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Propeller Shafting, Cutless Bearing, & Stuffing Box

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 project.

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, etc.  Yikes!

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 transmission coupling

  • Drivesaver/Galvanic isolator

  • New propeller shaft, 7/8"

  • New stuffing box, 1-1/2" hose, bored to accommodate 7/8" shaft

  • 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 install coupling

  • 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)

  • Install

  • Bolt shaft coupling to

  • Install prop

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)

Well, 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.

Update 4/17/01

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!

Update!  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.


Glissando, Pearson  Triton #381
www.triton381.com 

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