Predator 79 Transmission Options?

Discussion in 'Transmission / Drivetrain' started by ColdCruiser, Oct 27, 2015.

  1. ColdCruiser

    ColdCruiser Member

    I'm trying to decide what type of transmission to use on my first build. Seems like the Grubee 4G would have been a good choice but they seem to be out of stock permanently. Ghost Racer 7G might work but appears to be a bargain brand. EZ Q-Matic looks like a very viable option EXCEPT for the $300. That pretty much leaves the Comet TAV2 or the Blast LED. However, they are both 3/4" shaft and the Predator 79 is 5/8" so I bet it would just need an adapter.

    Does anyone have experience with this or opinions about the available options?

    - - - - - - - - -
    $14 Shaft Adapter
    5/8" x 3/4" x 3" Shaft Adapter Pulley Bore Reducer Sleeve Bushing Sheave & Key
    Designed to slip fit on your 5/8" diameter crankshaft with 3/16" keyway and enlarge it to 3/4 diameter with 3/16" keystock.

    - - - - - - - - -

    $99 - Blast LED - Predator 212cc GO KART MINI BIKE TORQUE CONVERTER CLUTCH #40/41 10T or #35 12T
    Compatible on most small engines with horizontal shaft. This unit replaces: Comet 218353A, 219552A, 219456A, 203814A, and 217610A TAV2 30-75 Torq-A-Verters, Yerf Dog Driver Unit Q43201W

    $119 GoPowerSports TAV 30-75 Torq-A-Verter, (Comet Clone)

    $126 GoPowerSports Comet TAV2 218353 Torque Converter
    Works On Predator Engines, 3/4 Driver Pulley, 5/8" Driven Pulley - 6" diameter
    30 Series Asymmetrical Belt Aluminum Backplate with all Hardware, comes with 10T and 12T Sprockets, Belt Guard included.

    $199 - Torq-A-Verter, 3/4" Bore 10 Teeth, #40/41 Chain Torque Converter. Made in the USA

    $289 - Ez Motorbike EZM QMatic Gearbox Drive Transmission with front pulley, belt, and all components needed to replace other brands and types. Belt cover is included.

    !!!NO "Grubee SkyHawk" [China Gas] 4G T-Belt Transmission Available!!!
    $140 - Grubee Skyhawk 4G belt drive torque converter with centrifugal clutch to lower the output RPM`s and raise the torque. 5/8 shaft, 76mm/3inch clutch, 6:1 reduction, 11T 1/2 inch drive Free Wheel output sprocket.

    $149 - 7G Ghost Racer Transmission for 49cc 5/8th STRAIGHT SHAFT ENGINE ($239 w/ hs engine $129)

    $50 Max-Torque 5/8" Pulley Clutch
    Last edited by a moderator: Dec 18, 2015

  2. The_Aleman

    The_Aleman Active Member

    IMHO, you should use a PMR jackshaft and MaxTorque clutch. The combo is about $175-ish, but that can be less or more depending on how you set it up.

    AGK sells one, theirs is set up for 2:1 reduction with a 9T #415 output, allowing for 12.44:1 overall with a 56T rear (22MPH @ 3600, 30MPH @ 5K RPM)
    link here

    You can also change the reduction and adapt it for a SBP shift kit or other secondary jackshaft if you want. Very easy to customize.

    Those torque converters you're thinking about using aren't very good for the 79/99s. They are wide and suck up quite a bit of power. Better for the the 120s and higher.
    Chris Duke and ColdCruiser like this.
  3. ColdCruiser

    ColdCruiser Member

    Aleman, thanks for your reply!

    Why would I need another jackshaft? Wouldn't I just run a chain from the clutch to my SBP jackshaft?
    (picture is not mine but similar)

    What about transmissions like the 4G/7G made for smaller 49cc engines? They don't appear as wide as the others.

  4. The_Aleman

    The_Aleman Active Member

    Figure out what your engine-to-pedal-crank reduction is with what gears you'll be using and then divide 1000 by that number.

    Take a look at that number and think about it for a bit. Double that number and that's how many rpm your pedal drivetrain would be at engine idle.

    This is why you need reduction with a shift kit. Otherwise, you're just building a flimsy illegal motorcycle with poorly done gear ratios.

    Edit: and dangerously useless pedals.
    ColdCruiser likes this.
  5. ColdCruiser

    ColdCruiser Member

    Thanks again Aleman,

    So, just to make sure I'm following along I made a drawing. This is what I've seen people doing and I've wondered about it. I guess the jackshaft gear would need to be very large. This is a flimsy illegal motorcycle with poorly done gear ratios?

  6. ColdCruiser

    ColdCruiser Member


    This image is more like what I originally thought of but I've been confused about what needs to happen between the engine driveshaft and the jackshaft.

    I figured that once I got it running I should be able to adjust the speed/torque by changing ANY of the sprockets. Of course if I could get closer on the first try that would save a bunch of headache.

    I assumed I'd want to use a 9t for ALL of the SM gears. It would be nice if some of the gears I already have will work. The one I don't have (or understand) is the reduction gear you refer to. In this drawing I took a guess and listed a 20t there.

    I'm not quite following along with your engine-to-pedal-crank reduction information. Which number do I need to divide by 1000? I believe the clutch grabs at around 2K and the motor maxes at 3.5K. I have no idea where to start to calculate the reduction. :(

    Are belts & pulleys a better option or should I just stick with chains?

    I would like to cruise along with my dog at around 20-25 mph in 2nd gear, shift to 1st for hills, and 3rd to go extra fast.

  7. The_Aleman

    The_Aleman Active Member

    Oh yes, indeed. That drivetrain would depend solely on the engine, and the pedal drivetrain would spin at absurd speeds.

    It could work great and run fast when the engine is running. But it's no longer a bicycle, really.

    Your second pic with 9T-20T-9T-17T-9T-48T yields an engine-to-pedal-crank reduction of 22.39:1. 1000/22.39 = 44.66.

    1000RPM = ~45 pedal rpm
    2000RPM = ~90 pedal rpm (around engine idle)
    3000RPM = ~135 pedal rpm
    3600RPM = ~162 pedal rpm
    4000RPM = ~180 pedal rpm

    That's still really fast. You'd be out of pedal before the clutch locks up. With pedal gears added:

    1st: 17.91:1 (8.7 @ 2000, 15.7 @ 3600)
    2nd: 13.43:1 (11.6 @ 2000, 20.9 @ 3600)
    3rd: 10.10:1 (15.4 @ 2000, 27.8 @ 3600)

    The overall ratio looks odd, if a bit conservative. 1st gear is tall, while 3rd gear is short. It would probably work okay, however.

    I think more engine-to-pedal-crank reduction and thus less pedal-to-rear-wheel reduction would work better because your engine has a criminally short powerband lol
    ColdCruiser likes this.
  8. ColdCruiser

    ColdCruiser Member

    Thanks again Aleman,

    I'm starting to get it (a little). I took your advice and ordered the jackshaft kit from affordable gokarts. The were out of clutches so I ordered one from mfg supply.

    I figured 15-20 mph is probably fast enough for me and the dog. If I need more power it looks like there are lots of options for the Preddy 79. Namely, a carb kit and removing the governor.


    The clutch is 11t and the reduction gear is 22t. So now I know what all my gears are! Hopefully this moves me in the right direction. I've updated my drawing but I still need to figure out what my reduction is and what that will mean for my riding experience. If I need to make one of my gears larger, the easiest to change is the 17t jackshaft sprocket.

    So, do I understand that I will most likely need/want to put larger gears somewhere. Maybe a 22 where the 17 is?

  9. The_Aleman

    The_Aleman Active Member

    Your updated drawing has a 20.15:1 engine-to-crank. Just under 50 pedal per 1000 engine. That's roflcopter pedal speeds.
    Engine alone it has a tall first gear (9.6MPH @ 2000)and a decent 3rd gear (~30MPH @ 3600).

    Let's say you replaced that 22T with a 33T. Easy to do with the way AGK mounts the 22T. It's like a cartridge sprocket lol
    You'd have quite low gears (20MPH @ 3600). With a 30-18, probably hub-breaking torque under load. The pedal gears must be revised:
    Switch inner crank from 30T to 36T and wheel sprocket from 18 to 15. This removes the overtorque to the hub and regains you your speed:

    1st: 16.79:1 (9.3 @ 2000, 16.6 @ 3600)
    2nd: 12.59:1 (12.3 @ 2000, 22.2 @ 3600)
    3rd: 9.47:1 (16.4 @ 2000, 29.5 @ 3600)

    The overall ratios may seem at first glance to be similar to your previous one. There is a key difference here, however: now your engine-to-crank reduction is 30.22:1.
    That's 33 pedal cadence per 1K engine. At 2K engine, your pedal cadence is about 66. That's like max torque for most people's chevrolegs, so you can accelerate much
    quicker, especially from a dead stop. Climbing hills will be easier, and you can attain better gas mileage by pedaling when the engine needs it.

    Of course, if you remove the governor...41MPH @ 5000 lol
    ColdCruiser likes this.
  10. ColdCruiser

    ColdCruiser Member

    Thanks yet again Aleman,

    I don't think I've encountered any "deal killers" yet so green-light to move ahead. I should get the new jackshafts and clutch in about a week. I can then try to mount it and see how everything is going to fit. It looks like I'm going to be pretty tight on space.


    - With anything close to what I currently have I would have to pedal impossibly fast just to help the motor. Which of course is not at all what I'm looking for, lol. I want to pedal just to get going, help leisurely (if at all), and just Cadilliac around. Want to go regular bicycle speeds with a lot less effort (longer range, cargo, etc).

    - By putting a smaller gear on the rear hub, there is less chance of damaging the hub. Also helps with the ratio.

    - Switch inner crank from 30T to 36T
    $7.95 - Chainring - Freewheel - 36 Tooth [SBP-CR036] ??

    - Switch AGK 22T with 33T ("Easy to do")
    ...33t Sprocket, #35 chain, 5/8" bore??

    1. 30T & 32T are less expensive than 33T. Need to figure out the pitch?
    ~Dia 4.14" Tooth Width 0.168" Length 0.875"

    $12.25 - Tritan Sprocket [25BS32X] 1/4" Pitch, 5/8" Bore, 32 Teeth
    $16.25 - Tritan Sprocket [35BS33HX] 3/8" Pitch, 5/8" Bore, 33 Teeth
    $11.25 - Tritan Sprocket [25BS30HX] 1/4" Pitch, 5/8" Bore, 30 Teeth
    $13.50 - Tritan Sprocket [35BS30HX] 3/8" Pitch, 5/8" Bore, 30 Teeth

    2. Use a chainring adapter and the extra 30t from above??

    $23.95 - Chainring Adapter [SBP-CRA001]

    $6.95 - Chainring - Freewheel - 30 Tooth [SBP-CR030] (HAVE THIS - NOT 33t)

    - Thought: If I replace the 22t with a 33t, should I consider putting that 22t where the 17t is? Would it help? Could I avoid switching the hub gear by doing that?

    "Of course, if you remove the governor...41MPH @ 5000 lol"
    - My ace in the hole. If/when I feel like 30-35. Any faster and I'll just buy a motorcycle (not likely, possibly cheaper though).

    Engine-to-Crank Reduction: 30.22:1
    - 1st: 16.79:1 (9.3 @ 2000, 16.6 @ 3600)
    - 2nd: 12.59:1 (12.3 @ 2000, 22.2 @ 3600)
    - 3rd: 9.47:1 (16.4 @ 2000, 29.5 @ 3600)

    20.15:1 engine-to-crank = roflcopter pedal speeds (50 pedal per 1000 engine)
    30.18:1 engine-to-crank = probably hub-breaking torque under load

    - - - - - - - - -

    Last edited by a moderator: Dec 18, 2015
  11. ColdCruiser

    ColdCruiser Member

    Tight on space...

  12. ColdCruiser

    ColdCruiser Member

    Going to need a different transmission option...

    I'm always a little hesitant to try a new supplier because you never know if you will receive your parts quickly, if it will be missing anything, if it will work, and if you can return it if it doesn't work. On top of all that, it's hard to tell if you're dealing with a rickety operation run from a garage or just what. Generally I'm willing to give people the benefit of a doubt.

    Anyway, I should have known there might be an issue when AffordableGoKarts com didn't stock the clutch they recommended to fit their custom jackshaft, especially since it seems to be the most popular clutch on the market. Not really a big deal, except now I have a max-torque clutch on the way from someone else, but no transmission! :(

    Here's the part that kills me... AffordableGoKarts com WILL NOT SHIP to anywhere EXCEPT your billing address. This does me no good because I live in California but I'm building a bike in Arizona. My billing address does not accept deliveries anyway! Why does every invoice ever printed have both a "billing" address AND a "shipping" address?? BECAUSE I'm not the first person with this setup! I even paid with PayPal who has verified me, my phone, email, hundreds of successful transactions, etc. This doesn't even seem like a real business to me.

    I admit that I'm a bit perturbed by this, maybe others will have a better experience trying to deal with them. Basically, I guess I feel a bit insulted because David Pothe wants me to trust him as a supplier and take the risk of dealing with his business for his profit but is not willing to trust me as a customer even when I pay in advance?? :( <sigh>

    Anyway, it looks like I'll need a different option for the extra reduction gear. Other suggestions?
  13. ColdCruiser

    ColdCruiser Member

    Perhaps one of these...

    $130 (plus $22 shroud) - GTC JACKSHAFT KIT [1201]

    $65 - 1056 - GTC Bicycle Engine Jackshaft Plate, GX120(3.5hp)/160(5.5hp)/200 Lifan(2.5)

    $109 - PMR Jackshaft (13t - 15t)

    $120 - PMR Jackshaft Kit 79-97cc

    $99 - Jack shaft kit only 35 chain
    Last edited: Nov 10, 2015
  14. The_Aleman

    The_Aleman Active Member

    #35 chain is 3/8" pitch, or 0.375". Your clutch will also be #35. You will want at least 3:1 reduction from your transmission (ie: 11T -> 33T). 4:1 is better, really.

    Not sure what you're asking here. Keep in mind that SBP's sprockets are for bicycle chain, 1/2" pitch, 1/8" or 3/32" width chains.

    The 17T will be a 1/2" pitch sprocket. The 22T will be #35. You can only make the 22T work in the 17's place if your transmission output is also #35.

    If you decide you want even more engine-to-crank reduction, we will need to rethink your pedal-side gears again to lower hub torque and increase speed.
    If you replace the 17T with the 22T, you will be increasing reduction, making taller pedal gears necessary. You may need a 44T inner crank to compensate.

    Regardless, you'll want to drop your hub gear to a 15T. You're going to making quite a bit of torque with engine and legs combined, it's easy to overload the hub.
    I have 69.09:1 EtoC reduction on my bike and run 44T -> 15T. Your engine with governor has effectively half the revs of mine, so around 40:1 reduction may be optimal.

    40:1 EtoC = 25 pedal rpm per 1000 engine. The average person pedals between 40 and 80 rpm. With a 44-15 pedal gear and 3-speed IGH you would have:

    1st: 18.18:1, (8.3 @ 2000, 15.4 @ 3600)
    2nd: 13.64:1, (11.4 @ 2000, 20.5 @ 3600)
    3rd: 10.25:1, (15.2 @ 2000, 27.4 @ 3600)

    38MPH @ 5000 no governor

    Slightly lower gearing, but now with a considerable torque advantage. Your bike would be a monster with engine + legs. Mine does 0-30MPH in 4 seconds, yours may too!

    Which is why you'll have to test fit things so you know what size gear you're limited to. I switched my 17T to an 18T, I can't fit any larger, for example.

    The GTC plate looks good. You're gonna need to customize the input/output gears on transmission anyway to achieve the reduction you want.

    Don't let AGK get ya down. They can be problematic to deal with. If they are a problem, do business elsewhere :D
    Last edited: Nov 11, 2015
    ColdCruiser likes this.
  15. KCvale

    KCvale Motorized Bicycle Vendor

    Then why the big engine and all the extra work and expense?

    You could have just dropped in a 49cc HS with a 4G right on the SBP JS kit you have installed, they work perfect together.



    No muss, no fuss, and work great with a 3-speed.
    Tom from Rubicon and ColdCruiser like this.
  16. ColdCruiser

    ColdCruiser Member

    That's a good looking ride. I actually had something real close to that in mind. I definitely considered everything I could think of. In retrospect, I probably should have started with a 49. It's still an option if it becomes too difficult this way.

    Honda GXH50
    $225 Honda GXH50QHA 2.5hp Horizontal 5/8"x1-5/8" Keyed Shaft,

    To answer your question...

    I wanted a 4-stroke for less noise and maintenance. The HF 79 is half the cost of the Honda (I thought that mattered somehow). I thought it was an American engine and that seemed like a bragging point. OHV sounded like a good idea. Easy to find cheap replacements. Lots (well some) aftermarket and performance parts.

    I actually DID decide that the Honda (or HS even) with the Grubee 4G setup WAS just what I was looking for. BUT they seem to be non-existent. There have been none for many months. I even came across posts about no availability from YEARS ago. Legal disputes, etc. "They're on the way" and stuff like that is not very reassuring. The other basic kits appear to be cheaper knock-offs of the cheap china kits which knock-off japan.

    The bottom line was that I figured if I build it using the best parts I can, it will last for a decade and I won't have to scrap it and build another one. I usually don't have access to a garage and tools.

    Another thing is I've been worried about the weight of me and the dog. I've put on a few pounds and she's put on a few pounds. Our combined weight is around 300 lbs. It's also a big heavy steel bike with a bunch of gear and pulling a little trailer for my dog. I didn't want to strain the parts too bad. I want to keep up with (or pass) regular bicycles. I don't want to push it up hills.

    Since this is my first one, I really don't know what I'm talking about. The 49 might be able to handle it. As I'm finding out, a lot has to do with the gears.

    It's starting to shape up as a real nice ride but progress has been slower than I'd like, everything is more expensive than expected, and I won't be able to really tell how it does until it's 90% finished. It's kinda fun to build it. I can choose specific parts for everything. It's not too expensive. I have a little budget because it might be my main transportation. This forum and others are very helpful. I enjoy reading and talking about people building these. I've wanted one for 30 years, lol.

    Last edited: Jan 11, 2016
  17. The_Aleman

    The_Aleman Active Member

    If you have to ask that, you're a decent but overrated bike assembler rather than the wise old bike builder you try to portray yourself as.

    You've never fooled me since day 1, FYI. I recall countless threads where you didn't know what the heck you were talking about; fumbling the simplest details :goofy:

    1) The 79 is cheaper, makes at least twice the torque (and down low), very reliable, replacement/performance parts are readily available
    2) The clutch system is far more robust, far less bushing fuss, no bearing mod necessary. Performance parts easy to obtain
    3) The transmission gearing is far more customizeable; the jackshaft system doesn't have to use SBP mount
    4) No waiting for Chinese slow boats for Huasheng or Grubee parts.

    Right about now you might like to advertise your own 10G shifter system. But I'll point out some things about your 10G:

    1) Your 10G has a terribad engine-to-crank reduction ratio, it just overspeeds the drivetrain, pedal is lost under engine
    2) Your system is nearly as wide as a 79 with PMR jackshaft, probably wider if using the 53CC Huasheng
    3) You're stuck with a Huasheng, while a nice little engine, it will lug under 3600 and doesn't have much torque
    4) Your system is supplied by Chinese slow boats, therefore subject to parts unavailability
    5) Your system is proprietary

    Overall the 79 route might cost more, but that should be no surprise. It's not a mass-produced kit; it's much more capable.

    Might as well do it the best you can the first time, right? I mean, get it as right as you can. Many of us keep tinkering even after we're "done" :D lol
    Last edited: Nov 14, 2015
    dave420, Nanonevol and ColdCruiser like this.
  18. ColdCruiser

    ColdCruiser Member

  19. ColdCruiser

    ColdCruiser Member

    I ordered a few new items today...

    - Switch inner crank from 30T to 36T
    I'm not sure how this will play out but I'm willing to give it a shot. (NOTE: The existing pedal/gear ratios are pretty good for easily cruising around at slow to med speeds.) Jim at SBP took a couple of minutes to help me solve a couple issues so I decided to throw him my business. He has 36T-44T, they are each around $9. I ordered a 40T. If that doesn't work out, I can try larger or smaller.

    - Switch rear hub from 18T to 15T
    Sturmey Archer Sprocket 15T x 1/8 - HSL715
    This part number is sold out in America. It's 3 Euros from England but that might take a while or get lost. A couple of US vendors have one but it is priced very high. The 15t and smaller are flat instead of dished. Sturmey-Archer 1/8" 15t coaster brake cog looks like exactly the same thing by the images and description (FW2206/HSL850?). I ordered one. I'll see if it works when it gets here I suppose.

    - Different option for extra reduction gear
    The one AGK was selling is the PBR jackshaft kit with a 22t instead of a 17t. The product literature boasts about all the gears going on the front, so I chose to go with the GTC one instead. GTC has a couple different versions. One seems designed more for a torque converter and has extra flanges. The one I ordered looks more like a flat plate of aluminum with some holes in it. It comes as a kit with bearings, hardware, shaft, and gears. The large gear is only a 17t so it will need to be replaced. I realized that gear goes on the front so there is no shortage of space. I can probably go pretty large there. I suppose I will take some measurements and see if I can find a 44(?). I'll probably have to get a "mini-hub"(?). I'll look into that.

    $120 - 1055 - GTC Bicycle Engine Jackshaft Kit

    I updated my drawing a little...

  20. ColdCruiser

    ColdCruiser Member

    Current progress...