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1970 t120 layshaft #530505
02/26/14 6:01 pm
02/26/14 6:01 pm
Joined: Nov 2010
Posts: 332
UK and michigan
M
malla1962 Offline OP
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malla1962  Offline OP
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M

Joined: Nov 2010
Posts: 332
UK and michigan
got a problem here, i have a tooth missing of the layshaft 4th gear part number for the assembly is 57-3864 can this be replaced with a later assembly?

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Re: 1970 t120 layshaft [Re: malla1962] #530608
02/27/14 6:39 am
02/27/14 6:39 am
Joined: Dec 2004
Posts: 9,660
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,660
Scotland
In 71 the layshaft changed the number of teeth by dropping one. So that will not fit.

Re: 1970 t120 layshaft [Re: kommando] #530666
02/27/14 1:41 pm
02/27/14 1:41 pm
Joined: Nov 2010
Posts: 332
UK and michigan
M
malla1962 Offline OP
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malla1962  Offline OP
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M

Joined: Nov 2010
Posts: 332
UK and michigan
the later layshaft I have here has 20 teeth the only difference I can see is the way it dogs in to the next gear
on the layshaft.

Re: 1970 t120 layshaft [Re: malla1962] #530669
02/27/14 1:48 pm
02/27/14 1:48 pm
Joined: Oct 2012
Posts: 4,173
Running from demons in WNY
Hillbilly bike Offline
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Hillbilly bike  Offline
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Joined: Oct 2012
Posts: 4,173
Running from demons in WNY
The gear can be pressed off quite easily if necessary..


I take off bike parts until it doesn't function, then put on just enough so it functions
Re: 1970 t120 layshaft [Re: malla1962] #530670
02/27/14 1:55 pm
02/27/14 1:55 pm
Joined: Dec 2004
Posts: 9,660
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,660
Scotland
The 71 high gears I have are a few 1000 miles from where I am but check the parts books and you can see the number teeth on the matching high gear and fixed layshaft gear changed, even if it was only on one gear then they both cannot fit earlier years as they changed both teeth profiles, the gear that dogs into it also changed but not in gear teeth just the way it mates with the fixed layshaft gear. This arrangement was a very short lived one as the 5 speed replaced it.

Re: 1970 t120 layshaft [Re: kommando] #530695
02/27/14 6:06 pm
02/27/14 6:06 pm
Joined: Nov 2010
Posts: 332
UK and michigan
M
malla1962 Offline OP
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malla1962  Offline OP
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M

Joined: Nov 2010
Posts: 332
UK and michigan
parts book does my head in,lists layshaft with gear 57-3864 but no number for the gear, but my gear has 57-3859 so I will look for the right one or a complete box.

Re: 1970 t120 layshaft [Re: malla1962] #530737
02/27/14 11:01 pm
02/27/14 11:01 pm
Joined: Dec 2004
Posts: 9,660
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,660
Scotland
The high gear goes from 26T which it had been for years to 25T, from memory the layshaft went from 20 to 19. The effect was to thicken up the gear teeth but why they did this only a year before the 4 speed died you have to wonder, no doubt 100% 5 speed was not expected. Trouble is in 69 they changed a lot of dimenions buy 2 or 3 thou so mixing 70 box parts with earlier ones is fraught with issues, so a complete box may be the best answer.

Last edited by kommando; 02/27/14 11:06 pm.
Re: 1970 t120 layshaft [Re: kommando] #530762
02/28/14 3:24 am
02/28/14 3:24 am
Joined: Nov 2010
Posts: 332
UK and michigan
M
malla1962 Offline OP
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malla1962  Offline OP
BritBike Forum member
M

Joined: Nov 2010
Posts: 332
UK and michigan
If I can't find the gear with the right number on it will be a complete box,

Re: 1970 t120 layshaft [Re: malla1962] #530785
02/28/14 7:54 am
02/28/14 7:54 am
Joined: Oct 2012
Posts: 4,173
Running from demons in WNY
Hillbilly bike Offline
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Hillbilly bike  Offline
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Joined: Oct 2012
Posts: 4,173
Running from demons in WNY
My 71 parts book, publish date Feb 71, lists layshaft with high gear as 20 tooth, mainshaft high gear as 26...


I take off bike parts until it doesn't function, then put on just enough so it functions
Re: 1970 t120 layshaft [Re: malla1962] #530786
02/28/14 8:09 am
02/28/14 8:09 am
Joined: Dec 2004
Posts: 9,660
Scotland
kommando Offline
BritBike Forum member
kommando  Offline
BritBike Forum member

Joined: Dec 2004
Posts: 9,660
Scotland
25T high gear 4sp box 57-4332

and here is the 4sp Trident equivalent

http://www.eBay.co.uk/itm/57-4346-T...arts_Accessories&hash=item19b32b08d4

It may only be for 72 but do not have 71 or 72 parts books with me

eBay listing

http://www.eBay.co.uk/itm/Triumph-6...nneville-TR6-Trophy-R-C-TT-/330902115962

Original Triumph late model Unit 650cc 4-SPEED GEAR CLUSTER with SELECTOR FORKS & SHAFT, CAMPLATE, SLEEVE GEAR BEARING, CIRCLIP & OIL SEAL, COUNTERSHAFT SPROCKET & NUT, from a 1971 T120R

part number 57-4332, 25 teeth



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