Propeller Shafting, Cutless Bearing, &
This page was last updated on
17 April 2001
Replacement of the entire engine shafting system was in
order. The original stuffing box had been a basket
case, nearly causing the boat to sink when we had her in the water for 24
hours to tow from the island where she had been located when we bought
her. The original shaft and propeller were removed and sold with the old
Atomic 4, and the cutless bearing required replacement because of its age.
The "new" engine we bought to replace the A4 came with a prop and
7/8" shaft, but the prop was badly damaged by electrolysis and corrosion,
and the shaft was overlong and showed some wear. A new coupling was in
order too, part of the "might as well" syndrome that has plagued the
Some general Triton specifications for the shaft log follow:
Original Cutless Bearing size: 1-3/8" OD x
7/8" ID (shaft diameter)
Original Shaft Diameter: 7/8"
Stern Tube (Shaft Log) Diameters, Aft End:
1-3/8" ID (Critical for specification of Cutless bearing)
Stern Tube (Shaft Log) Diameter, Forward End:
1-1/2" OD (Critical for specification of stuffing box)
I ran into some minor difficulty when spec'ing out the new
hardware at my local prop shop, H&H
Propeller. I asked for a new 7/8" shaft, which was not problem,
but we ran into an issue when trying to find the proper stuffing box and cutless
bearing sizes. The standard stuffing box hose size for a 7/8" shaft
was indicated as 1-3/4" ID; however, the stern tube, to which the hose
attaches, was only 1-1/2". I double checked the measurement at the
boat to be sure. OK, no problem: switch to a 3/4" shaft, and
the stuffing box hose on the standard arrangement changes to 1-1/2"
ID. Problem solved? No, not quite...it seems that the standard
Cutless bearing size for a 3/4" shaft is 1-1/4" OD...and the shaft log
is 1-3/8" ID!
Next step: switch to a 1" shaft. All seemed
hunky dory for a while, as there is a stuffing box available for a 1" shaft
with a 1-1/2" hose, and a Cutless bearing with a 1" shaft and
1-3/8" OD. Perfect. BUT...the next morning, the very attentive
and helpful Mike from H&H called me with concerns about the ID of the stern
tube on the inside of the boat. He figured that, with an OD of only
1-1/2", the ID must be pretty close to 1", leaving very little
clearance for a 1" shaft. I measured the ID to be 1-5/16", which
seemed awfully close and didn't allow any room for alignment error, vibration,
After some checking, it turns out that there is not a
1-1/2" stuffing box available for a 7/8" shaft. However, there
is a solution, which is how we are proceeding. It seems that a 3/4"
stuffing box can be modified to accommodate a 7/8" shaft, by boring out the
nuts to accommodate the larger diameter. Therefore, in a semi-custom job,
a 7/8" shaft diameter, 1-1/2" hose stuffing box can be obtained,
although apparently not from stock. Phew...
New equipment ordered on 1/23/01:
3 blade propeller, size to be determined by prop shop
analysis (12x9 as calculated, three blade Sailer by Michigan)
New coupling to match whatever size new shaft and existing
New propeller shaft, 7/8"
New stuffing box, 1-1/2" hose, bored to accommodate
New Cutless bearing 7/8" x 1-3/8"
After a few weeks, the new equipment arrived. It is
awaiting installation. I have already found one potential problem, or at
least something that will make the job more difficult: the clearance
around the stern tube is extremely tight, and the thick stuffing box hose fills
this narrow space entirely, making it tough to push the hose into place.
In addition, there will not be room for two hose clamps on the hose where it
attaches to the stern tube. Why did they build it this way? If
they'd made the stern tube a couple inches longer, it would have been far enough
forward that the keel would have been wider, and the clearance would have been
what it should be. I hate asinine issues like this, things that could have
been easily avoided during construction. See below for the solution.
The new coupling has been machined with the shaft on a lathe,
so that the coupling face is perfectly square to the shaft. This is
critical to the alignment process, since, when the coupling is installed on the
shaft, I will know that it is perfect. Installation of the new shaft and
associated gear will follow these basic steps:
Drill and tap stern tube for set screws
Install cutless bearing and set screws
Install stuffing box
Insert shaft from outside, through the stuffing box, and
Check rough engine alignment by contacting coupling faces
Adjust engine mounts as necessary to bring alignment into
proper specs--that is, within 0.004" all around (0.001" for each
inch of coupling diameter)
Bolt shaft coupling to
After several attempts to get the new stuffing box hose to
fit, I gave up and bought a length of standard hardwall, wire-reinforced wet
exhaust hose for the stuffing box. This hose has about half the wall
thickness of the other hose, but is plenty strong. With this new hose in
place, I could finally get a clamp to stay on and hold the stuffing box securely
to the stern tube. There's not enough of the stern tube inside the hose to
use two clamps at the after end--which would be preferable. Oh well.
Next, I prepared to install the propeller shaft. First,
I cut the new cutless bearing to fit--it has to be shortened by a little over an
inch. This leaves about 3/8" extending past the stern tube, which
should make it easier to replace later. I drilled and tapped two holes in
the exterior of the stern tube for the set screws that hold the bearing in
place, and installed the bearing. Later, when I like everything, I'll
remove the set screws and reinstall them with some silicone caulk.
I inserted the shaft from the outside, and went in to test fit
the coupling and Drivesaver. I dry fit (so to speak) the coupling and Drivesaver
to the transmission flange--I'm happy to say that the rough alignment of the
engine is excellent, as I had no trouble mating the couplings. Final
alignment will come a little later on.
Heading back outside the boat, I noted with dismay that the
shaft was way too short! I had had suspicions about this when I test-inserted
the shaft through the stern tube a few weeks ago, but without the couplings,
etc. I really couldn't get a true gauge. However, I'm happy to report that
this was not my error--the prop shop screwed up. I had supplied them with
the measurement from the aft face of the transmission coupling to the end of the
stern tube, and they were supposed to make an allowance for the new Drivesaver
(which they did) and also for the proper amount of taper and threads that should
extend past the end of the cutless bearing. This is what they forgot--they
used my supplied measurement as the overall length of the new shaft, including
the coupling and Drivesaver. This means that the end of the threaded
portion of the shaft is flush with the end of the cutless bearing--about
4-1/2" too short. More incompetence and delays--I hate outsourced
items. I may have made mistakes along the way, but I'm not the one who is
supposedly the professional, and at least I have no one to blame but
myself. I expected (and demand) better from a "pro". I wish
I could have made my own shaft, but no can do--so it's a new shaft and a couple
week delay before I can align my engine. Sigh.
Stay tuned for more. I've been promised
by new shaft by the beginning of next week (as of 3/20/01)
the new shaft arrived a couple days later than planned, but no big deal. I
installed it and pressed on the coupling, and set everything up with the Drivesaver
in place, then got off the boat to check the shaft length...too long! Will
it ever end? The last thing I need now is to run back and forth to the
prop shop 30 or 40 more times. I figure the shaft is about 1-1/2" too
long or so. I have no idea how this particular screw-up happened. I
had only one measurement to give to the prop shop from the very beginning--the
distance from the aft end of the transmission coupling to the end of the cutless
bearing. They were supposed to be able to figure out the proper additions
and subtractions. I don't know what the deal is, but now I have to get the
shaft cut down and the keyway remachined at the top end. At least now I
can work on aligning the engine, and
reinstalling the shaft is a piece of cake later on--it only takes an hour or
less, all told---presuming the engine is aligned.
I returned the shaft to the prop shop so they
could send it out on their Thursday truck, with the absolute promise that it
would be back on the Tuesday truck the following week. Tuesday arrived,
and the shaft was not on the truck. Absolutely, positively guaranteed for
the Thursday truck. OK...but on Thursday, there was no shaft! The
coupling made it back on the truck, along with
my new propeller, but no shaft. At this point, these delays became
humorous, and there was no point in being upset any more. I was told the
shaft had been shipped UPS, for delivery to me on Friday. I spent much of
Friday watching the seemingly non-progress of the shaft on the UPS website with
tracking number in hand. I had pretty much given up hope. My wife
and I were just leaving on Friday afternoon for the Easter weekend, when UPS
arrived...and when the driver came out of the truck, I could see he was wielding
a long package. It had to be the shaft...either that, or someone had put a
contract out on me and had hired an assassin who had snuffed out the regular UPS
guy and come after me...
Nah, too complicated. Fortunately, it
turned out to be the long-awaited shaft! Hallelujah!
I installed the shaft finally on Monday.
The length is perfect. The prop fits. All is well. What a
ridiculous three-month ordeal!
When we bought the new
engine, we had to get a new propeller, of course. We ordered it from
another prop shop and it arrived in about 3 days, perfectly. Details here.