[C320-list] Transmission Drive Flange Bolts Fall Out

[Ken Geiger]

A few days ago while motor sailing we heard a low vibration sound.  While continuing, I inspected the transmission output area and at first saw nothing shaking but then observed 2 bolts laying on the floor under the drive flange.

We stopped the motor and I found 3 of the 4 bolts had fallen out and the fourth bolt was loose with the nut still attached.  I found all the nuts bolts and washers under the engine and replaced them and got back under way.

Later at anchor I removed each bolt and nut, cleaned and re tightened with some blue loc tite that we had on board.

The 4 bolts were M10- 1.25 x 33 mm long except 1 was 35 mm long. The bolt used a 15 mm wrench and the thin nut used a 17 mm wrench.  The bolt head had a #7 forged on it.  There was a lock washer used but placed under the bolt head. On auto applications these nuts and bolts would be high strength and perhaps these are as well.

I intend to investigate replacing the above coarse thread with M10-1.0 fine thread bolts that will be more resistant to loosening; fine thread bolts are used on auto drive shaft flange applications.  

There is limited space between the back of the transmission flange and the transmission but I will also investigate using a nylock self locking nuts there.  There is also limited wrenching space between the bolt heads and the driven flange that may present problems finding a suitable bolt.  Perhaps this is why the bolt head is 15mm across the flats.

I also will had a look at the motor mounts and cutlas bearing as the prime source of the vibration that loosen the bolts.

A quick search of this forum found no similar discussion.

Comments welcomed.

Regards

Ken Geiger
Northern Dream #765
on Georgian Bay