I have a 383 that has an 8" balancer with no weight on it. I noticed the timing mark is pointing straight up but the keyway is pointing to TDC and I know the engine is at TDC be cause I have the heads off.

I am assuming this means the outer ring has slipped and the balancer needs to be replaced.

My question is what is the difference between the 8" balancer and the 6.75" balancer?

 

Do you have an aftermarket timing cover? Almost every one has the timing mark at the 2 position, but stock dampeners have the 12 position mark. They make covers with graduated timing marks on them that can solve this.

 

http://forum.grumpysperformance.com/...5&p=1864#p1864

http://forum.grumpysperformance.com/...hp?f=53&t=3554

 

As Joe said, sounds like you have a damper that was intended for TDC at 12 o'clock. Many 3rd gens came that way.

Note above that I called it a "damper". The proper term is "harmonic damper" (even though you will often see it called "balancer"). Its purpose is to dampen harmonics in the crank.

But the first question you need to answer is, is your crank "internally" or "externally" balanced? The factory used "external" balance for their 3.75" stroke cranks, and so do a lot of aftermarket manufacturers. However, many have gone to "internal" or "neutral" balance, like the factory did for 3.48" and shorter stroke cranks. Once you know that for certain, you can pick a damper (and the one you have may be okay).

Now, to answer your original question: The difference between an 8" damper and 6.75" damper is the 8" is bigger.

Really, that's the answer.

The factory used both. Personally, I'd take the 8", as long as you have room for it. And, in a 3rd gen, you should.

 

Thanks for the responses, I did not know they had a 12 o'clock TDC timing mark, The picture in grumpyvette's post looks exactly like mine so I'm just going to run what I have. It never had any vibration so I'm sure its fine.