Reply With QuoteIt must be internally balanced, doesn't need one if balanced properly.
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?
It must be internally balanced, doesn't need one if balanced properly.
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.
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)
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)
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:
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
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:
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...
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...
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