Gearbox part 3: Bearing renewal and Gearchange overhaul

I always worry when changing bearings- but in this case whatever I did to them they would still have to be better than the seized and rusty specimens I removed!

Whenever possible I prefer to wind in bearings using a couple of sockets and some studding (or in this case an M10 bolt. I found one socket to go outside the gearbox front cover and a second that was pretty much the same diameter as the bearing and could slip inside its mounting recess. I gripped the bolt head in a vice and  added Larger socket, Gearbox front plate, bearing, smaller socket, washers and nut for bolt in that order before tightening everything loosely and checking alignment.
Then it was possible to simply pull the bearing into the housing by winding the nut down the bolt- very satisfying! Tension on the bolt helps to keep the bearing square as it enters its housing. To make it easier I heated the housing first with a hot air gun and put the bearings in the freezer for an hour to maximise clearance- even so it was tight!

Sockets and bearing housing assembled on bolt - wind down top nut and...

Bearing safely installed

Of course you cant use this method for blind bearings- and sadly this meant there was no choice but to use a bearing drift. You can use sockets again but I have found that they can slip off the bearing leading to an ill-timed whack on the balls (if you get my gist) which can knacker the bearing once its in. Even so I don't like using the drift as there are so many opportunities for the bearing to go off centre- alignment square on to the housing is difficult but essential. Anyway I fitted the others using the drift...

Drift from a Draper bearing driver kit, bearing now fully home

job done!

Gearchange Mechanism

The gearchange mechanism contained in the box top cover wasn't working.when I got the box and when it was removed it looked pretty nasty- however its also pretty complex and I didn't want to mess with it if that's not necessary so I soaked in in WD40 before giving it a thorough clean using a can of carburettor cleaner- this blasted out a load of solidified grease and other nameless evils. I checked the two springs- one on the operating lever and the second on the pawl. Both were present and operational. I checked the box section...

This is the pedal mechanism; Screws were really tight and one was missing.

A couple of taps saw the cover coming loose

Mechanism inside was dirty but sound if rather basic.

I just cleaned this box out and applied some corrosion block grease before reassembling the lot with a new gasket to the front cover and re-oiling the rotary change mechanism. The splines on the pedal shaft are actually the same as those on the older hand gear change lever so although I don't have a pedal I was able to test it using a hand lever.- Mechanism seems to work well although I cant be sure until I get the box back together!

Rotary change mechanism (before cleaning!")

The rotating disc on beneath the cover has 5 notches- I assume these correspond to N and gears 1-4. There is a spring loaded pawl built into the column on the cover (beneath the two wire-tied nuts) that projects to engage with these cut outs in the disc rim. The odd shaped cut-outs in the disc engage with the operating heads on the gear selector forks. These can only move forwards and backwards along their selector rods, sidewise movement isn't possible so rotating the disc cause them to slid along their rods thus moving the  gears to and fro. At least that's the theory- I suspect getting the gears in with the forks in the right position will be very tricky. Not only do they need to be aligned in the correct orientation but they also need to slide into their bearings- and despite what it says in the manual this is going to be a very tight fit!