A camshaft phaser for use with an internal combustion engine for controllably varying the phase relationship between a crankshaft and a camshaft in said internal combustion engine, said camshaft phaser comprising: a stator having a plurality of lobes and connectable to said crankshaft of said internal combustion engine to provide a fixed ratio of rotation between said stator and said crankshaft about an axis; a rotor coaxially disposed within said stator, said rotor having a plurality of vanes interspersed with said lobes defining a plurality of alternating advance chambers and retard chambers; a camshaft phaser attachment bolt for attaching said camshaft phaser to said camshaft, said camshaft phaser attachment bolt defining a valve bore that is coaxial with said stator; a supply passage (88,106) extending radially outward from said valve bore, said supply passage (88,106) having a supply passage downstream (94,112) end that is proximal to said valve bore and a supply passage upstream end (96,114) that is distal from said valve bore, said supply passage downstream end (94,112) and said supply passage upstream (96,114) end being separated by a check valve seat (98,116); a check valve member (60,62) in said supply passage which prevents flow of oil past said check valve seat (98,116) from said supply passage downstream end (94,112) to said supply passage upstream end (96,114) while allowing flow of oil past said check valve seat (98,116) from said supply passage upstream end (96,114) to said supply passage downstream end (94,112), wherein said check valve member (60,62) is biased toward said check valve seat (98,116) by centrifugal force; and a valve spool moveable within said valve bore such that said valve spool directs oil that has passed through said supply passage to said valve bore. a stator having a plurality of lobes and connectable to said crankshaft of said internal combustion engine to provide a fixed ratio of rotation between said stator and said crankshaft about an axis; a rotor coaxially disposed within said stator, said rotor having a plurality of vanes interspersed with said lobes defining a plurality of alternating advance chambers and retard chambers; a camshaft phaser attachment bolt for attaching said camshaft phaser to said camshaft, said camshaft phaser attachment bolt defining a valve bore that is coaxial with said stator; a supply passage (88,106) extending radially outward from said valve bore, said supply passage (88,106) having a supply passage downstream (94,112) end that is proximal to said valve bore and a supply passage upstream end (96,114) that is distal from said valve bore, said supply passage downstream end (94,112) and said supply passage upstream (96,114) end being separated by a check valve seat (98,116); a check valve member (60,62) in said supply passage which prevents flow of oil past said check valve seat (98,116) from said supply passage downstream end (94,112) to said supply passage upstream end (96,114) while allowing flow of oil past said check valve seat (98,116) from said supply passage upstream end (96,114) to said supply passage downstream end (94,112), wherein said check valve member (60,62) is biased toward said check valve seat (98,116) by centrifugal force; and a valve spool moveable within said valve bore such that said valve spool directs oil that has passed through said supply passage to said valve bore.