Predator 79 Transmission Options?

Not open for further replies.


Local time
11:47 PM
Oct 12, 2015
United States
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:
Links to eBay may include affiliate code. If you click on an eBay link and make a purchase, this forum may earn a small commission.
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.
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.

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.
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?


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.

This is a flimsy illegal motorcycle with poorly done gear ratios?

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
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?

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
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:
Not open for further replies.