Reply To: MERCURY MARK 55 LOWER CRANKSHAFT SEAL

[mercuryspecialist]

Hi Jim,
According to even our oldest Mark 55 paper parts manual (my family was a Mercury dealership when the Mark 55 was introduced for the 1955 year model, and we sold them when new), both the single upper (crankshaft) oil seal and production with a single lower (crankshaft) oil seal do utilize the same part number oil seal. Said another way, there should not be a bleed hole in the oil seal frame. As to the oil seals, we prefer to utilize a Viton lip material oil seal (we sell these for 7.39 each) to have improved life against ethanol blended gasoline, especially so with a single (lower) oil seal version. Buna-N would be the original and currently available oil seal lip material for factory and most aftermarket sources. Yes, one can carefully drill the correct diameter hole in the oil seal frame to create the factory oil seal with the small hole(s) for later models with two lower (crankshaft) oil seals (where the oil seal closest to cylinder #4 has the small hole(s), and the oil seal furthest from cylinder #4 does not have a hole(s)).

Regards,
Joe
(770) 597-5992