Sheared prop shaft coupling bolt

[Jim Cate]

A64 hit it in his first post: with a 4 bolt coupler, you can not shear one bolt without shearing the other three as well. Without inspecting the failed bolt it is pretty hard to determine cause of failure, but shearing it wasn't!

Jim

[Dymaxion]

Post a picture of the bolt face where the failure occurred, a close up macro, and I can very likely tell you how it failed. Was it broken at a thread? If it failed in sideways shear the surface will have been smeared sideways. If it was over torqued it will have a rough but uniform "pullout" surface. If it failed due to cyclic fatigue it will have broken at a thread and will have "beach marks" starting on one side and look like sand ripples across the face.

If your coupling is out of alignment the bolt is being flexed each revolution and one of four bolts could go before the others, due to manufacturing or material variation. All 4 (3 now) should be replaced as mentioned.

[jkishel]

When replacing the bolts, check coupler alignment and run out. The engine may be misaligned and/or the coupler may be worn. Also check the cutlass bearing for wear.

[Sailorbob8599]

If the majority of couplings are located in as awkward a spot as mine, I would seriously question if the bolts were ever properly "torqued" as in with a Torque Wrench. More than likely, they were tightened with a combination wrench of unknown length and maybe even added torque by using some form of extension "just to make sure they're tight" … I agree with whoever said the bolt was broken due to "over torque" and most likely this happened the day it was installed, but went un-noticed … I know I couldn't get a torque wrench in my shaft bolts, I don't know about you folk, maybe your couplings are more accessible.