Re: Bowthruster - hex-nut securing he motor to down-tube is stripped out

Chris Doucette

Hi David,

I have done a lot of work on the bow thruster these last few months..  In Fact I have rebuilt the entire thing inclusive of the motor bearings.  Basically, count on drilling out that bolt and re- tapping the hole..  It really does not matter if it ends up 9mm vs the original 8mm. But first- get it drilled out. You might have to find a short 8mm drill bit with a right angle drill adapter. Those steel screws go into a brass fitting inside the bow thruster shaft.  It  is what you will tap eventually. Replace the bolts with quality 316 SS bolts, with copious anti-seize. 

Once you get it all out- be sure that the bearing in the base of the motor is going to be shot! I took everything appart in the motor also to change the bearings and snap washers, cleaned, brushed off rust, chemically treated the rust, and sealed that large steel base with epoxy and paint.  It looks like new and will not rust as it did. Re-tapped all the screw holes in the brass part. Almost all done here - bow thruster painting is underway and then assembling. 


Amarok, SM 385 

On Mon, Dec 6, 2021 at 8:10 PM David Vogel <david.vogel@...> wrote:
Greetings fellow Amelians,

Requesting help with a 'small' problem.  After an extended service interval (>3-years since last service of the Bowthuster by AMEL MQ, the unwanted delay due to cruising French Polynesia in COVID times, closed borders, and so on), we're now securely in NZ, primarily for the purposes of attending to long-overdue rounds of routine maintenance - including as a high priority the Bowthruster and C-Drive.

Three of the four 6mm hex-bolts that secure the bowthruster motor to the fiberglass (?) torque-tube have been removed without undue problems - desite some rust clearly evident (due I think to the aging neoprene compression seals) with just the regular tightness as expected, but overcome with normal force of a 15cm shifter (no heat or penetrating oil needed).

Unfortunately, the fourth bolt - the starboard-hand one oriented forward - was found to be almost completely stripped, and the limited attempt to shift it finished the job.   It now presents a round hole, which provides no ability to use an Allen key (either 6mm, or the next size up in imperial) to gain the necessary purchase.  The forward-facing location presents  challenges in terms of access needed to drill and tap in an "Easy Out".  Without drilling, the easy-out can not be inserted far enough to gain any useful purchase.  I have applied heat (MAP//Pro torch) as close as possible to the nut head.  I am also soaking the joint (and the whole motor-tube interface area) with PB Blaster (now also anticipating problems with dropping the tube away from the motor assembly).

Has anyone faced this problem with a rounded hex-bolt before, and found a solution?

Or are there any other tips and trick, hints or suggestions?

Thanking you in anticipation, and with kind regards,

SM#396, Perigee
On-the-hard, Riverside Drive Marina
Whangarei, New Zealand

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