Just quick question about tolerances in our beloved nailheads. If piston to wall clearance is set between .0004 - .0010 than when should overbore be considered? Thanks in advance,
According to the Buick chassis manual: " If cylinder bore is tapered 0.005" or more, or is out of round 0.003" or more, it is advisable to rebore for the smallest possible oversize piston and rings" The key concern is ring seal. New rings won't seal in an out-of-round bore, and excessive taper will make them expand/contract every time the piston goes up or down. I would guess piston-to-wall clearance up to 0.006" will still work fine (with cast pistons) but you'll likely have piston slap which could eventually case piston damage.
I've seen an engine put together with .006" clearance at the skirts and maybe .013" at the top from a home-brew "rebuild". All the new cast pistons cracked or collapsed at the same time, nearly 6 mos. of occasional use. Not much piston slap or noise from the .060" offset pins. Just a second or two on startup, if you listened hard.
