Forum bmwbike.com

I would like some guidance from those of you more learned than myself. I have purchased a 1966 machine with supposedly 8,000 original miles on it. I would like to know if replacement vibration damper centers are still available, and if they are, should I even bother myself with maintainence. I would be pleased to hear from anyone with their advice regarding restoration of these machines.

Hi Neil,

In the manual they say to check every 4000 miles for tightness and radial play. I think it should be checked everytime you have to open the front cover. Since the element is synthetic, it deteriorates over time and hardens. Even though yours may only have 8000 original miles, chances are it has been on there for 34 years. I would definitely change it. Mark has them available in his parts catalogue. If ever this elements disintegrates while you are riding, you can say bye bye to pretty much everything under the cover. Trust me it will be a good investment. Order 2 while you are at it!

Pierre

I have bought the rubber centers from Huggett and from Bench Mark Works, and probably Bob BMW and Blue Moon also have them. The complete damper assembly is hard to find, however. I have one on order from Huggett and their supplier is backordered - I do not know when it will be shipped. I then bought a used assembly and it cost twice as much as a new one.

The rubbers usually do not last long, and as they disintegrate, their rubber particles make a mess inside the front cover, getting into the generator and points. When enough rubber has gone so that the damper mass is no longer held tightly, the 5 lb mass starts to sling itself around in an eccentric orbit, which makes a hell of a vibration and gives the bearings a good beating.

Even back in the early 70's I was advised to remove the damper and run without it. And now it seems almost nobody takes the trouble to use and maintain the damper. Yet the R69S bikes are still running. So you don't need to use the damper if you run the bike normally like an R60/2. But if you want to use the extra 1000 rpm of the R69S motor, or ride at 90-100 mph, then you might want to use the damper. Otherwise you might break the crank, wear out the bearings, break a cylinder stud, etc.

The /2 crank has no center bearing - is like a wet noodle. The R69 can go more than 1000 rpm faster than a /2, and has the damper in front, and a special bearing in the rear, to help save the crank.

The vibration damper on the front of the generator, which is the front of the crankshaft, is to counteract the flex of the crank at high rpm.

Whatever flexing the damper does not cancel out, the special rear bearing then absorbs. The rear main bearing on the R69 is a special spherical bearing to allow the crank to flex at high rpm without damage. Imagine a bearing that allows you to move the shaft up and down as you turn it. This jewel costs several hundred dollars.

In 1970 I had a '68 R69s and the previous owner had removed the vibration damper. I rode it hard and within the year had broken the crankshaft. My advise is to install a new damper and maintain it.

Good riding,
Drew

I have a 1967 R69S. The exact mileage on the bike is unclear. The rubber mass of the damper disintegrated last year on a trip to Albuquerque. The primary effect was to spray everything inside the cover with semi-melted rubber. As the points were sprayed, I had some trouble getting the bike to run. The mechanic at Albuquerque Motorsport removed what was left of the unit and (unbeknownst to me) never replaced it. There is apparently a group of mechanics who think the damper is simply a superfluous performance item. The bike ran well for a couple thousand miles until I discovered the damper was missing. So I don't know haw critical it is. Nonetheless, I intend to replace it once Huggett gets them in stock again.

Drew,
If you can remember any of this, it would interest me: what were you doing when the crankshaft broke, and what did it sound like, and which part of the crank broke?

Although I had ridden the bike over 100 MPH, I was cruising aroound town when the crank broke. The break occurred at the generator which battered the field coils in the stator. The generator rotor was ruined. The tapered nose of the crank broke off. The sound was a banging and scraping from inside the engine cover.
Hope no one else has a similar experience.
Drew