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AdamL · 15-08-2023, 04:46

Having a leaky rear oil seal on my MD22L which was slowly getting worse, it was time to do the replacement.

The Rear Main Oil Seal is Volvo part number 859718 and the Rear Main Plate Gasket is Volvo part number 861404 (version numbers may change). It is suggested that you replace the main plate gasket while you have things apart which is situated between the engine block and a 10mm thick plate. The old seal is a nitrile Gaco INA 51727 anticlockwise rotation. A generic seal replacement is 3.5” x 4.135” x 0.375” anticlockwise rotation.

The replacement process can be done while in the water, assuming you can unbolt the prop shaft from the gearbox and slide it back about 150mm (I have a Volvo dripless shaft seal, which worked fine) to give you sufficient clearance to pull the gearbox back to uncouple the gearbox spline from the internal damper plate.

In my case, the MD22 is coupled to an MS2 gearbox. In this setup, you MUST fully remove the gearbox from the bell housing adapter plate to access 2 hidden bolts at the bottom, under the gearbox flange (this process is not in the service manual, as the diagram appears that you remove the adapter plate with the gearbox attached, not in my case). Hopefully, someone can learn from my lost hours and tears.

Once the gearbox is removed, the adapter plate is removed, the starter motor is removed, prop the engine up by supports under the rear of the oil pan (I made up my own screw jacks from some timber, washers and a couple of bolts and nuts) and remove the engine supports from the bell housing. Then the bell housing can be removed (watch out for the dowels at 2 o’clock and 8 o’clock) (a little bit of pry bar coercion worked a treat, but remember the bell is aluminium), then remove the dampener plate (elastic drive disc) and finally remove the flywheel…..And there it is.

If you plan to replace the gasket, remove the 10mm plate and replace the gasket (note there is a central dowel above the crankshaft flange). In my case, a gasket and liquid gasket were used on the original (from the factory). So, when in Rome do as the Romans do (no judging). Re-attach the plate following the tightening sequence in the service manual.

Once the 10mm plate is installed, install the oil seal and replace all the bits removed in reverse sequence using the torques and tolerances noted in the service manual.

The whole process took about 6 hours (excluding the hidden bolts drama) with two of us. This is not really a one-person job. No special tools are needed.

Tools and bits you will need are a set of sockets/spanners (preferably 6 pointed to deal with those rusty bolt heads), a torque wrench (or two) for torques ranging from 9nm to 65mn, liquid gasket (in my case), Locktite 243 (for the elastic disc bolts), a dial indicator and magnetic stand, small amount of engine oil or assembly grease (to lube the new seal) and a wheelbarrow load of elbow grease.

You can do it. Good luck.

The hidden bolts revealed after removing the gearbox