So have a very unorthodox question regarding upgrading from a Pred 212 to 420

[Rentalbeef]

Hi there folks! Newbie here and because the situation is so odd I'm not sure there's a concrete answer for it so all best guesses and advice welcome! I've been using this site liberally for help building this so I'm just starting here asking around. So we built a artcar for Burning Man this year and it's using a Predator 212 combined with a torque converter AND a F/R gear box. It's geared down incredibly low because speed limit is usually 5 MPH so really just need the torque to get it moving!



The problem were running in to is after about 5-10 minutes of driving around at 5 MPH you can hear the CVT belt start to whine and it's on the way to exploding. It's definitely aligned properly but I feel the real problem is the amount of weight it has to push and we're just too heavy for it to handle. Here's what it looks like fully put together. If you combine the weight of 2 passengers plus the art, we probably gain a additional 500 lbs. We did get a bigger sprocket that we were gonna switch to to adjust the gearing to see if that helps first.




So my question is do you folks feel upgrading to a Pred 420 and it's upgraded chonkier torque converter setup is powerful enough to solve our problems with what seems to be potential overloading! It is over double the power and like I said, we only need our top speed to be 5 MPH. Or is there maybe a better engine solution period! A GY6 was what was originally in this thing well over a decade ago, maybe that may work better? I'm sure I'm leaving out important info y'all might need to answer the question so ask away and I'll get it back to you asap!

 

[panchothedog]

A GY6 engine is the last thing you want in there. How many teeth on the axle sprocket. If is the original, it might be less than 40. 60 is ideal, and would lower the gear ratio significantly. A 420 Predator will certainly give you more grunt. If you are only looking for 5 mph or so, try a 72 tooth axle sprocket. Looks like your rear tires are tall enough for decent ground clearance. With a 72 tooth, the
212 cc might have enough. You want 10 tooth on the drive sprocket.

 

[BrownStainRacing]

Hi there folks! Newbie here and because the situation is so odd I'm not sure there's a concrete answer for it so all best guesses and advice welcome! I've been using this site liberally for help building this so I'm just starting here asking around. So we built a artcar for Burning Man this year and it's using a Predator 212 combined with a torque converter AND a F/R gear box. It's geared down incredibly low because speed limit is usually 5 MPH so really just need the torque to get it moving!

View attachment 142017

The problem were running in to is after about 5-10 minutes of driving around at 5 MPH you can hear the CVT belt start to whine and it's on the way to exploding. It's definitely aligned properly but I feel the real problem is the amount of weight it has to push and we're just too heavy for it to handle. Here's what it looks like fully put together. If you combine the weight of 2 passengers plus the art, we probably gain a additional 500 lbs. We did get a bigger sprocket that we were gonna switch to to adjust the gearing to see if that helps first.

View attachment 142019
View attachment 142018

So my question is do you folks feel upgrading to a Pred 420 and it's upgraded chonkier torque converter setup is powerful enough to solve our problems with what seems to be potential overloading! It is over double the power and like I said, we only need our top speed to be 5 MPH. Or is there maybe a better engine solution period! A GY6 was what was originally in this thing well over a decade ago, maybe that may work better? I'm sure I'm leaving out important info y'all might need to answer the question so ask away and I'll get it back to you asap!

There's a couple small things that I see that will help.

Is the driven pulley a 6" or 7" ???
The 7" has a lower gear then the 6". And will move more weight then the 6" at the same rpm.

Can you fit a smaller sprocket on the gear box?????
A 8t would work best for pulling weight. The smaller the better.

What axle sprocket are you planning on adding???

The yellow spring for the driven is the strongest spring available for the 30 series, and will hold low gear longer then the red or green spring.

You can move the driven spring over to the farthest hole, counter close wise.
This will keep the driven in the lowest gear longer, allowing the engine to make more torq, before it starts to shift.
It probably won't shift at all at 5 mph with the yellow spring in the most resistant hole, but that's good for you, and will get the most torq to the tires at the lowest rpm.

You can install white driver springs to bring the rpm engagement up to where the engine makes more torque before it starts to move the weight.

2 white springs will let the engine rev to 3100 rpm, with the STOCK zinc weights, before it engages the belt, and that's closer to peak torque then the stock 2200 rpm springs.

Thats probably 2-3 more ft/lbs of torq at 3100 rpm. It dont sound like much, until you calculate the gear reductions.
And that could be 50-60 more ft/lbs to the axle, before it starts moving weight.

Don't bother with the gy6.

The 420 would be ideal, but the cost would add up quickly.
I'm not sure if that gear box would handle the torq of the 420, and those big block gear boxes cost 2-3 times more then the small block gear boxes.

I think the small block hemi you have will work for your needs.
You are jus gonna have to use gear reduction and TUNE the t/c to help the lil engine out.

Heres what I would do

8t sprocket on gear box
60t on axle, if you have the space for it.

Aluminum flyweights for the driver with stock driver springs for a 3300 rpm engagement.

7" driven pulley
Yellow driven spring, in farthest hole counter clockwise.

Take the throttle stop screw out, and set the governor rpm to 4200 MAX.

With the gear box ratio included, this set up would give you a 30.5:1 low gear, that's hitting the axle with about 125-150 more ft/lbs then you have now.

On a regular buggy style kart, a 30 ft/lb increase is a HUGE gain when pulling up outta the hole, and less wear and tear on the drive train.

This site has the part numbers for for the t/c the parts I mentioned.

Comet 30 Series Torque Converters | Comet 30 Series Parts

Comet 30 Series Torque Converters for 3 to 8hp Go Karts and Mini Bikes. Comet 30 Series Clutches, Driven Pulleys and Comet Parts. Technical Information.

www.gokartsupply.com

 

[Denny]

Neither of you guys asked the important question. I thought I taught you both better. What brand of drive belt are you using? Because it sounds like you are using cheap ones and they only last minutes as opposed to months of a Genuine Comet! Go to the GoKart Supply website and look up CVT for the proper care and feeding instructions along with measuring for the correct belt! You can also play with belt length for limiting top speed. Lots of tricks if you read between the lines.

 

[Denny]

Would a 420 or bigger with a 40 series CVT be better? YES! Is it necessary? Not really!

 

[BrownStainRacing]

Neither of you guys asked the important question. I thought I taught you both better. What brand of drive belt are you using? Because it sounds like you are using cheap ones and they only last minutes as opposed to months of a Genuine Comet! Go to the GoKart Supply website and look up CVT for the proper care and feeding instructions along with measuring for the correct belt! You can also play with belt length for limiting top speed. Lots of tricks if you read between the lines.

ABSOLUTELY!!!! I agree 100%.

All the good stuff don't mean a thing without a good belt.

 

[Rentalbeef]

ABSOLUTELY!!!! I agree 100%.

All the good stuff don't mean a thing without a good belt.

Good call about the belts and good to know about prepping them! We were on last minute before finishing so we just got whatever Comet knockoffs Amazon could get to us in a day. Gonna make that the first purchase plus going through the break in process!

As to all of the rest of the good info in here, we just got home yesterday and everything is still on the trailers. I'm gonna get with the other co-project lead and go through what we have currently as far as gearing and what we need to adjust in regards to the advice in here. Will come back with a update tomorrow with exact details of our setup.

 

[Denny]

If you did not use a Comet belt that’s more than likely your whole problem then! Let us know.

 

[Rentalbeef]

If you did not use a Comet belt that’s more than likely your whole problem then! Let us know.

I'll give it a shot! That said one last thing I was thinking about last night was I definitely undersold the amount of weight on this thing. With 2 people, plus art, plus 80lbs from coffee we'll be transporting, it's probably closer to 7-800 lbs of extra weight. I'll go ahead and just order the comet belt and get that on there and see what happens and hey! Easy fix if so!

 

[Denny]

How much total weight are you trying to move? Just curious?

 

[Rentalbeef]

How much total weight are you trying to move? Just curious?

I think around the 7-800 is the most. The art itself is probably between 3-400 lbs (probably closer to 300 and I'm just being careful by over estimating, think I'll try to get it weighed out tomorrow), then add 2- 200lb folks, and then 2 coffee crafts which are 40lbs a piece filled so that's about what we're looking at total weight.

We can potentially fit 3 folks in to ride but it's a tight squeeze and unless they weigh around 100lbs we're worried about overloading the suspension and frame beyond what I wrote above. So long answer longer, about 800lbs is what we're trying to keep it at.

 

[Denny]

About how much does the kart weigh alone? Pictures might be helpful in this instance.

 

[Rentalbeef]

I'm heading up there tomorrow Denny, I will see what I can do about getting you a weight range but if I had to guess about 200 -250 lbs? 2 people can lift it off the ground with some difficulty, 3 could move it reasonably easy. Here's a better pic front and back.




Comet belt has been ordered in addition to a 8 tooth sprocket and yellow springs. I'm PRETTY sure the new sprocket that was purchased is a 60t. I'm ok with going ahead and doing this because there were times we were starting to creep over 10 MPH when we weren't paying attention so I'm ok dropping top speed down lower for torque trade off (I think that's how it works from how I'm reading y'alls posts)

 

[BrownStainRacing]

I'm heading up there tomorrow Denny, I will see what I can do about getting you a weight range but if I had to guess about 200 -250 lbs? 2 people can lift it off the ground with some difficulty, 3 could move it reasonably easy. Here's a better pic front and back.
View attachment 142027
View attachment 142028


Comet belt has been ordered in addition to a 8 tooth sprocket and yellow springs. I'm PRETTY sure the new sprocket that was purchased is a 60t. I'm ok with going ahead and doing this because there were times we were starting to creep over 10 MPH when we weren't paying attention so I'm ok dropping top speed down lower for torque trade off (I think that's how it works from how I'm reading y'alls posts)

When you say "yellow springs", what did you order???

Theres a yellow spring for the 30 series driveN.

And there's yellow springS, for the 30 series driveR.
You can mix the driver springs to fine tune the engagement that best suits you needs.

Here's the driver spring chart for engagement rpm with the different flyweights.

https://support.ombwarehouse.com/hc/en-us/articles/115006549267-Comet-20-and-30-Series-Spring-Engagements

 

[Denny]

So in reality you are pushing about 1,000lbs.

 

[Denny]

How did you increase your gearing? Multiple jackshafts? We will also need to see all of this. Rear tire size is also important.

 

[Denny]

I have a feeling you also have a gear ratio problem also from the one picture I was able to pull up. (Crappy internet service)
You may be geared more for 30 mph than 5. With that kind of weight and speed the weak link becomes the belt then.

 

[Rentalbeef]

When you say "yellow springs", what did you order???

Theres a yellow spring for the 30 series driveN.

And there's yellow springS, for the 30 series driveR.
You can mix the driver springs to fine tune the engagement that best suits you needs.

Here's the driver spring chart for engagement rpm with the different flyweights.

https://support.ombwarehouse.com/hc/en-us/articles/115006549267-Comet-20-and-30-Series-Spring-Engagements

Comet 216168A - Single Pack "Yellow" 30 Series Driven Clutch Torsional Cam Spring, 30 Series/TAV2 Yellow Cam Spring.

Belt Palace, Replacement belt Store

beltpalace.com

That's the one! Not sure which series it is though from the description. Also, I checked and it is a 60 tooth sprocket that we're moving to.

Denny I checked and atm, the very first photo at the top of the page is the best shot I have of our CVT setup but it's pretty much stock torque converter to the F/R Gearbox and then the gearbox sprocket (10 tooth) chain straight to the axel sprocket (40 tooth) so you're probably right about the gearing being higher to 30 than 5. Overloading was my original guess and it's starting to look confirmed. Gonna try some of BSRs suggestions and tweak some parts for torque and RPM engagement and see if that helps.

If that doesn't help then it'll be time to deep dive and effort in to properly gearing it down, which isn't ideal but hey, learning a new skill at least! Burning Man is over so we're not on a time crunch anymore and it's looking like January will be the next time it'll get brought somewhere with the intention of heavy use.

 

[Denny]

Hold on before you do anything. You MUST get the gearing straightened out first! With current gearing you’re so far away from what you need the belt probably blew up just thinking about it. You have a 4:1 gear ratio now, you need closer to 12:1. Maybe even more. To achieve that you would need to add at least one jack shaft and go 10 tooth to 60 tooth at least twice.

 

[Rentalbeef]

Hold on before you do anything. You MUST get the gearing straightened out first! With current gearing you’re so far away from what you need the belt probably blew up just thinking about it. You have a 4:1 gear ratio now, you need closer to 12:1. Maybe even more. To achieve that you would need to add at least one jack shaft and go 10 tooth to 60 tooth at least twice.

Gotcha and will do! Welp, off to google and youtube!