[C320-list] ST4000+ Autopilot Service Tips

[Warren Updike]

Isn't it fun!  I went though mostly the same steps.  Sharp minds work in
similar ways.

-----Original Message-----
From: Ray Durand [mailto:durand.mail at verizon.net] 
Sent: Monday, April 25, 2011 10:38 AM
To: C320-list at catalina320.com
Subject: [C320-list] ST4000+ Autopilot Service Tips

Thought I'd pass along a few tips on servicing the older ST4000+ (black)
wheel autopilot that I learned while working on mine.

 

A few weeks ago my autopilot stopped working after 10 years of service.
After discovering that Raymarine no longer sells parts for the ST4000, I
wasn't exactly looking forward to spending ~$1500 for a new one.  I decided
to do some research and found a ST4000 service manual  on the web:
http://www.ganssle.com/jack/st4000.pdf   

 

I opened up the housing (inserting a blade screwdriver in between the two
halves and prying it apart) and discovered the belt had broken and one of
the rollers had broken off.

 

I repaired the broken roller by inserting a 4-40 screw from the back side
through the mounting post, and secured it with a lock washer and nut.  I
ordered a replacement belt (~$18) from Polytech:
http://shop.polybelt.com/searchquick-submit.sc;jsessionid=FCCE20B52207EBC1AD
2339390A72B1B4.qscstrfrnt01?keywords=d169  

 

After putting it back together, it initially seemed to be working OK, but
after running it through its paces I discovered that the belt occasionally
slipped where it engages the motor drive.  

 

After playing with the belt adjustment (more on that below), I couldn't get
the belt quite tight enough where it didn't slip any more.  I was beginning
to think that the belt was the wrong size.   It turned out that the new belt
was stiff and needed some time to soften up.  In fact, a week later the belt
was so tight that I had trouble turning the wheel when the autopilot was not
engaged.

 

After finding more tips on various web sites, I decided to take it apart and
do more servicing.  I removed each of the rollers and lubricated each
mounting post with al small amount of lithium grease.  I lightly sanded both
surfaces of the housing where the belt rides on using 600-1000 grit sand
paper and  put it back together.  After more belt adjustment, I went out for
a test sail and it worked perfectly.  All of the noises (belt squeal,
rattles) that I had become accustomed to over the years were gone.   The
grease and sanding made a huge difference.

 

Belt adjustment tips - there's an adjustment access on the back of the
housing near the lever that engages the autopilot.  Pry off the cover and
you'll see a small metric size allen head screw.  Before attempting an
adjustment, you have to first loosen a circular nut that tightens the allen
screw - this was very difficult on mine since the nut was frozen and the
only way to turn it is using two small holes in the nut.  I bought a snap
ring removal tool and still had problems.  After several unsuccessful
attempts with penetrating oil, a heat gun finally did the trick.  As you
turn the allen screw, it adjusts the relative position of one of the rollers
with the belt.  You have to take it apart to see how it works.  It takes a
little bit of playing with the adjustment to get the belt tension right.  In
retrospect, the original setting on mine was probably OK even with the new
belt.  If I had to do it again, I would let the belt soften up first before
installing it.  Probably letting it sit in the sun or putting it in some
warm water would do the trick.

 

Ray Durand #822

Marina del Rey , Ca