Heavy oil should not be used in the gearbox. Engine oil of the same grade as that specified for the engine is the correct lubricant.
Sourced from Minor Monthly
WORKSHOP – Gearbox Options
Daniel Stapleton takes us through the many choices available to the Minor owner when uprating or modifing their gearbox.
THREE DIFFERENT gearboxes were fitted to the OHV Morris Minor. The 803 and 948 gearboxes differ from the 1098 in that they have inferior ‘cone’ type synchromesh, the latter has baulk ring.
They are readily identifiable by the easing which is smooth as oppose the 1098 box which is ribbed. Aside from the inferior synchromesh another problem with the earlier boxes are that all the parts for them are scarce or no longer available.
Therefore a switch to the later type 1098 box is a move in the right direction. Another alternative is to fit the Austin Healey Sprite/MG Midget gearbox from the 1275 engined car. Be careful here as there is scope for confusion between the Minor 1098 box and the early SpriteAlidget 1098 box for which the parts are not interchangeable. The advantage of the 1275 Sprite/Midget gearbox is that it is stronger and therefore better suited to a more powerful engine such as the Sprite/Midget or even 1.3 Marina engines (more of that if there is sufficient reader interest), than the Minor boxes. There are a whole variety of ratios relevant to each box and the Sprite/Midget 1275 box ratios are closer than the ratios in the other boxes.
If you are considering a gearbox swop the other parts you are likely to require are the engine backplate, flywheel and clutch assy. Although it may be possible to get away with just swopping the engine backplate, this is asking for trouble. There are several variations of flywheel/clutch and Mike Lennon of the Morris Minor Centre Birmingham confirmed to me that although the original parts can sometimes be used with a ribbed box you can run into problems with getting the clutch to work. So try and use the backplate, flywheel and clutch that goes with the box you are going to use. If, however, you are set on using a smooth case box, perhaps for concours or some other object of originality, Hardy Engineering advised me that it will take the Morris Minor 1098cc parts after some machining to get them to fit. It is also possible for both 1275cc and straight cut gears to be fitted to the smooth case box but as with fitting 1098cc engine parts the work is considerable and includes machining the case. The 1098cc Morris Minor box internals are not compatible with the later Sprite/Midget box except for bearings, baulk rings and layshaft. The later Sprite/Midget ribbed box is the strongest of all the boxes. Note that the gear lever and clutch release bearing arm are not always interchangeable between smooth and rib case boxes. Racing straight cut close ratio gearsets, are now only available for the ribbed 1275 box.
Whichever box you plan to use there are some uprated parts available from Mini Mania in the USA that are worth fitting. Mini Mania have manufactured new layshafts that are precision made of high quality materials that are reputed to provide stronger, straighter, more resilient shaft. The same company also developed a competion baulk ring which is cast in a high quaIity manganese bronze alloy and machined and then hand finished for optimum quality. Possibly of even greater interest, also from Mini Mania, is a gearbox drain plug that incorporates a magnet to trap metal particles, in a similar way to modem engine sump plugs.