A while ago, I thought it would be a good idea to pull out my perfectly fine hot-cammed engine out and build a stroker... Got an zero-balanced forged rotating assembly from Eagle (trusting that they did a good job neutral balancing it so the machine shop did not double-check), and after putting the car back together, realized there was a vibration in the engine at around 2,500 rpm. After a little research, I found out that I overlooked the fact that LT1s are externally balanced in the rear by the flywheel (oops), so I got the flywheel neutral balanced thinking this would eliminate the vibration.

Sure enough, the original vibration went away, but now I have a new vibration at around 2,100 rpm. The new vibration is not nearly as bad, but it is still annoying enough that I need it gone. However, at this point I am running out of ideas on what may be causing this vibration:

- It is my understanding that the stock harmonic balancer/hub assembly (which I am using on the new engine) are neutrally balanced, so I am assuming that this is likely not causing the vibration.
- During installation, we also decided to put a key in the hub to prevent any slippage. However, the machine shop put the key in the 10 o'clock position; hence, the balancer hub/balancer are currently at the 10 o'clock position when piston #1 is at TDC, when the manual that we have says that it should be at 12 o'clock. But if everything is neutrally balanced, it shouldn't matter where they are at, right???

My questions is: is the stock harmonic balancer/hub neutral-balanced or is there a possibility that they may be weighted? Also, if you have had similar issues, please let me know how you corrected it.

Thanks in advance.

 

LT1 harmonic dampers are not necessarily neutral-balanced. Its my understanding that they are use to "fine-tune" crank balance. This is a really good summary:

http://www.9c1.com/technical/LT1_rebuild/ar99928.htm

My guess is you'll need to get the damper neutral-balanced too. HTH

 

Thanks for that link, it was informative.

Any other opinions?

 

Bump....

 

you could go with an ATI damper if your's has been altered by the factory

 

I am actually thinking of trying a Fluidampr unit, but I wanted to get some opinions before I shell out $400 on one.

Thanks.

 

Had the same problem on my 383. Same RPM's and everything...scary ha

I figured it was my Eagle bottom end since i had heard of them not balancing them correctly-luckily i was wrong.

I knew about the lt1's being externally balanced in the rear, and told the shop that i dropped my stock flywheel to zero balance it as well as resurface.
I got it back, didnt get a reciept or anything (it was sent to my work, another shop accross town so i got it a bit cheaper) I assumed it was all good and right and put it on only to find out it was shaking like you describe.
Eventually went to that shop and asked them about it, they told me they dont even balance flywheels of any kind so they couldnt have possibly did mine.
so....I went and Bought a RAM Billet Aluminum flywheel, not cheap mind you, threw it on there and had the same vibration just not nearly as bad.
This time the vibration was whenever coasting in gear from 2500 to 2000rpm.
I could go on with my story, but to cut to the chase, the RAM flywheel turned out to be 3.5 ounces outta balance it was also supposed to be nuetral or zero balanced when i got it. My fault for not double checking i guess. Iam on my 3rd flywheel now, a Fidanza Aluminum piece, and am told it runs smooth as can be (the car is on vacation getting worked on for the winter, not by me this time)

((Please correct me if iam wrong here guys, i dont wanna tell this guy something wrong))--
But it was my understanding that the harmonic dampner was zero balanced, and took care of engine harmonics(dampend little vibrations that show up naturally as a result of the engine running) rather than actualy balancing of the rotating assembly.
Mine had a chunk missing out of it from a wreck (long story-dont ask) so i replaced mine with a stock Dorman replacement unit just for safety.
The stock Dorman one was not very expensive if i remember right, and Dorman has a very good reputation (around here anyway--used to work at a shop). I, too, would like to get a ATI piece eventually though.

My advice, if in doubt, replace the harmonic damper with either a ATI or even a stock one for now if money is a concern, and get your flywheel double and tripple checked for being zero balanced. Its bessed to try any and all other options before tearing it all back down again, trust me

 

The flywheel was balanced by a shop owned by a friend of my dad's so I doubt they didn't do a good job balancing it, but I suppose it is always a possibility...

At this time, I think I will go ahead and give the Fluidampr a shot. If it doesn't solve the problem, at least I will have a decent balancer after I tear the engine down to track the problem

Thanks.