When I check the oil, should I screw the dipstick in? And is my dipstick supposed to have an o-ring? Some other airheads have them, do I need it? Will a rubber O-ring from the hardware store work?

This oil checking and dipstick o-ring question issue keeps coming up.

Maybe I can shed some light. For those who don't know me, I'm a BMW mechanic with 27+ years of motorcycle experience. I have uncrated, sold, serviced, tended, modified and restored virtually every model of BMW built from 1970 to 2002. So much for the credentials.

On the question of checking the oil:

1) Unscrew and wipe off the dipstick. Insert dipstick into the hole until the first thread touches. Don't screw it in. Lift the dipstick out carefully. If you see oil between the engraved lines, your oil level is good.

If it is below the lower mark, add 1/2 quart and check again. Don't be tempted to overfill. If the level comes up BETWEEN the lines, leave it alone.

I run ALL BMW airheads 10mm below the top line. This change alone can reduce oil consumption noticeably in the R90 and R100 models. That's it. Don't carefully add oil up to the upper line. Get it BETWEEN the lines and LEAVE IT ALONE.

2) BMW changed the dipstick top to a plastic material beginning with the 1981 US models. This type dipstick incorporated an o-ring as part of the sealing scheme. The 1970-1980 models were fitted with an aluminum-topped dipstick with an asbestos-filled crush ring for sealing.

There's a lot of uninformed braying on the list about adding a dipstick o-ring. DON'T. The aluminum (earlier) dipstick WAS NOT DESIGNED FOR AN O-RING! (Sorry for yelling) Adding an o-ring to this type dipstick will lead to the o-ring splitting, the dipstick unscrewing, oil leakage, or, at the very least, introduction of air into the crankcase, which can lead to premature seal failures.

Unfortunately, installing the later stick in the earlier models is problematic as the oil pans were changed at the same time, and the dipstick length and marking positions were changed as well. It can be done, but you'll need to apply some sense and logic to get it right.

I've checked all the dipsticks on all five of our bikes- 1978, 1979, two 1981 and one 1983, and they are, so far as I can tell, dimensionally identical, with max and min marks at the same distance from the tip.

The only difference is in the materials used..the later years have plastic knobs - an improvement I thought, as I have scorched my fingers on the metal ones 3-4 times over the years.

As Nathan points out, I was mistaken in my statement about dipstick lengths. I had forgotten that BMW deepened the oil pan not once, but twice, the first time with the '76 models. I THINK that they lengthened the stick in '76 and left the length alone when they changed the pan again in '81.

For Mr. Newbie, I'll add this, as I'm sure it's your next question. Use any quality brand name oil rated at least SC service rating, and in a viscosity rating of 10W40 in the winter cold, and 20W50 or 15W50 in the warmer months. Change the oil and filter every 5000 miles, and your bike will see over 100,000 miles without opening the bottom end of the motor. Listen to the "Only use XXX brand oil" crowd, and risk seeing bearings in your future.

(An aside, DON'T use Mobil 1 oil that is not viscosity-rated on the container. The unmarked ones are 5W30, which is WAY too light for an airhead, and has lead to many dramatic and costly engine failures.)

Hope this helps.

-Tom Cutter

(Originally posted to the Airheads list)