Cutlass Bearing Epoxy Bedding ?

[ribbony]

While cruising recently we were gettinmg increasing noise from the drive train, especially at high revs. While cleaning the growth off the prop I noticed the prop shaft is loose in the back bearing (on a 5"skeg). It has only had about 60hrs of use since new ? Probably motoring with some barnacles on the prop caused the stress, the compressed fibre bearing probably could not take the wear.

So I need to put in a new bearing. We will use a nitrile one this time.

When we installed it a year or more ago, the cutlass bearing had to be shaved a little by hand to get it into the hole as there was some distortion if the SS tube when it was welded to the hull at the last slipping. I have read that bedding cutlass bearings in low temp epoxy glue is a good way to get them straight and in line. Getting the SS tube ground out true is not a contemplation as it would require removing the engine, etc. It has to be a short slipping.

Can anyone shed some light on using the epoxy method of bedding cutlass bearings and any suggestions for commonly available glues for the task ???

[never monday]

customary practice is to drill and tap the strut for set screws

[ribbony]

I did that when I last put in the bearing. The epoxy is to bed the bearing sleve into the housing that is no longer perfectly round. If I force the bearing in as a tight fit, it will distort (without shaft insitu). Apparently the epoxy method is you slide the bearing along the shaft into the housing that has the epoxy in it, the bearing will then be aligned to the shaft as it is sitting snugly on it. Everything then is aligned.

I would still use the screw to secure the bearing, just in case the epoxy failed somehow.

[never monday]

Originally Posted by ribbony

I did that when I last put in the bearing. The epoxy is to bed the bearing sleve into the housing that is no longer perfectly round. If I force the bearing in as a tight fit, it will distort (without shaft insitu). Apparently the epoxy method is you slide the bearing along the shaft into the housing that has the epoxy in it, the bearing will then be aligned to the shaft as it is sitting snugly on it. Everything then is aligned.

I would still use the screw to secure the bearing, just in case the epoxy failed somehow.

how do you know the shaft is true at that point?

normal practice it to locate the bearing, install the shaft, then align. Your way seems backwards.

[ribbony]

Shaft was checked for trueness before reinstalled at the last slipping. As there has not been trauma down there I am working on the belief that has not changed.

The alignment last time was good, it took some work but we did get it true. Now, I need to replace the cutlass bearing and the question is how to best do that without a full drive train and engine removal ???

We do not want to make this unexpected bearing change any more complicated that it is already.

When you say "locate" the bearing, how would you do that ?
Then how would you then align once the bearing and shaft are insitu ?

[ribbony]

Here is an extract from a posting elsewhere on the web.

"Working with bearings, one approach you could look at is to get one of the new marine composite bearings, these can be fitted as a clearance fit which means that with the shaft chocked th ebearing should spin in the carrier and on the shaft. Once this is achieved the bearing is bedded on epoxy.

For grp stern tubes you can put release agent on the bearing, you can then split the bond easily when you want to remove the bearing. These are now used on Lloyds class ships so it is proven technology. The solid composite bearings offer closer tolerance shaft support whch can reduced shaft whip and vibration. For metal struts/P brackets you just heat the metal and the old bearing will slide out as the epoxy softens."

[4HMainer]

Originally Posted by never monday

how do you know the shaft is true at that point?

normal practice it to locate the bearing, install the shaft, then align. Your way seems backwards.

Normal practice in some yards, the latest (past 10 or 15 years in some yards) method with Maritex is as the original poster has said. This is the method used in a large number of performance and commercial Al as well as grp vessels. Using the traditional/old method of press fit metal or phenolic sleeved rubber bearings, if the carriers are not aligned (with each other and with the output flange) then when the shaft is installed you may have uneven pressure on these bearings resulting in premature failure or vibration/noise. You could check the situation with feeler guages to see where the gap is between shaft and bearing (it should of course be at the top) but this can be very difficult in some installations.

With the Maritex method and materials you can dry run the installation, and check with feeler guages or eyes for where the gap is or better still chock the shaft and you should be able to spin the bearing in the carrier whilst on the shaft. This proves that all bearings/carriers and shaft are in line, then and only then do you adjust the engine to match the position and angle of the shaft.

With the old method you put a lot of effort into checking the engine alignment to the end of the shaft whilst the shaft may be bent out of true by the bearings. Many P brackets or struts have been moved at some time by the forces of debris round the prop and this is rarely checked.

The other benefit of the Maritex approach is that th euse of a low temp epoxy means bearings can easily be removed with the application of some heat, there are also corrossion benefits with some materials.

[Mark Zarley]

It sounds to me like the real issue is how to "support " the bearing inside a deformed bearing tube. Pounding a bearing into a tube over a shaft with a coating of epoxy , hoping the epoxy will fill the out of true voids and provide the bonding might work or it could leave voids.How about injecting the epoxy mixture from the center of the tube, small holes recomended. Or just forward or aft of the deformed spot. Not familiar with this type of bearing, but I can see the benefit of making sure it is in a good evenly supported bed.