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309 Posts
Discussion Starter #1
351 4V in '69 Mach / 128K original miles / engine stock

When cold under acceleration car engine makes a rapid knocking sound. Will not knock at idle, during coast, or cruise. Will not knock at curb. Once engine gets warm, knock is significantly reduced to almost inperceptable.

Have had opinions of (1) main bearing or (2) piston slap from cracked skirt.

Your guess? (and thanks)...
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