Going back through my own "bike code"....
The law one would be violating by "taking a lane" is ORS 814.430, "Improper use of lanes"
There IS an explicit exemption in the law for narrow roads, bolded below:
814.430 Improper use of lanes; exceptions; penalty. (1) A person commits the offense of improper use of lanes by a bicycle if the person is operating a bicycle on a roadway at less than the normal speed of traffic using the roadway at that time and place under the existing conditions and the person does not ride as close as practicable to the right curb or edge of the roadway.
(2) A person is not in violation of the offense under this section if the person is not operating a bicycle as close as practicable to the right curb or edge of the roadway under any of the following circumstances:
(a) When overtaking and passing another bicycle or vehicle that is proceeding in the same direction.
(b) When preparing to execute a left turn.
(c) When reasonably necessary to avoid hazardous conditions including, but not limited to, fixed or moving objects, parked or moving vehicles, bicycles, pedestrians, animals, surface hazards or other conditions that make continued operation along the right curb or edge unsafe or to avoid unsafe operation in a lane on the roadway that is too narrow for a bicycle and vehicle to travel safely side by side. Nothing in this paragraph excuses the operator of a bicycle from the requirements under ORS 811.425 or from the penalties for failure to comply with those requirements.
(d) When operating within a city as near as practicable to the left curb or edge of a roadway that is designated to allow traffic to move in only one direction along the roadway. A bicycle that is operated under this paragraph is subject to the same requirements and exceptions when operating along the left curb or edge as are applicable when a bicycle is operating along the right curb or edge of the roadway.
(e) When operating a bicycle alongside not more than one other bicycle as long as the bicycles are both being operated within a single lane and in a manner that does not impede the normal and reasonable movement of traffic.
(f) When operating on a bicycle lane or bicycle path.
(3) The offense described in this section, improper use of lanes by a bicycle, is a Class D traffic violation. [1983 c.338 §701; 1985 c.16 §339]
And for sake of knowledge, the statute referenced, 811.425:
811.425 Failure of slower driver to yield to overtaking vehicle; penalty.
(1) A person commits the offense of failure of a slower driver to yield to overtaking vehicle if the person is driving a vehicle and the person fails to move the person’s vehicle off the main traveled portion of the highway into an area sufficient for safe turnout when:
(a) The driver of the overtaken vehicle is proceeding at a speed less than a speed established in ORS 811.105 as prima facie evidence of violation of the basic speed rule;
(b) The driver of the overtaking vehicle is proceeding at a speed in conformity with ORS 811.105;
(c) The highway is a two directional, two-lane highway; and
(d) There is no clear lane for passing available to the driver of the overtaking vehicle.
(2) This section does not apply to the driver of a vehicle in a funeral procession.
(3) The offense described in this section, failure of a slower driver to yield to overtaking vehicle, is a Class B traffic violation. [1983 c.338 §640; 1991 c.482 §16; 1995 c.383 §68; 2001 c.104 §307; 2003 c.819 §15]