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Ouch, spun bearings hurt. Glad you found the problem. I lost a motor last fall due to a failed valve spring , and one back in 02' due to spun bearings (oil pump let loose).
Just read your post. I dont mean to be an arm chair Quarterback but by the way you explained it(VERY loud tap!). It had to be a rod bearing. You'll NEVER forget that sound! lol. Tell your buddy I feel his pain.