Lightweight gearbox questions

[Derek996]

The kickstart return spring on the 4 speed lightweight gearbox of my 1948 B32 broke this weekend. Fortunately Draganfly had one left in stock which I have ordered. I will be replacing it later this week and it's a job I'm not looking forward to. The spring is behind the inner gearbox cover so requires a lot of dismantling. There is virtually no information about this box available online, in fact, apart from an exploded diagram, no information full stop. I'd appreciate any advice from anyone who has worked on these gearboxes. I can see that the first problem is going to be accessing the 3 long bolts holding the outer cover which are at the rear of the inner cover  I really don't want to have to take the box out unless there is no alternative.
Obviously I've had to drain the oil. Previously I topped it up with SAE 40 engine oil but perhaps with modern lubricants there is something better.

[Rupert]

It should be fairly straightforward but working on it in situ is definitely more awkward than having it on the bench.
A few things to consider -
Removing the outer cover is easy other than the bolts from the rear which you mentioned. You may find there are 4.
Try not to disturb the gearchange mechanism but that may be unavoidable as one of the inner cover screws is behind it. If so try to remove it intact having first noted what gear the box is in and the position of the ratchet plate relative to the pawls for that gear. A photo prior to disturbing it would be helpful.
The inner cover should come away easily and leave both gear shafts and the selector shaft behind. Watch for any thrust washers off the shafts coming adrift, the favourite is the one on the selector shaft as that may be trapped behind the gearchange actuator which comes away with the cover.
Fit a replacement inner cover gasket of the same thickness as the old one so endfloat of the shafts is not altered. Kidderminster MC do a gasket set for it.
The kickstart shaft has a slot on the end so you can turn it with a screwdriver when reassembling to get things aligned.

[Derek996]

Thanks Rupert, I've found out most of the stuff already. My main concern is disturbing the selector mechanism as it's easy to get these things out of sync if you don't know the starting position. I'll photograph each stage so that I can refer back to them if necessary. I have gaskets and hope that they are a similar thickness to the ones fitted. Service sheet 306 states that end float should not exceed .001" - .002" which is pretty tight.

[Derek996]

I have successfully removed the outer cover and after a struggle accessing the nut on the back of the inner cover have removed the gearchange mechanism and have now removed the final bolt underneath it. However the inner cover moves easily outwards about ½ to ¾ of an inch but won't come any further. As far as I can tell I've removed everything that would hold it in place. Have I missed something?

[Greenfield]

Have a look down the gap top centre and see if the gear selector thrust washer is at an angle and jammed on the shaft. If so release it with a screwdriver. Try putting a little pressure on the end of the mainshaft to leave it behind. There should be nothing holding it.
Once it starts to move be careful that the other thrust washers don't end up on the floor; they're probably different thicknesses and need to be fitted on the correct shafts. Also watch out for the little plunger and spring behind the ratchet.

[Derek996]

Have a look down the gap top centre and see if the gear selector thrust washer is at an angle and jammed on the shaft. If so release it with a screwdriver. Try putting a little pressure on the end of the mainshaft to leave it behind. There should be nothing holding it.
Once it starts to move be careful that the other thrust washers don't end up on the floor; they're probably different thicknesses and need to be fitted on the correct shafts. Also watch out for the little plunger and spring behind the ratchet.

Thanks for that. I'll hopefully get back to it tomorrow and look out for that. I've already considered watching out for the thrust washers and the quadrant detent plunger.

[Pete C]

I worked on one of these a couple of years ago, complete pain compared to the later gearbox. As you noted, there is virtually no information available for these boxes but I did find the few remarks below.
Getting the kickstart spring tensioned while replacing the inner cover was a particular trial, if I remember correctly.
Finding parts is also not easy. I started with 2 "restored" boxes and got one decent one out of it, with a few parts from Australia added in.

Good luck!




These boxes are a further development of the gearbox fitted to the WB30...Another problem apart from the scarcity of parts is the fact the box has a fairly short main shaft and as they were only fitted for two years the correct clutch sleeve isn't that easy to find either...Further, only the poor quality 6 spring clutch will fit...

I've been struggling for several days with the selector mechanism arrangement until today when I solved the problem. So let me first say, if you have one of these gearboxes, TAKE NO NOTICE OF SERVICE NOTE PAGE 608. This refers to the M20/21 range and the set up is completely different. If you attempt to work from the diagram Figure M29, with the selector ratchet in top gear you'll never get it to work, the arm, which turns the quadrant on the selector shaft, is too far round clockwise to be able to operate.
Set the ratchet to neutral and you'll notice that the punch mark on the final tooth of the ratchet actually lines up with a corresponding punch mark on the end of the selector arm shaft. Tighten everything up in this position and bingo you've got first, neutral, second, third and fourth and back too.

[Derek996]

Have a look down the gap top centre and see if the gear selector thrust washer is at an angle and jammed on the shaft.

You were spot on with this diagnosis. The thrust washer on the selector shaft had tilted and jammed on the shaft. Since the thrust washer is behind the gear control quadrant it prevented any outward movement. I managed to get a screw driver into it, and with some effort got it straightened up and the cover came off with no problem.
I've now fitted the new spring, the next challenge will be putting it all back together again.

[Derek996]

All back together and I seem to have all the gears although I haven't done a road test yet.
Pete C, you were spot on about the dots in the selector shaft and the selector quadrant lining up in neutral.
The difficulty with the kick start spring wasn't tensioning while refitting the inner cover but when refitting the outer cover. The kickstart stop is in the outer cover and you have to tension the spring and hold it clear of the stop while pushing cover on. There a slot in the end of the kickstart which is probably intended for some kind of special tool to be used. I used a short length of ⅛" thick, 1" wide mild steel gripped in a Mole wrench to hold the shafting the slot, while my wife pushed the already loosely fitted outer cover fully home. Once it was on, the kickstart shaft rested against its stop in the inner cover and I could fit all the cover screws. I don't want to do that job again anytime soon.