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Hi guys, so upon driving shaft into coupler at trans, it did NOT take much force with clean shaft and coupler surfaces. I mean tap tap, not bang bang from the outside of the boat at the end of the shaft. Is this O.K.? It seemed to go in a lot easier than expected. The key does not have any play in keyway on shaft and coupler, and the set screws lined up perfectly, but should coupler to shaft have more of an interference fit than a "tap tap"? Thanks. Rocky.

Rocky,

No. That's the fit you want... Be sure that your shafts are dimpled to match the set screws, (should be two per coupler). and on final installation, safety wire with either stainless or monel wire. The wire will thread from one screw through the other and be wrapped & Twisted together, forming a bridge. The square heads of the set screws will need a hole drilled through two of the parallel faces. The set screws should set into the dimples by about 1/8". Use blue Loctite...

Couplers and shafts have to be matched on a lathe so that the coupler face is a true 90º to the shaft. I they are not done so, you may have some viberation problems...

Br,

Patrick

Thanks Capt., yes the shafts have dimples in them and I did safety wire them with a bridge. I did notice however, there is a third tapped hole through both couplers but with no dimple in shaft at that location. Should I go ahead and utilize the third tapped hole without that dimple for "extra precaution? Rocky.

You could if you want, but really isn't necessary. BTW, stainless keys are OK at the engine end of the shaft...

I have been an advocate of using Brass keys at the coupler. My reasoning is Brass Keys shear much easier then SS Keys and act somewhat like a fuse.

With a severe impact, such as hitting large debris e.g. a phone pole or a submerged rock, the brass coupling key can shear and may save the box and motor considerable damage. Does it defintely work, I don't know, does the key always shear before the box destructs, no. But I have seen brass keys shear on many occasions and that has to reduce the shock from contining forward. A brass key is cheaper and may save you money in the long run.