![]() 3 main bearing cars have no option but to retain the originals as the flywheel mounts are different.Ī relevant consideration is that the bellhousing of the full synchromesh gearbox was wider and enabled a larger flywheel and pre-engage starter to be fitted. For cars presently fitted with a 3 synchro overdrive gearbox, the propshaft needs to be shortened by an inch (or swapped for another propshaft – see below).įor cars fitted with the 5 main bearing engine, there are two ways of approaching the differences between flywheels & backplates – either retain the original ones on the engine, or to change to the later flywheel & backplate.The flywheel, engine backplate and starter are different.The gear lever position is a bit further back.The only significant differences between the two models are: ![]() The early D-type overdrive fitted to the 3 synchromesh gearbox of the Mk1 MGB is a relatively rare beast, so a very viable alternative is to fit the later full synchromesh gearbox and overdrive.īy and large it is a relatively direct swap – even the overall length of the later gearbox is the same as the 3 synchro non-overdrive unit, so the propshaft doesn’t need changing if you presently have the non-overdrive version. Overdrives are a polular retro-fit option for those MGB’s which were not fitted with one from new, particularly as cruising speeds now are higher thanks to modern roads being much faster than those in the period. ![]() ![]() ![]() If contemplating such a change, it is essential that this is checked out! It may be possible to enlarge the crankshaft spigot if the engine is out and stripped, but care would have to be taken that the oilway from the rear main to no 4 bigend. This however raises questions over the hardness of the resulting bearing surface on the modified shaft, and as I have not carried out this particular operation I’ve never been in a position to investigate it. As far as I’m aware, the only way around this is to reduce the diameter of the first motion shaft to match the early one. Note: In addition to the changes below, cars with 3 bearing engines have a much smaller crankshaft spigot bush (5/8″ against 7/8″). ![]()
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