Cutlass Bearing

[willin woodworks]

A client asked me to look at his cutlass bearing. He said the bearing was sliding out of the strut.
Well the rubber portion of the bearing was indeed sticking out the aft end of the strut by about an inch. When I hand turned the prop the bearing spun in the shell but was fused to the shaft. It took grabbing the bearing with pliers and some oomph to break the bearing loose from the shaft.

Replacing the bearing is a PIA but really not a big deal. Im more concerned with why and how this happened.

Ive never seen this before. Any thoughts on whats going on here?

Thanks.

[Dan McCosh]

Just a guess, but it sounds as if the bearing was run dry--maybe the engine put in gear with the shaft out of the water.

[Ian McColgin]

It could have been run dry. I've a friend who winterizes with the engine running and flushing clean antifreeze through the hose that is normally connected to the raw water intake. Just a matter of putting the hose end into the antifreeze jug. He has twice managed to do that with the engine in gear. One time it ran long enough to melt the cutless and suck it well into the shaft alley. The other time was briefer so only a little surface melt and then the cutless did stick to the shaft enough that he could feel the resistance to breaking it out by turning the prop by hand.

Another option might be that the boat was still a long time and an old deteriorating cutless and a bit of verdigris on the shaft started holding hands.

A third might be a bit of alignment problem or very small bend in the shaft causing excess wear leading to overheating the cutless. You might want to get the shaft out and inspect to see that it's true and undamaged all along its length.

The final option is that water is not getting down the cutless and into the shaft alley and up against the stuffing box. One handy fix for this is to tap a thin line off the raw water just before it flows into the muffler or the exhaust and feet it through a small nipple into the shaft alley just abaft the stuffing box. This is such a good idea generally that I am surprised more boats don't just make it standard.

G'luck

[Dan McCosh]

He did say the bearing was in a strut.

[Paul Schweiss]

Any evidence at the forward end of the rubber portion of the cutless that fishing leader got in and started tearing things up.

And how long has the bearing been on the boat?

[willin woodworks]

No evidence of fishing line.
Dont know if the shaft was ever spun out of the water but my gut tells me that at some point the bearing heated up, seized onto the shaft and spun out of the shell.
I cant tell by looking at the shaft if the zinc was crowding the forward end of the strut which is a common cause of bearing wear and failure as it will restrict the flow through the bearing.
I will have to pull the shaft to replace the bearing so will check it for straight and true.

Thanks for the input....

[Ian McColgin]

The fact that the cutless is on a strut when right past my notice. Ah well.

[Breakaway]

Make sure the shaft is straight and true; also make sure the strut is straight and true/plumb.

FYI: There are new bushings of a material called Vesconite which supposedly wear longer. I have no personal experience ( been some time sinc eI;ve owned a boat with inboard power) with these, but friends have switched to Veconite and been happy.

Kevin

[willin woodworks]

Thanks Kevin

[BrianM]

BEARING DEGRADATION FROM CONTAMINATION?

Any chance the bearing was in highly polluted water for some time? (i.e. petroleum?) ... This could soften and swell the rubber til it was rubbing on the shaft. Just a guess, but rubber and some petroleum products don't get along. Or some exposure to a solvent during a recent haulout? Paint thinner? This could really screw it up but not be obvious when you go to drop her back in.


VESCONITE VS RUBBER

I've experimented with Vesconite on a test rig vs the common Rubber Cutless bearings. I was Engineering a mixer used in public water tanks (millions of gallons.. the ones' on a nearby hillside..) The test tank was only 8' x 8', about 2500 gallons. When you drive 3 hp in that small a confines, the energy in the water has no place to go, so it beats the crap out of the impeller and shaft. Maximum turbulence and what we call "Accelerated Life Testing".....

I compared Vesconite to the standard Johnson rubber Cutless Bearing (but elected to use a food-grade version of the rubber). The Vesconite did not fair well. It had a great deal of wear on it. I got the impression from their Engineers that it was more commonly used on really big stuff (tugs and ships). The stainless shaft had clearly been abraided, almost like sand had been caught in the plastic.. except it was perfectly clear fresh water used in the tank.

In a water bearing (of which the "Cutless" and Vesconite are both), The water film between bearing and shaft develop a pressure that holds the shaft centered.
Something about the segments in the rubber bearing allow a better water film to develop to hold that shaft away from the walls, or the shaft moves, and the walls flex since they are rubber, and still don't contact?


The common rubber version did great. Just protect it from solvents and oil and it should be dandy.

[Canoeyawl]

I have seen shafts with enough electrolysis to resemble an octagon.

[willin woodworks]

The shaft is smooth and clean, not shiny bright but not pitted or overly tarnished either. I dont think its a chemical solvent problem.
I think its a waterflow problem, just haven't figured out what the impediment to clean flow is yet......

[J.Madison]

I've seen this happen from corrosion in the strut eventually opening up the bore so the bearing was not a snug fit. Once it spins for a while, then it is really not a tight fit.

Boring for some set screws can help.

[Dan McCosh]

The fact that the cutless is on a strut when right past my notice. Ah well.

Still lots of good ideas if it wasn't.

[John B]

With vesconite the idea is to freeze it overnight, install it cold and have that tight interference (equivalent) fit as it expands into the p bracket or tube.

I'm not so sure about them , I fitted them several years ago and get the feeling they need replacing again. (One in the p bracket and an intermediate in the tube.... need to haul the boat for a look.). I have a nagging feeling a standard cutless bearing would have better longevity.

Incidentally ,Most dripless seals want a vesconite or similar bearing at the inside of the shaft log ie close behind the seal.

[willin woodworks]

Still lots of good ideas if it wasn't.

Always appreciate Ian's insight.

[willin woodworks]

So on Saturday I squeezed into the port cockpit locker to separate the shaft from the engine to replace the cutlass bearing. 7 hours later the shaft and the coupling were still together....

The coupling was a nice big chunk of rust. The set crews broke off as soon as I put a wrench on them. They are apparently made of depleted uranium because it took six brand new cobalt bits to drill them out.

Not enough room between the coupling and the gland nut on the stuffing box to get e decent shim between the aft fitting and the forward end of the shaft. Finally worked a stack of washers in there and reefed down on the bolts....nothing.

The clearance between the coupling bolts and the rear end of the transmission is extremely tight. Tight enough that there is only enough room for a nut and lock washer. The bolts come in from the back. The nuts cannot be turned more than the offset of a straight wrench and the bolts can only be turned two clicks from a ratchet before the handle hits the stern tube. Maybe this is a detail specific to Westerbekes? Ive not seen such insane tolerances.

Diesel tank is way too close to the coupling to even consider heating it.

Back yesterday with a die grinder and a stack of new cut off wheels. Cut the coupling in half, front to back on opposing sides and still had to lever the two halves off the shaft with a pair of bars. Took about two hours.

God am I sore and stiff.....

As it happens the cutlass bearing has been in place since the owner bought the boat 25 years ago. So it stands to reason that the shaft has been in the coupling for 25 years. Jay-zuz....

The good news is the shaft is back at the shop for a polishing and a clean up and if it ever stops raining the new bearing will go in and all will be right with the world.

Couple questions....why are the set screws in the coupling square heads? Every coupling Ive seen has those little square heads. Is there a technical or engineering reason for those irritiating little buggers? Why not hex heads?
Does anyone put anything on the shaft when it goes into the coupling to make it easier to separate?

[navydog]

Square heads provide the maximum effort and surface area at 90* opposed to hex heads. They don't round over as easily under high torque.

I don't believe it is advisable to reduce the friction in the coupling shaft connection. The prop pulls on the shaft in reverse and it is only the coupling connection that keeps the shaft from exiting out of the boat. If the boat has a thrust bearing to handle these forces it would be a different matter.

[Garret]

What navydog says is true - but to really make them effective, you need a socket for the square head - as an open end wrench will round them pretty easily - assuming they don't just snap off - as yours did.

The real problem is that the couplers are steel or cast iron & therefore rust badly. 25 years in a marine environment means it has basically become one solid piece of rust that does have to be cut off. I know mine took torches even after 10 years.

Never-seize may help on getting them apart down the road, but with the tolerances in a coupler, there won't be much room for it - so I'm afraid its effect will be minimal.

[willin woodworks]

Hhmm, I didnt know that about square heads. Love learnin' new stuff.
Either way, the heads on these had not been square for a long time. They were mostly rust.
One thing Ive not see before; indents in the shaft for the set screws to engage. Maybe another Westerbeke detail.

[navydog]

It isn't uncommon that a shaft has to be cut to remove and be replaced, because it costs more in labor to remove the coupling then the cost of replacing the shaft and coupling.

[navydog]

The indents are to prevent the shaft from backing out.

[Canoeyawl]

(It sounds to me like the previous mechanic was aware that the shaft can withdraw in reverse and did his best to prevent it, from here it sounds like a good and proper job done to the best of his ability)

Some notes... Square head set screws often have holes drilled for safety wire. Note the angle of the point, usually 60°; not the same as a "drill bit". Dimples are an accepted procedure for securing the key, but not the shaft. If dimples are used they should be done with a special drill bit.
The shaft should be an interference fit in the coupler, and the coupler halves should be an interference fit with each other. I.e. the shaft is maybe .001" larger than the hole in the coupler and a "press fit".

I usually drill and tap the end of the shaft or taper it and thread the end, fit a woodruff key, then a nut or fastener and "special" washer to retain the shaft in the coupler. Those little drilled dimples are common, but a clumsy way of doing it. I have seen them fail. Note the typical disparity of methods holding the shaft onto the transmission vs. holding the coupler on the shaft. The transmision manufacturer is well aware of the the liability of that particular failure, and there will be no "dimples" and set screws holding that end together!

Because there is no room for a puller, I usually drill and tap holes into the face of the coupler so forcing screws can be inserted into the coupler flange to separate the two halves. I use 316 stainless bolts, safety wire and nickel based marine compatible antisieze on all the threads.

Vessels have been lost for that coupling and the shaft seperating in reverse.

[willin woodworks]

The original, or at least the last install was done in a proper and workmanlike manner. I have no issue with the work that was done before I got there Im just pissing and moaning and wondering out loud....some day I want to work on an engine that I can get to without advanced yoga training....

[navydog]

Boats that have actual engine rooms are like that. Power boats around 45' start having some space to work in.