Grumble down under- Main Bearing???

[LoadedGun]

Hey Guys,
I havent had my jet boat to long so Im a little new to Jets. Anyway, my boat is a 69' Aqua Craft with a 455 olds F block w/ C casting heads (good combo I understand) anyway I recently rebuilt the jet pump and got it all back together. I was running it in the driveway and it seems to have a grumbly sound only at idle coming from under the motor. It goes away when I throttle it up a bit. The jet drive had a similar sound coming from the Thrust Bearing. It was much louder and thats why I rebuilt it.
Do you think this sound may be the Main bearings going out on me? The engine is tight but I know these Olds motors have a oiling problems. P.S. Like a dumbass I did run it at 5000RPM for 3 miles straight right after I got the boat. I now know this was not good.
Is there anything I can do ? Do you think I can get away with just a crank polish and new bearings or am I looking at somthing more major?

[GofastRacer]

Is your oil pressure still normal or did it drop??, if it is bearings you won't know what you need to do until you tear it down and look at it!.. Did you check the driveline???...

[Oldsquirt]

A common source of a rumble at idle with a jet is the driveline. The splines of the slip yoke are not a tight fit on the pumpshaft. If the noise goes away as soon as you bring the rpm up a bit it is a "possible" cause. If you can get your hands on the driveline(engine OFF, of course ), give it a good shake. You will likely feel some play. If you feel adventurous, pull the driveline out and apply some fairly heavy grease to the inside of the slip yoke, reassemble and water test. I'll bet the rumble is substantially reduced.
While you are at it check all the motor mount bolts to verify they are tight.

[LoadedGun]

Thanx, You guys both gave me a few things to think about and check out. And come to think about it, I did run the motor a bit with the drive line and pump out of the boat and I didn't hear anything but a nice sounding motor :rollside: How far should the driveshaft be in over the shaft. It seems like mine could go on atleast another 3/4". Does anyone make a spacer to push the driveshaft off the flywheel? Or to mount between the two halves of the driveshaft? I did install new U-joints with the pump rebuild due to the fact that I originaly thought the sound was coming from that area. I can't tell you how releaved I amy right now. Im not seeing as many dollar signs when I think of the ol boat.
Thanks again.