The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: orabanda on 16.02. 2009 06:24

Title: Tacho ratio for Super Rocket
Post by: orabanda on 16.02. 2009 06:24

Hi learned BSAophiles,
Can someone please confirm what the ratio needs to be in a tacho to suit a 1960 Super rocket (tacho drive off oil pump, from front of inner timing case).
many thanks,
Richard

Title: Re: Tacho ratio for Super Rocket
Post by: beezalex on 16.02. 2009 16:24

Pretty sure it's 4:1.

Title: Re: Tacho ratio for Super Rocket
Post by: dpaddock on 16.02. 2009 21:08

You'll need a 2:1 CCW tacho. The magnetic Smiths part number on the dial will be RSM 3001/02A.

Title: Re: Tacho ratio for Super Rocket
Post by: trevinoz on 16.02. 2009 21:28

They are all wrong. It is 3:1.
Trev.

The tacho is a special as it is reverse to normal. Can't remember what is normal!

Title: Re: Tacho ratio for Super Rocket
Post by: flashblack on 16.02. 2009 21:35

I have to agree with trevinoz,i have that setup on my 1960 engine and the tacho has rc1303/03 written on it if that is any help *smiley4*

Title: Re: Tacho ratio for Super Rocket
Post by: beezalex on 16.02. 2009 22:24

Yup,  What trev said.  I shoulda looked it up instead of working from memory. *red*

Title: Re: Tacho ratio for Super Rocket
Post by: dpaddock on 18.02. 2009 17:17

Ah, Alex, that's what comes from having "too many BSA's . . ."

Let's get to the truth, here, Richard. Detach the drive cable at the tacho, attach a small c-clamp to the cable end and rotate the engine forward one revolution. If you observe the amount of rotation of the c-clamp, you'll have the ratio - and also the direction of rotation which will tell you how the tacho needle will swing. Please let us know.
BTW - are you using a magnetic or a chrono?

     David

Title: Re: Tacho ratio for Super Rocket
Post by: trevinoz on 18.02. 2009 22:21

David, in the BSA 3:1 Chrono tacho, there is a gear set to reverse direction.. Trev.

Title: Re: Tacho ratio for Super Rocket
Post by: dpaddock on 19.02. 2009 23:07

I didn't know that, Trev; Thanks!
     David