extra oil in the chaincase

[timharrison]

I had ridden 3000 miles since leaving our shores for the warmth of Spain. We took a trip to Granada and on our return to the apartment, on checking the bike over, I noticed quite a bit of oil on the rear tyre. I assumed that one of the chain case gaiters must have split. I checked both of them carefully and although it was pretty clear that the oil must have come from the top rear gaiter seal it looked OK.I assumed that there would be little or no oil in the chain case but on draining the opposite was the case. Instead of draining out around 75ml more like 300ml came out. I replenished with 75ml as per the handbook and the leaking stopped. I know that I did not overfill the chain case, albeit 3000 miles previously and the oil that came out did smell a little like gearbox oil but when I check that, although perhaps a little down, it was nothing like the additional amount that came out of the chain case. I assume that an oil seal must be letting some oil through but does anyone know which is the likely culprit?. Unfortunately I suspect that I have a days work ahead to replace a £5 seal. Thanks in advance for any thoughts. Tim

[Richard Negus]

Tim,It can only be gearbox oil, but due to the large surface area of the box, you don't really notice much of a drop in level.The culprit is, almost certainly, the oil seal behind the gearbox sprocket and is a PITA to replace. Unless they've been replaced recently, it's a good idea to fit new chain gaiters at the same time. Drain oil, remove l/h silencer, rear wheel, left suspension unit, l/h footrest plate, split chain, remove gaiters, gearbox outer cover, oil pump mount plate, & there's the SPROCKET!. Circlip out, sleeve off, O-ring, remove sprocket & there's the SEAL. Prise out seal, clean seal diameter and casing bore with solvent to remove all traces of oil, fit new seal and peen around the seal to stop it turning in the housing. Everything else in best Haynes tradition, not forgetting to RIVET the chain. None of those Mickey Mouse split links please.Say it quickly and it doesn't sound much. To do the job, with all tools and gadgest to hand - 4 hours??It can be very character-building, particularly if the sliding plugs in the rear fork don't.Good Luck!R.

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[gripper]

I had to do this job twice in quick succession as the seal supplied from Norton Motors must have been sitting around for years and didn't seal. buy your seal from a bearing/seal stockist that turns these items round frequently. The other issue is, the diameter of the boss that is running in the seal is smaller than the diameter that the seal is designed for so there is not much grip from the garter spring. I took the opportunity to replace the tywraps on the front end of the chain gaiters with two carefully bent to shape jubilee clips. It puts a reasonable amount of pressure on the rubber and seals well.

[timharrison]

Thanks Richard and Gripper for your advice. It looks like I have a fun filled day ahead! Tim