[Public-List] Season's Greetings and a question about stern tubes

mahseer at kos.net mahseer at kos.net
Sun Dec 26 07:31:17 PST 2010


I have removed my stern tube in the past and although daunting it was
straight forward.  The cutlass bearing is held in with two bolts threaded
into the fiberglass and were not difficult to remove.  The stern tube is
held in place by the gray mastic material and after removing it came out,
cleaning off the residual was a little time consuming due to limited
space.  Once out you will find the tube is threaded into the bearing
casting but not hard to separate. When removing the cutlass bearing you
will find that on the inside portion there will be a collar that stops the
bearing from going all the way through so I had the use a saw blade to cut
out a section then collapse the rest to remove.  When I installed the new
one it was about 1in longer rather that cut it off I left it on hoping the
next time I can drill through the exposed side and pull it out. I had a
different approach when it came to re installing the tube, my method
involved using the engine as an alignment tool.  Make sure that the
threads for the stern tube are in good condition, in my case they were not
so for better or worse I added SS thread inserts. I then installed the
engine in its bed temporarily, mounted the prop shaft to the engine with
the stuffing box installed loosely, finally pushing the stern tube with
new cutlass bearing.  Before adding the stern tube align the engine to the
center of the hole, with shaft centered and stern tube installed check for
correct alignment to the hull filing as needed.  This method (to me)
aligns the cutlass bearing, stuffing box and engine flange correctly. 
Before bolting down the stern tube add lots of sealant and I mean lots of
sealant.  After bolting on the stern tube and securing the engine I
removed the prop shaft then pushed in again if the shaft went all the way
into the engine flange I new the alignment was true. The last stage is to
add sealant to the inside portion stern tube to hull area, this means
removing the engine noting any alignment wedges etc.  Next (for me) was
the most difficult and messy portion, remove the stuffing box, adding
sealant around the stern tube especially underneath don't be shy with the
sealant you may have to spread it out by hand so use gloves, this is why
you use lots on the outside to make sure the hole is full of sealant. Re
install the stuffing and engine if you put the alignment wedges back in
the same place with any other alignment method you employ the shaft
alignment should be correct.  To make sure it is the prop shaft will run
true all the way into the engine flange with no binding.

Good luck

John Boor

> Ahoy maties! Very best of the season to yez!
> So, engine and gas tank removed, I can now properly inspect the
> stuffing box, prop shaft and stern tube. All have suffered years of
> neglect. I'm having a new  prop shaft machined because the old one is
> badly scored and corroded. With the prop shaft out of the way, i can
> see the inboard end of the stern tube, and it is not a pretty sight
> (see attached).
> It's clear that the upper bolt retaining the stern tube is badly
> corroded. The lower bolt is impossible to see - it's hidden behind and
> below a "lip" of GRP, but I'm pretty sure it's in as bad shape. The
> tube itself seems a little misshapen.
> Anyway, it looks to like I'll have to replace  the stern tube bolts,
> at least and maybe replace the stern tube itself. I confess that I am
> little bit nervous about the whole thing because I've never done it
> before, and because I am concerned about a cascade of problems once
> I've done it.
> Have any of you ever removed/replaced a stern tube? How hard was it?
> What problems did you run into while doing it? What should I look out
> for? Any and all advice welcome and appreciated.
> best.
> mel
> Hull 452
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