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I'd probably try a new 29oz-in flywheel first, and see if it works. You might get lucky and get "close enough" for a daily driver. Engines can generally be out quite a bit before any imbalance is actually FELT to any significant degree. I'd try a new flywheel and see what happens.

Do you know what harmonic dampner got installed? Do you know for sure if it's a 28 or 50? Do you have a part number?
 

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Discussion Starter #22
These are the pistons I am using. There was a difference in weight but not significant i.e. +- 5 grams with rings and wristpins. Although lightyears far from being the quality like Probe or similar brand, I think their tollerances are OK for running a normal compression engine for years for street use. I guess summit would not sell them if they were not.

They have slightly higher deck height (increasing compression from 8:1 to about 9:1) yet this still should not affect the balance yielding to vibration and shorter engine life.
 

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These are the pistons I am using. There was a difference in weight but not significant i.e. +- 5 grams with rings and wristpins. Although lightyears far from being the quality like Probe or similar brand, I think their tollerances are OK for running a normal compression engine for years for street use. I guess summit would not sell them if they were not.
They have slightly higher deck height (increasing compression from 8:1 to about 9:1) yet this still should not affect the balance yielding to vibration and shorter engine life.

Your most immediate problem is your balancer and flywheel, the replacement pistons and stock type rods are not causing the problem you are having, they will work just fine in a mild / stock lower rpm application. A complete balance is a good idea, but it will give satisfactory service with out it as long as it is relitivly close. Get a 28oz flywheel and balancer and your problems will go away as long as the shop didn't screw up your crank in their attempt at balancing.
 

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Discussion Starter #24 (Edited)
What about crank? is it also designed for 28 or 50 oz? What if I tried 50 oz damper with the 50 oz flywheel (that I already have) on the original crank (1973 engine)? (It is just much easier to ship 50 oz front damper rather than 28 oz flywheel). Are there any advantages running 28 oz.in compared to 50 oz.in imbalance?
 

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What about crank? is it also designed for 28 or 50 oz? What if I tried 50 oz damper with the 50 oz flywheel (that I already have) on the original crank (1973 engine)? (It is just much easier to ship 50 oz front damper rather than 28 oz flywheel). Are there any advantages running 28 oz.in compared to 50 oz.in imbalance?
If you have a28oz balanced earlier crank you need a 28 balancer and flywheel. As far as what's better, at the level yor at it really doesn't make much difference, but in a high hp / rpm race motor internal zero balance would be prefered.
 

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Discussion Starter #26 (Edited)
In the meantime I got a new 28 oz.in flywheel. The engine runs nearly identical; not better, not worse. Same slight shaking (engine, body, bumpers). Just wondering, what would break first if the engine ended up incorrectly balanced?
 
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