This is an easy and informative way to magically see inside your engine.

To read the filter, simply replace it, and leave the old one hanging overnight above the drain pan, so the oil drains off.

Slit the outer perforated paper cover and discard it, then use a stout pair of pliers and a little muscle to rip the end cap off the filter. Take a knife and slit the pleated paper on each side of the metal joint, and peel the pleated paper away. Stretch it out on a piece of paper or paper towel, and take it out into the direct sunlight (the sun light makes the subtle colors of various bits much easier to distinguish, and makes the reflective bits really evident). Look it over one pleat at a time, and count the quantity and color of the various bits that you see. A magnifying glass is also useful (and when you finish reading it, it's fun to ignite the oil with the magnifying glass and sunlight).

You are looking for bits of parent metal and from there you will have to think some to determine their origin. Shape of the particles, as well as color, will be important here. As a rule of thumb, if it is smaller than a pinhead, ignore it. It IS a filter, and engines DO wear.

There are a few characteristic "bad warnings" that a filter can give you.
The first and foremost is shards of babbit material, which can only originate from the connecting rod and main bearing shells. These are instantly recognizable because they will be a flat, dull gray on one side (the tin babbit) and coppery color on the other side of the flake (the copper bearing base material). The flakes will be from 2-4mm in size, like a small fish scale.

You may also see chunks of aluminum (nonmagnetic) that are torn away from the corner of the main bearing carrier when a timing chain reaches the end of its' life (more likely on the pre-79 models). These will be from 1-3 mm in size, shaped like a real rough snowball.

If the cam chain tensioner is getting shredded by a whipping chain, you will see torn away chunks of rubber, or hard plastic, depending which type of tensioner shoe is fitted in the motor. Earlier bikes had rubber, but replacement shoes are hard plastic. These will usually be shards, long and pointy, 3-5mm in size.

If you see a shaving of brass or bronze, this is from the valve guide, the only bronze part in the motor. If you recently had a valve job, this is not usual to see a couple shavings.

If you see soft white rubber, that is from cutting the O-ring on the oil filter. This indicates that you need to reread the $2000 O-ring articles in the archives and on Snowbum's site. This can indicate the possibility of a future failure of the O-ring, though you just replaced it. (see step 1).

You may observe balls of various types of silicone sealant in the filter. This is to remind you that you should NOT use ANY sealant anywhere on a BMW Airhead motor except Hylomar at the cylinder base, in a very thin film. None should ever turn up in the lubrication system.

If you find any sand, stones or dirt/sticks and eggshells, you need to clean your work area, and review your basic clean working techniques. Every time a motor is opened at ANY point, including the dipstick and valve covers, total sterile technique MUST be observed. Tools, hands, new parts, removed/reinstalled parts should all be solvent washed, water rinsed and compressed air dried. The work area should pr protected from airborne dirt, so a windy day in the driveway is OUT for a valve adjustment. You will do more damage inside the motor by introducing dirt than you will prevent by maintenance.


-Tom Cutter

(Originally posted to the Airheads list)