Systems+Engines

Ask Sail: Straight and True

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Bruce Colton of Annapolis, Maryland, asks:

The stuffing box on my 1986 Bristol 35.5 has been running too hot, approximately 135F in 80F water. I followed Don Casey’s advice and had the machine shop true the propeller shaft to the shaft flange. The shop shaved 0.008 inch off the flange face. Before I re-launch the boat should I also have the shop check and true the transmission output shaft to its flange? This is a lot more work, but I’m prepared to do it to get things lined up properly.

Don Casey replies:
Unlike the propeller shaft flange, which is field-installed, the transmission flange is a constituent component of the transmission and was installed to the same close tolerances as the rest of the box. The likelihood of any misalignment between the output shaft and the flange is very slight. With the prop flange trued to the shaft, all that remains is to raise, lower, skew and tilt the engine to get the two flanges in perfect bore and face alignment. If your stuffing box then continues to run hot, it is either set up too tight or the packing needs replacing. Gore-Tex or a similar modern packing material should initially be adjusted quite loose to allow for sufficient lubrication to avoid overheating or shaft scoring.

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