Often used seasonally, then stored and unused during the offseason, condensation and moisture within the engine promote rust formation.  In addition, the combustion process and short trip driving create condensation and acids that further promote corrosion and rust.

    Rust is as abrasive as dirt, causing problems such as scratching and pitting on cylinders, pistons and bearing surfaces, leading to blow-by, lower compression and reduced power and performance.  When rust forms on needle bearings, bearing failure results.  Rust also causes excessive wear on bearings, camshafts, lifters and gear surfaces.

    Motor oil has little or no natural ability to prevent rust.  It must be formulated with special rust inhibitors.  However, because rust inhibitors typically sacrifice wear protection by competing with antiwear additives for the metal surface, many motorcycle oils are formulated without rust inhibitors.  AMSOIL Synthetic Motorcycle Oils are formulated with breakthrough technology that provides outstanding protection against rust without sacrificing wear protection.

    The ASTM D-1748 humidity cabinet test measures a lubricant’s ability to protect against rust and corrosion.  A standard metal reference coupon is immersed in the test oil before being placed in a humidity cabinet for 24 hours at 120 degrees F. Following the test period, the coupons are removed and inspected for rust. In order to pass the test, an oil may allow no more than three rust spots less than or equal to 1 mm in diameter. Oils allowing more than three rust spots, or one rust spot larger than 1 mm in diameter, fail the test.

    Two separate tests were performed for SAE 40 and SAE 50 oils. As seen in the graphs, failing oils were divided into three categories: oils showing 1-10 spots, oils showing 11-20 spots and oils showing over 20 spots.  As seen in the photos and graphs, both AMSOIL 10W-40 Synthetic Motorcycle Oil (MCF) and 20W-50 Synthetic Motorcycle Oil (MCV) showed no rust spots, placing them at the top of their respective test groups. Many competing motorcycle oils failed the test.  AMSOIL Synthetic Motorcycle Oils provide unsurpassed rust protection, allowing motorcycles to perform better, last longer and require less maintenance.