[C320-list] FW: Drive shaft problem

[Irv Grunes]

-----Original Message-----
From: Irv Grunes [mailto:igrunes at comcast.net]
Sent: Tuesday, June 27, 2006 10:59 PM
To: C320-List
Cc: Seiden, Bob; Richard Wendt; Oryniak, Tom&Coryn; Cleverly, Grant
Subject: Drive shaft problem


Guys,
Thanks to all for your input.

I just got back from fixing the problem

The shaft key on used on #851 when we had the bent bronze shaft replaced
with a stainless one is 1/4 inch square BRASS or Bronze. It sheared after 3
years on Monday and the shaft dropped out of the coupling.  The crew on
board managed to sail the boat back to the slip.

First we bought a 1 inch doughnut zinc per Jeff Hare's album and
recommendation.

We then mounted the zinc to keep the shaft in place and called Tow-Boat US
to tow us to the boatyard to get the problem fixed.  Since there were small
craft warnings out, Tow-BoatUS would not do a slip to slip transfer.

Finally decided to take the coupling off the tranny.  Found all the bolts
loose including the square head set screw bolt that was not turned all the
way in to capture the shaft.  No hole in the head for a seizing wire, yard
used loctite.

Back to yard to get a new brass key (It was 2 inches long) and to hardware
store for 6 inch mill file to clean out the shaft and coupling keyway,
loctite, emery paper to size the key by rubbing it, and a new longer set
screw bolt.

The set screw bolt did not fully extend past the coupling ID until we forced
it past a bad thread right at the ID.  Was then able to reuse the original
setscrew.

Sized the key on the emery paper to fit the shaft and coupling, but key too
long and wouldn't sit flat in the shaft key slot and no hacksaw to shorten
it to match the coupling length.
Took the file and cut a groove all around the key, stuck the good part on
the coupling keyway, popped it with a hammer and it broke at the groove,
just the correct size.

Everything then slid together nicely.  Lined up the shaft set screw hole
under the coupling. According to the yard mechanic, it was IMPORTANT TO
REALLY TIGHTEN THE SET SCREW FIRST TO LOCK IN THE KEY, and we did so with a
liberal coating of loctite.

Slid the shaft coupling up to the tranny coupling, Matched the marks we put
on both of them and used the brass bolts, lock washer and nuts we removed.
I assume that brass (bronze) bolts are used so that they would shear under
heavy stress as well as the key.

Installed and tightened the shaft coupling bolts and we were done fixing the
key.

Moved the zinc back to about 1/2 inch of the packing nut, tightened it, and
tapped it with a hammer and tightened it some more.

Ran the engine in forward and reverse with no significant vibration or heat
at the stuffing box.

Moral of the experience, CHECK and TIGHTEN all the shaft coupling bolts
every spring and sometimes during every season.  I am convinced the key
sheared by the loose set screw and coupling bolts working on the key for
three years.

Again thanks to all that contributed.

Irv Grunes
Isle of Wight #851