Gents (& ladies)
I've searched the forums and either missed or can't find this answer for a big block.

Can one of you tell me what the outside diameter is for the stock harmonic balancer (some call it a dampener) an 1970 Olds 455 big block?

While we're at it, would the diameter for a 1966 Olds 425 big block be different?

And for that matter what is the diameter for an early underbred Olds 400?

I'm seeing different values from 6.6 to 6.75 online and would like to install a the right length timing tape (for however long it may last...)

Thanks in advance
cf

 

From what I remember, none of the standard size timing tapes are "exact" for the Olds balancer. Additionally, my experience was the timing tape exited after a couple of 5000 RPM pulls (and that was with several coats of clear sprayed over it to help keep it in place).

You can mark your balancer with a paint pen. Turn the engine over until the balancer mark aligns with 0 on the timing tab and make a line at the 10º notch. Then turn the engine by hand until the your new line is at 0 on the balancer. Keep doing this until you have as many 10º marks as you want. I made three 10º marks then started making 2º marks from 30 to 40 so I had more resolution.

So now to answer your questions. I went to the garage and measured the balancers in my stash:

1972 455 balancer = 6.5" diameter
1967 400 balancer = 7.0" diameter