Back in 2003 I had a 383 shortblock built that was internally balanced. I was told by the engine builder it would accept a OEM 350 flywheel. I used an internally balanced B&M flexplate & all was fine. Fast forward to 2006. I swapped the 700R4 for a TKO 600. I used all Mcleod stuff from the flywheel to the hydraulic throwout bearing. I used Mcleod's neutral balance flywheel. I now have a servere vibration 1800 rpm & above, clutch in or out, car moving or still. All things point to an imbalanced rotating assembly. Has any used one of their flywheels & had a problem like this. I was told neutral balance was the same as internal balance, but that seems to be wrong.

I recently replaced my old 305 with a balanced 350, and used a neutral balanced flywheel to mate up to the clutch. My car also shakes very badly from about 1500 rpms on up, moving or not, clutch engaged or not. The motor came with a flexplate (which obviously doesn't help since I have a T-5) and so I originally swapped the flexplate with my old flywheel. When that caused the vibration, I tried the neutral flywheel but with no change in apparent balance. Does the motor need to be rebalanced with the flywheel attached or is there a simpler fix? Any help would be appreciated.

Well, from what I have been told, stock 305 and 350 TPI motors are balanced externally at the flywheel and internally at the balancer (neutral).

So the stock flexplate you originally used was correct. The mistake you guys made was ordering neutrally balanced flywheels when you should have ordered a 153 tooth externally balanced flywheel.

Summit Racing has a Hays part number HAY-10-530 and Jegs has a Centerforce part number 183-700170 which either one should do it.

The problem I had was my engine builder used a completly externally balanced crank so I actually need to have my neutrally balanced balancer machined, and flywheel, with the rotating assembly before the engine was assembled.

hmmmm....this is interesting. i am swapping in a 383 that is internally balanced for my old 305 as we speak. keeping the t-5, i was planning on reusing my flywheel from the 305 on the 383.

sounds like this won't work now...will it?

2 piece rear main seal 305 and 350 cranks are 100% internally balances

1 piece rear main seal blocks are 50% internally balanced, and %05 externally, the rear side is externally balanced.

Solved the problem. A neutral balance flywheel is not the same as an OEM internal balance one. I sent a brand new OEM 305//350 flexplate & my neutral balance flywheel to my machine shop. He rebalanced the flywheel to match the OEM flexplate. Problem solved. Engine is smooth to 6k. A neutral balance flywheel is made to be balanced with your rotating assembly. Optionally Mcleod sells counterweights to be attached to the back of the flywheel for various engine configurations. An OEM plate has a 125 gram counter weight on the back, so it's not neutrally balanced.

Ricktpi, are you saying my Eagle 383 stroker kit (1 pc rear seal crank + balanced crank/pistons/rods from Eagle) will not work with my Spec neutral balance flywheel? I didn't have my engine builder do anything to the flywheel. I too am using a TKO600 (I haven't dropped the motor and tranny in yet).

well for starters eagle assemblies are not internally blanaced, so thats a definate HELL NO!!!!!!!

if the assembly was internally balanced at your mahcine shop yes maybe, depending on if its a 1 piece of 2 piece rear man seal, the 2 piece end section has that last 135grams to balance, the 1 peice down not, its perfectly round, so the flexplate/flywheel has the 135grams.

12SecondTA, thanks for the info but let me clarify guys:
I just spoke with Eagles' tech support today and my kit (along with ALL rotating assemblies that use a 1 pc rear seal 4340 crank) are INTERNALLY balanced from them. I ordered the following kit for my engine: B12107 That's a 5.7 Rod, 3.75 stroke, 4340 crank, competition rotating assembly that is balanced from Eagle. So, the my neutral balance flywheel I purchased with my clutch will work. As far as the dampner I can use a factory 91 piece from my 350. Just wanted to clarify the "balance" statement regarding Eagle's rotating kits that have 1pc rear seal 4340 cranks.

to my knowledge this isn't true. Every kit i've always seen was externally when using that crank.

It always came with the balancer and the flywheel so it could balance. If not, then well, your in luck, you got one internally balanced.

Never heard of them doing that, how much was the kit?

I ordered ESP-B12107030 from Summit almost 2 years ago. The cost was just shy of 2000 bux. Summit shows the pistons incorrectly though, mine are negative 16cc and not positive like their saying. I don't know if Eagle has changed their process or when. If you go to Eagle Specialty Products, Inc. and download their PDF catalog they have a pretty nice writeup on why they internally balance their competition rotating assemblies. They actually say they will internally balance a 4340 crank even if the vehicle came with an externally balanced crank from the factory.

AC, Like I said above "Neutral balance" is different from "Internal balance". "Internal balance" is what the factory does. The crank, pistons & rods on a 1pc RMS block are balanced so that the flywheel needs a counterweight on it to complete the balancing. "Neutral balance" is where the crank, rods & pistons are completely balanced & the flywheel has no counterweight. My rotating assembly was balanced to accept an OEM flywheel with the counter weight, because the builder did not have my flexplate at the time. He was in Indiana & I am in Pennsylvania. If your flywheel has a a counterweight or is drilled out on one side, it is most likely internal balance type. No weights or holes, neutral balance.