Starter Motor

When needing a new starter I found the original Yanmar/Hitachi part for $621 and an after-market part from dbelectrical.com for $59. I thought I'd buy the after-market part and take a look - if nothing else I'd keep it in the bilge for emergency use. However after disassembling both the after-market unit and the original I'm hard pressed to find any significant difference. I'm not an expert, but to me these units looked and felt almost identical.