The noise doctor: metallic clicks during startup

[TommoT]

My 1956 G80 has developed a strange noise lately:

At first start up in the morning when releasing the clutch in 1st gear, to get going, a clicking noise sounds from "somewhere around the bottom of the engine". Noises are difficult to diagnose so I cannot pinpoint a specific area of origin. It disappears after the first hundred meters or so and is not heard again till next start.

The engine is otherwise very quiet and runs smoothly without any undue noises through the entire rev band. I cannot provoke the noise under any other kind of driving conditions.

Last time I had the pressed steel primary chaincase apart I noticed that the splines on the drive axle carrying the cush drive are somewhat worn. They are not equally worn, the worst are reduced in width by about a third of their orginal size. Could this cause a noise? and should I replace the axle at the earliest opportunity?

[Biscuit]

1956 - Cush drive? Sounds as though you have an AMC box. If you have, you need to renew the mainshaft and probably the spider.

[Don Madden]

If original, a 1956 would have the Burman B52 gearbox & cushion drive.

The sound may very well be the cushion drive cam on the worn shaft. I would monitor it & if it wears more, plan on replacing it. Otherwise, I would wait until the next rebuild.

I am replacing my the drive shaft on my 1956 scrambler, but it is about 2/3 worn, somewhat worse than yours but it had no obvious symptoms. Of course mine, with a low restricton exhaust, makes enough racket to mask almost any noise.

The sound might also be loose cam followers in their guides which could get quieter as the oil flowing from the rocker box flooded them

Cheers, Don.

[TommoT]

You're correct Don, it is the last year of the B52, so it has the cam type cush drive with spring and cup. I will leave the drive axle alone for now and check both cam followers and the cams themselves for play.

[Biscuit]

Cush drive equals rubbers in clutch centre, cam and spring on crankshaft equals shock absorber. If we used the right terms I wouldn't go rabbiting on about AMC boxes and spiders.

[itma]

...rabbits, spiders, its zootime again

[Don Madden]

I would worry about spiders in my localtity as they are often the deadly Black Widow. If you leave a bike standing outside for long you will find exactly one, usually fat. Excepting her tiny babies of course, which she will also attack unless they leave promptly.

Cheers, Don.

[TommoT]

quote:
Cush drive equals rubbers in clutch centre, cam and spring on crankshaft equals shock absorber. If we used the right terms I wouldn't go rabbiting on about AMC boxes and spiders.


Sorry Alan, won't happen again, at least not until next time