14 CFR § 125.137 - Oil valves.
(a) Each oil valve must -
(1) Comply with § 125.155;
(2) Have positive stops or suitable index provisions in the “on” and “off” positions; and
(3) Be supported so that loads resulting from its operation or from accelerated flight conditions are not transmitted to the lines attached to the valve.
(b) The closing of an oil shutoff means must not prevent feathering the propeller, unless equivalent safety provisions are incorporated.