Harmonic Balancer Sizing
 

I was recently helping out my buddy replace the gaskets on his TPI. he decided it was time to remove the air pump system. My car has this system removed. I brought over an old belt that I used on mine and when we routed it the same as mine it was way short. At least a couple inches. After screwing with it and several trips to the auto parts we got the right size belt. Both of us where dumbfounded on why mine would not work, until I went home and looked at my car. My balancer is way smaller 5.25" to his 7.25". Mine is a 91 305 and his a 92 305, his is a G92 car. Did GM use 2 different size balancers, switch size with model year or maybe one of the 7 previous owners of my car change mine to an underdrive?

Thanks

Re: Harmonic Balancer Sizing
 

The actual balancer is likely the same, but the sheaves bolted to it could be different.

Re: Harmonic Balancer Sizing
 

Sounds like somebody put an underdrive pulley on your car at some point in its life. Was a VERY popular thing back in the day.

Re: Harmonic Balancer Sizing
 

Thanks Guys, I think it is an underdrive pully as I know my alternator has one on it.

Re: Harmonic Balancer Sizing
 

Good catch I wasn't even thinking pulley but yah 5.25 is a common UD crank pulley size. I was like, did someone take his outer ring off?

No but to answer the OP there are other size balancers/dampers. I think all modern(before sbc was replaced) vehicles got the same size but trucks n some performance cars use to get a larger one and the really old lower displacement sbc like 283 or smaller got a smaller one I've herd.

Re: Harmonic Balancer Sizing
 

Yeah the 265 & 283 didn't even really have a "damper"; it was just a pulley flange that went onto the end of the crank.

7" was a real common 327 & 350 size, a few were 8". Of course you always have to be concerned about the timing tab to match. Then starting in the late 70s they were pretty much all 6¾" on both the 305s and 350s. 262.5 & 267 as well.

Re: Harmonic Balancer Sizing
 

Sofa, do you have any guidelines for selecting the proper sized balancer, i.e. - smaller & lighter should be used with __________, and larger & heavier with _________?

I have always chosen the smaller & lighter for shorter stroke engines that you are purposely revving higher in the rpm band. And, of course, the opposite for the longer stroke, lower revving engines.

Re: Harmonic Balancer Sizing
 

Ran into the same thing with mine.

Re: Harmonic Balancer Sizing
 

If there was a guideline, I'd guess it would be something like, use the biggest one you can, given your accessories, timing tab, and everything else. I don't really think there's any material advantage to a smaller one other than that. Of course, the shorter the stroke, the less need there is for a damper at all, in the first place; so it's less critical. Which may be why the 283 and 265 (3" stroke) didn't have one, for all practical purposes.

AFAIK on the SBC, all dampers have their pulley flange in the same plane. LS motors for example aren't that way, there are different "depths". But that makes the SBC easy to swap around in this area.

Re: Harmonic Balancer Sizing
 

I just run a Fluidampr on anything I give crap about - especially if it's changed stroke, operating RPM range, etc as is the case for a LOT of the performance applications. At least this way I don't have to try and calculate what damper I need or mess with ATI and their selection of "elastomers" :rolleyes:

GD