One cylinder of a two-stroke cycle locomotive engine was converted to operate with methyl alcohol (methanol) as primary fuel and pilot injection of diesel fuel for ignition. Two fueling schemes, featuring injection of methanol and pilot fuel at different locations in the cylinder, were evaluated. Results showed that the methanol-fueled cylinder produced power outputs and thermal efficiencies very close to normal diesel values at rated engine speed and load, with methanol fueling rates up to 95% by BTU input. However, the highest thermal efficiencies with high percentages of methanol fueling were accompanied by pronounced diesel-type knock. An explanation of this phenomenon is put forth in this paper.