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#374963 - 05/24/11 11:17 am Difference between zb34a and zb34 gs  
Joined: May 2011
Posts: 1
sebastien Offline
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sebastien  Offline
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Joined: May 2011
Posts: 1
Paris France
Hello,

I wanted to know the difference between zb34a and zb34 gold star?
I know this is a bsa zb34A of competition with an aluminum engine but I know no more.
Thank you

Seb

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BSA Gold Star forum This board is dedicated to BSA Gold Star motorcycles.

#374970 - 05/24/11 12:30 pm Re: Difference between zb34a and zb34 gs [Re: sebastien]  
Joined: Dec 2004
Posts: 8,878
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,878
Scotland

#375100 - 05/25/11 12:16 am Re: Difference between zb34a and zb34 gs [Re: sebastien]  
Joined: Sep 2001
Posts: 2,766
Gordo in Comox Offline
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Gordo in Comox  Offline
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Joined: Sep 2001
Posts: 2,766
Comox BC Canada
Seb: There were ZB33, ZB33A, ZB34, ZB34A and ZB34GS engines.

As to your question, from what I have seen and read, everything except the ZB34GS engine used what was really a ZB33 bottom end with the small nuts and locking rings on the bigend bearing and the small drive side roller bearing without the bolted in bearing support plate. The ZB34GS should have the big nuts with a screw to lock them and should have the larger drive side roller bearing and the bolted in support plate. The ZB34GS flywheels seem to be of a higher standard and the conrod was polished. It appears that there was more than one type of one piece (no separate rockerbox) 500 head depending on what the engine was built to do. However some/a few engines were made that did not follow the above specs so almost anything is possible to find.

A slight anomally was that midway through the 52 model year the 4000 series engines stopped when the ZB34GS adopted the BB type separate rockerbox and started numbering the engines at 5001.

In the 53 model year the BB34GS engines replaced the ZB34GS 5000 series engines and looked identical as far as I can tell.

Gordo


Without frequent roadside repairs there is no fun in riding!
#375170 - 05/25/11 1:19 pm Re: Difference between zb34a and zb34 gs [Re: Gordo in Comox]  
Joined: Dec 2008
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Stephenrc45 Offline
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Stephenrc45  Offline
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Joined: Dec 2008
Posts: 138
England
What Gordo said. I have a ZB34A but its fitted with a Gold Star cylinder head and crank. However it doesn't have the plate to retain the drive side main bearing. I think the only real difference between the a ZB34A and a ZB34GS is crank and larger bearing. I'm not sure if mine came from the factory like this it was done at a later date.

#379408 - 06/17/11 1:49 pm Re: Difference between zb34a and zb34 gs [Re: sebastien]  
Joined: Dec 2008
Posts: 138
Stephenrc45 Offline
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Stephenrc45  Offline
BritBike Forum member

Joined: Dec 2008
Posts: 138
England
Here's a question.

Whats the difference between ZB34A cylinder heads and ZB34GS heads. Both have different part numbers but use the same valves etc. In my BSA parts books they even list the same sized carbs apart of the racing head for the GS which use a larger inlet port.


Moderated by  Rich B 


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