max

I recently freshened my 468 blower motor and when I put the motor back in and test drove the boat I noticed a strong vibration under WOT conditions between 4000 and 5100rpm. The freshening included 3 new pistons (which all weighed within one gram of the other pistons, new rings, new bearings,new REV 1.88 innoconel exhaust valves and new exhaust seats. The bravo drive has 800 problem free hours on it. I pulled the drive back off, rechecked the allignment (which was fine) regreased the u-joints and put it back on. I currently run a 26 pitch bravo 4 blade so I borrowed a different 26 bravo to see if it made any difference. The vibration changed to 4000-4400rpm. I have since pulled the motor to have the bottom end checked and all seems ok? Does anyone have any suggestions? I think the vibration is comming from the drive system.

Dennis Moore

Did you spin the gimbal bearing when you had the drive off? Grease it up real good with the engine idling on the flushing attachment (best way to grease em).
Pull the drain plug on the drive and look for metal shavings on the magnet.
I hope the crank isn't bent (don't know why you replaced the pistons). Could be a bent connecting rod also. Are you sure the same flywheel went back on (the back of the flywheel for a 454 has a balancing weight).
Good Luck
Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Cord

iTrader: (2)

I had to pull my engine back out because the flywheel was off 180*. The engine would idle just fine, but it went into severe harmonics around 3k and didn't cleaned up above that. I never tried to put the boat in the water with that condition, so I don't know how it would have felt. When we pulled the engine, you could just barely see where the pin used to be before it was cut off. I have no idea as to why somebody would cut the locating pin off, but they did. You mention that this is a blower motor. If the balancer/blower snout was cut for two keys, you may have it off 180*, but then I'd expect the engine would run poorly because of the timing problems.

max

Thanks for the quick responces. My locating pin is still on my flywheel, and I am sure that the flywheel is mine. I replaced the 3 pistons due to minor galling on the wrist pins. This motor is ballanced, so we bought new pistons (J&E blower)verses oversizing the wrist pin holes. I felt the gimble bearing and put grease around it with my hand. It felt fine. I also replaced the coupler 2 years ago as preventative maintenance. Can a coupler that is close to malfunctioning cause this type of vibration? I will check the drive drain plug.

Brad Perry

Check your u-joints good! I just had mine let go with the same symptoms. It only took 5 minutes at mid throttle to do it. Are you greasing the gimbal bearing from the zerk outside the transom assembly? Check the u-joints very close for any slop. Better off, just replace them for good measure. 800 hours is a lot to expect of them. Might be good to try a friends bravo quick to rule out areas.

Brad Perry

Might take drive off and connect hose directly to raw water pump and rev engine in driveway to rule out driveline vs engine. Mine only happened under load.