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  #1 (permalink)  
Old 03-08-2005, 08:00 AM
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Cobra Make, Engine: FFR #2776, 351w, never dyno'd, just know it has more guts than me.
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Default 351w engine/flywheel/clutch balance

I just picked up a 351w long block which had recently been built and balanced. I'm now shopping for a flywheel and clutch to hang on the back of it. Can I reasonably just balance the flywheel/clutch assembly and hang it on the engine and assume all is well or do I have to pull the guts out of the engine and do the whole thing together?
OK, now here's the "dumb" question...I've been around engines all my life (mostly furrin stuff) and I'm quite familiar with balancing the internals. Now I'm faced with this 351 and I hear all this talk about 28 oz. and 50 oz. imbalance in the flywheel. Hey, I thought the whole idea is to balance these things. I know there's a logical and simple explanation for this, but so far I haven't been able to find it. Anybody wanta take a shot at it?
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  #2 (permalink)  
Old 03-08-2005, 11:34 AM
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My engine is internally balanced. Flywheel and clutch are balanced. I use a light weight flywheel.
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  #3 (permalink)  
Old 03-08-2005, 04:30 PM
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First, you need to check to see if the engine was internally balanced or balanced with the normal 28 oz. flywheel and harmonic balancer. The machinist who did the work should be able to tell you.
Did the engine come with a 28 oz. flywheel?

If the engine was balanced for a 28 oz. imbalance, any 28 oz. flywheel and harmonic balancer you put on it should work fine and you shouldn't need to rebalance. Same with internally balance- if it has been done this way you can buy zero balance flywheel and harmonic balancer and be fine. The clutch and pressure plate shouldn't be an issue. I've never heard of needing to balance with the pressure plate except for on extreme high end race engines turning maximum revs.
Best bet is to check with the machinist who built the engine and have him explain it to you.- Bob
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  #4 (permalink)  
Old 03-09-2005, 06:13 PM
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Post External balance

Cheapsnake
Unlike performance engines where you balance your internals and externals, Ford on their production engines used weighted externals, H/Balancer and flywheel to achieve a reasonable balance, hence the term you hear - "external balance".
They've used two different weights - 50oz and 28oz. You will suffer vibration problems if you mismatch the flywheel and h/balancer unless of course during your build you have done a complete balance.
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Old 03-10-2005, 04:53 AM
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Thanks guys, I'm always amazed at the quality of information I get off these forums. I'm at the point of putting my drivetrain together and this is very timely info for me. I thank you, my Cobra thanks you and my wife thanks you for finally shutting me up about balancing.
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Old 03-14-2005, 07:30 AM
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It's normal to balance the flywheel and the balancer with the rest of the rotating assy.
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Old 03-19-2005, 07:30 PM
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All 351W engines came off the assembly line with a 28 in/oz external balance built into the flywheel and crank damper. Hence, any flywheel and crank damper with the standard 28 in/oz balance will bolt on and work. The clutch doesn't factor into this at all.

The confusion comes in with the 302's, and thus, parts interchangability with the 351W, specifically the flywheel and crank damper. Up until '85 or so, 302's also used a 28 in/oz external balance. Then for some reason, Ford in its infinite wisdom changed the external balance of the 302 motors to 50 in/oz.
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