Shaft Couplings - Why Not To Re-Use One

This video show the difference a little bit of rust makes.

The fit of a straight coupling to a 1" diameter shaft is supposed to be a light press fit or .001" or better for split couplings per ABYC standards and SAE J-756 standards for shafting. .001" is the maximum allowable variation between the OD of the shaft and the ID of the coupling, if it is "split coupling", if it is solid, as this one is, then the fit should be a light press fit.

For reference a sheet of standard 20 Lb. paper is .0038" thick. A sheet of paper is 380% larger/thicker than the maximum allowable variation between shaft and a "split coupling". The coupling in the video is a solid coupling not a split coupling so a light pess fit is required.

If you remove a coupling, and there was rust between the shaft and the coupling, it is a good idea to replace the coupling and have it fitted and faced to the shaft by a competent machine or prop shafting shop..

The last thing you want to do is ruin an expensive shaft, or worse, put the boat in reverse and have your shaft come out of the coupling.

Category:

Howto & Style

Tags:

• sailing

[mechone1]

first of all abyc is full of shit .0005 is max fit over (BEARING FIT) and any drive shaft should be keyed with 2 set screws one on the key and 1 at 90 degrees.

For drive applications it should be size for size and the coupling heated shrink fit

good for life.

[techdavey1000]

If the shaft is fitted with a key and Loctite Stud & Bearing Fit is used you won't have a problem. Personally I think that joining a shaft direct to what is basically a car engine is extremely crude but its a popular method on US built ski boats. Over in Europe we have the Vetus Bullflex and also the "Aquadrive" coupling. With the latter sixteen degrees of misalignment can be tolerated. Note that where a boat has a long shaft, in water and out of water alignments may differ. (hull bends!)

[zachsace]

They are supposed to have a key, With the key it shouldn't really spin at all.