When good bearings go bad
Vibration problems seem to have multiple causes. Most causes though, seem to have a common result – bearing wear. Most engine related vibrations are transmitted down the length of the shaft causing bearing wear. Worn bearings need to be replaced, but first you need to determine and rectify the vibration problem.
Good and Bad Bearings
In order of most common causes, check:
- Engine alignment
- Engine mount problems
- Unbalanced or damaged prop
- Bent shafts
- Strut problems
After eliminating the cause of the vibration, you can proceed with bearing replacement. This is not an easy job if your shafts have not been removed for some time. It will require a thorough cleaning of the shafts to allow them to be removed through the bearings. They often will be stuck in the couplings due to corrosion, pressure, etc. They then will require special tools to remove them. The bearings will most times also require specialized tools to remove. We have a hydraulic press to press them out.
Inserting the new bearings is the easy part. We put them in the freezer overnight to cause the bronze to shrink. It is then easy to reinsert. When we install new bearings, we usually check the whole drive train from the transmission to the prop. If stuffing boxes need rebuilding, this is the time to do it.
This is not a cheap job, but if it is done properly, you can expect the new bearings to last a long time – assuming you will keep vibration issues at bay.
[...] Usually the first step we take is to remove the shaft zincs. Now we can start cleaning the props and shafts. Sometimes this is an easy job, sometimes it is not. Any barnacles have usually been removed when the boat is pulled, but not always. And heavily barnacled shafts and props leave a lot of hard residue that can only be removed by sanding. We find that emery cloth is the best solution for this. After a thorough cleaning of the shafts we can install the new zincs. At this time we also do a quick bearing check. If a shaft wiggles in the bearing, the owner is alerted to a potential problem. (see When Good Bearings Go Bad) [...]