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View Full Version : Big block Chevy without harmonic balancer?



Wizard29
10-16-2006, 04:33 PM
I am having a new 632 stroker with 8-71 blower being built for my show/pro-street car. The builder informed me today the engine will not use a harmonic balancer, but will instead use a crank hub behind the lower blower drive pulley. Apparently, since the engine is being fully balanced to within 1/2 gram, a harmonic balancer isn't needed.
This would be my first experience with an engine not using a balancer. No balancer just sounds weird. Anybody else heard of this and/or used a crank hub instead?

Havasu47
10-16-2006, 04:36 PM
It must be internally balanced, doesn't need one if balanced properly.

SmokinLowriderSS
10-16-2006, 05:18 PM
As Havasu47 said. If it is internally balanced at all the crank counterweights, there is no purpose for the "balancer" except as a pulley mount (aka damper). There will also be an "unbalanced" flexplate instead of the weighted one. 396 & 427 chevy's had a torsional damper, it was not counterweighted as a "balancer". A lot of Fords the same but I don't know Fords well enough to know which ones.

Havasu Carrera
10-16-2006, 05:41 PM
Ballancer-Ballances
Harmonic Balancer?Damper- Dampens the shock of the pistons fireing??
Blower motors have the belt and the blower doing the dampening??
(Mert Littlefield) Oh also if going to use for years on end and not just race and rebuild frequently you should use a Harmonic Ballancerrrrr Not counter weighted hub. (ok yell at me)

Bense468
10-16-2006, 05:56 PM
If the motor is internally balanced. He will probably use an internally balanced crank hub (i.e. this 427 crank hub) and like someone else said, you will also need a internally balanced flex plate.
This is a BDS crank hub from good vibrations, yours may be a different mfg. but you get the idea.
http://img154.imageshack.us/img154/6848/bds109dq6.jpg (http://imageshack.us)

Cheap Thrills
10-16-2006, 06:04 PM
Ballancer-Ballances
Harmonic Balancer?Damper- Dampens the shock of the pistons fireing??
Blower motors have the belt and the blower doing the dampening??
(Mert Littlefield) Oh also if going to use for years on end and not just race and rebuild frequently you should use a Harmonic Ballancerrrrr Not counter weighted hub. (ok yell at me)
Ding !
Harmonic balancers do just that, The rubber and the outer ring of the balancer, Balance (absorb) the harmonics ( multiples of frequency) caused by fireing of the power stroke. without it there would be uncontrolled harmonics (Vibration)(Frequencies)( oscilation) ( call it what you want) radiating through the crankshaft the uncontrolled harmonics can become intense enough to break a crank. ( Like an opera singer breaking a glass )
A well balanced engine will have less harmonics
Alot of new engines dont have one and rely on the accessory drive belt to absorb the harmonics.
A wide Blower Belt does the same.
At least that's my understanding of it.
C.T. :wink:

wsuwrhr
10-16-2006, 06:40 PM
A harmonic balancer has little to do with balance of the reciprocating assembly.(crank-rods-pistons)
However is does have everything to do with dampening the harmonic vibration of the reciprocating asembly. Hense why it is also called a vibration dampener.
In some engines it serves both purposes, balancing the reprocating assembly, and dampening the harmonic vibrations.
When the spark plug fires the crank is bent ever so slightly, when it springs back it causes a violent vibration, over time this can fatigue the metal by workhardening and causing it to break.
The best I can describe it right now is when you hit a hammer on something REALLY hard and it springs back and it vibrates your arm. It happens with a sledgehammer sometimes if you hit it wrong too.
Cast cranks are normally EXTERNALLY balanced, forged cranks are normally INTERNALLY balanced.
Externally balananced means the harmonic balancer serves both purposes as it carries an offset weight, as well as the flywheel or flexplate/torque converter.
I have never heard of the blower belt serving this purpose, but it is possible.
The best way to break a crank is not to run a balancer. IMHO.
Horizontally opposed engines don't normally use one though. Subaru being the exception. The opposed engine design cancels out the vibration.
Hope this helps.
Posted this in the gearheads and blower motor sections also.
Brian

wsuwrhr
10-16-2006, 06:41 PM
Yea what he said
Ding !
Harmonic balancers do just that, The rubber and the outer ring of the balancer, Balance (absorb) the harmonics ( multiples of frequency) caused by fireing of the power stroke. without it there would be uncontrolled harmonics (Vibration)(Frequencies)( oscilation) ( call it what you want) radiating through the crankshaft the uncontrolled harmonics can become intense enough to break a crank. ( Like an opera singer breaking a glass )
At least that's my understanding of it.
C.T. :wink:

Wizard29
10-16-2006, 06:56 PM
Interesting.
It does make sense that a tensioned accessory drive belt or wide blower belt would absorb the harmonics if the belt was under enough tension. Hopefully that will be the case in this build. I can assume so since this builder (a quality shop) is doing it. This will be the third engine they've done for me and the first two were quite good.
A large blower motor like this is a little bit of uncharted territory for me. If anybdy has any other info to add, by all means...

wsuwrhr
10-16-2006, 07:04 PM
I am skeptical.
I would inquire about this, seriously.
A blower cog belt shouldn't be very tight either.
The motor and blower grow taller with heat.
Too much tension can wear the front main bearings and the blower drive snout.
Brian
Interesting.
It does make sense that a tensioned accessory drive belt or wide blower belt would absorb the harmonics if the belt was under enough tension. Hopefully that will be the case in this build. I can assume so since this builder (a quality shop) is doing it. This will be the third engine they've done for me and the first two were quite good.
A large blower motor like this is a little bit of uncharted territory for me. If anybdy has any other info to add, by all means...

Cheap Thrills
10-16-2006, 07:14 PM
Interesting.
It does make sense that a tensioned accessory drive belt or wide blower belt would absorb the harmonics if the belt was under enough tension.
It doesn't require alot of tension to couple the crank harmonics to the drive belt. An overly tight belt will wear the bearings out of whatever it is driving. (A blower in your case.) and a belt that is too loose wont couple the crank harmonics.
I agree with Brian here the best way to break a crank is to run without one.
If it were mine I would run a Rattler or a Fluid Damper or any SFI approved unit on it just for peace of mind.
Cheers.
C.T. :wink:

Wizard29
10-16-2006, 07:39 PM
Just did a little bit of reading and found that running a blower without a balancer is common and just about as reliable. In fact, it was recommended a balancer not be run because balancers do not handle the added stress of turning the blower along with the rest of the accessories well. Apparently, they tend to come apart. BDS recommends that on any large cubic inch high HP application, only a crank hub be used.
Depends on who you talk to, I guess.

Havasu Carrera
10-16-2006, 07:56 PM
http://unix-scripts.com/hb/uploads/BlownSleekn2n.jpg
I got this BHJ when I got the blower Broke a ton of parts but its not one of them. I guess if their SFI certified they tend not to break as easy. This one spun 8500 rpm a few times!! YEP!! I KNOW.

Moneypitt
10-16-2006, 08:27 PM
We've ran for several seasons (all) with just the drive hub to solid driveshaft. No blower or accessories, both internally and externally balanced. (different hub and flexplate ). Very few of the circle flats use Harmonic Balancers, but it should be noted that these engines don't see the type mileage that a street car would, and a street car won't see the type of extended high Rs these engines see every heat.............MP

Froggystyle
10-17-2006, 07:18 AM
My last blower motor had no balancer. A double-keyed crank nose with hub was all it took. I have heard from more people than not that this is the way to go.
I have a Fluidamper on the Revolution's, but they are turbocharged so it doesn't really apply.

superdave013
10-17-2006, 07:58 AM
you can do it both ways.
On the drag race engines we did not run a balancer. It made a big difference on how quick it went from idle to 9K. It does not matter if the engine is intrenal or externally balanced. They make hubs with and with out the counter weight.
BHJ and fluiddamper both make balancers that will take blower pulleys. I think if I was building a blown daily driver or pleasure boat I'd go for the balancer.

Wizard29
10-17-2006, 07:43 PM
It apears to be a matter of opinion.
I've spoken to a few people and some of them say use a balancer while some of them say I don't need one. The general concensus amongst those who say I don't need one is that the blower belt sucks up any harmonics pretty well. Gotta figure that if some auto manufacturers aren't using a balancer on their engine and relying on the tensioned belt instead, there must be something to that theory.
The builder says I don't need one and is building this engine for "big streetable power" as he wrote on the order. He's built quite a few. Like I said, this is for a show/street car. It will see very little run time, and will probably be trailered to most places it goes.
If it breaks the heavy duty forged crank that is being put in there, then I'll know to have a balancer next time, I guess...

sawtooth
10-17-2006, 08:23 PM
A good friend of mine ran a Hondo drag flat in IHBA for three years with no dampner, BBC with dual carbs ran modified elemanator 10 sec class. Ran good enough to get high point champ in '93. He used a blower hub that he turned down, never had any problems. Just some useless info.

Bense468
10-17-2006, 08:58 PM
All you need is the hub. Look at post 6.

blowngas
10-18-2006, 11:46 AM
I've run just the pulley hub on my race boat-----most other lake guys use some sort of a harmonic balancer-----I've seen some with the drive pulley stuck out so far you would think the crank would have come apart, but still goin!!!-----to each their own