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BSA A7SS/A10 Tach Drive Direction? #717769
12/05/17 12:03 pm
12/05/17 12:03 pm
Joined: Apr 2015
Posts: 354
Kenya
P
Peter Gee Offline OP
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Peter Gee  Offline OP
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Joined: Apr 2015
Posts: 354
Kenya
Hi does anyone know if the BSA A7SS (I suppose the A10 too) tach drive offtake is CCW or CW- lockwise.

I am looking at a Smits Chrono Tach RC 1370/01 which is Triumph one and CCW, but could as well fit BSA if the rotational direction is the same?

Surely all Chrono tachs work at 2:1 ratio to engine speed ?

Thanks and Happy Xmas

Peter in Africa

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Re: BSA A7SS/A10 Tach Drive Direction? [Re: Peter Gee] #717784
12/05/17 3:18 pm
12/05/17 3:18 pm
Joined: Jan 2004
Posts: 3,723
ca, us
D
DMadigan Offline
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DMadigan  Offline
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Joined: Jan 2004
Posts: 3,723
ca, us
Looking at pictures of the A7, the magneto turns backward to the crank. The worm turning counterclockwise (looking at the timing side) pulls the drive gear counterclockwise (looking from the rear), so clockwise looking at the end of the tachometer cable.

Re: BSA A7SS/A10 Tach Drive Direction? [Re: Peter Gee] #717789
12/05/17 3:47 pm
12/05/17 3:47 pm
Joined: Mar 2011
Posts: 836
derby england
wak Offline
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wak  Offline
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Joined: Mar 2011
Posts: 836
derby england
Yes clockwise , 2 to 1 tach with a 1 to 1 drive or 4 to 1 with the 2 to 1 drive (the most common)


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Re: BSA A7SS/A10 Tach Drive Direction? [Re: Peter Gee] #717800
12/05/17 5:24 pm
12/05/17 5:24 pm
Joined: Feb 2014
Posts: 453
Cork Ireland
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chaterlea25 Offline
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chaterlea25  Offline
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Joined: Feb 2014
Posts: 453
Cork Ireland
Hi Peter,
It depends on what year the BSA is and the location of the drive
Earlier engines have the drive taken from the magneto, later engines have the drive taken from the oil pump drive
the oil pump drive units are 3:1 ratio Left hand rotation they are rare and sought after
Good chronometric speedo refurbishers can build one from a donor speedo

John


Moderated by  Allan Gill, Jon W. Whitley 


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