glass headlamp lens rotation - R100s

schrader7032 · Post by **schrader7032** » Mon May 05, 2008 5:35 pm

The lens on my '78 /7 (in the Lufty fairing, but was on the headlight bucket) says "Top" at the top and "Bosch" at the bottom. I recall that when I'm looking at the reflection of my light in the rear panel of a vehicle in front of me, the low beam seems to come from the top half of the headlight. When I flip on the high beams, the lower half of the light fills in. The chrome ring is secured with a screw at the 6 o'clock position.

HTH...Kurt in S.A.

grumpitybug · Post by **grumpitybug** » Mon May 05, 2008 6:27 pm

High-beam=top, low-beam=bottom is what makes sense to me too, but I had to put the assembly in sideways to make that happen.

I can rotate the headlight assembly within the chrome ring to any position I like -- it's the relationship of lightbulb to lens that's causing the problem!

The lens is attached to the mirrored reflector (which holds the bulb) by a think, rubber gasket. Seems to me that the only solution is to pull the lens off the gasket, rotate it 90 degrees, and put it back on.

Any experience with doing that?

schrader7032 · Post by **schrader7032** » Mon May 05, 2008 7:00 pm

I opened up my headlight, but didn't want to go too far. What I see is the back of the bulb and an intricate wire catch that holds the bulb in place. I don't see a gasket there. Maybe you're talking about the gasket that sandwiches between the reflection and the lens/chrome ring. From this diagram:

http://www.realoem.com/bmw/showparts.do ... g=63&fg=05

it looks like there might be some kind of divider or something sticking inside the cone of the reflector. I'm not sure how that works.

I noticed that my bulb has three blades sticking out the back...the electrical wires connect to these blades. Two of the blades run vertical and one runs horizontal. The horizontal one runs across the top of the two vertical blades. That should be the proper orientation of the bulb. How the reflector has to be oriented is currently a mystery to me.

Kurt in S.A.

grumpitybug · Post by **grumpitybug** » Mon May 05, 2008 7:05 pm

Yup, it's the gasket labeled #4 in the diagram that I'm talking about - in between the reflector and the lens.

The bulb situation is fine ... the way the socket and bulb are made is that there's only one way the thing can fit, and it's obvious what it is.

Thus my logical conclusion that the lens is oriented improperly.

Which brings me back to my actual question; how to (and is it advisable to) reorient that lens?

schrader7032 · Post by **schrader7032** » Mon May 05, 2008 7:48 pm

Well, you got me there... It can only be three things - bulb, reflector, lens. You say the bulb is oriented correctly. The lens should have some sort of orientation marks...as I said my Bosch lens has the word top on it. I would think that one of the functions of the lens is to create that cutoff beam that extends out to the left. I believe this is to not blind on-coming drivers on two-lane roads. That leaves the reflector...and what it might contribute to the emitted light.

Look at the orientation of the lens in this picture:

http://www.omnilex.com/public/bmw78/78bs03.jpg

You can zoom on by clicking on the button in the lower right corner. This is exactly how my lens looks, with the vertical lines at top, a horizontal line in the middle, and the relatively clear swath on the right side...you can see the horizontal line and then another line arcing below it with no apparently markings within the swath as it makes a sweep on the right side (as you look at it in this picture). That's the way a lens should be oriented.

Rotate things around and see what happens...couldn't hurt I suppose. Just be careful if the light pattern is not right at first... Let us know what you find out.

Kurt in S.A.

VBMWMO · Post by **VBMWMO** » Mon Feb 15, 2010 2:52 pm

After much head scratching, I've come to the conclusion that the headlamp assembly (reflector +gasket+lens) in my '77 R100s was put together wrong.

With the bulb slotted in, the only way to get the high/low beams oriented correctly is to put the assembly in the bike at a 90 degree angle. In other words, you have to tip your head sideways to read the "BMW" on the glass lens.

My question: is it possible (or even advisable) to pull the lens off of the reflector and rotate it? If so, how does one go about it? Can the grommet be reused?

Any advice would be welcome; Chilton and Haynes don't have a thing to say on the subject.