Bad Vibrations? Part 2

If you missed Part 1 in the Bad Vibrations? series, you can view it here. Bad Vibrations? Part 1

In the first article we were on the hunt for a bad vibration in this boat. We removed the jet from the boat, disassembled the jet and concluded that the jet was worn out, but not causing the vibration. By installing my break-in pump, we were able to run the engine and confirm that the vibration was still present.


Our next move was to disassemble the backside of the engine. To remove the break-in jet we needed to shore up the back of the engine. Because we were going to remove the bellhousing, we had to shore the engine up by the bottom of the oil pan. This boat had plenty of room for pan access, so it was easy to secure the engine by the pan. In cases where this is not an option, we would sling the engine up by our engine hoist. This boat is set up with a 3 point mounting system where most of the engine's weight is secured by the side motor mounts.



The first thing to remove is the break-in pump. Once that is out of the way, we removed the starter and bellhousing. With the bellhousing removed, we can get a good visual on the driveline and flexplate. We didn't have to look too far before we realized that the flexplate was bolted on the engine backwards. This was no doubt causing our vibration problem. Upon removing the driveline we noticed that the crank bolts were also loose. With the driveline off, we had to fight the flexplate off of the crankshaft. Flexplate's feature a tapered center bore. This usually prevents problems like this from happening. My customer used the crank bolts to pull the flexplate on, a sure sign something was wrong. Knowing the flexplate has been stressed during installation and stressed to remove, we opted to replace it.


With our new flexplate installed, we re-installed the driveline. To insure the bolts stay secured, we used red loctite on the crank bolts. We can now re-install the bellhousing, starter and the break-in pump. We ran the boat again with our new flexplate installed correctly, and it ran perfect. Problem solved.








Now that the vibration problem is behind us, it was time to focus on the fun stuff. It's jet drive time! I had previously disassembled the jet and stripped the paint off the parts. I taped off the parts and sent them to powdercoat. A few days later, we got all our parts back and we are ready for mach up and assembly.






For our rebuild we're using a high quality rebuild kit from BJ's Marine. Our kits feature high quality gaskets, TTO seals, a ZKL main bearing, graphite rope packings and a shouldered bronze wear ring. We opted for a .025 under wear ring. This required us to machine the impeller. I like to machine the impeller on the actual shaft that will be installed in the jet. This insures that the impeller will be cut true to the shaft


If you remember from the first article, the pump shaft we removed from the boat was too far gone to re-install. I sold my customer a reconditioned shaft that I had in stock. The splines on this new shaft fit his driveline really well so we will eliminate any spline chatter when the boat is running. The reconditioned shaft also features a re-sleeved tail stock. Note the wear on the tail of the old shaft compared to the re-sleeved shaft from BJ's Marine.

After the impeller is out of the lathe, we go to work on the details. We blended this impeller for maximum performance. When installing the impeller, we set up the forward clearance at .030. When the impeller nut is tightened, that clearance will snug up to .025. With everything double checked, we install the bowl, oil and grease, and the pump is ready to install in the boat.

The finished product is a big difference from where we started. My customer will be able to run this boat without begin rattled from vibrations. The pump work will provide much more efficiency and performance. Cosmetically, the pump is a great addition to this immaculate boat.

Written By: Bob Jeanblanc - BJ's Marine

Bob Jeanblanc
BJ's Marine Recycle Performance
1260 N Redgum St
Anaheim Ca 92806
714-630-3905
[email protected]
www.marineiw.com