There is an old thread here that discusses:
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A copy of that text (so it is in one place):
is quite a small unit and it is fixed to the engine
by 8 bolts around the bell housing, 4 bolts on the prop shaft and releasing the control cable, easing the prop shaft gland we were able to slide the prop shaft back a couple of inches sufficient to allow the gearbox
to move back and be lifted out. Not having the right tools on board I was able to put the gearbox into a carrier bag and take home with me.
an area on the workshop bench, I drained the oil
, removed the 4 bolts that held the control lever in place and removed it. The gearbox is accessed by removing the 8 bolts holding the bell housing to the gearbox, the jointing was just liquid cement so having removed the bell housing I could now see inside the gearbox. You need to be careful to protect the seals
at each end, there are 3 shafts an input shaft, an intermediate shaft and the one that we are interested in the output shaft, which is recognised by being the largest and has a locknut on each end. Note: these nuts are left handed threads.
You need to clear the locking tab and using a long handle socket or torque wrench to remove the nuts. You will then need a puller to remove the roller bearings and collar (2) and the bearing inner race
and collar (2). You should then be able to lay out the whole shaft on to a nice clean surface, clean the individual components and inspect for damage or wear. The main area’s to look at are the bearings and the drive cone. Having said earlier that the reverse gear
seemed ok, I was hoping to reverse the drive cone if possible as I felt this was not as important as the forward gear
but I found that the gearbox had been opened up previously and that the cone was worn both sides, however there was some grooving left on the cone with a possibility of reclaiming the contact surface.
The cone is moved in and out of the large gearing by the selector mechanism, the tapered surface of both forward and reverse gear were very shiny, possibly were they had been slipping ? I could not find any referance to this in the manual, so I decided to lap the tapered surface’s with some fine grinding paste ( I was surprised what a difference this made ) When fitting the tapered surfaces together they now locked 100 % and I felt that I had done the right thing.
were then meticulously cleaned before starting to reassemble. You will need a piece of tube to knock the bearings and collars back on. If you have been careful you can reuse the seals
and the locknuts, when fitted these need to be torqued up to approx 10 kg/m or 70 ft/lbs, check that all is ok before using liquid sealant
and refitting the bell housing. Note: A Large vice is very helpful for stripping down and reassembling and don’t forget to relock the locknuts.
Before fitting the control mechanism, use the aperture as an inspection
hole to see that the gears are turning and that the cone moves forward and backwards, you should now be able to fit the control mechanism, Check the O ring is ok and that the shifter which actually locates in the centre of the cone is set to its lowest point (it is possible to be 180 degrees out), loosely fit the 4 bolts, hand tight and fit the control lever to the correct angle.
Note : the bolts holding this plate are over size, allowing for movement to be able to adjust the control lever, so as you can set the same amount of lever movement forwards and backwards, when this is correct you can tighten the 4 bolts.
Before refitting the gearbox, check that the damper plate which is fitted to the flywheel is all ok, then you should be ready to fit the gearbox, lightly grease the spline on the input shaft and slide the gearbox back into position, fit and tighten the 8 bolts, you can then adjust and fit the control cable, put in the required amount of gear oil and secure the filler plug
. Slide back the prop shaft and secure the 4 bolts, you should then be in a position to carry out operational tests. At this stage I found that I wanted to readjust the control lever movement and I found it was just as easy to remove the gearbox, lift
it into the cockpit
and do it rather than struggle in the engine locker. My friend then carried out some tests and found a big improvement, so how long had the cone been slipping ? I quite enjoyed doing the job although as you get older it is more difficult to get in and out of the engine compartments, a bottle of whiskey changed hands which was very nice and it saved my friend putting money
into someone else’s kitty.