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twinshock

Joined:

Nov 12

Posts: 8

twinshock says:

3TA/5TA Gears

I have found a 3TA or 5TA bottom half in the back of my garage but cannot identify the gear cluster fitted in it.

I believe it is a close ratio box but the strange part is the sleeve gear and matching pinnion on the lay shaft, they have 26 and 18 teeth which is different to my other similar Triumph boxes where they only have 22 teeth on the sleeve gear. It also has a large 20 tooth gearbox sprocket which leads me to believe it was originally destined for the track.

The profile of the teeth on these two gears is different to the other gears and I believe they are meant as a very high top gear but where did they come from or who made them and what effect would it have on a good condition 500cc top end.

Any info would be appreciated, cheers

Twinshock

  

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  • Posted 2 years ago (23 November 2012 14:23)

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smidget

Joined:

Nov 07

Posts: 2433

smidget says:

Hi Twinshocks

Try cheneytriumph, I think they may still be in Churchcrookham near Aldershot, they are the guys who should be able to tell you.

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twinshock

Joined:

Nov 12

Posts: 8

twinshock says:

3TA/5TA Gears

No, thanks for the response but Cheney's couldn't throw any light on them

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smidget

Joined:

Nov 07

Posts: 2433

smidget says:

Are

there any numericalmarkings on the mystery gears.

Is it possible that you could post pictures of the gears?

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twinshock

Joined:

Nov 12

Posts: 8

twinshock says:

3TA/5TA gears

There are no markings on the gears at all, they have a slightly different tooth profile to the others in the cluster.

I will try and get a picture on this post.

Cheers for trying to help

 

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smidget

Joined:

Nov 07

Posts: 2433

smidget says:

Will

check to see what I have in my spares bin, will be in touch soon.

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smidget

Joined:

Nov 07

Posts: 2433

smidget says:

Gear information

T100 G/B Sprocket 18 teeth.

5TA G/B Sprocket 20 teeth.

T90 G/B Sprocket 17teeth.

Internal Ratios For the above are:

1.00:1          4th gear (top)

1.22:1          3rd gear

1.61:1          2nd gear

2.47:1          1st gear (bottom)

 

Alternative data for sports models fitted with A.C. Magneto Ignition equipment.

Internal Ratios (close)

1.00:1          4th (top)

1.12:1           3rd

1.35:1          2nd

1.99:1          1st (bottom)

Internal Ratios (wide)

1.00:1          4th (top)

1.37:1          3rd

1.97:1          2nd

3.18:1         1st (bottom)

G/B Sprocket options are 17,18,19,20 teeth.

To meet special demands for certain sporting events there were available alternative close and wide ratio gears which enabled the gearbox to be suitably converted for road racing and trials riding. For details of the parts for such a change over, you will need to consult the appropriate Truimph Replacement Parts Catalogue.

You could contact the Triumph Owners club in your area or alternatively try 'Old Bike Mart' to see if there is someone with the 'knowledge' of what you seek.

Hope this helps you find a solution to your mystery.   

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twinshock

Joined:

Nov 12

Posts: 8

twinshock says:

3TA/5TA gears

Hi Smidget

I really appreciate your assistance, many thanks.

I took a couple of better photos today and have added them in here.

I have a friend who worked at Triumph in its heyday for many years and he went to a Triumph reunion dinner recently and met with all the long serving boffins that used to work in development, testing and technical departments and none of them could shed any light on the source of these 26/18 gears. They suggested they could have been sourced from the USA as they made some up to produce a high top gear for racing over there but I cannot find anyone to support this theory. I have spoken to Quaife's and Cheney's and neither can help.

This combination is not listed in any Triumph replacement parts books or spec sheets, supported by the boffins not knowing them.

Unless anyone can assist me I guess I will sell the engine "with a very high top gear". The motor will be up for sale as soon as reassembled, its a 3TA bottom end with 500cc barrels and high compression pistons, lightened timing gears, fully restored head with splayed inlets and twin Mk1 Amals.

Overall its in superb condition if you know anyone who's looking for something like this.

Cheers 

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smidget

Joined:

Nov 07

Posts: 2433

smidget says:

Twinshocks

I'm sorry I have no other information to hand or further ideas of where you may find an answer.

I would like to know out of curiosity why you have decided to build the 500 top end ontop of the 350 bottom end though if you don't mind my asking.

Just as a last thought could the gears be from a 650 gear box? I have no information on the internals so am not sure, just an idea.

Good luck and let us know if you ever find out.

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smoto5

Joined:

Mar 09

Posts: 4548

smoto5 says:

Interesting thread,

and detective work :smile while I don't know a great deal about the intricacies of Triumph twins, some thoughts have occurred to me, if indeed the gearbox as a whole comprises a close ratio cluster, then apart from road racing, it might have been built up for speed trials or sprints of the type held on redundant airfields and such places, a more likely scenario than drag racing I think, a high top gear ratio would be of some advantage on a long course. Alternatively, if the gearbox is wide ratio effectively, at least in the three lower gears, then use in what was formerly known as long distance trials or cross country trials (The most famous example being the International Six Days Trial) is a possibility as this was gradually changing in the sixties into what is known as Enduro now (now the above event is called International Six Days Enduro) the bikes were moving away from being modified road bikes towards modified scrambles (or motocross later on) bikes, later developments being the unit BSA singles and early Spanish imports Bultacos, Montesas etc. as well as British two strokes. Anyway, if you had to run lower final drive gearing to enable the gearbox to be effective in technical, relatively slow off road sections, once you are on faster fire roads in the forests or open moorland and on the road, a higher top gear would restore some reasonable top end speed to get to the next section  in good time, something less critical in a conventional trial but essential in a time trial. These events were becoming popular in the States where of course there was plenty of open space, however you wouldn't neccessarily want a bike of the size of the desert racers of 650/750cc or indeed the scramblers which were 500/650 in the open class, and you wouldn't require that high top gear on a scramble track either, so that sort of discounts it as a scrambler I would say. 

A lot of supposition admittedly :hmmm: Perhaps Eric Cheney might have known had he still been around.
Good luck :smile

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twinshock

Joined:

Nov 12

Posts: 8

twinshock says:

3TA/5TA gears

Thanks smoto5, I tended to agree with you until I have now been told the gears are early (pre 1960) road gears.

The teeth are as follows working from the clutch/sleeve gear side, 26/18, 23/28, 28/23, 19/32, can anyone verify that they come from a pre 60 road bike. I was told they were close ratio and the 26/18 was a bit unusual so I am still mistified.

The engine is rather odd with some interesting changes,its a 3TA crankcase, 500cc barrel with 9:1 pistons and a Daytona twin carb head with lightened timing gears and I now think it will be better to sell it as separate major items, ie head, crank, cases, barrel & pistons, gear cluster, clutch, side covers, and a box of sundry items etc. etc if anyone is interested.

Cheers  

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