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#704226 - 08/07/17 3:59 pm Bobber bolt on rear end. T21  
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atlime Offline
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Hi all,

Im hoping someone can confirm a few details for me please, I'm new to Triumphs and would like to convert a 1958 T21 I just bought.

Its the 350cc version which seems to have been called t21 and then changed to 3ta in 1959? Also did a 5ta which from what ive read was the same bike as 3ta except for the top end?

So firstly am i correct with this info?

Secondly, was the t21 in 1958 different to the newer 3ta?

Reason im asking is I want to find a bobber bolt on rear end and can find a 500 bolt on that looks like it would fit from the bolt holes but i have no idea about dimensions!

Im not sure if its for a 5ta or some other 500 though!

Anybody have any advice or done a t21 before?

Thanks in advance 😁


Triumph T21 1958 Bobber project - HELP!!!!! smile
#704312 - 08/08/17 12:40 pm Re: Bobber bolt on rear end. T21 [Re: atlime]  
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atlime Offline
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atlime  Offline
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Can anyone comfirm if the 3ta and 5ta frames are the same?
At least then I can search for that dub frame.


Triumph T21 1958 Bobber project - HELP!!!!! smile
#704319 - 08/08/17 2:44 pm Re: Bobber bolt on rear end. T21 [Re: atlime]  
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AngloBike Online content
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UK Berks
99 % certain yes.

The 21/3ta has a swan necked frame- as does the 5ta
Later, they used a different frame design but I am pretty certain that again the 350/500 series shared this
You need to either use the correct tank with early bikes or brace the headstock if not

I have a 3ta also destined to get a hard tail one day ( looking at factory metal works)

Afaik

You need the cylinder head, barels and Pistons from a 500 along with the conrods
Rumour has it that you can use tiger cub Pistons on a 350 to achieve 400cc

Can't do it now but a way to confirm the frame is to check out parts boooks

#704320 - 08/08/17 2:45 pm Re: Bobber bolt on rear end. T21 [Re: atlime]  
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#704326 - 08/08/17 4:16 pm Re: Bobber bolt on rear end. T21 [Re: atlime]  
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I'm no genius on 3TA / 5TA, but did look at a couple of parts books for those two models and found that 1958 front frame is part no. F4157 for 3TA, next parts book available is 1960- this shows that 3TA, 5TA, and T100A also used part no. F4157. As member Anglobike indicated- you can check parts books for other years to confirm when and if the frames changed to a specific one for the 350 vs. 500.

A good source for parts books is available here, 3TA and 500's are about halfway down the page:

https://www.classicbritishspares.com/pages/free-triumph-bsa-norton-parts-books

#704503 - 08/10/17 9:14 am Re: Bobber bolt on rear end. T21 [Re: atlime]  
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Stuart Online content
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Scotland
Hi,

Firstly, welcome to the Forum. smile

Originally Posted by atlime
Its the 350cc version which seems to have been called t21 and then changed to 3ta in 1959?

The unit construction (gearbox in a compartment attached to the crankcase, rather than being separate) 350 twin was new for 1957, its model name was just "Twenty One" because 1957 was 21 years of the Triumph Engineering Company - founded in 1936 to rescue the motorcycle-making of the earlier Triumph company - and 350 cc is 21 cubic inches in the US. The model's code was "3TA".

That first 350 spawned 5TA "Speed Twin" (500 cc), T100A "Tiger 100" (sporty 500), US-only TR5AR and TR5AC "Trophy" (sporty 500), and T90 "Tiger 90" (sporty 350). The names were all from superseded pre-unit (separate gearbox and engine) models/versions/variants, the "A" was added to the model codes because Triumph at least supplied parts for pre-unit 3T, 5T, T100 and TR5. "T90" had previously been the model code of the pre-war 500 cc "Tiger 90" single but all tooling and drawings for the singles had been destroyed with Triumph's then works in Coventry by the infamous bombing Blitz of 14th/15th November 1940.

Originally Posted by atlime
Reason im asking is I want to find a bobber bolt on rear end and can find a 500 bolt on

The whole unit 350 and 500 range was known by Triumph as the "C-range" (singles being "A", pre-unit twins and unit 650's being "B"). By-and-large, major parts - frame, swinging arm, crankcases, etc. - are common to all models and variants in the range. So, yes, a bolt-on rear-end from a unit 500 will fit your 21.

Originally Posted by atlime
did a 5ta which from what ive read was the same bike as 3ta except for the top end?

Yes. As traffic generally got faster through the 1960's, the basic 18 bhp 3TA became a bit of a slug; common upgrades were either a 500 top end or Tiger 90 bits. Not so easy to convert a 3Ta these days.

Originally Posted by atlime
I'm new to Triumphs and would like to convert a 1958 T21 I just bought.
Reason im asking is I want to find a bobber bolt on rear end

Depends how complete and original the 21 is; the more complete and original it is, the more I would not - complete and original bikes are rare, already-mutilated Triumph twins are still pretty common. Keep an original and complete bike original and complete, or pass it on to someone who wants an original and complete 3TA; "bob" an already-mutilated twin, and you'll likely prefer a 500 for riding in modern traffic.

Hth.

Regards,

#704534 - 08/10/17 4:04 pm Re: Bobber bolt on rear end. T21 [Re: atlime]  
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The 3ta is also (apparently) desirable to older riders who find kicking over a 650 increasingly hard and "downsize"
It's so long since I kicked a 500 i don't remember how hard it was compared to a 350

My 3ta seems to have been assembled from bits but does have the advantage of matching numbers and enough bits to make a second engine, which I will do when I have time. The original tinware on mine is gone but if you have it, it is worth money so either keep it or use it to fund the build
I would only use a bolt on hard tail

#704708 - 08/12/17 9:33 am Re: Bobber bolt on rear end. T21 [Re: AngloBike]  
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Stuart Online content
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Hi,

Originally Posted by AngloBike
original tinware on mine is gone

Without wishing to hijack the thread, do you know about these? Dunno anything about the quality tho'.

Regards,

#707728 - 09/08/17 5:02 pm Re: Bobber bolt on rear end. T21 [Re: atlime]  
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I just bought a factory metal works 4 stretch 2 drop hardtail from a guy in the U.K.
I assume he imports a lad at a discount
It worked out at about the same price as me doing it direct from FMW but no I rot issues

#707756 - 09/08/17 8:46 pm Re: Bobber bolt on rear end. T21 [Re: atlime]  
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Andy Higham Online content
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I HATE what the term "bobber" has become.
Way back a bobber was a bike that had all the unecessary tin ware and other ancilliary equipment removed and making it lighter and better handling, usually for racing.
Today it seems to mean taking a perfectly sound handling bike and replacing the suspension with a rigid back end and primitive forks, adding a seat with buttons and tassles and even hand shift gear levers. Usually this means a bike that is slower and worse handling


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
Modified Nu-Trak GM500cc sprint/LSR bike "Deofol"
2003 Aprilia RSV Mille "Lo Stregone"
#707763 - 09/08/17 10:13 pm Re: Bobber bolt on rear end. T21 [Re: atlime]  
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ohio, usa
that's what "chopper" used to mean in america.


Into the distance a ribbon of black
Stretched to the point of no turning back
A flight of fancy on a windswept field
Standing alone my senses reeled
A fatal attraction is holding me fast how
How can I escape this irresistible grasp?
#708139 - 09/12/17 8:23 am Re: Bobber bolt on rear end. T21 [Re: atlime]  
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AngloBike Online content
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UK Berks
Andy - have you ever seen "cafe racer" a yank tv show? Was on quest recently
All your comments fit that as well

What I started with is little better than a field bike and I like chops. As a bar hopper they are fine but I come from an era when most of the bikes at my pub of choice were British cafe racers or chops

Nothing is undoable and you cannot make a 3ta handle worse



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