O.D. for QD-18 drive shaft

[DrummermanBob]

No micrometer in my tool kit and I want to be sure I purchase the correct drive shaft seal for a QD-18 Johnson 10hp outboard. Also, is there a taper on these shafts? The lower third of the shaft slides much easier than the rest of the shaft through the seal and housing just below the seal.

[fleetwin]

OK, so this 10hp still has the larger gearcase, correct?  I don’t know of any taper on the driveshaft, but it is possible.  Wear in the seal area of the driveshaft should be fairly obvious as either a grooved area, or rusted/pitted area.

What part number seal are you using?  Is it OEM?  And yes, there were changes to some of the OD dimensions of some of these seals, so it is not difficult to end up with the wrong one, especially if the gearcase has been swapped out over the years.  Does you new seal appear as the its OD will fit properly into the gearcase casting?

I don’t think the driveshaft OD dimensions changed over the years of the style of gearcase, mid 50s to late 6os, but I could be wrong.  I would have to research it.  There are so many little changes that have occurred over the years, we often don’t discover them until we are working on the stuff and pieces don’t fit.

[Mumbles]

The shaft size for your ’57 QD should be 1/2″ or 0.500″, the same as the eighteen horse FD’s.

[frankr]

Some of those drive shafts had a band of hard chrome plating in the area where the seal rides to reduce wear and grooving from the seal.  That is a thin band of chrome plating but might account for your observation of suspected increased size or “taper”.

[Mumbles]

The lower third of the shaft will be factory fresh and clean with no carbon buildup or corrosion on it. Maybe try cleaning the other two thirds with some abrasive cloth and see what the result is.

[Author]

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