The engine has done 800 miles since a complete rebuild and the gearbox developed an oil leak from the output oil seal (slow-speed shaft), when I striped the primary drive side to gain access I found that the oil seal had moved away from the bearing to the edge of the journal and was allowing oil to leak. The spacer looked a bit worn with a grove where the seal ran.
New oil seal and spacer fitted along with jointing compound on the back face and bore of the spacer, the oil seal was fitted so it was running central to the spacer width.
The gearbox was filled up with oil and left overnight with no oil leaking from the new seal.
After 50 miles the gearbox is leaking oil again, and I think the seal has moved to the edge of the sealing journal again, when fitting the seal I thought the fit was lighter that I would expect.
Has anyone seen this issue before?
Sleeve gear moving in, or seal moving out?
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Main shaft end float.
I wonder if the mainshaft ball bearing has been fitted without a retaining circlip?
This circlip is not shown in the exploded diagram in the Norton Twins manual. Nor does it get a mention in the strip/rebuild text.
Operating the clutch will push the main shaft and sleeve gear outboard, where you want it. Without the bearing location circlip, the main shaft and sleeve gear will drift into the gearbox, giving the symptom you describe.
You could check the mainshaft endfloat while you have the primary drive off. Secure the clutch on the mainshaft and give it a good tug on and out.
Far too hot today for such strenuous work, so let us know how you get on later.
Peter
I should just add that the sleeve gear and mainshaft bearings are likely only going to float in their housings when the motor is hot. So you may tug at the clutch and feel no movement even if the circlip above is missing. Depends how tight the fits are.
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Having striped down the…
Having striped down the primary drive casing I have found that the new oil seal is still oil tight so I filled the gearbox backup with oil to a high level and found that the oil is leaking from a small hole next to the lay-shaft sleeve bearing (see photo), I can see no external sign of the bush having spun.
So I think that the locating pin has come adrift, if I could find out the length of the bush I can make a new location pin and fit it from the out side, being reluctant to strip the gearbox as it is working very well.
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Layshaft bush locating pin
Hi Steven,
Well done for locating your leak point. It does indeed look like the locating pin on the inside has become dislodged. Its function is to stop the layshaft bush moving/spinning in the crankcase. Your gearbox (I can see from the photo) is the 'later' Electra-type gearbox. The layshaft bush has an anti-rotation pin for a very good reason!
In the earlier gearbox, this bush WAS NOT pinned, and quite a few engines were ruined when the bush rotated in its housing. Pinning it was a sensible mod.
I would suggest to you, that it would be a worthwhile investment to strip your gearbox, and ensure that the pin is replaced, if indeed it has popped out (or gone missing). If the pin is still in place, then oil is seeping past it, so replace it with some sealant.
I would not be happy using the bike if that pin were not in place.
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Hi Steven,
You seem to have done a good job and investigation. In your opinion, has the seal ring moved in, or has the seal perhaps moved out?
Peter