A lubricant injector for injection of lubrication oil into the cylinder of a large slow-running two-stroke engine; wherein the injector comprises an injector housing configured for being mounted in a cylinder wall of the cylinder; the injector housing comprising a nozzle tip at one end of the injector housing for reaching into the cylinder when the injector housing is mounted in the cylinder wall; wherein a nozzle is provided in the nozzle tip, the nozzle extending from an inner cavity inside the injector housing and through a wall of the nozzle tip for ejection of lubrication oil from the inner cavity out of the injector housing through the nozzle; wherein a valve member is provided inside the injector housing, the valve member being mounted reciprocal between an open and closed state of the injector; the valve member sealingly covering the nozzle when in the closed state for preventing access of lubrication oil to the nozzle, and the valve member being movable away from the nozzle during an open state for giving access of the lubrication oil from the inner cavity to the nozzle during an oil ejection phase; wherein either, A) the injector housing comprises a plain bearing with a first surface, and the valve member comprises a stem with a second surface, the second surface being provided slidably abutting the first surface in order for the stem being reciprocally guided by the plain bearing along a contact region between the stem and the plain bearing; wherein the valve member comprises a valve needle in coaxial longitudinal extension of the stem, the valve needle comprising a needle tip which is closing the nozzle when abutting a cooperating valve seat in the nozzle tip; wherein the first surface and the second surface are hardened surfaces; or B) the injector housing comprises a cylindrical cavity part with a first surface inside the nozzle tip, the nozzle extending from the first surface through the wall of the nozzle tip; wherein the valve member comprises a cylindrical sealing head with a second surface that is arranged slidably abutting the first surface in order for the sealing head to sealingly cover the nozzle when in closed state; wherein for the first surface and the second surface are hardened surfaces. A) the injector housing comprises a plain bearing with a first surface, and the valve member comprises a stem with a second surface, the second surface being provided slidably abutting the first surface in order for the stem being reciprocally guided by the plain bearing along a contact region between the stem and the plain bearing; wherein the valve member comprises a valve needle in coaxial longitudinal extension of the stem, the valve needle comprising a needle tip which is closing the nozzle when abutting a cooperating valve seat in the nozzle tip; wherein the first surface and the second surface are hardened surfaces; or B) the injector housing comprises a cylindrical cavity part with a first surface inside the nozzle tip, the nozzle extending from the first surface through the wall of the nozzle tip; wherein the valve member comprises a cylindrical sealing head with a second surface that is arranged slidably abutting the first surface in order for the sealing head to sealingly cover the nozzle when in closed state; wherein for the first surface and the second surface are hardened surfaces.