Vibration

[Shaun Quilty]

I noticed a slight vibration last weekend. Went under the boat and found nothing on the props and the cutless bearing were fine. I did not hit anything. Yesterday when I powered up the vibration was so bad that the whole boat shook. Has anyone had this problem? Could it be a coupler?

 

[fwebster]

Misalignment can cause a vibration, however, a vibration from a shaft whipping due to misalignment doesn't just happen over night. It starts being barely noticeable then usually gets worse and it changes in intensity with rpms increase.

If your vibration just happened all at once, it more than likely is a bent blade on a prop or a bent shaft, assuming that the props and shaft are clean and have no marine growth on them. You can only spot serious damage and a seriously work cutlass bearing while swimming under the boat. You have to deflect the shaft with enough force to wiggle it inside the cutlass bearing and that is hard to do while under the boat unless you are standing on the ground. Besides, a bad cutlass bearing usually lets you know about it with a rumbling from under the boat before there is enough wear to cause a shake in the shaft. Also, it doesn't take very much for one bent blade to shake the heck out of a high hp boat and that little bit is very hard to spot underwater unless you rig up some kind of a jig under water to check the blades........that is usually done by clamping something on a rudder that contacts the blade tip; rotate the shaft and each blade tip should contact the jig in exactly the same place with exactly the same clearance between the jig and the blade tip.

In terms of the most likely cause for vibration.....and this is also pretty close to the order of the cheapest to fix up to the most expensive........here are the usual causes:

Marine growth on the props and shafts.....look up in the shaft tubes as well.
Bent prop
Bent shaft
Engine coupler alignment
Cutlass bearing wear
defective shaft with a partial break behind the strut..........Some Sea Rays have experienced shaft breaks, but they are usually 340DA's, not larger boats.


Hope that helps...........

 

[Shaun Quilty]

Frank, I notice a small vibration the last couple of weeks but wasn't to concerened until yesterday. I hope that its the alignment coupler. Is this a big deal to replace?

Thanks

 

[gregkjones]

Ive heard a few guys mention here on prior posts that they had a vibration and changed the plugs and or cap and rotor or plug wires and had the vib go away. I guess a missing cyl can cause a similar vibration. My boat has had a slight vibration too that worsened a few days ago. I am changing plugs first since they are due anyway then its to the dreaded prop/shaft scenario. Thinking about taking it out first though and running up to the vibration RPM and pulling the power off one engine at a time to see if I can narrow it down to one side at least. Good luck in your search for the cause.

 

[Shaun Quilty]

I did the same thing at the dock and found it to be my port engine. Good luck

 

[fwebster]

You don't replace couplers..........you realign them. The coupler that connects the transmission to the shaft is made in 2 halves. The mating surfaces on each side must be perfectly parallel to each other. You achieve that by adjusting the nuts on the motor supports........so alignment means moving the engine so that the coupler half on the transmission mates properly with the one on the shaft. It can be easy if you have done it before or it can take hours if you move an engine too far or in the wrong direction.

Some gas engines have a harmonic vibration at certain rpms. I haven't owned gas engines in 15 years, so this is from observing others around out dealer/marina, but I believe that the harmonic issues happen with the 8.1's. While the 7.4 is not prone to harmonic vibrations, any engine with a dead cylinder will shake a little. A dead cylinder could be fuel related as well as an ignition problem. You have a 2006 so you have EFI engines. You could have a bad injector (or 2) that is preventing one or more cylinders from getting a fuel charge and the effect would be the same as an ignition miss. Try running the engines at WOT for a minute.....if they or one of them will not run up to WOT rpms, then you most likely have either a bad injector or an ignition problem.

 

[La Maddalena]

Frank is the expert so I defer to him for helping you diagnose your problem, but I will describe a similar event that happened with our boat when we first purchased it 18 months ago. The boat ran fine for the first 3 weeks, then the first time my wife and I took it out on our own (without our broker, who was training us) it developed a vibration on the starboard engine above about 1600 RPMs. Long story short, the coupler had come loose, tore the coupler gasket and the transmission was leaking fluid all over. So you might look for transmission fluid as a sign of a loose coupler. After several attempts to repair thisnin place in our slip, Our dealer ended up hauling the boat and reinstalling the coupler, realigning, etc. It has run fine ever since.

In hindsight, after reading this forum for 2 years, I am fairly certain our problem was the result of the boat being stored on the hard in the dealer's lot for several months while it was for sale, and then the hull settled when it was back in the water. Had I been better informed (as I am now by reading Clubsearay!) I would have requested the dealer to check the alignment of the couplers after the boat had been back in the water for a couple of weeks.

 

[Shaun Quilty]

Last night I stopped by the boat last night and found that the 4 bolts that hold the shaft at the back of the transmission was missing 3 of the bolts and the fourth one was loose. When I checked my starboard engine all four bolts were loose. I would suggest everyone check. Good luck.