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Old 12-13-2012, 06:37 AM
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Harmonic balancer size question

I'm going to have to get another harmonic balancer, I been using a 6 3/4 in. balancer on my sbc internally balanced. The outer ring is moving towards the timing cover. I don't know if this has anything to do with but I did put on a new flex plate when I changed over to a 700r4. Any how I read that a 8 in. balancer wasn't really needed,it just added more weight to the crank. The 6 3/4 was bought new but it was a cheap one only about 70.00. But now I'm thinking I might be better off with an 8 in. as this engine does see 6 grand some times but not alot. When walking around the junk yard I see 6 3/4 balancers on V6 engines, all V8's have 8 in. I like the idea of having less weight on the crank but maybe an 8 in. would be a better choose. Please inlighten me. And yes I know that a Rattler is the best but I didn't want to spend 300.00 plus for a balance.
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Old 12-13-2012, 06:57 AM
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The best buy for your money is a Pioneer (Powerbond-Australia) harmonic damper. S.B. Chevy V8, #872022, 6.720" O.D. internal balance, $135.

I am using Pioneer #872021, 6.100" O.D. and it is a excellent damper.
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Old 12-13-2012, 11:33 AM
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Old 12-13-2012, 12:51 PM
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Quote:
Originally Posted by dogwater View Post
I'm going to have to get another harmonic balancer, I been using a 6 3/4 in. balancer on my sbc internally balanced. The outer ring is moving towards the timing cover. I don't know if this has anything to do with but I did put on a new flex plate when I changed over to a 700r4. Any how I read that a 8 in. balancer wasn't really needed,it just added more weight to the crank. The 6 3/4 was bought new but it was a cheap one only about 70.00. But now I'm thinking I might be better off with an 8 in. as this engine does see 6 grand some times but not alot. When walking around the junk yard I see 6 3/4 balancers on V6 engines, all V8's have 8 in. I like the idea of having less weight on the crank but maybe an 8 in. would be a better choose. Please inlighten me. And yes I know that a Rattler is the best but I didn't want to spend 300.00 plus for a balance.
If you're using an OEM style bonded damper the 8 inch is more effective in dealing with a wider range of frequencies than the 6.75 or 7 inch. Certainly a lighter damper allows faster shaft acceleration but you need to be careful that the damper does in-fact snub the frequencies in the operating range where the crankshafts critical harmonic response also occurs. You will find this level of technical information is one of the biggest secrets on the planet, so it is difficult to know if you got this correctly till time passes and nothing happens, or a short time after putting the damper on you're greeted with a broken crank snout or a set of blown rods on the number one throw. The bonded rubber dampers are application specific and are tuned to unique frequencies needing to be snubbed on that particular engine, using a V6 damper on a V8 could be an invitation to sweeping up a lot of expensive pieces of parts from the pavement, or not, like I said itís really difficult to get engineering data from the OEM or the aftermarket as to what the generated frequencies are on the shaft and what the snubbing frequencies and effectiveness of the snubber is for those frequencies.

Things like the Rattler and Fluid Damper snub a much wider range of harmonic frequencies on the shaft than the bonded rubber type damper, for the money they bring, me at least, a lot more peace of mind that inside parts of the engine won't be hanging out of the block. The larger and heavier damper also snubs a greater frequency range and a larger amount of amplitude from those frequencies.

I have had failures happen that could be directly attributed the failure to the damper to adaquatly squash harmonics on the shaft so this isn't just theory. These failures occur in the nose extension, the number one main, and the number one rod journal. The classic sign is the undamped harmonics are causing the snout to wander and orbit off the center of rotation. This carves out the front seal one of the first signs is an oil ooze from the seal. This on a cast shaft will most likely followed by a fracture where the snout steps up the main bearing. Usually a forged shaft will survive this but the orbital motion will be transferred into the number one main where if carves out the bearing. Oil pressure eventually is lost in the number 1 main which then starves the number 1 rod on the number one throw. You can guess what happens next.


Bogie
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Old 12-14-2012, 07:34 PM
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Thanks for the reply, and I agree an 8 in. damper would be best, but I still don't want to hang more weight on the crank. I'll most likely have my 6.75 rebuilt which I didn't know anything about ( Thanks for the info. Techinspector ) or check on the Pioneer balancer. Obogie, I do searchs of your older post an save some because of the detail you have in them. Thanks again to all.
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Old 12-14-2012, 08:10 PM
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Obogie, I do searchs of your older post an save some because of the detail you have in them.
Me too, bogie is one of my heros.
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Old 12-14-2012, 11:42 PM
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Quote:
Originally Posted by dogwater View Post
Thanks for the reply, and I agree an 8 in. damper would be best, but I still don't want to hang more weight on the crank. I'll most likely have my 6.75 rebuilt which I didn't know anything about ( Thanks for the info. Techinspector ) or check on the Pioneer balancer. Obogie, I do searchs of your older post an save some because of the detail you have in them. Thanks again to all.
There is no downside to using a 8" damper vs. a 6-3/4" damper on a street/strip type engine. Only upsides. The idea of hanging more weight on the crank is a total non issue in this case. The timing tab will need changed, I suppose that could be a downside.
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Old 12-15-2012, 06:20 AM
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I was hoping someone was going to answer how to select a balancer. Since i have always used either racing type or factory replacement or One picked by a specialty company. But never been able to figure when you need each different size balancer.

I aks because i have an old engine that was born with a 8" balancer now its going into a c4 vette and will need the 6 3/4 that fits the car. Now how will i know the balancer is doing a good job. I would not want to wait for a failure to see be sure its wrong.

I do understand how it works and why larger on can be better but it seems to me that large or small could be very effective if properly matched up. I have noticed the key way is in different locations on different size balancers. I assume this effects its balance point in relation to crank angle. But how do i know which one is right for my engine. I know almost any of them will work ok. There must be some way to know what is needed before its built and in the car not working right.

Hoping someone knows more than me about balancers. Recommended balancers are always the most expensive ones and factory is ones come apart at high rpm. Now they make a bunch of middle of the road balancers but no way to select one Leaving the 40-80 dollar balancer on the shelf and has everyone buying the sfi approved 400 dollar balancer thinking the most expensive is the correct one and that is really not the case. I would love to know how to select the proper one for stock to wild builds. Since they sell a proper balancer for every application it should be pretty simple to find the correct size and offset along with the keyway angle and wieght.

For my 1989 corevtte rockauto.com sells 5 balancers all of them usable and a few of them perf. And none performance from the same company. I know from useing rockauto for years that the expensive one and the ac delco will both work great and the rest will fit and be usable. But which one is perfect choice for my built gen one short block. I have no clue. The car will need the correct size and the engine will need to be dampened but i have no clear info on how to select the balancer.

Thanks bogie for the info it was good stuff.
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Old 12-15-2012, 11:14 AM
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Use the heaviest damper you can fit on the engine. A good damper is a Pioneer 872023, SFI 18.1, 8" O.D., 11 lb. , if it will clear everything. I would have used that damper but I had to use the smaller and lighter Pioneer 872021 damper instead. The Pioneer 872021 damper is SFI 18.1, 6" O.D. , 5-1/2 lb. and has a better fit on the front of the engine and timing tab.

I had to use a brake hone to give the damper a .001" interference fit on the crank which is not unusual.
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Old 12-16-2012, 02:55 PM
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For factory torsional vibration dampers, use the largest available, for Chevy that is 8". I believe David Vizard proved that larger dampers actually allowed the engine to produce more HP than smaller ones. Don't sweat the extra weight issues, its not an issue. Factory dampers are pretty questionable for sustained RPM/performance use too.

Aftermarket dampers are usually smaller in diameter, but they get away with it because they actually do a better job at canceling out harmonics than factory units. ATI dampers actually use 2 (not 1) inertia rings to cancel out harmonics. These are the best since such a wide range is canceled out. I would highly suggest getting an SFI rated damper while you are at it. And if you have a cheaper Eagle or SCAT crank, you better pony up some cash for a good damper!
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Old 12-16-2012, 03:52 PM
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I've had a size issue recently. She kicked me out. No, not that.

The 8" hits the screws of a Cloyes two piece timing cover. I had to make a spacer to bring it out about 70 thou.
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Old 12-17-2012, 01:54 AM
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The 8" hits the screws of a Cloyes two piece timing cover. I had to make a spacer to bring it out about 70 thou.
Couldn't use buttonhead screws or take the screws down some instead of spacing out the damper?
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Old 12-17-2012, 03:33 AM
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Couldn't use buttonhead screws or take the screws down some instead of spacing out the damper?
They already give button head screws and its too thin to countersink. Its that tight.

It worked out with no problems. Belts might be a tinch off but not noticable at all.
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