It's an '82 R100RS. It's the third time it's happened in 32 years, so not a crucial problem by any means.
The first time it started doing it was just out of warranty, 30-ish years ago, the needle would swing +- 1,500 rpm about the correct reading, i.e. at 3,000rpm the needle would be swinging between 1,500 and 4,500rpm on the dial. I had a look inside and found a hair across the little curly spring around the needle pivot- a spring that looks like the balance spring in a clock. I took that off very carefully with a camel hair artist's paintbrush and put everything back together and it worked OK for the next 25 years. I have no idea how the presence of this little hair could possibly cause the needle to swing like it did but it was the only obvious irregularity I could see and that's why I removed it.
When it did it again for the second time it cured itself for no apparent reason after a week, and it did it again last week for a couple of days and now it's OK once again, the chances are of course that the little hair never had anything to do with the swinging, it seems to me that it would be more likely to damp any swing rather than to cause one.
Anyway, does anyone have any experience of such a fault?
The first time it started doing it was just out of warranty, 30-ish years ago, the needle would swing +- 1,500 rpm about the correct reading, i.e. at 3,000rpm the needle would be swinging between 1,500 and 4,500rpm on the dial. I had a look inside and found a hair across the little curly spring around the needle pivot- a spring that looks like the balance spring in a clock. I took that off very carefully with a camel hair artist's paintbrush and put everything back together and it worked OK for the next 25 years. I have no idea how the presence of this little hair could possibly cause the needle to swing like it did but it was the only obvious irregularity I could see and that's why I removed it.
When it did it again for the second time it cured itself for no apparent reason after a week, and it did it again last week for a couple of days and now it's OK once again, the chances are of course that the little hair never had anything to do with the swinging, it seems to me that it would be more likely to damp any swing rather than to cause one.
Anyway, does anyone have any experience of such a fault?
