I have a 96 4.3 liter vortec V-6 that was just rebuilt and installed. New 0.030 over hypereutectic pistons and ground the crank 0.010. A local machine shop balanced the assembly as well and then I installed the components in the block and then into the boat.
There is a strange engine vibration above 2,000 rpm that was not there before and does not seem right at all.
What I am curious to know, is if the balance shaft has to be in a particulair position when assembling the motor? Anybody know or help?

Anybody????

Check out this thread, could be a similar issue.

http://www.offshoreonly.com/forums/s...d.php?t=105864

Dave

The balance shaft does have to be timed I beleive. On the one balance shaft motor I worked on it had a dot on the gear that had to line up at same time as cam and crank. It wasn't a chevy v-6 though.

Thanks Wobble - I will try to get a chevy motor service manual to get more details.

Gary

The balance shaft as suggested was the first thing that came to mind, how about motor alignment and ujoints on the drive???

Fountainatlast: The factory mounts and settings were not not disturbed. I think alignment is not the culprit. I beleive the U-joints are ok as well. Good questions though.
When I put it together, I did look to see if there was a mark on the balance shaft gear to align but did not find one. Without seeing a mark, I ignored it after that and put it together in "whatever" position.
If in deed this must be in a certain position, then it could be where the vibration is coming from. Will have to read up on this.