Oil leak

[LaceyDucati]

Hi Joe and all,
The oil return thrower on the early sprockets is designed to push the oil back into the engine should it try and find its way out. The narrowcase engines and early widecase engines used this thread and you will note the casings of these engines have a slot in the bearing housing underneath. This slot is to allow any oil to return to the engine. Later widecase engines including Spanish engines, do not have this slot or the thread on the sprockets. I don't think I recall seeing a 450 sprocket with a thread on it, well not recently anyway. Without the drain slot there is no reason to have the thread and I saw little reason to include it on the 450 sprockets.

I always build engines with 6204 C3 2RS bearings in them with both seals intact. In the 23 years I have been building these engines I have not experienced any problems with doing this. As most pattern sprockets that were available during the 80's and 90's did not have the thread (at least in the UK) I have always blocked the drain slot under the bearing and in conjunction with a 2RS bearing not experienced any problems. Caution should be taken when selecting bearings to avoid rubber sealed bearings intended for electric motors as they don't have contact seals and without a thrower and drain slot they are very likely to leak. Otherwise just ensure the bearings are contact seals as not all bearing manufacturers use the RS designation. The surface of the back of the sprocket also needs to be flat otherwise this may lead to a leak. Some pattern sprockets are pretty rough on the back and if a sprocket has been allowed to run loose it might not seal (especially if it has been used on another engine before with a different thickness inner bearing face). Either way check the surface and flat accordingly. If there are any marks on the sprocket back face, sometimes a very light (and I mean light!) smear of silicone can help on this face. Our sprockets which Talon make for us are flat and square.

Most of the other reasons for leaks seem to have been discussed already, the most obvious being too much oil. I have never run the amount of oil recommended in the manual in a race bike. I have always used 3.25 UK pints in a narrowcase engine and 4.25 UK Pints in a widecase engine. Obviously running slightly less oil you need to be a little more diligent with checking oil level but in all the years of running these bikes, it has never been a problem. That does also include countless Manx GP's on the Isle of Man completed by customers (a race is 160 miles +). Running this slightly lower oil level will of course reduce the risk of oil leaks from behind the sprocket. Of course the other thing is, as mentioned, if the nut is not fully tightened then you are most likely going to get a leak.

All of our latest 428 sprockets that we have had manufactured do now include the thrower thread and any new ones we will have produced in the future will also have threads on them. All the 530 sprockets do not have the thread. Basically this replicates what was available in the period. One final word, I have noticed that there are a lot of old stock sprockets circulating that actually have a right hand thread cut on to them which of course will throw the oil OUT of the engine. We do actually have some of these sprockets but if we supply then now we would inform customers that effectively they are only to be used if you don't require the thread (These are not available on our website, more a bargain clearout if anyone asks!) So if you are relying on it, check that the thread on your sprocket is left hand!
Best Wishes
Nigel

[LaceyDucati]

Forgot to mention the 20.2x38x0.5 mm washer is only necessary if you are using the original metal shielded bearing and relying on the thrower thread and drain (ie as original). I have never fitted one in an engine as to me its just another slip face & possibility of the sprocket working loose especially under race conditions. Most washers out of engines I see show signs of gauling & fretting & that's not the ideal surface to tighten against or seal. OK so yes the sprocket will be theoretically 0.5mm out of line, but you don't really think Ducati made the cycle parts (frame & swingarm) within 0.5mm!! Never noticed any real problems or had any reported by customers. There is always the possibility you may improve matters and there is a slight advantage of moving the sprocket in as most heavy duty 428 chains with the larger sprockets have a tendency to chain saw the back of the selector box so moving the sprocket in 0.5mm will help matters.
Best Wishes, Nigel

[joe46ho]

Hi Nigel, That's certainly true ... I think I have maybe 12 different shift selector boxes here from various models in my "cache" of parts, and every single one has had at least a minor "run in" with a chain. Some are worse than others, I had pondered the idea of removing material off the back face of the sprocket where it meets the bearing, or washer... But I wasn't sure if anyone really did that to correct the problem, or if it was more a matter of keeping your chain clean and adjusted properly... Many of these motorcycles where thoroughly abused by previous owners, so I wasn't sure if this was considered "normal" for the ducati singles, or if the damage was really from lack of service to the chain.

Joe