Volvo Penta Engine Part Catalog - volvopentastore M = manual steering. I = inboard. X = exact steering. Volvo Penta diesel engines have several naming methods. The diesel names are a combination of letters and numbers. As a guideline, the following code letters are used to name the diesel engines: MD22A, MD22A-A, MD22L-A, TMD22A, TMD22-A, MS2B-A, MS2B-R, MS2A-E, MS2B-L, MS2L-E, 120S-E