How do I remove and refit the saildrive seal on a Monsun 31?
My Hallberg-Rassy Monsun 31 still has its original-style saildrive setup, and the hull seal is now well over ten years old. I need to replace it while the boat is on the hard this winter. How do I go about separating the engine and drive in such a tight space, and what are the exact steps to fit the new diaphragm correctly?
Answer
To replace the saildrive diaphragm on your Monsun 31, you must support the engine, slide it forward into the saloon, and unbolt the saildrive leg so it can be lifted out of the hull. The standard Volvo Penta seal kit costs around £250 and includes the main rubber diaphragm, the clamping ring gasket, and replacement O-rings for the upper gear housing.
Moving the Engine Forward
The Monsun 31 engine bay sits tightly under the cockpit sole. You cannot lift the engine straight up. Owners with the original Volvo Penta MD11C and a 110S drive, or a repowered D1-20 with a 130S, must slide the block forward.
Drain the oil from the saildrive leg. Disconnect the battery, exhaust hose, raw water intake, fuel lines and wiring loom. Unbolt the engine from its front mounts.
Rig a chain block from a sturdy timber placed across the companionway hatch. Ensure the boat is securely shored up. Support the engine fully on the block before unbolting any mounts. A dropped block causes severe injury or hull damage. Hoist the engine just enough to take the weight. Unbolt the flywheel housing from the saildrive. Slide the engine forward about 30 cm into the cabin to clear the splined input shaft.
Extracting the Saildrive Leg
With the engine out of the way, focus on the drive unit. Vertical clearance beneath the cockpit sole dictates if you must split the drive to extract it.
- Remove the propeller and zinc anode. Peel off the rubber fairing flap from the outside of the hull.
- If headroom restricts lifting the entire leg, undo the Allen bolts holding the upper gear housing to the lower leg. Lift the top section away.
- Undo the 8 bolts securing the metal clamping ring over the rubber diaphragm.
- Lift the intermediate housing and the old seal up and out of the boat. Lower the bottom leg to the ground outside.
Fitting the New Seal
Preparation dictates the success of this job. Clean the GRP seating flange thoroughly. Leftover salt crystals, oil or old adhesive will cause a leak.
The Volvo Penta replacement kit (part number 21389074 for 110S, 120S and 130S models) provides everything required. Slide the new rubber diaphragm onto the drive leg. Volvo Penta dictates installing this seal completely dry. Do not use Sikaflex or any marine sealant on the rubber or the GRP flange.