The Stovebolt Site Forums The Shop Area Engine Shop harmonic balancer does size matter?

i want to get a new harmonic balancer for my engine and was curious on the fact that say my old balancer is a 6" would it cause any problems if i bought an 8"?

thanks
Nate

Nate,

I don't know nuttin about your setup but I do know this, everything driven by that new 8" crank pulley will now spin 33% faster. That might not be OK!

Stuart

i'm in the process of having an engine built for my 49,a .30 over 350.i just had this conversation with my builder.he builds alot of race motors and a pretty busy guy so i would hope he knows what hes talking about.he said pretty much it didnt matter either one would work since their internally balanced.se said they would run fine without a balancer.that their basically a place to bolt your pulleys and to keep it from leaking oil out the timing cover.i asked him which he preferred,and was told the 6 3/4 only because of less rotating mass.but then said its not that big a deal.i had bought a junkyard 8" he said it wasnt worth spending the money to switch either would be fine..........dave

If the balancer were not really needed-- do you think the manufacturers would have spent the money to install them? They are there to do just one thing--- dampnen the harmonics in the crank-- has nothing to do with the internal balance of the engine. if you look at some of them, they have a rubber insert to allow the outer dampner ring to float. As for the driven speeds of the accessories, that is dependent on the pulley size-- which bolts to the balancer so you can install whatever size you need on the balancer. On some of the old engines, it was in fact just a cast plate to bolt pulleys to, or it was the pulley itself.

David: I would seriously doubt anyone who claims to be an engine builder if he made the statements you claim this "race" builder made. Why not use the one that is supposed to used on your engine?
Frankly I think he is full of prunes. I hope Hotrod Lincoln chimes in on this as I do respect his opinion. We're sure to get a lot of input on this one.

Good question David and Thanks for posting it. Thanks to you also OldIron.

just relayin what the man told me...........dave

Old Iron didn't say what he's working on but I assume its a SBC. Ive always used the 8 in. on 350's & the 6 in on the 305's & smaller. Thats pretty much the way they came from the factory. I too would question the opinion of an "engine builder" that made a statement like that. I would like to hear Hot rod Lincolns opinion on this also.

Yes, the damper is important- - - - -it relieves torsional stresses on the crankshaft created as the cylinders fire. On a V-8, the longer the stroke, the more twist the crank gets at each firing impulse, so the 350's and other engines with a 3.48" stroke need a bigger damper. The 265's and 283's had a 3" stroke, so the damper ring could be smaller. I think a 327, which has a 3 1/4" stroke had a slightly larger damper than a 283. The small block 400 didn't have enough crankcase room for big enough counterweights to be internally balanced, so the damper and the flywheel had to be intentionally manufactured off-balance, and the 3 3/4" stroke required a really big damper ring.

Bottom line, I'd reccomend using whatever size balancer the factory engineers chose to use. It might avoid a stress fracture in a crankshaft somewhere down the road. If you're using the original type front engine mounts on a 55-up pickup, it might be necessary to trim the mounting brackets that bolt to the front of the block for damper clearance when using the 350-size damper.
Jerry

..................dave

there was a guy years ago on the inliners board that claims his race engines didn't need har. balancers. so you never know what someone will say or believes so your builder wasn't the only one. i can attest they are fairly important, having one fail on a 292 years ago. since those bent 8 cranks are so small and light mabey you can get away with just using a nut threaded on for a balancer.......hehehe

Sometime during the last year I read an article on the design and function of the harmonic balancer. It had original design test data showing crankshaft distortions with and without the damper. The difference was very dramatic.

i'm sorry guys i posted it up so fast forgot to put in the correct info its a 350 Chevy, and also i feel embarassed/stupid.... i measured my harmonic balancer earlier today and its 8 inch.... so i kinda answered my own question.... i figured it was 6 inch but obviously my eyes are not as acurate as a tape measure.... none the less this was a very informative discussion

thanks for all the input
Nate

For those who need it, The Damper Doctor is a source for whatever damper/harmonic balancer (or motor mounts, etc.) issue you have.

Damper Doctor

Good to deal with, in my experience.

-Michael