Gearbox/chaincase oil leaks

Previously tom_mcewen wrote:

My 99 drops a lot of oil when parked, and I'm hoping to reduce the leaks. The tin primary case on my "dynamo" wideline Dommie seems to leak mainly from the gearbox mainshaft/ inner case area. I am confused about which seals or washers should be between the tinware and the gearbox, and also in the N/S footrest support arrangement. The handbook is silent on this subject. I think a seal is AWOL which, with a tired gearbox leak is not good. I am reluctant to rebuild the gearbox at present, just hope to contain the leak. Can you list the sequence of seals,or help with this anyone? The big rubber seal on the outer case works well, amazingly.

Tom,,,

Oil from the gearbox leaking around the clutch area may be from the sleeve gear bush and you have to take the box apart to fix/if its oil from the primary drive it will be hard to stop/I used to run my dommi for a while after all the oil had leaked out with just spraying the chain but the standard clutch's. are not as good as a belt drive and that's the way I went .i now no oil leaking from that area and a better clutch.

Tony.

You need to identify where the leak is from as the breather and box are as suspect as the case. I used EP (green!) oil in the box, red ATF in the primary and dirty brown in the motor. Soon found that most came from the breather. Re-directed to the oil tank. the leak of primary oil via the gearbox shaft was stopped by removing the clutch and forming a half circle of Dow corning mastic on the case to deflect oil . Main cover leak is often caused by the cover fouling the propstand mount . File a clearance. Two felt seals are needed on the footrest mount inside the case. oil level in case should be just below level plug.if the chain has a bit of slack it will dip in. Mastic the alternator lead at the grommet.Green box oil can migrate through the sleeve gear spacer which needs mastic. Once all sorted I changed primary oil for a mixture of mono 40 oil and parafin as I cant readily find 20 mono.

Previously tom_mcewen wrote:

My 99 drops a lot of oil when parked, and I'm hoping to reduce the leaks. The tin primary case on my "dynamo" wideline Dommie seems to leak mainly from the gearbox mainshaft/ inner case area. I am confused about which seals or washers should be between the tinware and the gearbox, and also in the N/S footrest support arrangement. The handbook is silent on this subject. I think a seal is AWOL which, with a tired gearbox leak is not good. I am reluctant to rebuild the gearbox at present, just hope to contain the leak. Can you list the sequence of seals,or help with this anyone? The big rubber seal on the outer case works well, amazingly.

Hi Tom,

there is a sealing arrangement for the gearbox mainshaft which consists of a pair of sheet metal discs which were spot welded together originally, one of which was located inside the primary case, behind the clutch, with the other behind the case, very close to where the final drive chain runs. The discs are fitted with enough clearance so they can be positioned to allow the gearbox mainshaft to pass through. The disc, when assembled has a pressing to locate a felt seal. This seal runs concentric to the gearbox mainshaft.

The discs aren't mentioned in the parts lists as they were originally as one with the inner primary housing as supplied by the factory. New discs and felt seal can be obtained via the usual suspects. These can be pop riveted together when the time comes for overhaul of this area. A boon when painting the inner primary and the discs.

As for the gearbox leak, make sure it isn't overfilled, a common error. Ditto the engine oil, as overfilling can cause crankcase pressure to overwhelm the drive side crankshaft seal. Such pressure in the chaincase will lead to the leaks you describe. Extra sealing shouldn't be necessary. The proper setup will weep eventually but that can be seen that its time your pride and joy gets a wash.

I agree, the big rubber seal on the outer case works well, if fitted correctly.

David Chambers