Help W/ Torque Converter

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exd3686

New Member
#1
#1
Howdy,

Been lurking here for several years and learning a lot. I'm about to build up an (adult sized) mini bike using an American Racer 215 kit with 8" wheels (16" diameter). I hope I can build this to reach 45mph or faster. I'm 275 lbs and will mainly be driving on flat pavement but it will see some dirt/grass and hills as well. Given my weight and riding, I assume that a Torque Converter will be a necessity.

To push me and the bike, I'm planning on using a 6.5HP Predator with governor removed and built out to Stage 2 including billet flywheel & billet rod. From all that I read, this set up will get me past 5500 RPMs and produce much more than the 6.5HP.

Given the specs of the GTC TC2 30 series torque converter to fit the 3/4" shaft and lower end HP limits, can this unit handle the RPMs and HP that the modded engine puts out? If a 40 series is recommended, I assume they make them to fit the 3/4" shaft? I noticed that GTC does not make a 40 series with a backplate and built in jackshaft so I would need to fabricate a jackshaft (which is out of my league) or look at a different torque converter manufacturer. What tooth # sprockets should I aim for on the Torque Converter and rear axle to achieve my speed and riding goals?

I'd appreciate your experienced input and suggestions.

Thanks,
exd3686
 
chrisr

chrisr

Active Member
#2
#2
the 30 series should work ok for your application. The 40 series typically do not come with a jack shaft setup as a bolt on set like the 30 series.
 
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exd3686

New Member
#3
#3
Chrisr,

Thanks for the quick reply and your input. You don't think I'll destroy the 30 series or shred belts consistently running the modded Predator 212? From reading I may be able to get 13HP and over 5500 RPM with the Stage 1 and 2 mods. I was thinking a 10T sprocket on the Torque Converter and 54T on the axle...or should I go with something closer to 6:1 ratio?

Thanks again!
exd3686
 
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exd3686

New Member
#4
#4
CORRECTION to Original Post - I did find that GTC makes a 40 series (Model TC2 1004) with a mounting plate and cover but it uses a 1"engine shaft instead of the 3/4" shaft on the Predator 212. Maybe a 3/4 to 1" shaft adapter sleeve can be used? I wonder if the plate mounting bolts will line up with the 212?

Also, I see GoPowerSports has a 40 Series with a mounting plate but its out of my price range.
 
chrisr

chrisr

Active Member
#5
#5
The 40 drivers are 1" whereas, you can get the 44 which is 3/4", but typically the 44s are more money. I have many adult size bikes with both 30 and 40 and the 40/44 are good up to 16 hp and the 30 they rate up to 8 hp; even though many run more than 8 hp and they seem to last if the gear ratio is ok. The 54t rear sprocket is a good all around sprocket which would allow you to run a 8 - 14t on the 30 series driven 5/8 jack shaft. This combo would give you a wide range of gear ratios depending on if you want top speed or hill climbing along with a 30 clutch setup which is reasonably priced and easy to install. Lots of options depending on what works for you.

https://www.bmikarts.com/Go-Kart-Torque-Converters
 
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exd3686

New Member
#9
#9
I'm planning on a 1:5 ratio for the sprockets. Maybe 10 on the Torque Converter and 50 on axle. I'd like to reach 45-50mph. What ratio would those with more experience recommend for a gear ratio?
 
danford1

danford1

#10
#10
5:1, torque converter, 5500 rpm, 16" tire - yes should do 45-50mph provided the engine can actually rev to 5500 under load.
You mentioned stage 2. Does that kit have the Mod2 cam? If so, I suggest you read up on that cam. A lot of people say it is way over rated and not as good as you may think (or were told by GPS). A CL, CM or CS cam is supposed to be better.

The torque converter will amplify your low end tq. Be careful the first time you hammer it out of the hole. It may wheelie and throw you off the back. You should have plenty of grunt for a 275 lb rider. Just go easy on the throttle at first :)

DISCLAIMER: I have not owned a Mod2 cam. I have not owned a CL, CM or CS cam. I am only reporting what I have read on this forum and other forums. Your actual results may vary.
 
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massacre

massacre

#11
#11
today I installed a 53 tooth sprocket instead of the 60 that was on there. I was thinking that the top speed should be higher and was wondering if a smaller sprocket would help. Well, it did help a lot. That and I moved the engine ever so slightly forward. Now the torque converter seems to engage around 2600 and I was able to get the motor up to about 3900 and it was def faster (top speed) with the smaller sprocket.
Bike seems to ride better overall with smaller sprocket.
It doesn’t really get into overdrive though, the driver will get big but the driven won’t get small. I have red driven spring on stock middle setting. Maybe i’ll change it to street setting and see if I can get it to go into overdrive.
 
danford1

danford1

#12
#12
3900 rpm under load? I thought you were going to turn 5500 rpm under load.
What cam did you put in it?

You mentioned the driven wouldn't get small. When you put the red spring in the middle hole, did you wind the spring about a half turn tight before you put the clutch back together? That could be your problem. You Have to pre-load that spring.

This video shows you how to do it.
[video=youtube;kmGY0qsgW4Y]https://www.youtube.com/watch?v=kmGY0qsgW4Y[/video]
 
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exd3686

New Member
#13
#13
Danford1,

Thanks for the input. Maybe I'll start a little slower on the engine mods like listed below and see what kind of power and performance I get.

Remove governor
exhaust
air intake
jet
18lb valve springs
billet flywheel

Any thoughts?
 
massacre

massacre

#14
#14
danford1 said:
3900 rpm under load? I thought you were going to turn 5500 rpm under load.
What cam did you put in it?

You mentioned the driven wouldn't get small. When you put the red spring in the middle hole, did you wind the spring about a half turn tight before you put the clutch back together? That could be your problem. You Have to pre-load that spring.

This video shows you how to do it.
[video=youtube;kmGY0qsgW4Y]https://www.youtube.com/watch?v=kmGY0qsgW4Y[/video]
Click to expand...
I didn’t mess with the driven at all, it came with red spring in middle position and was fully assembled so I just bolted it on.

I remember preloading my Comet driven on my Manco, I disassembled that whole thing driver and driven, cleaned and used the Comet dry spray lube, etc new garter springs the whole 9.

I was able to get it to work a little better today, I might need to move the spring on the driven Question is which direction do I move it to?
BTW this is with stock cam
 
danford1

danford1

#15
#15
You move it to the hole that causes you to wind the spring a little further for more tension.

In post #1 you mentioned built out to stage 2... a stage 2 kit comes with a cam, that is why I was asking.

If you build the engine for more rpm, then you need a better rod. Most people put a billet flywheel on at the same time. You should Also put in some 18lb springs. The stock cam should be good enough for 5500 rpm. Have you tried the 60 tooth sprocket yet? The engine should rev more than 3900, the bigger sprocket will help.
 
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exd3686

New Member
#16
#16
danford1,

I'm very much a newbie so please forgive my ignorance. I am working through the process of figuring out what is and is not needed to achieve certain results, safety, performance, as well as weighing the costs.

Good to hear that I can run the stock cam and the 60T sprocket is a great idea. Would it be good to keep the 5:1 ratio meaning the use of a 12T sprocket on the TC jackshaft?

I appreciate your input and guidance. I'm learning a lot!

exd3686
 
danford1

danford1

#17
#17
Yes. try the 12 tooth and 60 tooth sprockets. You are learning, that is great, awesome, wonderful etc. We all learn and keep on learning.
One way I learned is by experimenting. If you have different gearing options, try them all and see what works best for your type of riding.
Some guys Only ride on flat paved streets, others ride on dirt while still others ride up the sides on mountains over logs and bogs.
Every situation requires different gearing. Experiment and try it.
The stock cam may rev to 5500 rpm, but it won't have much power that high up. You will definitely need new 18lb valve springs, billet rod and billet flywheel. If you remove the governor on a pure stock 212 then try to hold it at 5500 the rod will break first in my opinion. Some say the flywheel will fly apart also. Bottom line, if you plan to remove the gov, then plan on getting a billet rod and billet flywheel. Of course jetting and exhaust header as the stock muffler isn't good for high rpm.
From there, you can build, ride and test, decide if you want to build more or not. Somewhere along the line you should change the carb to either a bored stock or 22mm Mikuni style carb. My vote is 22mm, not stock carb.
Those mods will make a big improvement in power. One of the biggest improvements would be a cam. Please read all about those before you go out and buy one. Don't get sucked into the mod2 as the best cam available, it isn't.
You have to use your brain also when reading cam threads. Keep in mind what type of riding or racing the guys are doing. Someone that is going 80 mph on an 1/8 mile dragstrip will be using a cam that would not work for your set up. Watch a video of those fast guys in an 1/8 mile drag race. Notice how they don't have any low end? They have to use their feet to help them along getting out of the hole. A big cam robs all your low end grunt. You only have high end power. I'm just trying to say don't go buy the biggest and baddest cam you THINK is good. In my opinion, others Will vary, I would say the CS cam or the 216 grind from Dyno Cams. They both are good for 7000 rpm and still have some low end torque. https://www.dynocams.com/item/cl-cs/cl-mod/
You can do a lot to the engine without spending money on having the head reworked or machined. The stock head will work well and with the mods mentioned and will double the stock hp.

You don't have to buy all of this at once. Do it a little at a time. The engine is easy to work on. Start with the rod, flywheel, carb kit, valves springs and header with muffler. Ride it. It may be all you need. If not, you can build it from there.

Be safe.
Danford1
 
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exd3686

New Member
#18
#18
Danford1,

That's the kind of advise I was looking for and needed. Thank you. Too often, I get caught up in the buzz and "tech" talk and then overthink the project. I really appreciate your input and help. I'll get started slow with some minor/safe mods and go from there. I'll post build pics and progress as I build.

I'm actually more looking forward to the build process than the end results/ride. Maybe that's a little strange, but sometimes I enjoy the learning and building more than anything else!

Thanks again,
exd3686
 
danford1

danford1

#20
#20
exd3686, looking more forward to the build than the ride is a common trait among true builders.
True builders like to build, fabricate and make things. Once the project is done, it gets boring. Some sell their creation and build another.
Sometimes some of my builds sit there complete without being ridden. I got more enjoyment out of the building than the riding.
I seem to always have a beater of sorts to ride when I want to ride :)
 
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