cutlass bearings

[Birdseye]

There is a forum user who is in the cutlass bearings business and I have a specific cutlass bearing proble, I f someone could give me his ID it would be a great help.

The problem by the way is that I have a Starlight 35 , a boat which in almost every way lives up to its reputation, but which has in my view one piece of poor design - it uses an epoxy tube as a stern tube carrying the cutlass bearing. The thick walls of this tube mean that the bearing has to have a thin shell and thinnish rubber and so wears irritatingly quickly.

 

[aslabend]

pm sent regarding possible chap.

 

[jon711]

I have a bit of knowledge, used to (briefly) work for a company that made them...

Jon

 

[burgundyben]

Neil_Y is your man.

 

[NickRobinson]

My Mirage has a very thin shelled cutless bearing, I chose a phenolic/GRP backed one from Lakes or ASAP.

Might be worth considering why it's wearing so fast? Thick or thin, wear limits, ie sideways shaft movement, are the same aren't they?

 

[Tranona]

Neil_Y is your man.

Yes, Neil of H4 Marine is your man. He will make you a composite bearing which you can epoxy into your tube.

 

[Bandit]

Have you checked shaft for truth and engine alignment, is the cutless bearing worn unevenly ie front 3 o'clock rear 9 o'clock ?

 

[Birdseye]

Shaft is new but wear happened with the old shaft too. Wears in all directions. About 1 mm play. Engine alignment was good.

 

[PuffTheMagicDragon]

It could be that your prop is not balanced.

 

[dial-a-monkey]

on topic?

Can anyone say how much play is OK between the Cutlass bearing and the epoxy stern tube? Mine has about 1 mm play. I have a phenolic bearing with no outer brass sleeve.

I have a good snug fit between the cutlass bearing and the stainless propeller shaft but the 1 mm of play to the stern tube causes an annoying amount of vibration and seems to me to be too much?

The cutlass/sleeve bearing came with plastic screws to hold it from turning in the stern tube (which if in the past the puny plastic screws have failed - would allow the bearing to turn with the shaft in the stern tube and might explain the play?) - but I was far to paranoid to use the plastic screws and used the stainless cut off bolts that the last owner had used - although sometimes in heavy sea they might be coming in contact with the turning shaft making a grinding noise.,...hmm

I very much appreciate any info and advice thanks.

 

[NickRobinson]

on topic?

Can anyone say how much play is OK between the Cutlass bearing and the epoxy stern tube? Mine has about 1 mm play. I have a phenolic bearing with no outer brass sleeve.

I have a good snug fit between the cutlass bearing and the stainless propeller shaft but the 1 mm of play to the stern tube causes an annoying amount of vibration and seems to me to be too much?

The cutlass/sleeve bearing came with plastic screws to hold it from turning in the stern tube (which if has happened in the past might explain the play?) - but I was far to paranoid to use the plastic screws and used the stainless cut off bolts that the last owner had used - although sometimes in heavy sea they might be coming in contact with the turning shaft making a grinding noise.,...hmm

I very much appreciate any info and advice thanks.

Have I understood correctly? You have movement between the bearing and the housing? If so I'd thought it needs sorting ASAP. (FI, My phenolic cutless is epoxied into the housing solidly)

 

[Birdseye]

Have I understood correctly? You have movement between the bearing and the housing? If so I'd thought it needs sorting ASAP. (FI, My phenolic cutless is epoxied into the housing solidly)

If it is epoxied in, how do you get it out when you need to renew?

 

[Birdseye]

on topic?

Can anyone say how much play is OK between the Cutlass bearing and the epoxy stern tube? Mine has about 1 mm play. I have a phenolic bearing with no outer brass sleeve.

I have a good snug fit between the cutlass bearing and the stainless propeller shaft but the 1 mm of play to the stern tube causes an annoying amount of vibration and seems to me to be too much?

The cutlass/sleeve bearing came with plastic screws to hold it from turning in the stern tube (which if in the past the puny plastic screws have failed - would allow the bearing to turn with the shaft in the stern tube and might explain the play?) - but I was far to paranoid to use the plastic screws and used the stainless cut off bolts that the last owner had used - although sometimes in heavy sea they might be coming in contact with the turning shaft making a grinding noise.,...hmm

I very much appreciate any info and advice thanks.

There should be no play at all between bearing and stern tube. Like ( I suspect) you, the i/d of my stern tube is not perfectly round albeit nothing like 1mm out, so the bearing that is in at the moment is sealed with silicone. It also has two stainless grub screws holding it in and when I fitted it I ground two small flats on the brass sleeve of the bearing just where the screws fit. The screws arent intended to clamp the bearing shell tight so much as to locate in the ground flats and prevent the bearing from turning.

Unfortunately the silicone is doing too good a job and I am having to grind the bearing shell out.

 

[dial-a-monkey]

Ok thanks all for the info will have another look at the stern tube..might need some repair.

 

[xeitosaphil]

I was told by a Marine engineer that they should be a snug push fit pushed in by hand, with no adhesive of any sort as he phenol expands a little when submerged in water. This being so, it is possible for the rubber to actually bind on the shaft if the bearing is limited from this expansion prior to being put in the water?
I have replace two Phenolic type bearings in the past using his advise and always had to hack saw them out as they were tight in the stern tube. If you have 1mm play between bearing and the stern tube case, I would say you may have he wrong size bearing? It maybe that it should be a brass cased bearing type which I think my have an larger o/a case size but I have no experience of these so only guessing.

My bearings are also held in with a s/s grub screw which is always a concern that it isn't wound in too far to distort the inner rubber, I usually drill a shallow hole for the grub screw just a little smaller in diameter but only through the phenol case to stop it revolving, but not too far in, so it does not effecting the inner bearing.

Seems to work for me.

 

[Tranona]

Ok thanks all for the info will have another look at the stern tube..might need some repair.

Sounds like you have the wrong bearing. Beneteau stern tubes and bearings are unique to them and there should be no play. The tube itself is stainless steel so unlikely to have worn, so the bearing is probably the wrong type.

 

[Neil_Y]

First thanks for the suggetsions for the poster to ask for our help.

A few points regards bearings that are worth considering, the bearing should be held firmly in its carrier whether P bracket or stern tube. The options for fitting are very important as they effect the final running clearance between bearing and shaft. You can press fit or fit as a clearance fit (ideally just 0.05-0.15mm clearance) but make sure the bearing manufacturer knows which you choose or if it's an off the shelf bearing check if it is sized for clearance or press. Most old style shaft bearings are made for a press fit but this also seems quite variable in how tight, a very tight fit will mean there is more bore closure.

Because the carrier is your point of alignment a large gap between carrier and bearing will mean that the bearing may sit off centre unless the bearing is supported centrally when bedded. The bearing is there to support the shaft on the centre line to prevent movement and reduce shaft flex under thrust.

When a bearings ID is finished it is made to an accurate clearance on the shaft as an example a 25 x 35 bearing will run a new clearance of 0.13 - 0.23mm on the shaft. If you were to press fit this there would be bore closure and it would be tight on the shaft. If we know a bearing will be pressed in we make the ID bigger.

Bearings should really only wear at start up or run down when they are effectively dry before a water film is established.

 

[NickRobinson]

If it is epoxied in, how do you get it out when you need to renew?

The housings I've worked on were metallic, so I removed the shaft and worked away with a hacksaw blade and a thin screwdriver on the old cutless. I've also read here that some epoxy glues soften with heat.

 

[PuffTheMagicDragon]

A cutless bearing should not need any screws to hold it in place. Ideally it should be a press-fit. Mine is on a P-bracket and I pulled it in place using an M14 length of studding, packing as appropriate, and heavy pulling on a long spanner to turn the M14 nut. The photo should give the general idea of the set-up.

FWIW, one should be aware that cutless bearings are not necessarily 'all metric' or 'all imperial'. In fact, mine has a metric bore and an imperial shell. I mention this because it could well be a reason for a bearing of the wrong size to turn within the housing.

 

[Tranona]

A cutless bearing should not need any screws to hold it in place.

It is very common to have a set screw through the housing into a dimple in the shell of the bearing for extra security. The Beneteau referred to earlier has a special top hat shaped bearing held in place in the stainless tube by a set screw as standard.