespike]

Re: Darn Vibration! Need some help here please!

A bad prop can also cause premature wear in the gearcase as well.
You might check for a bent prop shaft.

 

[solar7647]

Re: Darn Vibration! Need some help here please!

Even a small bend in a prop can cause a lot of vibration. I would start there, when you remove it make sure that there isnt any damage to the prop shaft. If you still have the vibration after a new prop start working your way up the sterndrive. Good Luck.

 

[CruiserSHO]

Re: Darn Vibration! Need some help here please!

Fellas,

Thank you for your feedback. General concensus tells me to head for the prop first, so therefore thats the first item on the troubleshooting list. As I had mentioned, it occurs around 1700-3000 rpms. Being that it was my first time out on the water with a brand new engine, I didn't want to rev it too high. Last Sunday, in terms of a boating aspect, was what I called a very good day and I didn't want to tempt the fates, especially in the middle of Utah Lake with no backup plan. I will say this, when it was at 3000rpms, it did seem like the vibration died down a little. Not much, but not as harsh as it was at 2000rpms. I will do some research and post again when i've got the prop issue cleared. Up. Thaks again for the good advice! Dave.