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Old 10-14-2008, 10:33 PM   #1 (permalink)
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28 oz vs 50 oz harmonic balancer

I have a 351W stroker motor. I was told that it was 28 oz. balance. How can I tell the difference between a 28 oz. and a 50 oz. balancer? Here is a couple of pictures of the balancer that I have. Is this a 28 oz. balancer?





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Old 10-14-2008, 11:00 PM   #2 (permalink)
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I thought I saw something, that was the 4 hole balancer was a 50 oz and the 3 hole was a 28 oz. This is the mounting holes for the pulley
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Old 10-14-2008, 11:21 PM   #3 (permalink)
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That balancer looks very used up. I would buy a new one. They are about $50. Cheap insurance for a 351 stroker.
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Old 10-14-2008, 11:42 PM   #4 (permalink)
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Joe, I agree. That is why I am needing to know if this is a 50 or 28 oz balancer. Anyone know how to tell?

Paul
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Old 10-15-2008, 12:17 AM   #5 (permalink)
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I always though that was the flywheel folks were talking about.
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Old 10-15-2008, 12:47 AM   #6 (permalink)
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Is this a used stroker you bought and want to replace the balancer and not sure which to order?
Balancers typically are part of the rotating assembly and should be present when the rotating assembly gets balanced. So whether it be a 28 or 50 oz it may not be that any more as when/if it were balanced with the assembly some weight may have been removed. (see those 1/2 holes) that's how weight is removed during balancing..
If you replace a balancer that came off a balanced engine the new balancer should get balanced to match the old one.
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Old 10-15-2008, 12:58 AM   #7 (permalink)
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Convincor, Amen!!! Should mention a factory engine is alot different than a stroker or even a good rebuild. A good rebuilder will even balance a stock motor as an assembly.
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Old 10-15-2008, 01:09 AM   #8 (permalink)
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If you have the original balance NOs you could take the new balancer to the original shop and they can match it to the balancer that was originally done ,,,helps to have paperwork
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Old 10-15-2008, 01:36 AM   #9 (permalink)
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Thats a 50oz. A 28 will have half of that weight.

All 351w are 28oz. Most strokers are 28 or Zero.

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Old 10-15-2008, 02:03 AM   #10 (permalink)
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Stock 351w 28oz balancer:

Looks to me you have a 50oz off a 5.0/302 later 4 hole. Looks more like a 5.0 86 and up.
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Old 10-15-2008, 02:16 PM   #11 (permalink)
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I have to agree. The balancer looks the same as the balancer on my donor 302 out of my 88' GT. I am just a bit confused about the balance.

I plan on having crank rebalanced, but was hoping to get a new correct balancer before I bring it in. I have a new flywheel with a bolt on 28 oz weight already. I guess I need to get the 50oz weight for the flywheel and bring it in to verify that it is the 50oz balance. Is it possible that this crank (4.170 stroke) could be balanced 50 oz?

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Old 10-15-2008, 02:48 PM   #12 (permalink)
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If you have a 28 oz flywheel, use it. The flywheel and balancer both need to be 28 oz imbalance. To rebalance a rotating assembly to 50 would be very expensive, requiring slugs of mallory metal be installed in the crankshaft. Also, if the engine is assembled, you will have to completely disassemble the engine for the rebalace. If this engine assembly has been previously balanced, it will be at 28 oz. Buy a 28 oz balancer and use your 28 oz flywheel. I don't understand why you want to have it balanced to a 50 oz imbalance. A 28 oz imbalance engine is easier on the bearings, and runs smoother than a 50 oz imbalance.
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Old 10-15-2008, 03:37 PM   #13 (permalink)
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I was (still am) confused over the whole imbalance issue. I have a '90 stock 302, and it is 50oz imbalance. Then I got a 331 stroker short block, with a 28oz imbalance. Why the difference? Why don't car companies just design fully balanced engines? Is there rhyme or reason for the imbalance?
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Old 10-15-2008, 03:49 PM   #14 (permalink)
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Quote:
Originally Posted by Mark_VA View Post
I was (still am) confused over the whole imbalance issue. I have a '90 stock 302, and it is 50oz imbalance. Then I got a 331 stroker short block, with a 28oz imbalance. Why the difference? Why don't car companies just design fully balanced engines? Is there rhyme or reason for the imbalance?
Money spent per unit. The 50oz imbalance engines are cheaper to manufacture. There is slightly more crankshaft harmonic with the 50oz imbalance, but the factory feels it can get away with it because of the small engine size and short stroke. Stroker engines are easier to balance at 28 than 50.
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Old 10-15-2008, 04:20 PM   #15 (permalink)
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The best option is to have a zero balanced engine - ie it is balanced internally on the crank shaft and does not require weights on the flywheel etc. When you have your rotating assy balanced, you need to take the flywheel and the balancer in. Usually the weight on the flywheel will get adjusted a little rather than the balancer (if needed)- this way if you need to change the balancer you don't need to get the whole set up rebalanced - you can just swap out the balancer. If you need to replace the flywheel then you just switch over the weight from the old flywheel to the new one. The less weight needed to balance (ie zero vs 28oz vs 50oz) means that there is less rotating mass and the engine will be able to rev faster. The 28oz is a good compromise between achieving that goal without the expense of zero balancing.
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Old 10-15-2008, 04:34 PM   #16 (permalink)
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It's my experience that a machine shop that changes or adjusts the flywheel imbalance is cutting corners. The shops that I have always used will drill the crank to adjust the imbalance. This allows any 28 0z flywheel to be used incase a replacement is required. Some flywheels and harmonic dampners don't use a bolt on weight. Centerforce billet flywheels start with a 0 balance flywheel, and drill holes to lighten the light side, making it a 28 oz imbalance. This design akes for a smoother running flywheel because the imbalance is spread over a greater area. The Romac dampner also doesn't use a bolt in balance weight. The imbalance is machined into the dampner hub.
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Old 10-15-2008, 05:12 PM   #17 (permalink)
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Mark a lot has to do with how much material is on the crank shaft and it's stroke.
This has more to do with the actuall balance then the "harmonic" of the engine.
If you were to compare side by side. your stock 90 302 crank. then the 331 stroker crank.
You would notice more material on the counter weights of the crank on the stroker crank.
This makes for better/more balancing that can be done with the crank itself. Why the lighter,less weighted 28oz balancer is used.
Your 302 crank haveing less material on the counter weights. Needs more 50oz weighted balancer to offset the less weight of the crank.
The harmonics of the engine are a bit different. these are in inbalance's or harmonics sent thru the engine from the rotating parts inside. when the piston fires. when the valves open or close along with valve train motion. These sent for lack of better terms. Vibrations thru the engine. Another factor the balancer/damper needs to control.hth
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Old 10-15-2008, 05:39 PM   #18 (permalink)
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try www.network54.com/forum/119417

The guy that seems to answer a lot of the questions about SBFs knows his stuff and there are a lot of good question/answer pages there.
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