Mercruiser 165 vibrations over 3200rpm

[Fantasmal]

I've got a mid 70's mercruiser 165 inline 6 pushing a Winner Viscount 21ft deep v. She purrs like a kitten at idle and is smooth up to a plane. At about 3200rpm 22+mph it develops a strong vibration, any more power will increase the vibration. If I back the throttle off (as I always do) the vibration goes away. It appears to be directly related to exceeding the 3200rpm point. Does anyone have any ideas?

Thanks

 

[AviatorJim]

Re: Mercruiser 165 vibrations over 3200rpm

Sounds like the prop. The small diameter of the prop keeps you from feeling them until the speed get up, increasing the vibration. I suspect your prop has some damage, or is worn down.

It could also be a U-joint on the drive. They need to be checked and lubed if necessary every time you have the drive out.

And if the boat has suffered a lot of neglect, the gimbal bearing might be bad, damaged, or just plain missing. You can see the bad gimbal bearing if you watch the shaft going from the engine through the transom while you are underway.

--Jim

 

[Fantasmal]

Re: Mercruiser 165 vibrations over 3200rpm

Thanks for the response. One blade of the three blade prop has a slight bend out of alignment. The strange thing is there is no vibration then strong vibration right at and above the 3200RPM mark. I would have thought the prop would have caused increasing vibration with RPM not an all or nothing condition. No noise or vibrations at full turn and it doesn't seem to have a problem running on muffs out of water.