Reply To: MERCURY MARK 55 LOWER CRANKSHAFT SEAL

[billw]

Just to address the OPs original question directly, fuel and oil naturally puddle in the bottom of a two stroke crank case, especially at idle. Getting rid of that puddle can improve idle quality on some engines. This is what Frank R was getting at in his original post. Different manufacturers and different engine models do this in different ways. I don’t do much with Mark 55s but I know Mark 20s had a lower seal with a factory-drilled hole, to get rid of this puddle. ( I have no doubt that Joe Poole is right about the Mark 55 not having one original seal.) Think of it as a controlled leak, that’s all. It should be a tiny hole, way smaller than found in your standard drill set. #53 comes to mind but I forget. It’s small size makes it somewhat insignificant in the overall run quality but will still allow the puddle to be blown out by positive crank case pressure. Some of the seal cases can be tough to drill, too. I remember doing it once, and it took two drill bits to drill one hole.

Long live American manufacturing!