Weird noise

[pat76r90]

Bike is a 76 R90/6, 42000 miles. I've owned it just about one year. Lately it has been making a funny noise at random times, kind of a screeching squawking sound, usually at idle at a stop sign when cold, or within the first 3-4 miles. Goes away. Yesterday we were on a fairly long ride, and it got pretty loud and more constant and the noise stayed through the gears, at least until I couldn't hear it for the wind.(un-faired/no windshield).

The noise would go away when I pulled the clutch in, first time it's ever done that, and by the time I got home it was completely gone. While it was making the noise, everything operated normally, ran fine, clutch worked, shifted good. I'm thinking maybe throwout bearing, or these transmission splines I keep hearing about? I don't know any service history, but it doesn't look like it received a lot of care in it's life.

[khittner1]

I don't think un-lubed transmission input splines cause weird noises in motion---just clunky shifting. From your description, I'm assuming that your directionalizing the source of the noise as coming from the engine or transmission, and not from a wheel or final drive, etc. Have you changed your transmission's oil since taking ownership? If not, do so before riding further and report on the nature/quantity of crud you find on the drain plug's magnetic tip. More experienced ears will probably weigh in shortly (in 5 airheads, I haven't yet had a significant transmission failure myself---knock on aluminum), but I guess I wouldn't be surprised by a failed/failing transmission bearing. I hope I'm wrong.

[pat76r90]

I did change all fluids, filled the trans with 75/140 full synthetic. I don't remember it being horrible, I think this morning I'll pull the drain plug, see what it looks like, maybe pull the clutch lever off, it looks like I should be able to at least lube the throwout bearing from the back? Off to a search and destroy mission.

[jagarra]

To me it sounds like the actuating rod is touching the throw out bearing and spinning it, making the noise. How much free play in clutch actuating assembly, maybe adding some will fix your problem.

[pat76r90]

DIng ding ding, I think we have a winner with Mr. Jagarra. I pulled the trans, drain plug had no large metal fragments, some black schmutz, not horrible gritty. Fluid definitely has a bit of glitter, but except for this noise, which is intermittent, trans works and sounds ok. Splines look ok, to my untrained eye.

The boot over the clutch operating set-up was torn, the seal on the outer puck was rolled, the wafer bearing was full of mung. I'm betting/hoping this is the problem. Going to order some parts up and see what happens.

[Duane Ausherman]

"..........not horrible gritty." If you rub the stuff between your fingers, you shouldn't feel any tiny grit at all. Any grit is a bad sign.

Did you read my article on transmissions? http://w6rec.com/duane/bmw/trans/

Did you try Google with "bmw motorcycle transmission" for info? There are 3-4 good articles on your question.

[pat76r90]

Believe me Duane, your site is the first place I go. Since this is my only ride, and it's dead in the middle of riding season, I'll run this trans(assuming the clutch control parts fix it). As I said, it works pretty well, and I don't have a spare. Someday maybe, but not right now.

[Duane Ausherman]

If the transmission was assembled correctly, the clutch rod bearing gets lubricated automatically. Did you find the tiny roller bearings from the /6, or the ball bearings from the /5? The roller (needle) bearings from the /6 were a very bad idea. They wear out quickly because one end of any one needle is trying to go at a different speed than the other end. They don't roll as much as they skid along. Not smart.

Never put rollers in a radial fashion. Kind of seems a Kindergarten thing to me. I remember when one of the mechanics removed one and brought it out to the showroom to show me. He was laughing at the colossal stupidity.

[pat76r90]

It's the newer /6 style, wafer/roller bearing, and yes it looks like a pretty cheap design. I'm theorizing that the dust boot being torn let a lot of grunge in, and the lubrication couldn't keep up with it. It's all worn pretty well, I'm going to try and replace the rod, both pucks, bearing and seals, we'll see what parts availability is.

[Duane Ausherman]

usually the rod is still OK and the right length. Check the front end for still being a smooth taper and not having steps worn into it.

At one time Flanders made up a 3 piece clutch rod. It looked like the original cut in half with a ball bearing in the middle. The purpose was to make a rod that could be inserted without pulling the box. However, it functioned as having an extra bearing to act like it should if the rear bearing got stuck.

Let us know what you find when you use the new parts. I am not there to hear and inspect the issue, but I have some doubts. I hope that you have found the culprit.

Did the clutch ever feel grabby, especially when cold?

Are you going to remove the rear cover for a full inspection? I have seen a rear coupling slip from time to time, but it was not very noisy. Usually, once they slip, they don't catch again.

In operation, does the clutch seem to fully release with the lever pulled in while both hot and cold?