455 OLDS vibration

[sweet41k]

I just took a fresh unstarted 455 Olds motor out of a jet boat and put it in my jet boat that blew up a couple years ago. The engine that blew up had an "automatic tranmission flexplate" on it. The engine I installed originally had a manual trans steel flywheel on it. I put the flexplate and harmonic balancer from my blown engine on the other engine before I installed it. The engine runs great, but has a vibration above 3000rpm. Is there a balance difference between these engines that I don't know about? I'm not sure who built the new engine or even sure that it's a 455. It looks identical to my 455 and I was told it was a 455, but who knows for sure. Any ideas????????

[Back Forty]

All of the 455's were balanced basicly the same(external). The earlier engines were set up a bit different. Go over to realoldspower.com and post the block numbers. You may have a 425 OR somebody did a balance job requiring a change on the flexplate/flywheel side. I don't know sh!t of balancing details..! From the factory you should be ok. You may have a driveline alignment issue..! That would be an easy fix if you can simply correct the misalignment. Never had to mess with mine yet so I don't have much to offer in driveline details.

[sweet41k]

My jet is not even hooked up yet to the engine. I wanted to start it first without any jet attached. Once I get the vibration out, can you run the engine with the jet hooked up and not damage the jet? Do I just connect a garden hose to the connection at the back of the engine where the pump sends water to the engine and turn the water on?
Steve

[BrendellaJet]

What condition is the stock dampener in? Might be a good idea to replace it with a quality piece. The cost of a rebuild for a motor that vibrates itself to death is far more than a 200-300 part. As far as the flex plate, I dont know enough about the balancing of the rotating assembly to know if the flex plate needs to be balanced with the crank. I wonder if you could find one that had a neatral balance to it...seems like that would not effect the balance of the other parts?

[malcolm]

The 425 should have a different bolt pattern on the flywheel than a 455 because of it being an earlier motor. It's not missing is it?
I put 455 stuff (flywheel and balancer) on my SB 403 and it's smooth as glass. I was going to try a flex plate this year, wonder if it's a mistake?
Did the flexplate still have the counter weight on it? I think mine had a pretty good sized one on it.

[Back Forty]

Ahh crap. I wasn't making sense to myself...:D
RETRACTION!!!

[Wet Dream]

Does the vibration go away at higher rpms or does it get worse?