Mk II Cutlass Bearing Replacement

The following photos and captions relate to the process one can follow to remove and replace the cutlass bearing.

Shows the shaft log (bronze housing bolted to back of keel), shaft and propeller assembly in place.  The cutlass bearing is housed within the shaft log and provides support for the propeller shaft as it turns.  The end of the cutlass bearing is barely visible just forward of the shaft zinc in this photo.  These bearings are designed to be an interference fit with the housing and need to be either pressed or cut out when being replaced.  The shaft has to be removed to get at the bearing.

The shaft collar on the forward end of the propeller shaft needs to be removed first to allow the propeller shaft assembly to slide backwards out of the boat.  The rusted collar was sprayed with penetrating oil and left to sit for a few days. 

A flexible coupling (black rubber disk) shown here mounted between the shaft collar and the transmission was then unbolted and removed.

The four socket head cap screws and two set screws have been removed from the collar.  The collar is a tight fit on the shaft and needs to be pulled.  A simple puller is shown made out of a short length of ¾” brass pipe and a couple of 6” pieces of 3/8” threaded rod.

These three photos just show the freed collar from different angles.  Once the collar was off, and the shaft seal removed, the shaft assembly slid out the back end.

 A reciprocating saw was used to make a couple of longitudinal cuts in the bearing to free it from the shaft log.  The first cut is seen here.

 Two halves of the extracted cutlass bearing show the poor condition it was in.

 With the old cutlass bearing removed, one of the cuts is seen to have scored the inside of the shaft log.  While you try to avoid this, it really doesn’t harm anything or affect the performance.

 To get a new bearing inside the shaft log you must either press it in, or briefly change the size of the two units so they can slide together.  I chose to heat up the shaft log to expand it, and cool down the new cutlass bearing to reduce it’s diameter.  This photo shows a heat gun directed at the housing for about 20 minutes to heat it up.

This project was done during the spring – in northern Canada.  To cool down the new cutlass bearing, it was simply stuck in the snow next to the boat for a little while the shaft log was heating up.  A refrigerator or cooler of ice would also work just fine.  The new bearing was a bit too long so it had been shortened using a carbide tipped blade on a carpenter’s miter saw.  This produced a clean, square cut.  A film of lithium grease was applied to the outside of the bearing before being cooled. 

The new bearing is seen inserted in the shaft log.  The two slid together fairly easily by hand but required a couple of light taps with a hammer and block of wood towards the end.  This procedure should be done quickly since the temperatures of the two pieces will equilibrate rapidly once they come in contact. 

Photo shows a new brass key for the shaft collar made from 5/16” square bar stock, a tap used to clean out threads and new stainless socket head cap screws & set screws for the collar.