lightweight gearbox leak

I have similar problems! I have solved the leaking gear and kick start shaft with new o rings, the club sell square profile ones which are supposed to be better, but I just used what I had. The o rings are easy to change if you tip the bike over on the lawn you donât even have to drain the box! To be honest I donât expect it to be oil tight for long, I think I may have the case machined to take ânormalâ oil seals.

oil should not be leaking from the blanking plugs for the layshaft and shift shaft ( assuming the plugs are there and you are not just looking at the bronze bushes - my plugs are steel. If you can get them out without tapping them from the inside (which easier than it Sounds!) then you buy new or fit with loctite sealant or similar.

Finally donât let the gear box oil level drop below the level, that way lives the damaged layshaft bush demon! Although it sounds like you have a later gearbox which has a pegged bush. The earlier boxes had a tendency to grab the bush which would then spin in the case and if unlucky damage it beyond repair. That shouldnât happen with yours but keep the level topped up.

Oil travelling down the clutch rod shouldnât be too much of a problem as it will only run into the chain case although I have heard of people fitting small o rings.

My gearbox now only leaks ( profusely!) when running from the gearbox sprocket area (clutch side) Iâve done the sleeve gear seal and chaincase seal so that needs further investigation!

dan

I replaced the sleeve bearing seal on my late 1964 Navigator earlier this year Bryon using one from the NOC shop, I've done almost 1000 miles since and it is still oil tight so I think you can have confidence in the new seal! Mine has the later gearbox like yours from the sound of things. However, I have found that if I fill the gearbox up to the level plug it tends to weep oil from around the hole where the clutch cable enters the gearbox and the breather hole on the filler/inspection plate. I therefore filed the gearbox with the recommended 2 1/4 Pts / 1.25 Ltrs which seems to sit the level just below the level plug and that has stopped the leaking. That said I have been using 20/50 engine oil in the gearbox which 'froths' a lot even after a relatively short run which can't help either lubrication or the weeping. At the next oil change I am going to us Castrol classic EP90 GL4 gearbox oil which should be safe with the bushes, give better lubrication and less frothing. As for the two bushes if they are leaking you may have a more serious problem - the design of the gearbox makes oil level critical and earlier bikes had a tendency for the bushes to wear and start turning in the crank cases as a consequence of lack of oil due to leaks. Norton introduced a mod to pin them in place to stop this - was their evidence of gold/bronze particles in the gearbox oil when you drained it? If there is that would suggest you need to investigate further. If your Jub engine number is post 106838 the bushes will be pinned so hopefully that isn't the case - when I stripped my Nav' my bushes were dripping with oil but once I degreased it and replaced the seal it was clear that there was no leakage so good luck and hope that helps!

Nick

Great advice from Dan! While I was doing the gearbox oil seal I did the crankshaft seal and clutch seal too because engine oil was topping up the primary chain case and leaking out via the clutch seal - fiddly getting both pressed in square but it has cured the leaks so well worth doing. I still had an excess of oil 'lubricating' the chain even though the oil level in the gearbox and primary chain case was not changing. The penny then dropped, in my enthusiasm for good engine lubrication I was over filling the oil tank and the excess was running down the oil breather pipe onto the chain when I was taking left hand corners! When I filled the tank to the correct level (2" below the filler) there was a huge improvement and no indication that the engine is running hotter due to lack of oil. Luckily my engine seems to be reasonably healthy without excessive blow by so the chain lubrication isn't excessive. The joys of lightweight ownership!

Nick

That's too much of an oil leak even by Lightweight standards.

I have never worked on the later gear box but I would agree with Dan that oil should not be leaking from the blanking plug and it definitely needs curing. I don't know if it is the same as the earlier box but I used a coin locktited in to cure a similar leak on the early box. I doubt if any new blanking plugs are available but check first.

I have used the (expensive) square O rings and correct imperial size O rings from NOC as well as the metric O rings from the usual assortment found in a box. If anything the metric O ring works better as it is very slightly oversize but they all dribble oil after a bit of use. The standard O ring from NOC seems at bit slack but it surprised me as the one I fitted a few weeks ago in the 1959 Jubilee is still oil tight -well it was yesterday.

Tipping the bike on it's side sounds a good idea- Dan has obviously benefited from his trial riding experience. BMC works mechanics used to tip the Mini Coopers on their side to work underneath.

Patrick

On the later gearbox the design of the gearbox sleeve gear seal seems a bit suspect.

The seal works against the OD of a hardened spacer between sleeve gear bearing and gearbox sprocket. So normally, no leakage at this contact point.

But - nothing stops oil leaking under the spacer except the fit of the spacer over the output shaft (loose) and the fit of the spacer to the inner of the sleeve gear bearing. If your gearbox sprocket securing nut is not tight, oil can seep steadily between the bearing and spacer, under the spacer, and out. Until the oil level has dropped to the bottom of the spacer - about 1 inch below level plug.

If you go to this investigation, on reassembly put some sealer between the spacer and the sleeve gear bearing inner race, and over the sleeve gear to fill clearance under the seal spacer.

While you are at it put a straight edge over the primary inner back face and over the clutch seal. Owners bash seal into place when replacing the clutch seal, . This dishes the primary inner towards the clutch and can position the seal right off the end of the sleeve gear where it does no sealing at all. To restore, get a flat piece of wood or thick ply on the inside of the cover and bash the dished surface flat while supporting on suitable flat surface. Gently, gently.

These lightweights have many and unique challenges for the unwary.

Good luck

Peter

Do you mean in the area by the gearbox sprocket, ie the crank cases or in the cover that the kickstart and gear-lever come through?

If itâs the crank cases you might be able to get it welded from the outside without splitting the crank, but youâd prob be wise taking the gearbox internals out (easy!) Or drain oil, de grease and try JB Weld as a temporary fix for the summer?

dan

Keep us posted!

Previously bryon_currington wrote:

Your advice Peter on the wave spring on the Electra was good. I still had to touch the wave spring slightly on the two places where it slips on the slip ring with the edge of the grinder to get traction so far it is working good Bryon

Bryon, apologies to be off subject, but if you go back to your original thread for Electra you'll see I got my apprentice to make you the missing spacer under circlip on starter ratchet. Tried sending you an email through the links on message board. Did you get email? Do you want this spacer? Peter