Stock BMC cams have opening/closing ramps, and are designed for .012" clearance..
Because most sports cams are designed to lift the valve off the seat quicker (gives more power) they are designed to run bigger clearances.
eg Kent Cams are usually .016", Graham Russell's RE-13 is .016-.018".
Stock Cooper S cams are often set at .015" for competition.
With hi-lift 1.5:1 rockers, you need generally .003" more clearance again.
This is because if you don't, you are reducing the cam's designed `lobe to lifter' clearance at a given rocker clearance due to rocker ratio change.
eg. my RE282 runs the recommended .022" on inlet and .024" exhaust, with 1.5 rockers.
No, they don't rattle, either.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
