Smiths Chronometric rev counter fault RC. 1303/03

[pete3000]

Hello everyone,

I hope someone can help. I have a smiths chronometric rev counter fitted on my BSA A10 number RC. 1303/03. Cable is connected to the oil pump.
The other day, when I went out for a ride, the rev counter has started to show incorrect indication, 6000 RPM while the engine was probably at 4000 RPM.
Sometimes it went back to normal, correct RPM engine and correct rev counter RPM indication, sometimes not, specially when I turn quickly the throttle. 
Really don't know what can cause that ? Vibrations ? Tacho had always worked good since I've bought the bike and run 5000 miles with it.

I move out the rev counter, test it on a bench, but nothing appears to be wrong. Check the cable, but didn't notice anything wrong.
How to be sure that the fault comes from the tacho ?
Any thoughts ? Has this happen to anyone ?

[jachenbach]

I have no experience (yet) with the Chronometric, but with all the other speedos I've had go bad, this was a sign of a sticky cable. I've never had it get better and if continued long enough generally wrecked the speedo. I would disconnect it until the cable is replaced with a new one.

[terryg]

It's possible that too much oil/ grease from the cable has found its way to the 'slipping clutch' part of the chrono mechanism. If that's the case a clean of the internals (think ultrasonic in alcohol) and a light re-lube will put it right.

Chronometrics UK (Russell Smalley), amongst others, would be able to help.

[stu.andrews]

Totally agree with terryg. Sounds as though too much grease has entered the speedo head.

[bobandbec]

I can vouch for Chronometrics UK.
They serviced a dodgy speedo for me. Very pleased with them.

Peter

[pete3000]

Many thanks for your answers ! Terry solution sounds very good, notice lots of oil/grease on the cable. For sure, the tacho will need to be dismantle and cleaned.
I know Chronometric UK, and totally agree with bobandbec.