Gearbox fell off

[JonJon]

Just a heads up for all you guys with Perkins 4108 and Hurth Gearboxes mine fell off the other week just executing a real slick manouevre up behind another boat moored to the pontoon - engaged reverse to stop, engine revved but no reverse with the inevitable consequence. Subsequent investigation showed all six bolts had vibrated loose ( you cant see them they are behind the gearbox flange plate engine side). Reverse was just enough to pull the whole unit free of the engine. No serious damage but could have been a lot worse just grateful I was in the marina.

Probably worth a waggle when you are next upside down on your back underneath the prop shaft!

 

[alb40]

I had a similar experience with my old boat, and a BMC engine.

Except the gearbox bolts sheared off, instead of loosening. Investigations revealed that the shaft had a sight twist, causing misalignment, and eventually the bolts gave up...

 

[JonJon]

This gave no sign of excessive vibration I have owned the boat for 3 years, only one thing different this year I was forced to motor for a short while with a prop that had considerable marine growth. Maybe thats what did it. The gearbox engages on a profile on the flange housing so there shouldnt be any excessive torque or shear imparted to the bolts. Loctite and spring washers fitted so we´ll see what happens.