I just fired up a rebuilt LS5 454 for the first time and it has a serious vibration at 2000-2500 rpm. It's connected to an M-21 and I'm not running any accessories yet. Could this be the clutch, flyheel, harmonic balancer or what? I bought the engine this way so I/m not sure about the internals.

RC,
First of all make sure that what you have is actually a vibration caused by something being out of balance. Usually an out of balance situation will get worse as the RPM's are increased, just like an out of balance tire that gets worse the faster you go. If the vibration gets worse as the RPM's go up, then it could very well be a problem with engine balance, such as the wrong flywheel or damper, or an engine assembled with very missmatched parts, weight wise.
On the other hand, if the vibration is just there at 2500 rpm or so, it could be a characteristic of the camshaft, an ignition miss or timing problem, bad motor mounts,or any of a host of things that can cause a motor to seem to vibrate.
If you are not sure, I would see if you could find someone with a bit more experience to hear and "feel" the vibration and give you his ideas. I am only saying this because we recently had a customer bring us his 69 Mustang, with a 428 motor we built, to us complaining of a vibration. The problem was the headers hitting the frame at a very close clearance point and transmitting the normal vibration of the motor to the rest of the car. That gives you some idea of what can seem like a balance problem but is not. Hope this helps.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

.
,Bill is right, I learnt the hard way, chased a vibration in a 396-350 for about $2000.00 worth, replaced everything that could possibly vibrate, finally snatched the motor out and gave it to a new engine guy, come to find out my old engine guy had somehow assembeled the motor(after he balanced it???) with the wrong set of rods , that had been part of another balanced motor!! mann wat a lesson, still wonder how that other guys motor runs with my rods in it?? http://www.chevelles.com/forum/smile.gif Good Luck L89SEDAN. ps. dont forget that a 454 is a xternally balanced motor so u must use the correct flywheel


[This message has been edited by L89SEDAN (edited 01-10-99).]

This is the first time you have run the
engine after a rebuild?
Is there a miss? Are the valves set?
Run a compression test on the engine. You
could have a lifter that pumped up.

Joe

Thanks Guys, Here's some more info:

This is the 1st time its been run, It doesn't have a miss and compression is within 5%. It actually idles well at about 700 rpm. The left header (Hedman) is touching the lower control arm mount so I'm going to clear this and see if the vibration was normal but transferring from the engine to the car. Next step is to check the flywheel - I'll keep you posted