Author Topic: YA7S star twin crankcases  (Read 686 times)

Offline terryk

  • Valued Contributor
  • ****
  • Join Date: Oct 2006
  • Posts: 455
  • Karma: 3
  • Townsville Queensland Australia
YA7S star twin crankcases
« on: 23.02. 2011 14:51 »
Has anyone every seen YA7S Star Twin crankcases before?
YA7 is 1948 and Roy Bacons book says Star Twins started as ZA7S 1949 but I have come across YA7S cases. I suppose maybe BSA had some YA7 cases and just stamped the S for star twin to use up the cases or maybe someone has done a bodge.
Any thoughts?
1950-53 A10 rigid/plungers, 1958-61 A10 super rockets, 1947-50 A7 longstrokes, 1949 Star twin,
1951-54 A7 plungers, 1940s M21, WDM20s,
1948-50s B33s rigid/plunger/swingarm, 1948-50s b31s rigid/plunger/swingarm

Offline stephenrc45

  • Moving Up
  • **
  • Join Date: Feb 2011
  • Posts: 27
  • Karma: 0
Re: YA7S star twin crankcases
« Reply #1 on: 23.02. 2011 20:42 »
There must have been some preproduction Star Twins so maybe it's possible. I know almost noting about anything twin wise though so shoot me down all you like.

Offline Howard

  • Moving Up
  • **
  • Join Date: Jan 2011
  • Posts: 65
  • Karma: 2
Re: YA7S star twin crankcases
« Reply #2 on: 23.02. 2011 22:09 »
Hey Terry, My books state that the Star Twin was introduced in 1948 however it only gives the engine number prefix for the A7 of that year which is YA7-101 as I guess you know the 1949 A7 Star Twin engine prefix is ZA7S-101 so it would stand to reason that the 1948 model could infact be YA7S. Best of luck.

Online Brian

  • Wise & Enlightened
  • *
  • Join Date: May 2007
  • Posts: 1699
  • Karma: 40
  • Mt Gambier, South Australia.
Re: YA7S star twin crankcases
« Reply #3 on: 24.02. 2011 06:01 »
Terry I have been through every bit of literature I have on the 48' models including parts books etc. I cant find any reference to a Star Twin or any other "special " model in 48'.

In D W Munro's book of BSA twins he states that the Star Twin made its first appearance at the start of the 1949 season which would have actually been late in 48'.

Its possible the cases you have found have been altered or the S could mean something else. They supplied lots of different variations to Police forces etc etc.

You would need to get the number checked with the dispatch records to be certain.

Offline terryk

  • Valued Contributor
  • ****
  • Join Date: Oct 2006
  • Posts: 455
  • Karma: 3
  • Townsville Queensland Australia
Re: YA7S star twin crankcases
« Reply #4 on: 24.02. 2011 15:00 »
Thanks all. Yes Brian the S could mean special for police or something.
Anyway its a bit of a mystery anyone want to own up to having the dispatch records. I wouldnt mind a copy.
1950-53 A10 rigid/plungers, 1958-61 A10 super rockets, 1947-50 A7 longstrokes, 1949 Star twin,
1951-54 A7 plungers, 1940s M21, WDM20s,
1948-50s B33s rigid/plunger/swingarm, 1948-50s b31s rigid/plunger/swingarm