How do I replace the cutless bearing on a Hallberg-Rassy Monsun 31?
I need to replace the cutless bearing on my Hallberg-Rassy Monsun 31 and would like to order the replacement before hauling out. What size should I buy, and can I remove the old bearing without damaging the stern-tube housing?
Answer
Replace the cutless bearing with the Monsun ashore: remove the propeller and retaining screws, then extract the bearing with a properly supported puller or press. Measure your installation before ordering, as Monsun owners report different outside diameters, and driving the bearing out through the stern tube can damage the carrier.
Check bearing size and housing
On the Hallberg-Rassy Monsun 31, check the shaft diameter, bearing sleeve diameter and bearing length against previous invoices or measurements from the installation. The model name alone does not establish the replacement size.
A replacement confirmed on a 1978 Monsun, hull number 621, was the bronze-sleeved Vetus RL2540, measuring 25 mm bore × 40 mm outside diameter × 100 mm long. Another Monsun owner reported a 38 mm outside diameter. A further successful replacement used a plastic-sleeved bearing with a metric bore and imperial outside diameter.
- Bore: match the measured shaft diameter.
- Outside diameter: establish whether your carrier takes 40 mm, approximately 38 mm, or a specified imperial size.
- Length: measure the existing sleeve and check the available seating depth.
- Sleeve material: confirm suitability for the housing and its retention arrangement.
Do not assume a reported 38 mm measurement means exactly 38.00 mm: 1½ inches is 38.10 mm. That difference matters in a fitted sleeve. If the old bearing is concealed, arrange to measure it immediately after lifting and allow time for parts delivery.
Find both retaining screws
Before dismantling, lift the shaft gently beside the bearing and feel for movement between shaft and rubber. Check whether the bearing sleeve itself moves in the housing. If it does, there is a retention or housing problem as well as possible bearing wear.
Have the boat securely supported ashore and isolate the engine starting circuit before working on the propeller or shaft.
- Photograph the installation and record the bearing's position, including any projection beyond the carrier.
- Remove the propeller using the correct puller for its hub; retain the key and any spacers in order.
- Carefully clear antifouling from the carrier and locate the two retaining screws, which may be completely hidden.
- Remove the screws fully and check for additional retention or previous modifications before applying extraction force.
- Support the shaft if it will lose bearing support; do not leave its weight hanging from the gearbox coupling.
The carrier, extractor and available clearance determine whether the shaft must come out. Check the withdrawal path towards the rudder before disconnecting the coupling; some installations require additional dismantling.