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Any oil in the bell housing space will have come from the engine rear main, the gearbox or have dripped in from the top face of the crankcase. In the former case, it will have found its way past the rear main bearing oil thrower and the aluminium bearing cover which forms part of the oil seal.

To ensure that the oil thrower is living up to its name, it is best to fit a new one and ensure it is nipped between the flywheel and the bearing inner race.. * One way of checking the nip, before installing the crankshaft, is to measure the gap between the inboard face of the flywheel and the rear bearing face on the crankshaft and subtract the " thickness of the inner race. Alternatively, if you have an old inner race, remove enough metal from the inside diameter to enable it to slide easily on to the crankshaft and then make a trial fit of the thrower and flywheel. Don’t be tempted to use an aluminium cover plate with a poor “oil return screw” on its inside diameter. If in doubt, fit a new one.

The first motion shaft on the gearbox also runs inside an “oil return screw" in an aluminium housing but new ones are not available (unless anyone knows differently). Here, as with the main bearing cover, it may be appropriate to machine out the housing to accommodate a lip seal – as found on moderns. If you do this, make sure the mating face on the rotating part is smooth and polished; if not it will soon chew up the rubber lip with disastrous results.

Apart from possible leaky gaskets on the various joints within the bell housing, a possible oil leak path is through the centre of the first motion shaft. The apparent blind hole in this shaft is, in fact, a through hole with a " dia core plug sitting on a spigot face half way along the hole! A leak here will bring gearbox oil straight on to the clutch plate. If fixing a new plug, fully degrease the hole/seat, coat the spigot face with Loctite Studlock, tap the plug in with a 5/16" socket and finally whack it in tight with an old gudgeon pin aimed at the centre of the plug.

* Prior to fitting the crank into the crankcase, it is good practice to gently lap the flywheel on to the crank until a matt finish is seen along the taper of both components. Do not over-do the lapping or the flywheel will finish too far up the taper.

 

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