The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Seabee on 29.04. 2013 12:58

Title: Auto advance tach drive
Post by: Seabee on 29.04. 2013 12:58

Hi Guys,

My 57 RR has an auto advance mag.  I have finally collected all the bits for a tach set up, but wondered if anyone had figured a way to drive the tach from the auto advance assembly?  I hate to go to the bother of converting my mag to a manual advance (to get the right drive gear), but I'm afraid that may be the only solution. I thought about tapping the securing nut and adding a slotted button to drive the tach.  I wonder if this would effect the auto advance mechanisms functioning?  Any thoughts?

Seabee

Title: Re: Auto advance tach drive
Post by: muskrat on 29.04. 2013 13:58

G'day Seabee, I think your idea sounds feasible. I can't think of any problems with the auto advance.
Cheers

Title: Re: Auto advance tach drive
Post by: Triton Thrasher on 29.04. 2013 17:34

Don't do it. It will delay or prevent the ignition from advancing.

Title: Re: Auto advance tach drive
Post by: muskrat on 29.04. 2013 21:00

 Doh, you are right TT, any drag in the tacho/cable will work against the AA.
Thats why tacho's were only fitted to the sportier models with manual advance.
My brain goes to bed a lot earlier than my body.
Cheers

Title: Re: Auto advance tach drive
Post by: Greybeard on 29.04. 2013 22:08

Ok, shoot me down but isn't the AR retaining bolt threaded to the camshaft? If so it cannot affect the AR unit.

Title: Re: Auto advance tach drive
Post by: gavinoz on 30.04. 2013 04:06

Sorry Neil,

Think you'll find that AR bolt is threaded to Magneto shaft, Cam is attached to cam Timing pinion,

gav

Title: Re: Auto advance tach drive
Post by: Greybeard on 30.04. 2013 08:43

Quote from: gavinoz on 30.04. 2013 04:06

Sorry Neil,

Think you'll find that AR bolt is threaded to Magneto shaft, Cam is attached to cam Timing pinion,

gav

Duh! Of course, and now I can see why the tacho idea won't work. Silly me.

Note to self: engage brain before committing thoughts to screen!

Title: Re: Auto advance tach drive
Post by: Seabee on 30.04. 2013 12:45

Thanks for the feedback guys.  Unfortunately, you have confirmed my fears.  I hadn't taken the time to sort the rotation in my mind to determine if the cable drag would retard or hold the advance full on.  I hate the idea of going to the trouble of converting the mag to manual advance, but I guess that's what the bike should have had originally anyway.  It was a bitsa chopper when I bought it three years ago, and now is in excellent original condition if I do say so myself!

Title: Re: Auto advance tach drive
Post by: Greybeard on 30.04. 2013 12:50

On the plus side; Just think, you'll have a nice new lever to fiddle with! *smiley4*