Replacing cutlass bearing

[Talulah]

That sounds a good plan although I have no overhead access so would have to jack the back of the engine up (carefully) about 6" to slide the shaft out under the gearbox. Better still if I can find a yard with a special tool available. I might then leave it up to the experts....

Gosport Boat Yard use such a tool and do a decent job.

 

[carpediem32]

Thanks again Talulah. I am over in Portchester so Gosport boat yard is very handy. At the moment, there is only slight play between the shaft and bearing so I am hoping this will wait til the boat next comes out but I like to be prepared!

 

[Ruffles]

I've replaced our bearing four times in 13 years with the shaft in place using nothing more than a 20 mm piece of mild steel filed to fit the gap between the shaft and the lip on the P bracket. But I guess a lot depends on the interference fit of the bearing.

Last time was a couple of months ago and took all of 20 minutes. The first time took all weekend and was necessitated by being unable to remove the shaft!

I have since mastered the art of removing the shaft so that I could replace the stern gland. But still find it easier to replace the cutless bearing with my magic bit of scrap steel.

 

[Jcorstorphine]

Is it possible to replace the bearing without removing the propshaft? The shaft on my boat will not pass the skeg and I would like to avoid having to shift the engine forward to do this. I wondered if the bearing would turn on the shaft if it was tapped lightly, after releasing the grub screw. Any ideas?

I managed to pull my cutlass bearing out without removing the shaft but it was a solid rubber insert 0.300" wall thickness so was able to use a "dent puller" as used in car body work. see link

http://www.screwfix.com/p/dent-pull...tracking url&gclid=CJrn24OesbUCFUu4zAodKEoA5Q

The technique was to use one of the screw bits in the puller kit and screw that into the end of the bearing. Then used the "thumper" to pull out the cutlass insert.

That was the easy bit.

These inserts are no longer available but I have a replacement which has a Phenolic shell of the same OD and supposedly a rubber insert with an internal diameter of 1.000”

The shell is 0.300” thick so is much greater than the conventional Phenolic shell bearings.

My concern is that the shaft which is bang on 1.000” +/- a thou is like a sausage in a shirt sleeve with about 40 thou movement. It is actually worse than the one I removed.

I have been told that once the boat is in the water the Phenolic sleeve will expand inwards thus gripping the shaft.

I am not convinced. Anyone have experience of these types of bearings?

 

[Neil_Y]

There will be some moisture absorption however this will not be as great as the thermal expansion so you need to have running clearances to take account of this. Our phenolic bearings would be made with 0.12mm running clearance on a 25.40mm shaft. This is for a clearance fit in the carrier, if you choose to press fit then the clearance would be an extra 0.02mm as a minimum to allow for bore closure as the bearing is squeezed. We supply bearings to any size shaft and OD

You don't want to run below minimum recommended clearances, as this causes friction which leads to heat and bore closure from thermal axpansion.

As an example for a 1" shaft bearing clearances
This is made up of (for a carrier of 38.10mm)
0.03 basic min running clearance
0.0375 due to water swell
0.06 due to thermal change/expansion

 

[Jcorstorphine]

Thank you

There will be some moisture absorption however this will not be as great as the thermal expansion so you need to have running clearances to take account of this. Our phenolic bearings would be made with 0.12mm running clearance on a 25.40mm shaft. This is for a clearance fit in the carrier, if you choose to press fit then the clearance would be an extra 0.02mm as a minimum to allow for bore closure as the bearing is squeezed. We supply bearings to any size shaft and OD

You don't want to run below minimum recommended clearances, as this causes friction which leads to heat and bore closure from thermal axpansion.

As an example for a 1" shaft bearing clearances
This is made up of (for a carrier of 38.10mm)
0.03 basic min running clearance
0.0375 due to water swell
0.06 due to thermal change/expansion

Thanks for the information. I am being a bit dim here, can you tell me if the units in your allowances are metric or imperial

My new Stuart replacemnt phenolic bearing with its rubber insert (dry and not fited to the Bronze housing) has about 30 to 40 thou clearance between the shaft and the ID of the rubber insert. It is very worrying as the one I took out has about half that of the new bearing. My shaft is dead nuts on 1" within a thou and I just cannot see how the new bearing will compress down on the shaft. The phenolic carrier is 47.74 mm in diameter.

Many thanks

 

[Neil_Y]

Clearances above are for Maritex (all manufacturers should be able to give the same data) and they are in mm so 0.12mm is just under 5thou" and is for a clearance fit (no bore closure)

If you press fit a composite shell it will squeeze but only 0.1-0.15mm I would guess, but it depends on how tight a press fit (which is the inherent problem with press fit)

With a 47.74 ID carrier as yours min clearance (for Maritex) new would be 0.18 (takes account of increased thermal expansion of thicker bearing wall) But we would advise changing bearing when clearance gets to 0.64mm or 25thou"

For most smaller engine / shaft set ups you may get away with big clearances but it's not something we would be happy with.

 

[Jcorstorphine]

Clearances above are for Maritex (all manufacturers should be able to give the same data) and they are in mm so 0.12mm is just under 5thou" and is for a clearance fit (no bore closure)

If you press fit a composite shell it will squeeze but only 0.1-0.15mm I would guess, but it depends on how tight a press fit (which is the inherent problem with press fit)

With a 47.74 ID carrier as yours min clearance (for Maritex) new would be 0.18 (takes account of increased thermal expansion of thicker bearing wall) But we would advise changing bearing when clearance gets to 0.64mm or 25thou"

For most smaller engine / shaft set ups you may get away with big clearances but it's not something we would be happy with.

Thanks Neil for your information. Wish i had know of your product as I could only find this particular size of standard bearing from one company.

I have measured the running clearance of my new bearing by several means using electonic calipers as well as narrow feeler gauges and I would confirm that the difference in diameter between my shaft and the bore of the rubber insert is 40 thou or 1 mm so my radial clearnce would be 20 thou or 0.5mm

The new one really is a rattling fit and about twice that of the one I took out, it was about 0.5 mm greater in ID than the OD of the shaft.

The supplier has assuured me that it will be ok but for the insert to close upto an acceptable clearance the Phenolic section would need to swell by 2% and I just cant see that happening.