how rare is a star twin ??

[mrshells]

Out of interest
how rare is a Star Twin ??
Id never heard of them untill i bought mine and Googling doesnt reveal a great deal of info
i have the model history and years of production
I wonder how many survive  ????

[Brian]

Firstly welcome to the forum and please leave your bike like it is, dont restore it. I love original bikes.

Where I live in Aust I have never seen one of the later ones like yours. I know of a few of the earlier ones like mine.

No doubt there are some somewhere but I have never come across one and if I had I would have tried to buy it.

You have a very nice bike, good luck with it.

Brian.

[fido]

The Star Twin was the original sports version on the A7, replaced by the Shooting Star  for the swinging arm models. The Shooting Star is still fairly common but there are not too many Star Twins around

[flatdeck]

Hi,
Star Twin was a name used for only a few years between 1949 and perhaps 1952 I think. Is yours a long or short stroke motor? I thought they stopped the long-stroke in '51. The configuration of the Star Twin appears to be a bit flexible also in that some were ordered with the rigid rather than the plunger frame and I think some had a single carb rather than twins ... All very interesting. I've got photos of 5 or 6 examples off the net.
Dave

[Brian]

Just for interest I did a bit of research on Star twins.

First introduced in 49' with the twin carby and earlier or long stroke engine, plunger frame. Transfers on tank.
The same for 1950.

The new engine design, same as A10, introduced in 51'. Single carby, plunger frame but had metal tank badges. (same as mrshells).
The same for 1952.

1953 starts to get interesting. same single carb engine with plunger frame but round plastic tank badge and painted Green. I've attached a photo I found of a 53' model.

1954 is nearly impossible to make any sense out of. Going by the engine and frame nos I think you could get a plunger one the same as 1953. It would appear that a swing arm framed Star Twin was also available as well as a swing arm Shooting Star. It may be that the first s/arm ones were called Star Twins but later in the year were re-named Shooting Stars.

Hopefully this helps or maybe just makes it all more confusing.

[mrshells]

Dumb question time ??
i know mine is high compression as its stamped on the crank case
but how do i found out wether its long or short stroke ?
also would appear that rocking horse Pooh is more common than a genuine star twin ???

[Brian]

Yours is a short stroke. The engine in your bike is the same design as a A10 whereas the earlier engines although similar to look at are quite different with virtually no parts interchangeable. Probably the easiest way to tell with a quick glance is the shape of the timing cover. The cover on your bike is the typical "Y" shape but if you look at the earlier motor the section that goes out to the generator is flat, it doesnt curve up. The early, or longer stroke Star Twins all have the engine prefix of Z, yours will start with a A. Just for your info the early motor has a bore and stroke of 62mm x 82mm (495cc) whereas yours is 66mm x 72.6mm (497cc).
It would appear that the earlier Star Twins are more common than the later ones like yours, maybe because the A10 had been released and people bought them instead.
You have a very nice bike, good luck with it.

[fido]

Long stroke engine also has individual round valve covers instead of the double ones on the later engine.

[jfligg]

Hi Guys
  I have a 1949 Star Twin.  I would think they are pretty rare.  At shows I go to I have never seen another one.  Thankfully through the internet I have met some other owner in other countries.  I would think the early long stroke models would be the rarest.  They only ran to 1/2 way through 1950.  But one the other hand I have only seen one other A7 and it was a shooting Star.  Jeff

[olev]

Gday,
This is my first post. I live in Brisbane. oi! oi! oi!
I have a 52 star twin in a million bits and would appreciate an opinion on the motor.
The drive side case has had major surgery which has taken out half of the engine number.
The motor is a plunger type and only has the number 1103 remaining, with the prefix missing.
There is a dim letter 'C' below the engine number (part of HC I'd guess)
Until I read MrShells post where his star twin has HC stamped, I thought I'd had old A10 cases.
Now I'm totally confused.
The frame number of the thing is ZA7S26264.
Assuming these are the original cases, would anyone hazard a guess what the original engine number was.
cheers
will try to attach a pic.

[LJ.]

I have heard in the past of authorities using x-ray to find original numbers that had been ground off cases. I dont know if this is true or not but might be worth looking into. It seems that the shock of numbers being  punched onto the case leaves an impression well into the metal. Nice to have you with us by the way and we look forward to hearing of your looooong process in bringing together those million parts! Dont forget your photos when done! I might be well into old age by then... 

[RichardL]

...and lots of photos along the way would be great, as well. Good having you with us. This will be a very interesting project for you, and we look forward to following along.

Richard

[flatdeck]

Hi olev,
That frame number is '52 but could be an A7 or A10 motor (According to Bacon's book).
The following is from http://www.motos-anglaises.com/bsa/identification.htm
1952                  Engine               Rigid                      Plunger
A10 Golden Flash  ZA10 12.001      ZA7 8.001               ZA7S 26.001
A7                     AA7 5.001         ZA7 8.001               ZA7S 26.001
A7 Star Twin       AA7S 1.001                                    ZA7S 26.001
Which would indicate an A7ST especially since I don't think either the standard A7 or the A10 were H.C.
I'm not sure of the numbers but the 500 vs the 650 also had  a different number of cooling fins on the barrels (7 vs 10 perhaps).
Hope that helps.
Dave

[Brian]

Hi Olev,

I am also in Australia, Mt Gambier in S.Aust. Can you put a photo of your tank on, a 52' Star Twin has metal badges with the words "Star Twin" on them, same as mrshells. A standard 52' A7 has the small winged badges.

Brian.

[olev]

Gday Dave,
Thanks for the info. The bike is complete though the engine is in very poor condition.
It is definitely a 500 so maybe the engine no. was AA7S 1103 which would fit your information and the year?? It might be easier to find and rebuild another engine though. The bike was a star twin. I have a couple of photographs of the tank badges for Brian and will post them when I figure how to reduce the file size.They are almost 1 gig each.
Cheers, Tom