Replace ST4000 Mk2 AutoPilot Belt

KZW

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May 17, 2014
831
Catalina 310 #307 Bluewater Bay, FL
A month ago, my Raymarine ST4000 autopilot stopped auto piloting. It was obvious the belt was the problem as bits of yellow belt teeth were falling out. Although I'm the 3rd owner, I'm sure it was the original belt, 16 years old. Picture 1 shows the wheel mounted autopilot ring. You can see a bit of the damaged belt at the bottom of the ring, peaking out below the stainless steel retention band.
I went to West Marine before taking the autopilot apart. That was a mistake as they were sure I needed the gray belt shown in picture 2, inside the damaged OEM belt. They did take the grey one back and ordered the correct belt, Raymarine Part # A18083.
When I did take the autopilot apart, the part shown in picture 3 fell out. This is a plastic nub with a brass insert to hold the retaining plate (the 3mm hex head on the right in picture #1). There is only thin plastic holding this onto the wheel mount backplate. I used superglue to put it back in the correct position, and then plastic bonding epoxy around the thing to reinforce. If it breaks again, I will through bolt it.
The real surprise was picture 4. This is the bolt holding in the right side of the retaining plate. Note the complete lack of threads. Some worker in the assembly plant just picked it out of the box and inserted it without ever looking for threads. Needless to say, I replaced that item.
Bottom line, the belt swap out worked and the autopilot functions again - a real plus when single handing.
 

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Rick D

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Jun 14, 2008
7,132
Hunter Legend 40.5 Shoreline Marina Long Beach CA
Good job problem solving! On another thread years ago, a poster said that the motor was available at a hobby shop, for future reference.
 

KZW

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May 17, 2014
831
Catalina 310 #307 Bluewater Bay, FL
Thanks for the heads up. I build and fly radio control airplanes and use electric motors. I will keep it in mind.
 

KZW

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May 17, 2014
831
Catalina 310 #307 Bluewater Bay, FL
JK,
Thanks for the info. However, you have the wrong belt for my autopilot. The belt you list is for the Mk1 autopilot (black wheel housing). I have a Mk2 autopilot (grey wheel housing). The belts for the Mk1 will not fit the Mk2 and vice versa. The one for the Mk2 is Raymarine part no. A18083.
http://shop.polybelt.com/searchquick-submit.sc?keywords=A18083

I have no idea why the Mk2 belt is $30 more?????!!!

Are you still in the Bahamas, or have you sailed into the Gulf?
 
Last edited:
Nov 18, 2010
2,441
Catalina 310 Hingham, MA
Sorry. Thought you had the MK1. Yeah, that's strange that the MK2 is that much more. The MK2 belt is only $46 at Defender.

We are in the Caribbean. We will be staying in St. Thomas for a while to make some money and restock the savings.

Happy Holidays
 

KZW

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May 17, 2014
831
Catalina 310 #307 Bluewater Bay, FL
JK, I envy you. St Thomas is beautiful.

Given the shipping from Defender, and the sales tax with West Marine, it was a wash between the two.