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Cutless Propeller Shaft Bearings

How To Install or Modify a Cutlass Bearing

Cutless Propeller Shaft Bearings


Cutless Propeller Shaft Bearing Clearances and Tolerances
How to Choose A Propeller or Rudder Shaft Bearing and the Differences Between Bearing Types

Hole Drilling Diagram for Flange on Flanged Propeller Bearings

Guideline For Cutless Marine Bearing Replacement:
Replace your cutless flanged or sleeve bearing when the V shaped water lubrication grooves are roughly 1/2 worn away.  Other indicators are that the shaft is loose inside the bearing. 

If your vessel will not be in dry-dock again for many years, it may be advisable to replace your bearing(s) as a precaution.  Bearings are not costly compared to re dry-dock of the vessel.
Information Needed for Ordering a New Cutless Marine Bearing:
- Shaft Diameter (inches or mm)
- Stern tube (bearing housing) inside diameter or bearing outside diameter (inches or mm)
- Bearing length (inches or mm). Bearings have standard lengths, but it is good to check.   Many vessels are non standard.
- If your bearing is flanged then we need:
     - flange diameter
     - flange thickness
     - flange hole pattern or order a "blank flange" with no holes
     - flange type: male pilot or female recess
Old Cutless Marine Bearing Removal:
Disconnect the shaft from the gearbox and remove the shaft from the vessel.   Depending on bearing location(s) you may be able to slide the shaft aft toward the stern enough to have access to remove the bearing without removing the shaft entirely.

Once the shaft is removed you can remove the existing bearing.  Most bearings are press fit but sometimes that can be installed with set screws.  You may need to cut out the bearing.  You can also purchase or rig up a bearing puller using all thread rod, nuts and steel plates.

Once the bearing is removed inspect the stern tube to be sure the new bearing will install smoothly.
New Cutless Marine Bearing Installation:
The new bearing will be for a press fit installation and will be oversized by the amount shown in the table on the Cutless Propeller Shaft Bearing Clearances and Tolerances page. 

Put the bearing in the freezer overnight to shrink the bearing down by a few thousandths of an inch.

WARNING: Do not use dry ice to cool the bearing down.  Dry ice will cool the bearing too fast and cause the nitrile rubber interior to separate from the naval brass or non metallic exterior shell.

Once cooled down, the new bearing may slide into the stern tube easily or it may need a few taps with a rubber mallet.  Once the bearing warms back up it should be press fit in place.  On occasion set screws are needed, if so, be sure they are short enough not to enter into the nitrile rubber bearing interior.

Be sure that water installation grooves are clean and clear before installation of the shaft.  If for some reason you are using a 2 piece bearing, be sure that the water lubrication grooves are lined up. 
Modification of Cutless Marine Bearings:
For various reasons some vessels require bearings that are not standard size.  Such reasons include: older vessels with non standard sizes, bearing size is a non stock size or that the vessel has bearings that are in mm when inches are required and vice versa.

Following are tips for making adjustments for cutless bearings:

- If the shaft size fits but the outside diameter (od) of the bearing is too large then the od can be turned down with a machine process.  Be sure that there is enough bearing wall thickness for the shell after the turn down.

- If the shaft size fits but the outside diameter (od) of the bearing is too small then the bearing can be installed with Chockfast Orange to fill the space between the bearing and the stern tube.  Be sure to follow the guidelines of Chockfast Orange.

- If the outside diameter of the bearing is acceptable but the bearing inside diameter is too small then the nitrile rubber id of the bearing can be turned down.
Be sure there is enough rubber inside the bearing after turn down.

- If the length of the bearing is too long then a cutless bearing can be cut to the proper length without damage.

- If the length of the bearing is too short then 2 bearing can be purchased and installed together.  Be sure the water lubrication grooves are lined up after installation.  You may want to set screw the 2 bearings to be sure the water lubrication grooves stay lined up.

- If the bearing has a flange but the vessel requires one without a flange then the flange can be cut off.

- If the flanged cutless bearing flange does not mate up with the stern tube flange then a flange adapter can be made by a machinist.

- If there is enough time for a non standard bearing production (about 6 weeks) then any size bearing can be manufactured regardless of size.

- If there is not enough time to make a traditional cutless bearing then a composite marine bearing can be made in just a few days.  Composite marine bearings can be made with and without water lubrication grooves.  Composite marine bearings can reduce propeller shaft noise going into the water which is desirable for a fishing boat application.

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