Gearbox Reassembly

Both the case and the gearchange mechanism cleaned up quite well, gearchange operation functioned when the splined rod was turned.

I was concerned about reassembling the gearbox, the secondary shaft slid most of the way into its rear bearing although the primary was reluctant.

Secondary shaft in,. primary introduced through the case

Both shafts in poosition but both are standing too high in the case and its not possible to fit front cover unless they are tapped farther in to their rear bearings.

Case supported on wooden blocks before tapping the shafts down

The speedo drive bushing was inserted into the speedo drive hole and checked that it seated correctly at the bottom

Front cover fitted, this was tight where the bearings bore on the  shafts and needed to be tapped firmly home before the bolts could be done up, top two holes are for the selector rods

At this point there was a mishap! Having forgotten to fit the front cover gasket (Duhhhh!) before tapping the front cover home, consequently it was now necessary to remove it again to put the gasket in! Sadly doing this meant that all the bearings remained on their shafts and pulled out of the case so reassembly was needed all over again! At this point though, with all bearings on the shafts I was able to try the second half of the alternative method of assembly- ie fitting bearings to shafts (by default mine were now fitted) and then  inserting the shafts plus bearings into a preheated case. Having now tried assembly both ways I can confirm that the second method is by far to be preferred since it means that the bearings can be pressed onto their shafts using a sleeve which should apply force only to the centre race in contact with the shaft. The outer race then fits easily into the cases when these are heated up. This method thus avoids any need to stress the bearing by tapping on an unsupported centre or heating them. I started applying heat using a hot air gun, this was OK for disassembly, but for assembly you really must use a gas torch, the bearings then slip in very easily, only gentle hand pressure was needed. However, remember to introduce the cork washer behind the primary shaft rear bearing before the shaft is mounted. As the bearing is now firmly fixed onto the shaft there will be no opportunity to insert the washer afterwards. The case was of course hot when this was done and I had to use a rod through the clutch pushrod hole, cork washer and into the primary shaft centre bore to hold it centrally as the hollow primary shaft is fitted. Fiddly but not too bad.

Finally there is no obvious shoulder or "stop" that the bearings could reach to show when they are pressed fully onto their shafts. Therefore, if you are going to try this method its probably best to mark of measure the position of the bearings before pulling them off their shafts. 

Once the shafts are in I fitted the selector forks:

The first selector rod is mounted through the first fork and 

screwed home, a lock nut then secures the gearbox

 front cover

The second rod has to be fitted simultaneously with
the second fork as it has to pass through both forks

As seen here, rod pushed home and screwed into the case wall, locknut as above.

I cleaned and oiled the collars for both shafts and fitted them over the splines. The oil seals were then lubricated and slipped over the collars and into their recesses before they were tapped home using a drift (in this case a deep impact socket).

Output shaft fitted

followed by clutch seal

Gear selection could then be checked, Front and rear gear pairs are always meshed and always turning. Neutral is achieved when none of the central gear dogs are engaged; 1st gear is when the front dogs on secondary shaft (i.e. closest to speedo drive) are engaged; Second is when the rear dogs on the secondary shaft are engaged (i.e. those nearest to the output shaft). Third is achieved by engaging the forward dogs on the primary shaft (i.e. those closest to the clutch) and fourth when the rear dogs on this shaft are engaged. I checked that all slid easily and lubricated the shafts with fresh oil.

When I took the box apart nothing was turning and it had been easy to remove the clutch centre nut (ring nut). Now that the gears turned it was necessary to engage two gears at once before the clutch centre could be tightened. I found that a clutch centre nut adaptor from a Honda was a close fit and with a little filing fitted the ring nut perfectly.

Clutch ring nut, fit this with the machine side towards the gearbox. Using a new tab washer it was easily tightened using a Honda  clutch tightening tool (see at rear attached to ratchet handle)

Tab washer folded into one of the ring nut grooves.

New gasket fitted before reattaching the selector mechanism 

in the lid, the steel pegs on the selector forks mus

engage with the grooves in the gear selector disc

In order to engage the pegs in the disc the selector disc must be set to neutral (centre of the three closely spaced notches). The pegs must then fit into the grooves but they have a fair degree of to/fro movement whilst the gearbox is still in neutral. I made a "jig" by tracing the selector disc profile using a "brass-rubbing" approach and then cut this out of cardboard. Using the gearbox ribs and studs as a guide it was possible to align the cardboard disc with the case and ensure the pegs slipped through the holes.

Tracing

Cardboard template mark alignment with stud holes, invert
 and place over the selector forks

Pegs through grooves in template

The selector fork pegs could then be inserted with minimum trouble into the grooves on the selector disc as the gearbox top was fitted. Any fine adjustments were indicated by putting a blob of grease on the pegs and then offering up the gearbox top, removing the top then showed trace grease "scars" where the pegs needed to be moved as below:

Circular mark showing the peg on this fork needs
to be moved slightly in towards the centre of the box

Finally the lid was fitted and tightened down not forgetting the shake-proof washers- several of mine had been missing. Box finished!