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

[Denny]

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

Now you’re thinking! Also go to GoKart Supply and check out their excellent tutorial on the care and feeding of a CVT and gear ratio calculators.

 

[BrownStainRacing]

Now you’re thinking! Also go to GoKart Supply and check out their excellent tutorial on the care and feeding of a CVT and gear ratio calculators.

Jus a heads up, that gear box has a 1.3:1 forward gear reduction.
That's a total of 3 gear reductions.

Another jackshaft would work better for more gear, imo.
But can he move the axle sprocket for another jackshaft???

I still havnt figured out if he has a 6" or 7" driven.

6" is 2.7:1 low
7" is 3.13 :1 low

There's gonna be around 40 ft/lbs of torq difference to the axle, if he goes with what he has and 60t/8t sprockets.

It's definitely an interesting build, I like low rpm grunt.

I getting too old for that screaming high rpm hp anymore.

 

[Big Bob]

Being you are at Golf Cart weight maybe a golf cart drive? 780 seris stuff.

 

[ezcome-ezgo]

If it was me I would put the largest sprocket I could find and that would fit on the axle.

 

[bob58o]

I mean if you are trying to do 5 mph at 3600 RPM with 22” diameter tires…

You would want an overall 40 :1 reduction from crankshaft to axle.

10T on a clutch to 60T on a Jackshaft.
10T on other side of jackshaft to 60T on axle.

36 :1

 

[bob58o]

If the CVT doesn’t work out, perhaps try a 10T clutch and a 60T sprocket on the input of the gearbox (not sure what adaptalators are needed), then a 10T on the gearbox output with another 60T on the axle.

I’m not sure the reduction ratio of the gearbox.

1.3 :1 ?

So maybe something like a 10T to 48T and then a 10 T to 60T.
1.3 x 4.8 x 6.0 =

37.4 :1 overall ratio
Mossy slow 6.3 mph at 3600 RPM with 22” tires

 

[MTScott]

I'm sure I'm repeating what others have said, but, 1000 lbs should not be a problem for that engine or TC to move it at 5mph, IF your gearing is correct. The issue is more likely that you're having to run it right on the edge of converter engagement to go that slow, which is what is going to kill your belt. To do it right, your rpms will have to be ramped up while moving that slow.

This engine can run a 25 ton log splitter... to crawl at 5mph you should be fine. The 420 won't solve your gearing and belt destruction issues... it might just make them worse.

Also, I'll second getting a comet brand belt.

This tool is helpful:

Go Kart Gear Ratio Speed Calculator

www.bmikarts.com

If you have the same forward/reverse transmission I do, you'll divide your clutch side sprocket by 1.3.... because the transmission gears it down for you, not up. So a 10T sprocket is effectively 7.7 teeth for the calculation. With 22" tires, 7.7T -> 60T comes out to 25mph at 3000rpm (I think you should try for no less than 2000 rpm continual speed). You will need more gearing.

You'll have to find the biggest sprocket you can put on your axle and not have clearance issues, and the smallest that will effectively work on the transmission. 85T (the biggest 41/420 I can find) would put this setup at 14-17mph for 2500-3000 rpm. If you drop to a 8T sprocket in the driver, it goes to 11-14mph for 2500-3000 rpm. I don't like such small sprockets, but maybe it'll work for this. That still doesn't get you where you need to be for 5mph... even 2000 RPM is 9mph. The lowest engagement for most of these TCs is 1600rpm. If you're at a lower RPM, you might not reach the full 1:1 ratio on the TC-Driven pulley, which may also help your gearing. The ratio from the TC starts at 3:1 and works its way to 1:1 (I would guess by 2500 rpm in a standard setup, but I don't know for sure). At 2K you might have a 2:1 ratio out of the TC/Driven pulley, so the 85T sprocket with a 8T on the transmission might work.

So, get that 85T and slap it on, it may work with the TC gear reduction. If that doesn't work, you might have to look at building a jackshaft after the transmission for an additional gear down step.

No question, I'd get the absolute biggest axle sprocket you can find and go from there.

P.S. A warning on that transmission, they are not exactly 5/8 they are metric and 16mm... oh so slightly bigger. 5/8 sprockets will not slide on. I went to a different sprocket on my transmission, and I had to get creative to bore it out enough to fit on the output shaft (emory cloth glued to the perfect size, fuel line, and a drill), and also had to grind it down to fit the width. The key slot had to be filed wider as well. Unless you want to go through that headache, you might want to stick with the sprocket options that came with it.

 

[Rentalbeef]

Jus a heads up, that gear box has a 1.3:1 forward gear reduction.
That's a total of 3 gear reductions.

Another jackshaft would work better for more gear, imo.
But can he move the axle sprocket for another jackshaft???

I still havnt figured out if he has a 6" or 7" driven.

6" is 2.7:1 low
7" is 3.13 :1 low

There's gonna be around 40 ft/lbs of torq difference to the axle, if he goes with what he has and 60t/8t sprockets.

It's definitely an interesting build, I like low rpm grunt.

I getting too old for that screaming high rpm hp anymore.

So we've all been decomping and not even wanting to look at the artcar and I'll be honest, I didn't realize the thread had moved to the second page so I'm just now seeing these comments. Sorry about the delay! We have a 6" drive on the cvt. The rear tires are 18".

Here in the next week we're gonna convene and take a look at options. One of the worries is there not being room for a jackshaft but we'll just have to get the tape measure out and see what we can find. I think we just need to flip the axel to the other side since our rear brakes aren't working right now (Caliper locked up but we're so heavy we still stop hilariously quickly. Fronts still work)


So we don't HAVE to have it down to 5 MPH for the top speed, really at this point we just want it and the gearing low as possible. Really the main goal is to keep belts from exploding.

This above is what we're aiming at right now at the bare minimum for what we're gonna modify and if we can't fit a jackshaft, might just have to try and see if it'll work. I'll look up the 85 tooth and see if we can make that fit. That would put us at 10.5-1 and that's pretty solid gearing. This is worst case scenario.

Ideally I wanna do a jackshaft to go from 8-60 and then 9-60. That's gonna put us down close to 10 mph range. I know we'll have more than enough torque and be geared at that point and I'd like to think that between that, the Comet belt, and some of the part tips (I've already purchased the yellow CVT spring and some other parts to keep the CVT engagement down) it's enough to handle the weight........ I hope. We'll see!

I'm back so any more questions hit me!

 

[Rat]

P.S. A warning on that transmission, they are not exactly 5/8 they are metric and 16mm... oh so slightly bigger. 5/8 sprockets will not slide on. I went to a different sprocket on my transmission, and I had to get creative to bore it out enough to fit on the output shaft (emory cloth glued to the perfect size, fuel line, and a drill), and also had to grind it down to fit the width. The key slot had to be filed wider as well. Unless you want to go through that headache, you might want to stick with the sprocket options that came with it.

I'm pretty sure they're 15mm because 5/8=15.88mm and I know a large number of the Tav2 and misc Comet clones (like GTC) use a 5/8" jackshaft through the back plate bearings, then stepped to 15mm for all the running gear.
(I suspect some may in fact also be 16mm stepped to 15mm as much as 16mm or 17mm stepped to 5/8")

I know what you mean by being a PITA though because I had to turn the profile down on a 9t for #41 chain to fit a 415MX chain as well as hone the bore a bit and polish a few lumps off the shaft because it simply would go beyond the threads... keyway matched at least

 

[Rentalbeef]

So just wanted to give this a proper epilogue and ending. Finally quit being burned out and got to work on this thing last week. It has all of the art on it, I drove it for 40-ish minutes today and no signs of belts exploding so problem (so far) seems to be solved.

Found out with one person riding it, plus the art, it weights between 1000-1100 pounds so that's what we were working with. Did a few main changes to fix the belt problem as per this thread.

Gearing of course, though it ended up not being as drastic as I feared. Thankfully didn't need a jackshaft. Changed to a 8-60 tooth sprocket. Can definitely tell the top speed is lower and more umph.

Did a deep cleaning, polishing, and dry lubing of the required parts of the CVT as per Comets instructions. There was exploded dried crappy amazon belt that had melted in to both pullys so the remains got gently sanded off. Which on that note, the Comet belt is a beast. Y'all weren't joking about the quality. After driving today it still looks pretty new. Also hasn't exploded so definitely happy about that. I have a spare and I'm gonna order 2 more just in case for the next event.

Changed to aluminum fly weights.

And I know the gearing is a big reason for helping but just as a feel thing, I can't understate just how helpful changing the compressions spring to the Yellow/gold. It's no longer a balancing act trying to fumble with the gas pedal to keep it in low gear. I have to floor it to get this thing in to higher gear and since speed is the opposite of what I'm going for, perfect.

Need more testing, but the one remaining problem is pretty sure it's a one person rider. We did a quick lap with 2 people riding and that extra 200 lbs started making the engine struggle a bit when it didn't chug whatsoever before. Which sucks cause one of the fun things about having this kind of thing is giving people rides but oh well. I bought a 80 tooth sprocket that I feel would solve the problem and could potentially install that instead but it would involve heavily modifying the engine mount (again ) and just not sure I care that much at this point. I'm just happy it's not a paperweight anymore.

Anyways, thanks for all the help, it seems to be a-ok now. There's oil coming out of the breather but apparently that just means it's over filled so I'm not gonna worry about it. Here's a photo someone took of it cruising across the playa the short time it actually worked out there lol.

 

[Rentalbeef]

Oh and forgot about this little note. Ordered the correct comet belt only to discover that the CVT we bought off Amazon was NOT 7" between the drives. Infact it was a whole 3/8s shorter than the product specs said which means the smallest Comet 30 series belt was too big. So that was a night of modifying the engine mount and F/R gear box so the damn belt would actually fit. Not the worst problem but super annoying.

 

[Rat]

Oh and forgot about this little note. Ordered the correct comet belt only to discover that the CVT we bought off Amazon was NOT 7" between the drives. Infact it was a whole 3/8s shorter than the product specs said which means the smallest Comet 30 series belt was too big. So that was a night of modifying the engine mount and F/R gear box so the damn belt would actually fit. Not the worst problem but super annoying.

Most of them seem to be 6&15/16 center to center, which is precisely what the smallest genuine Comet belt fits but it doesn't sound like you're using the backplate. Don't forget, new belts are just a b★tch, and will seem a hair too small until you get a good run on them to loosen up the fibers... they're just stiff.

At any rate perhaps you need to find an older UTV.
I say this because I was given one [it was an eyesore wanted gone and partly as a test of my skills].

Its a 2006 Kawasaki Mule 3010 4x4, and I do have a thread on here as I'm going through it... it single biggest issue is neglect because it took nothing but fresh gas being gravity fed for it to gag and sputter to life, of course it fairly promptly clogged the carb.
After some work it now runs great drinking fuel from it's own original fuel tank.

I got side tracked, my reason for suggesting it is that it has a curb weight of 1366lbs, supposedly can drag 1200lbs, and power is coming from a 617cc liquid cooled Vtwin engine rated at 20hp with gobs of torque [FD620D] and basically the same giant TC that Kawasaki put on their Club Car golf kart engines also found on many if not most old snow sled.

I think something like what you built might go a lot smoother and do exactly what you originally wanted with something like an old mule stripped from the top down to the rails.

I have the gearbox speed limiter disabled, and it's not exactly slow in high gear, but low gear won't do more than maybe 5 or 10mph just for how it's geared... but it just might climb a wall

 

[Rentalbeef]

Most of them seem to be 6&15/16 center to center, which is precisely what the smallest genuine Comet belt fits but it doesn't sound like you're using the backplate. Don't forget, new belts are just a b★tch, and will seem a hair too small until you get a good run on them to loosen up the fibers... they're just stiff.



I think something like what you built might go a lot smoother and do exactly what you originally wanted with something like an old mule stripped from the top down to the rails.

Yeah we used the backplate as a template but we made a custom gearbox/engine mount and then tossed it. Which was a lot of work but helped in the end when it came to fixing the center to center issue cause the framework was already there to be modified. Only took about 2 hours.

That mule sounds nice but the amount of work that would have to go in to re-arting it out and rewiring it would be a repeat of last summer and none of the 3 of us have any interest in doing that again. All of the panels are custom made along with that..... I'll just call it a roll cage, roll cage which is what it all attaches to. If we had to do it all over again I would DEFINTELY change some design choices but it is what it is now.

The fact that it's driving perfectly with all of the art is a huge win and I'm ok with. After sleeping on it I've decided I'm gonna mod the mount to get that 80 tooth on there after all.

 

[Denny]

Wise decision Grasshopper!

 

[bob58o]

80T are better than 60 teeth. Remember you only have to floss the ones you want to keep.

 

[CrazyAirborne]

this is really a cool "kart"! Thanks for sharing!

 

[Big Bob]

Just an FYI. I have a 6 seater golf cart with a 440 Duromax engine. It's modified. The gear ratio is very low on this heavy cart. I use a 780 series Comet driver. At about 5K rpm it is doing 22-23 mph. I hauled 6 people around the other day, I figure at least 1,000 lbs of human beings! Can't tell the difference with that load or me solo in it! LOL

You built a cool project!