B1 Via 454 MPI Vibration
 

Had the boat out a few weekends ago and over 3500 rpm I started feeling a vibration in the cockpit floor. 1996 vintage 454 LX MPI's and Bravo 1's. Is there a go to component to consider first? I'm assuming replace both gimbal bearings, all U-joints and check alingments. What else? And other than shift cables and bellows what should I replace when the drives are pulled?

Engine 0F884005, 0F886167
Drives. 0F813383, 0F813384

Thanks for any insight you can lend.
Keith

Condition of props? Check run out on prop shafts.

Transom solid as a rock and the motor mounts solid and tight ? Stingers Solid ? Engine coupler ? and what above said for the easy areas to look at first before anything else.

Props were just balanced/adjusted last year, haven't hit anything. I'll check the shafts, thanks.

I'll get it all checked prior to drive pulling thanks!

forgot to add - Harmonic balancers as well. Check them out.

I see this especially if an engine has an oil leak that collects on the back side of the balancer and or a water leak like from water circ that collects on the back side of the balancer that ruins them for a jist of it.

try bringing up the RPM's up out of gear, see if you pick up vibration there, isolate if engine or driveline, if only in gear ck U-joints 1st, feel the gimble bearing while drive is off..

U-joints are spinning all the time. Pull the drives. I'm sure you'll find the problem quick

to ask from post number 1 - You posted the vibration starts at 3500 rpm and above. So you have no vibration from 650 rpm thru 3450 rpm ???

Get it up to vibration and pull back throttles 1 at a time. Will probably show which side is the problem.

1996 and no offense Baja - man more times than not in the past when I did see 1990's boats ---- I have seen rot somewhere in the structure of the hull. Just saying because I would make sure before throwing parts and money at it, that all of that end is GOOD and strong to go.

I am not picking on your boat just pointing out the % of odds for a form of rot.

Yes zero vibration below the 3400 rpm mark. While on the boat last week for attempted impeller change I did notice the vertical motor mount bolt (into stringers) washers loose. That will be my first adjustment then hit the water again and see what tightening nets vibration-wise.

Thanks for everyone's input to date, very helpful and gives me a lot of points to check.

I guess I have my answer. SB engine 3 of the 4 vertical forward mount bolts will not tighten, just spin. Port 1 of the 4.

Keith