I have a fresh 383 and SPEC aluminum flywheel(with weights still installed) that I had the machine shop balance out for me. I am also running a SPEC Stage 3 clutch with this setup. I am running the stock harmonic balancer. The main issue I am having is around 2,600 rpms I start getting a vibration and it worsens as the rpms increase. The vibe starts to go away around 5,000 rpms. I am rying to figure this out before I hurt my motor. When I rev the motor I can feel it but it is more pronounced when the car is under a load, especially in the higher gears, but is noticeable in all gears when rpms get around previous mentioned rpm. I thought the SPEC clutches were neutrally balanced so I didn't have the machine shop neutrally balance it or check it. I installed the harmonic balancer at 12 o'clock position with #1 cylinder at TDC. My AFR stays around the 15 to 16 area during normal driving. Sometimes spiking up around 18 when I am in the higher rpms. I checked to see if the exhaust was contacting the car and it wasn't, spark plug wires are good. I am trying to get this vibe figured out before taking it to the dyno for retuning. Does anyone have any possible idea what it could be or where I could start looking? Thanks for any advice. Zane

 

Motor is internally balanced I'm assuming? If so, did they "zero" balance the flywheel?

 

I asked the machine shop and they said they balanced the flywheel with the internals. I am confused about whether the LT1 is internally or externally balanced and if the flywheel is supposed to be neutrally balanced. I don't want to drive my car until I igure it out.

 

A stock LT1 is externally balanced, with a neutral balanced harmonic damper on the front of the crank, and a large weight on the stock flywheel (or flexplate) at the rear of the crank.

Whether yours is internally or externally balanced would have been determined by the crank selection, and the person who balanced the rotating assembly. If they balanced the rotating assembly internally, they would have used a neutral balanced flywheel. If they balanced the rotating assembly externally, they would have used a flywheel with a weight approximating the stock mass.

As I noted in the PM response, the device on the front of the LT1 is not a "balancer"... its a neutral balanced harmonic damper.

 

I wil check the dampner for cracks. So my other option is the clutch being outta balance?

 

I bet your motor was internally balanced and the weight is still on the flywheel. Had it happen to me

Cody

 

I am gonna drop my starter, inspection cover, remove the weight and see if it makes a difference. Will post my findings as I troubleshoot it more.

 

Did you install a pilot bushing in the back of the crank? Eric L

 

Look in your balancer and see if you have weights there too....GM did put some weights in the balancer if the assembly needed them. See item "77" in figure 12 below. Depending on how your rotating assembly was balanced, you may or may not need them.

 

Yes I installed a pilot bearing in the back of the flywheel, is there one in the crank that I missed?

 

Probably the same one. Its not the flywheel though, its the center of the crank your putting it into.

 

Yeah I believe your right. I checked harmonic damper and no weights were in the small holes around outer edge of it.