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Posted: Fri Sep 29, 2017 7:47pm

Post Subject: technodrive gearbox

I have a technodrive gearbox fitted to my Lambordini engine, today the coupling cmae away from the gearbox drive shaft, and I had no propulsion, the nut holding the coupling to the drive shaft had undone itself. I managed to put it back together and tightened the nut as much as i could, all was well until i put it in reverse then suddenly no propulsion again and looking at the engine the nut had come off again. have i missed something, should there be a cotterpin of some kind to secure the nut?


Posted: Sat Sep 30, 2017 7:23am

Post Subject: technodrive gearbox

In general across a range of gearboxes those nuts are usually self locking nuts or in some cases castellated nuts with a split pin. You will recognise a castellated nut y the cut outs like a castle tower and a self locking nut by a nylon i9nsert around the top or a funny, slotted semi-domed top. There may be some form of washer under the nut or even two, one being a spring or toothed washer designed to stop the nut undoing. Best search the bilge/drip tray to make sure they were not used originally. It might be that the nut had been loose for a very long time so the splines in the coupling and on the shaft are worn. If this is so then each time you reverse direction the nut and shaft will start to revolve a fraction before the slack is taken up and the coupling moves. This will potentially help loosen the nut. However I suspect this is a hydraulic box and as such without the engine running you can not put it in gear. This means that without a special tool you will not be able to stop the coupling turning enough to get the nut tight enough. On my mechanical box the torque for that nut is 100Nm and a liquid thread lock is used. On a larger PRM hydraulic box the torque is 340Nm or 250 ft lbs. This is exceptionally tight so you will need a long "spanner" to get that degree of tightness and a way of preventing the coupling turning. The proper tool is a sort of strong steel paddle with a hole in the centre for a socket to fit through then a series of holes to accept pins that locate in the coupling bolt holes. I doubt you will easily get access to one of those so try either a very large stilson pile wrench on the coupling but remember to fill off any burrs they produce or two bolts and nuts in two of the coupling holes with a large steel bar wedged between the to stop the coupling turning while you use a socket to do the nut up. Ideally with a torque wrench set to whatever Technodrive say it shoudl be. Otherwise as tight as you can.

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