The BSA A7-A10 Forum
Bikes, Pictures, Stories & more => Chat, Offtopic & Everything Else => Topic started by: mrshells on 20.08. 2008 22:47
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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 ????
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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.
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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
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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
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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.
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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 ???
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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.
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Long stroke engine also has individual round valve covers instead of the double ones on the later engine.
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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
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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.
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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... *smile*
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...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
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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
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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.
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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
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Gday Brian,
I've been struggling to get my photo to a smaller file size.
If this doesn't work I'll try later.
cheers.
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Hi Tom,
everything looks right for a 52' Star Twin so I think you are right with the engine no. AA7S 1103. The 51' models started with engine no AA7S 101 so without knowing how many they made its hard to know.
The next possible no. would be 11103 but that would mean that they made around 10,000 Star Twins in 51' and 52' which seems unlikely.
You mention the engine you have is in poor condition but hopefully you can find another A7 engine to use.
Good luck.
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Hi There,
Just come across this Forum, and decided to make a few comments.
I have a 1954 Star Twin sitting in the garage, and is about a 1/3 of the
way thru a restoration project.
How Rare are they... I am in New Zealand and the story I have been told is
there where about 4 brought into this country in 1954 the same year the
Shooting Star was released. So if you ordered a 1954 Star Twin you might have
been lucky to get it, or you might have recieved the Shooting Star.
So mine is the same colour as the SS (Dark green frame, Light green body work)
I have found it very hard to find any colour photo's of this model, most seem to
be earlier Star Twins or the Shooting Star.
According to engine numbers, I have 2 sets of crankcases (only 1 is good enough
to use) so there may-be only 2 other bikes down-under.
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Welcome to the forum, Porty. Do you think your bike was painted the same colours as the Shooting Star? When I restored my A7SS you could get the polychromatic green paint from Polly Palmer in the BSAOC. I don't think it was a perfect match as bits of original paint inside the toolbox were more like an apple green with less silver than in the new paint. Having said that, BSA themselves did not bother too much with consistent colour shades so you have a fair bit of leeway.
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Hi
Thanks Fido, like I said before, in NZ I think the ST and also the SS are very rare
down here. So I haven't seen either models in real life. So I have of been relying on
the photo on page one of this thread and a bit of detective work. The only original light
green colour I had was on the inside of the rear brake backing plate and the dark
green, I found some on one of the plunger spring covers and frame. I took these
samples to an Automotive paint supplier and they matched up the colour. I have since
been told they weren't a bad match. And that was going by keen BSA owner's memory.
I have also noticed in all the colour photo's of ST's and SS's, there seems to be different
shades of green depending on quality of photo, and light.