I had to install an oversize bolt and spacer into the crank to retain the balancer due to stripped out threads. The question I have is will this throw off the balancing of the engine enough to Case a driveling vibration? The engine is a SBC 350, bored .40 over, with flat top pistons (4 valve reliefs), 186 heads (2.20/1.60), wined single plane intake fed by a Holley 750 ZDP, with a 400 crank, and externally balanced flex plate connected to a TH 350 trans and 10 both posi rear with 3.42 gears. Any suggestions any?

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I use a huge bolt and hang a 6" mandrel and a bunch of gears on my crank, and have never caused an issue.
People add all kinds of weight and 99.999999999999999999% of the time it's fine.

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I use a huge bolt and hang a 6" mandrel and a bunch of gears on my crank, and have never caused an issue.
People add all kinds of weight and 99.999999999999999999% of the time it's fine.

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Agreed
I don't think you could possibly drill it that crocked that you'd need to worry ,unless you've had to dimple the hood for clearance:)