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Old 10th November 2011, 03:28   #1
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Default Seeking help on gearbox modifications

One of my friends owns a TVS STar City 2006 model and wants to alter the gearbox to a 5 or 6 speed one.

He feels handicapped with a 4 speed gearbox but does not want to trade off for a new bike. Not sure if anyone has heard of such alterations being made in the past.

He is seeking help and expert advise on the following

1. Is it safe and viable to make such alterations. Please highlight any roadblocks or risks of undertaking this conversion.
2. What precautions to take?
3. What other significant alterations need to be made (e.g. disc breaks, etc) that complement the increase in speed.
4. Are there any legal complications (RTO regulartions, FC, etc)
5. What could be the advantages or disadvantages
6. Does anyone knwo of a mech in Bangalore or vicinity who could get this work done.

help.
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Old 10th November 2011, 18:39   #2
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Default Re: Seeking help on gearbox modifications

Adding another ratio or two won't necessarily make it faster, especially with the quality of work we have in the unorganised after-market segment. I remember wanting a 5th gear for the RX100, only because the overall gearing was too short. Is that the case with the TVS Star?

The TVS Star isn't built for speed. If your friend is still keen, changing the final drive will be the simplest way to get better cruising ability. Or, what I'd recommend, is buying a nice performance bike. No better excuse to pick up one from the new breed of performance motorcycles on the block.
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Old 10th November 2011, 21:53   #3
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Default Re: Seeking help on gearbox modifications

Quote:
Originally Posted by GTO View Post
especially with the quality of work we have in the unorganised after-market segment.
+1. As far as my experience goes, in the two wheeler service segment, the quality of labour is so bad that often, even OE troubleshooting of newer bikes is becoming an issue.

And, with that quality of labour going in for major transmission work is NOT recommended. Also, considering the cost-to-practicality factor, its better to sell this bike off, and get a nice used 150+ cc bike.

Reliability rules!
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Old 10th November 2011, 22:45   #4
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Default Re: Seeking help on gearbox modifications

Quote:
Originally Posted by sunil.nv View Post
One of my friends owns a TVS STar City 2006 model and wants to alter the gearbox to a 5 or 6 speed one.

He feels handicapped with a 4 speed gearbox but does not want to trade off for a new bike.
Why? What does he expect of the 5/ 6 speed. Are the expectations realistic?

Coming to the actual question, unless it is a bolt on solution, don't think of it.

Regards
Sutripta
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Old 10th November 2011, 23:07   #5
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Default Re: Seeking help on gearbox modifications

The best thing to do would be change the rear sprocket. Max 2-3 teeth down than original. Multiple permutations and combinations is the best that can be done without so much cost.

And it might feel that 4 speeds are not enough, but the bike is not having such grunt that a 5 speeder would have done justice. The Star city motor is best suited to relaxed motoring.

Best is to try out by changing the rear sprocket IMO.

Last edited by aaggoswami : 10th November 2011 at 23:16.
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Old 10th November 2011, 23:51   #6
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Default Re: Seeking help on gearbox modifications

Here are a few things to consider while attempting this kind of a conversion.

1.> Do the drive and output shafts have additional slots to accommodate 4 additional gears (2 on each shaft if you want to go from 4 to 6 speed)
2.>If the answer to 1 is NO, then is the GB case wide enough to accommodate new input and output shafts with additional gears. (If you can even locate/make such a shaft)
3.> Say you CAN achieve 1 or 2. Next question will be, Does the shifter drum have slots/space to machine additional slots to accommodate a new shift Fork.
4.> All the above is something that comes to mind before even getting into the GB. There will be a ton of other things to worry about.

So the gist of the above is NO. You cannot convert your TVS star city to 6speed in a shade tree garage or a dealer service centre.

Playing around with your sprockets is your best/easiest bet.

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Old 11th November 2011, 00:26   #7
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Default Re: Seeking help on gearbox modifications

Quote:
Originally Posted by aaggoswami View Post
The best thing to do would be change the rear sprocket. Max 2-3 teeth down than original. Multiple permutations and combinations is the best that can be done without so much cost.

And it might feel that 4 speeds are not enough, but the bike is not having such grunt that a 5 speeder would have done justice. The Star city motor is best suited to relaxed motoring.

Best is to try out by changing the rear sprocket IMO.
+1 to changing sprockets.

Adding a gear is an expensive exercise (if at all possible) & then too it may do irreversible damage.

Play with different sprockets it should give you the desired effects.
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Old 11th November 2011, 00:56   #8
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Default Re: Seeking help on gearbox modifications

Thanks all for the feedback so far. From the looks of it, I would probably have to suggest him to do away with this alteration.

Quote:
Originally Posted by GTO View Post
Adding another ratio or two won't necessarily make it faster, especially with the quality of work we have in the unorganised after-market segment. I remember wanting a 5th gear for the RX100, only because the overall gearing was too short. Is that the case with the TVS Star?

The TVS Star isn't built for speed. If your friend is still keen, changing the final drive will be the simplest way to get better cruising ability. .
@GTO, he is not very keen on riding faster nor is he looking for low end torque. What he feels is that by the time, the bike hits about 60, the bike is no longer cruising and a lot of vibration and rattle catches on. He wants to be able to cruise at lower rpms even at speeds of 60 to 70.

Do you think this can be accomplished by changing the final drive.
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Old 11th November 2011, 01:01   #9
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Default Re: Seeking help on gearbox modifications

Quote:
Originally Posted by Technocrat View Post
Play with different sprockets it should give you the desired effects.
Quote:
Originally Posted by sunil.nv View Post
Do you think this can be accomplished by changing the final drive.
Altering the sprockets WILL have an effect on the initial of the bike. Well, this practice was done on the two strokes where one had more than enough initial, but on a 100cc star city?.. I seriously doubt the practicality of the mod. But still, its worth a try, considering the ease of work, when compared to transmission work.

Last edited by dhanushs : 11th November 2011 at 01:02.
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Old 11th November 2011, 01:14   #10
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Default Re: Seeking help on gearbox modifications

Yes, the Pick up will Definitely go down but he will get the relaxed riding at higher speed that he is expecting.
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Old 11th November 2011, 09:43   #11
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Default Re: Seeking help on gearbox modifications

Hi.

I think your friend may try adding a tooth to the front sprocket, or fitting one with 2-3 teeth less than stock at the rear wheel. This would effectively make the gearing taller and the bike would cruise much better.

But be warned. As mentioned before, the star has limited power reserves.
I tried this modification on my Bajaj Platina (now sold) around 2 years back. The bike has plenty of low and mid range torque so coped well. Pulling power will suffer a bit, so try this only if he rides solo. i had to slip the clutch a bit more than usual with a pillion while pulling off the lights.
The bike cruised quiet well on the highways, and i did not record any downfall in fuel efficiency. Definitely gave it a bigger bike feel.

Overall, i'd say its worth a try. Cheap and easily undo able.

PS: I also had a free flow filter with a custom intake designed to boost low end grunt and the sprocketing was done along this mod.
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Old 11th November 2011, 09:59   #12
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Default Re: Seeking help on gearbox modifications

Instead of adding gears look at a 4th gear ratio change. See if the gear pair is removable from shafts & try getting a new hi ratio pair made. Feasible than extra gears but in no way easy, no usual mech will do & above all the effort doesn't seem justifiable on engine said here.
so your friend should better work on sprockets & may try reducing engine vibes.
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