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Discussion Starter #1
Years ago I built and balanced my 289. Now I read they purposely leave the harmonic balancer in a 20 ounce or someting unbalanced condition. Should I have done the same? What is the purpose of the imbalance? As I recall I balanced my engine to 0 imbalance. I no longer have that engine but am curious.
 

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65 Mustang fastback, GT350 clone
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You can internally balance an engine (the new crate Ford engines are zero balance). You just need a zero balance flywheel and harmonic dampener.
 

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I think the 20 oz harmonic damper only applied to the hipo 289. The rest of the front weight was a "hatchet" weight that was slid onto the crank behind the timing cover.

For zero balance your harmonic damper would have no imbalance factor. If you didn't provide your damper to the balance shop you would have needed to buy a zero balance damper to run with the engine and also a zero balance flexplate or flywheel. Usually, the balancer technician wants the damper and flexplate or flywheel for a balance job along with everything else. If its a flywheel they should also request the pressure plate because it will likely not be balanced.
 

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From my understanding 289s and 302s up into the 80s were 28 oz externally imbalanced. Beginning in the 80s the 302s including the 5.0 liters were 50 oz externally imbalanced. A neutral balance is preferred but is generally not practical for stock stuff due to cost. This is why you have to be careful mixing and matching parts between early engines and the later 5.0 liters such as balancers and flywheels. Most aftermarket cast stroker cranks (like SCAT or EAGLE) are 28oz imbalance. High end forged cranks may be 28oz imbalance or neutral.
 

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Discussion Starter #5
I think the 20 oz harmonic damper only applied to the hipo 289. The rest of the front weight was a "hatchet" weight that was slid onto the crank behind the timing cover.

For zero balance your harmonic damper would have no imbalance factor. If you didn't provide your damper to the balance shop you would have needed to buy a zero balance damper to run with the engine and also a zero balance flexplate or flywheel. Usually, the balancer technician wants the damper and flexplate or flywheel for a balance job along with everything else. If its a flywheel they should also request the pressure plate because it will likely not be balanced.
I did my own balancing at least 40 years ago and I was not aware of 28 oz imbalance back then so I suppose I did a 0 balance. I don't recall ever seeing anything like a hatchet weight. I had access to a machine shop and good supervision when I built my motor so was able to do all machine work myself. I did balance with the damper and flywheel installed. After balancing the crank I added the pressure plate and balanced it as well.
 

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1965 Ford Mustang fastback T5 Ncas 9in Locker
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The hatchet weight was used to compensate for the hi pos bigger rod bolts and nuts. When i had my engine balanced the shop wanted everything that would be reciprocating except disc.
 
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