Engine oil screens aren’t in common use today but they do have a useful function.
First, they trap larger particles that are always left over from machining operations so you should expect to see some debris on the screens at the first few oil changes. So don’t be alarmed when you see it in the first couple of oli changes
Second, they’re a good indicator of engine health.
Oil filters will trap the same larger particles but unless you cut open your used oil filter each time and examine its entrails, you’ll never know about internal problems until it’s too late.
It’s very important that screen be removed and inspected for debris at each oil change. Some dealers don't do it, explaining that the blockage to flow is small - so don’t worry. But even if it is checked, the early warning sign of particles collecting on the screen is often ignored. The most common rationale being that the filter screen captures particles of aluminum remaining from the machining process, so seeing them shouldn’t necessarily be cause for concern. At your first couple of oil changes this argument has merit, but if you see particles at subsequent changes you should investigate further.
In any event, change your own oil, or be there when it’s changed to see for yourself.
As most of you know by now, there are two problems common to Ducatis that can be identified by, and diagnosed by the particles they deposit on the filter screen.
The first problem is a design flaw in the pre-2000 model-year bikes that have an aluminum crankshaft oil gallery plug that can loosen and back-out. In doing so, the rotation of the crankshaft will machine the plug down until the plug eventually comes out and the engine experiences a catastrophic loss of oil pressure that destroys the main bearings (among other things.) The aluminum particles will end-up on the filter screen.
The second problem is the design problem with the chrome plating flaking-off the cam-contacting surface of the rocker arms. The sure way to know if you have rocker problems is to pull the cams and look, but your dealer won't do this unless you authorize an additional labor charge. Chrome particles on the filter screen will give you a good reason to spend the money to have them do this.
(Fine debris stuck to the magnet on the drain plug is from normal wear and no cause for concern. The most likely cause of small fingernail clipping-shaped particles on the drain plug magnet is normal transission wear. Chrome and aluminum are non-magnetic so they don’t attach themselves to the magnet on the drain plug.)
So how do you tell which you have - chrome or aluminum particles on your filter screen? Here’s a simple test.
Draw a small amount of battery acid and put the particles in it. Battery acid is dilute sulfuric acid, so when you add chromium to it you’ll get a release of hydrogen bubbles and the chromium will turn the darker violet color of chromium sulfate. Aluminum doesn’t react this way.
For you chemistry majors:
2Cr + 3H2SO4 > Cr2 [SO4]3 + 3H2
So, if you do it, you get to see the early warning signs of transmission damage or the crank oil gallery plug backing out.
There was a very interesting thread on the yahoo st owners group recently about a ds1000 engine, ST3 shares the same bottom end with the DS 1000 afaik, that suffered severe damage/failure due to the oil screen not beging properly reinstalled, ie it was not torqued down to spec. It backed out and blocked an oil galley line.
The xtra bolt underneath is a capped off oil galley hole that was (is) machined into your sidecase. It never needs to be removed.
The oil screen is the suction point of your sump. yes it's a daignostic tool , but also...IT IS IMPORTANT because it keeps the "sticks and boulders" from getting sumped up, into and thru your oil pump !!! Click on that little photo that Shazaam provided...would YOU WANT THAT CRUD going thru your oil pump? And then the next part of the oil tour is your normal spin-on filter...