Autopilot Raymarine ST 6000, unplanned maintenance.
Jan 5, 2019 10:28:33 GMT
Post by sailbleu on Jan 5, 2019 10:28:33 GMT
Hello all ,
would like to share some information concerning one of the most important accessory on our boats , the autopilot , in my case the ST 6000 .
Last summer I heard some disturbing sounds coming from the drive unit . It was obviously a kind a grinding noise you get when mechanics are not sufficiently lubricated .
Therefor I excessively sprayed some lithium grease on the out sliding arm that turns the quadrant , hoping the grease would find it's way to where it was needed .
Wrong assumption , I had to find out afterwards .
A month ago I was on the boat for a few weeks and decided to address the problem in a ' professional-do it yourself way ' . I'm aware of the prophetic rule " if it ain't broke , don't fix it " , but my philosophy has always been the kind of the preventive maintenance , and in this case I don't want the AP to let me down when crossing the Atlantic .
So disassemble the unit and do a proper grease-job was the name of the game .
Easier said than done , I was unable to get the cast-iron or is it cast-aluminum alloy back cover off to get an understanding on how to dismantle the unit so I could reach the actual non-lubricated parts . That cover is held to the rest of the unit by 4 cornered allen screws , and eventually I found out that also 2 long brass bolts kept the cover on , but that was after I messed up .
You must understand the unit was on location as the electric wiring was still attached to it .
Therefor I wanted the solid cover off to disconnect the leads and take the unit to a more comfortable place on the boat .
At that point I had no clue on how to get the cover off so I thought of working around it and try to get the out-sliding arm off in order to grease the driving mechanisms .
I searched the internet but strange enough there's little or nothing be found on the matter .
Now there's a lot of parts involved of which I don't really know how they're called , so I hope you can bear with me on my used terminology .
Long story short , I got the cap of the main pipe off , pulled the arm completely out until it jammed and could see the drive is a combo of worm and worm-holder. By pulling harder ( I wanted that worm-holder & arm out of the way) and I my enthusiasm to get this job off my bucket list I managed to pull the lot out and so came a bunch of bearing balls too . They flew in every direction , in holes , in gaps , straight down to the bilge .
It's one of those awkward moments you realize you're in trouble , and that's putting it mildly.
Drastic times call for desperate measures , I just cut the wiring and took the unit to the OT ( operating theater) inside , the saloon .
Let me explain with pictures and some guiding comments under each pic.
Exploded view of the autopilot , unfortunately no explanation / indication of the actual worm-drive itself.
This is where I started , remember it was this inner-pipe with attached worm-holder I was desperate to pull out with a fireworks of bearing balls as a result .
The main pipe with worm inside , on the top/end a groove for the cir-clip that gave away .
The worm-holder , and if you look close you can see a few bearing balls here and there , I managed to retrieve some more , but the rest is to be found in the bilge somewhere.
Very interesting pic this is , the main pipe , and notice the red arrow , that's the spot where you can find a small hole . Yes ,....... a hole to spray in some lubricant . I missed that one , silly is it not .
Up to date I still don't know how this main pipe is fixed to the unit , if I could gotten that off that would of saved me all the work that comes next . I tried everything , most likely it's screwed on/in , but I didn't want to press my luck by using brutal force to unscrew it .
Also notice the long brass yellow bolts holding the heavy back cover in place together with the 4 corner allen screws.
The back cover
Again a very interesting picture , the worm-holder and the ' recirculating bearing ' . Never heard of it before , but in this type the bearing balls are continuously in a loop of circulation and are being prevented to escape . See one of the next pics.
The back cover off with a nice view on the actual drive itself .
Very ingenious system , but that goes for the complete autopilot .
Center view is the solenoid that commands the drive-section and consequently the position of the rudder by pulses of the CPU in conjunction with the date from the flux-gate compass .
Another thing to worry about , notice the lefthand corner next to the solenoid . Drive belt debris , need I say more .
The drive belt specs , another spare part to have on board I guess . Suggestion : don't buy Raymarine's , unless you don't mind paying 3 to 4 times more than this easy over the counter obtainable small belt .
I'll focus on the drive-section itself now because that had come off so I could get the worm out and re-unite it with the worm-holder .
Clock work mechanics , the planetary gears . 2 dowel pins hold this ' contraption ' on the worm .
Some explanation on the planetary gears , they run on the little axles no bearings involved . Big problem , due to a lack of grease they will wear down and will make a rattling / grinding noise. Maybe something to think about when hearing a suspicious sound coming from the AP . Lubricating this part is fairly easy , take the back cover off after you get the front cover out , grease the worm ( through the little hole remember) and also spray some lithium on the little gears , no harm no foul . I make sure to , at all time , have my supply of 3 in 1 on board .
uk.rs-online.com/web/p/greases/4638413/
Worm's out , more to come
When this was done , I was back in business . Get the worm back in from the other end and mount the worm-holder with it's recirculating ball bearing .
before sliding the worm-holder on it had to be separated from the inner-pipe . If not I would not succeed in getting the cir-clip ( the one I mistakenly pulled off ) back on to keep the holder on the worm . The inner pipe is just screwed on .
Also have a look at the re-circulation loops . They're in 2 parts and each side of the worm-holder carries a set . Notice the small lips on one side of half a loop , this is what keeps the bearing balls in the loop . When the worm-holder slides over the worm the balls are pushed in a direction and the lips will force them to enter the loop again . Great stuff .
The cir-clip that nearly gave me a heart-attack is ready to go home again .
First fill the worm-holder with bearing balls and make sure it completely loaded . That's done easy by pushing balls in one hole and gently sliding the holder over the worm until the balls appear on the exit of the other hole . Re-do that a few times so the channel is full.
Then fill the loop itself and stick it in the holes and fix it with the bridge that holds it in place . The whole procedure is to be repeated for the other side .
As for missing bearing balls , I never went looking for them in the bilge , my wife was able to get some from the local bike store . The size is 3 mm . So my end is well , all is well .
Once the cir-clip was on the inner pipe was screwed back on and so was the end cap on the main pipe .
Eye bolt ( to put over the quadrant pin ) in place
Getting the other side assembled .
leaves me to get a new belt on when we get back to the boat .
I see this project as a blessing in disguise , my mistake by ripping the thing apart to start with , gave me a chance to understand how it really works , might come in handy later ,although I hope it never has to .
That's it gentlemen , it's clear our AP does need a minimum of maintenance , better safe than sorry .
Regards
at 
