[C320-list] Transmission Drive Flange Bolts Fall Out

[Warren Updike]

Ken, of course there may be different ways of dealing with the issue; but, from what I know, it is common to use bolts with drilled holes. A wire is then passed through each of the bolts and twisted tightly. This prevents any bolt from backing out. Look for the holes in the bolt heads.

Warren and Pattie Updike
1994 C320 "Warr de Mar" #62

-----Original Message-----
From: Ken Geiger [mailto:kendgb at aol.com] 
Sent: Monday, August 10, 2015 9:52 AM
To: c320-list at catalina320.com
Subject: [C320-list] Transmission Drive Flange Bolts Fall Out

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