350 drone/vibration help

[LIQUID FIRE]

I'm new to the forum, so if I'm asking questions on a concern that already has a thread, please forward the link.

I have a 31T Contender with twin 350s. They have 490 hrs. At about 350 hrs, the starboard motor began to develop a low drone/vibration that can be heard and felt through the deck. This has not seemed to affect the way the motor runs. It still tachs at 6100 rpms. It only makes the noise/vibration when bumped into gear for slow *****ing. It does not do it in reverse and isn't noticeable above slow ***** rpms (700-750 max ).

The water pumps have been replaced, prop checked, and lower unit oil checked and changed (no metal found).

Any assistance would be greatly appreciated. Thanks in advance.

Mark

[boats.net]

Check to see if prop shaft is bent, if they didn't grease the drive shaft extension bushings when had gearcase off then may need to be greased.
Have your dealer check the serial number to see if needs the flywheel update.

[LIQUID FIRE]

Thanks for the reply. When I got to the SKA Nationals, Chad Smith, the Yamaha technician who travels to the events took the time to check it out. He found the drive shaft had some abnormal play in it. He diagnosed the problem and replaced the lower unit in 30 minutes!! Great service Chad!! It's great when someone cares and takes pride in their work. Thanks.