Final Drive Gear questions?

31 posts in this topic

Posted

Alright friends,

So their are a lot of different options out there for final drive gears. I will most likely be getting a Hoca or NCY, but which one?

1st question: Does it matter what what engine you have for which setup you can get? (171cc)

2nd question: Can it be installed with a vice instead of a press?

3rd question: Or can you order them pressed already?

Right now thinking of picking up a 18X35.

 

 

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Posted

Hey Kachi, 

Brand question: I am currently using a chinese brand and they run perfectly fine (Dan may have a few options) of course just like anything else, the variance is quality, tolerance, rolled/ raised edges. 

1st question: The gear ratio all depends on: your build, riding conditions, style of riding, wants/needs. I'm not sure what your stock ration is but that is a pretty big jump your going for. I moved to a 15:37 and there is a noticible reduction in acceleration but it lowered my cruizing rpms. This is a really shallow answer and there is a lot more into it. Engine performance is a big factor, using a taller gear with no increase torque= poor acceleration, no increase in hp= you can't use the potential of the taller gearing.

2nd question: I use a vise all the time, use with care and dont damage it up

3rd question: you can order them already pressed, not worth the money in my opinion, I get mine done in a few mins.

I actually got my hands on a taiwan gy6 engine because the CPI engine I have didnt have options to change the gearing. I had to spin the engine up pretty high to reach over 110km/hr. Key note it didnt last long because the bolts for my case halves vibrated loose and those rpms. That engine had a 155BBK ported Taida head 26mm flat slide carb, good pipe and my piston was zero decked. It ran great other than the whole engine coming apart. Now for any performance builds I use Nordlock to ensure they dont come loose. 

If I was able to get a taller gear, I would be able to reach the same speed with less rpm and I know the engine had the torque and power to pull hard.

Remember this is my madness and I do not recommend this to anyone to be used as a daily ride. PS I rode this setup for almost a year flogging it every day :D

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Posted (edited)

Alright friends,

So their are a lot of different options out there for final drive gears. I will most likely be getting a Hoca or NCY, but which one?

1st question: Does it matter what what engine you have for which setup you can get? (171cc)

2nd question: Can it be installed with a vice instead of a press?

3rd question: Or can you order them pressed already?

Right now thinking of picking up a 18X35.

 

 

1.) No

2.) I've never done and don't know how you can use a vice to press off your original.... I advise just using a press, if you don't have one, any mechanic shop will have one and likely only charge a few bucks)

3.) Not that I'm aware of

18 x 35 : Ask yourself why... Sounds like you're just making a random selection.... Gearing is simple, it's all about ratio's... 

Lets do this simple:

1:1 means gears will be at the same speed....  1:2 means everytime 1 makes 1 revolution, 2 will make 2.... This will make 2, 2x faster than 1 (This is for top end speed)

... Now Flip it: 2:1 This will make your final gear twice as slow, but give you way more power (Take off power)....

From that, you can extrapolate...  Most GY6's I have worked on have 13:40 (but there ARE exceptions) final drive gear ratio....So, if you want more top end at the expense of take off 12:40, 11:40 - extrapolate.... If you want more take off power at the expense of top end, 14:40, 15:40 - extrapolate....

18:35 will give you hell-a-fied take of power, but you will lose a lot of top end speed.... 

 

Edited by DMartin95
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Posted

Thanks Daniel, I was thinking this might need your expertise.

With my A14 Cam my take off speed is top notch already so I'm diffidently want my gears to address my top end speed. 

It will be one of the last mods I will do.

 

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Posted (edited)

Lets do this simple:

1:1 means gears will be at the same speed....  1:2 means everytime 1 makes 1 revolution, 2 will make 2.... This will make 2, 2x faster than 1 (This is for top end speed)

... Now Flip it: 2:1 This will make your final gear twice as slow, but give you way more power (Take off power)....

From that, you can extrapolate...  Most GY6's I have worked on have 13:40 (but there ARE exceptions) final drive gear ratio....So, if you want more top end at the expense of take off 12:40, 11:40 - extrapolate.... If you want more take off power at the expense of top end, 14:40, 15:40 - extrapolate....

18:35 will give you hell-a-fied take of power, but you will lose a lot of top end speed.... 

 

I think there may have been a mistake with the gear ratios discussed above. This was already discussed in the "gearing" thread but never fully explained.

18:35 will not give you better take off or less top speed as compared to a stock ratio of say 13:40. 

This is simple and the concept is used by stunt riders so they can pop wheelies easier and do mad burnouts. Go look at any video of a professional stunt bike, the rear sprocket is huge as compared to stock. They do this to multiply the engine's torque. They gain crazy acceleration and loose top speed. We want the opposite.

This is the same concept used in a chain block/ come along for one person to lift a heavy load. You turn the input gear about 100 times to get the output gear to turn once, equals a torque multiplier

For those interested I have typed and explain in detail gear ratios and how our gy6 transmission works.

Let me back this up easily as this is simple mechanical theory

40/13 = 3.077 This means for every 3.077 revolutions of this input shaft (Engine), the output shaft (Wheel) will turn once

1000 Engine rpm = 1000 / 3.077 = 325 Wheel rpm 

as compared to

35/18 = 1.944 This means for every 1.944 revolutions of this input shaft (Engine), the output shaft (Wheel) will turn once

1000 Engine rpm =1000 / 1.944 = 514 Wheel rpm

For the same 1000 engine rpm a gear ratio of 18:35 will give you greater distance covered by the back wheel which results in an increase in top speed. 

Comparing ONLY these 2 gear ratios, the results are as follows:

13:40= increased acceleration, less top speed

18:35= decreased acceleration, more top speed

The terms Engine and Wheel used above was only used to prove the simple concept. 

For our gy6 engines, the gears that we change are not actually the true gear ratio.

Let me explain with a picture.

After-the-women-did-not-fight-Used-Scooter-GY6-125T-original-transmission-gearbox.jpg_640x640.jpg

The Shaft to the top right is the clutch input, it has a small gear that drives a big gear.

It will take that small gear many rotations to turn that big gear once, this is the first stage of gear reduction and torque multiplication.

For this transmission, the first gear ratio is 15:42 meaning it will take 2.8 rotations of the clutch input shaft to turn the "middle" shaft once

On that same "middle" shaft there is a small gear that we can't see, that drives the big gear on the output shaft to the left, this is what your wheel is driven by.

This is the gear ratio that we are altering. 

It will take that small gear a few rotations to turn that big gear once, this is the second stage of gear reduction and torque multiplication.

To determine the overall gear ratio of the transmission it would be= 2.8 (from the first gear ratio) X 3.077(Stock 13:40) OR 1.944(18:35)

Stock =   1:8.6        8.6 rotations of the clutch input shaft will turn the wheel once

"18:35"= 1:5.4         5.4 rotations of the clutch input shaft will turn the wheel once

I hope this clears up any misconceptions of the gear ratios of the gy6 transmission.

Edited by bcyprian25
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Posted

All I can say is...Dam

Oh, thought of something else to say...THANKS!

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Posted (edited)

No problem at all, I too mix up my theories and concepts and I depend on all of you guys if I do. I've always found that no one ever fully explained the transmission. I still left out a few parts concerning the CVT. Maybe I'll do a write up when I get some more time, there are many misconceptions out there about variator and CVT tuning that I too got caught up in before going back to basic principles and fully grasping the concepts. There are many BIG named scooter companies that share a lot of misinformation when coming to this topic.

There is also a big misconception concerning a high compression engine but that is a huge topic with many variables. 

Edited by bcyprian25
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Posted

Kachi, this is how I go about choosing my gear ratio. This is the way I do it and do not recommend this unless you are aware of all the variables involved. Use this guide at your own discretion and only as reference to help you make your decision. This is a rough guide as there are many variables that have cause and effect in the engine and CVT happening as we make changes.

1) Determine the cruizing speed and top speed I want to achieve? I want to hit 140km/hr 

Please note that our scooters were never designed to reach these speeds and I do not recommend for anyone to attempt these speeds. Also I do not encourage or recommend that anyone break the law by violating the designated speed limits. My Top Speed goal is totally theoretical and I only attempt to reach those speeds in my dreams while I race Marc Marquez for the Moto GP championship.

2)Determine the current gear ratio of the changeable gears. Think mine was 13:40 or something like that.

3)Determine your current cruising speed and associated RPM and also top speed and associated rpm. My cruizing speed =80km/hr ; top speed= 105km/hr I d not have a tach so I didnt know what the rpms were. If you do have a tach this information is valuable

4)Considering that EVERYTHING else remains the same, we can make an ASSUMPTION that speed is directly proportional to the change in gear ratio. This is not a bad assumption for a ball park. I create a table with all the available gear ratios on the market. An example below 

                                        Ratio                              Speed

Stock (13:40)         13:40= 13/40 = 0.325                100km/hr

Therefore                    1= 100/0.325                        307.7km/hr

14:38                        14/38= 0.368                    307.7 X 0.368 = 113.2km/hr  

14:36                        14/36= 0.389                    307.7 X 0.389 = 119.7km/hr  

15:38                        14/38= 0.395                    307.7 X 0.395 = 121.5km/hr

15:37                        15/37= 0.405                    307.7 X 0.405 = 124.6km/hr 

15:36                        15/36= 0.417                    307.7 X 0.417 = 128.3km/hr  

16:38                        16/38= 0.421                    307.7 X 0.421 = 129.5km/hr  

16:37                        16/37= 0.432                    307.7 X 0.432 = 132.9km/hr

16:36                        16/36= 0.444                    307.7 X 0.444 = 136.6km/hr  

17:36                        17/36= 0.472                    307.7 X 0.472 = 145.2km/hr  

18:36                        18/36= 0.5                        307.7 X 0.5 = 153.85km/hr        

So basically there are many more combinations you can get but my hands are tired. you get the point, choose the gearing that gets you close to your goal. 

Understand that if you ONLY make this change in gearing from stock to achieve a higher top speed, you have effectively decreased the torque multiplication of the transmission and you WILL have a decrease in acceleration. DO NOT LET YOUR SENSES FOOL YOU

Conversely There are gears that further increase the torque multiplication of the transmission to increase the acceleration at the expense of top speed. This is usually used for tight race tracks where the top speed of a longer gear is unachieveable and will result in lower lap times. Again your senses may tell you that you are accelerating quickly but if everyone else racing optimized their gearing to suit the track you will be in last place. Ask Piston how much gear kits and sprockets his team walked with to a race. 

Hope this helps out. I added all the calculations so anyone can replace them for their own and know what is going on.

Quick add in. If everything else remains the same and you increase your RPM ONLY this works the same way RPM is directly proportional to speed assuming all else remains the same. This was how I was able to get from 90km/hr to 110km/hr even though I couldn't get replacement gears for my engine. I increased the RPM, I DO NOT RECOMMEND DOING THIS AT ALL. All engines have their limits and I found mine. Dont go looking for yours.

 

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Posted (edited)

Thanks again BCY!

Your the best brother, not only a subscriber to my channel, but seem to have a background in teaching like myself.

When I get some shirts printed up, I will be sending you the 1st one!

Don't worry, you don't have to wear it...but can wipe down your bike after washing.

 

Edited by Kachi's Kid

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Posted

Good write up BCY, you will not be getting a shirt from me, unless you want a 2003 Sturgis one with some holes hahaha

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Posted

Fifty,

Just send me some of those holes.

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Posted

Cheap to send, they don't weigh much ahhaha

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Posted

Hey no problem at all guys, I'll be happy to wear the shirt Kachi, appreciate it. No worries Fifty when ever we meet up we'll have a drink.

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Posted

I'll drink to that.

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Posted (edited)

something also to consider is were you particular motor makes peak hp and torque.

The A-14 flatness out around 7,000rpm and peaks at around 7,7500 before she starts to fall off. theres a point were you out of hp and she simply won't pull that tall a gear.

I really like the profile of the A-11 from 7,000-8,000rpm then with little fall off flattens out for around 500rpm of overrev..

 

Cam_Profile_Graph_4.JPG.46a5040a592e549a8e1e408033ff56bb.jpg

Edited by pistonguy
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Posted

To me the A9 looks like a good cam , nice pull up to 8500, for an all around cam , nice smooth pull up to there, just my .2c worth.

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Posted

Thanks Piston,

I will check tomorrow when riding if the RPM's drop off. I just know she is kicking booty off the line right now.

I will pick up an A11 also though.

What are the numbers in the left column? (10.0, 10.5 etc.)

Also I see this is based in theory and modeled after a 155cc engine, but theory always helps real world testing.

I have so much to upgrade already and my summer is running out of time, which sucks. I think the filming gets in the way of the work but I just want create a guide to upgrading without others wasting their $$$.

From your pic I see you have a flat slide carb. which is beautiful by the way.

What is the difference between a 28 or 30mm flat slide and a CVK? besides the auto choke?

Does flat slide "actually" perform better?

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Posted

To me the A9 looks like a good cam , nice pull up to 8500, for an all around cam , nice smooth pull up to there, just my .2c worth.

Yeah, I agree and The Ruck Shop swears by the A12 cam but per the chart it looks pretty stinky.

I thought we (Chinese scoots) had the A9 in as the stock cam but of course mine isn't marked.

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Posted

I thought we (Chinese scoots) had the A9 in as the stock cam but of course mine isn't marked.

according to ParstForScooters, they should be labeled as such:

  • A8 = HA
  • A9 = HB
  • A10 = HC
  • A11 = HD
  • A12 = HE
  • A13 = HF
  • A14 = HG
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Posted

Thanks Piston,

I will check tomorrow when riding if the RPM's drop off. I just know she is kicking booty off the line right now.

What are the numbers in the left column? (10.0, 10.5 etc.)

Also I see this is based in theory and modeled after a 155cc engine, but theory always helps real world testing.

I have so much to upgrade already and my summer is running out of time, which sucks. I think the filming gets in the way of the work but I just want create a guide to upgrading without others wasting their $$$.

From your pic I see you have a flat slide carb. which is beautiful by the way.

What is the difference between a 28 or 30mm flat slide and a CVK? besides the auto choke?

Does flat slide "actually" perform better?

Hey Kachi,

The numbers on the left should be a measure of power such as Horsepower of Kw.

Concerning the RPM's, you wont see them drop off, the engine will rev, but what the graph is saying here is that at higher revs, the engine produces less horse power.

That's why from the graph, I would choose the A11 as there is more area under the power curve from the start (I know the graph only starts from 6000rpm) of the curve till around 8500rpm as compared to the A9.

Even though the A9 has slightly more after 8500rpm, both of the curves fall off the same and I would prefer to have more HP lower in the rev range. This is where your gear choice comes in to play.

Because power drops off considerably after 8500, I would run my calculations for top speed with the engine somewhere at 8000rpm for my desired top speed so I know the engine is most capable (or has the greatest potential) to pull that taller gearing I install.

I run a flat slide carb and I love it. So again there is massive theory behind both style of carbs and though I have good knowledge of both I don't think I can do it justice. Basically due to the working principle of the CVK, which works on pressure differential to lift the slide, it takes a longer time to react as compared to the flat slide/ round slide/ D slide carbs which use the throttle cable to lift the slide directly. The response if quicker. Also in my experience, CVK carbs are very forgiving on the rider.

For me I prefer it as it is easier to work on, I don't have to worry about tearing the diaphragm, I hate that autochoke enrichment garbage.

 

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Posted

Does anyone know if the A14 delivers more HP from 4000-6000rpm? It seems that it might.

M

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Posted

Something to keep in  mind is that these sorts of gearing charts and calculators work quite nicely in manual geared systems. You record the various gear ratios along the drive train along with the drive wheel OD, calculate and have a accurate answer - if the engine is spinning x rpm's then the machine is going y mph. But these GY6 machines have basically a second transmission, the CVT, which has infinite gearing. That can schew the math.

I used to have a calculator that I made up for snowmobiles, same sort of thing, but I couldn't get any where trying to include the CVT ratio's.  I decided to consider the CVT only at the 1:1 ratio which essentially ignores it from the equation. But if the CVT can actually up shift beyond the 1:1 (I don't know if these can or not) that will add to the top speed if it can pull it.

The other thing with the CVT is the Torque Sensing feature of the driven pulley (angled slots) . For example the Torque Sensing will see a higher geared gearbox as an additional load and try to counteract it by forcing a lower gear ratio within the CVT.

Of course this is theory and how much of it translates to real world I don't know. I'm not sure if these smaller CVT get as much impact from the Torque Sensing as the larger CVT's.  That's why testing is so important.

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Posted

You are very right here SD12, when I go about doing calculations for gearing, I always assume the CVT as a 1:1 ratio (or constant ratio).

The main reason for this is at top speed even though the CVT has a given ratio, the engine is running all out and if we only consider the effects of changing the gear set, the CVT gear ratio will remain unchanged with the engine wide open and therefore we can eliminate if from our calculations as a factor.

You are on point about the "torque sensing " aspect of the CVT also, but again I think that torque sensing feature of the CVT goes out the door when we talk about top speed. I'm not talking about the whole run from a dig, but only up at the top of a run.

It would be great if someone could do a write up of the theory behind the CVT on the GY6 engine and the working principles of each component and the effects of changes in the system.

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Posted

The torque sensing is in play from bottom to top.. Physics would dictate that the load presented to the driven pulley would increase with speed.

I actually find it easier to think of it as load sensing rather than torque sensing. But either way the amount that the load is leveraged against the driven pulley movable sheave is affected by the  angles of the slots. So if  the slot angles vary (curved) then the sensing impact will change throughout the CVT shifting.

Basic CVT tuning can cover up some of the torque sensing parameters and I think that some folks may be "washing out" some of the TS benefits by over tuning the flyweight/contra spring setup.

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Posted

Thanks Piston,

I will check tomorrow when riding if the RPM's drop off. I just know she is kicking booty off the line right now.

I will pick up an A11 also though.

What are the numbers in the left column? (10.0, 10.5 etc.)

Also I see this is based in theory and modeled after a 155cc engine, but theory always helps real world testing.

I have so much to upgrade already and my summer is running out of time, which sucks. I think the filming gets in the way of the work but I just want create a guide to upgrading without others wasting their $$$.

From your pic I see you have a flat slide carb. which is beautiful by the way.

What is the difference between a 28 or 30mm flat slide and a CVK? besides the auto choke?

Does flat slide "actually" perform better?

Couple notes on the Flat slide, if considering you may want to work your way up from a Round Slide first as you may find is easier to jet having no experience, many jump directly to the biggest badest and have with little to no experience and have a hell of a time getting a Flat Slide jetted correctly, everything I rode as a kid and growing up had Round Slides on them two or four stroke and we rode mostly two stroke back in the day. if ya messed up the wrong way on the two stroke ya stuck a piston so we learned how to jet or pay the piper. So the Flat Slide thats on my KX was a easy transition for me.

Yes the Flat slide is the snits but how much more on a GY with your combination over a easier to tune Round Slide?  probably not that much to nada for the jackin with it..

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