Trouble with the chain slipping

[BrianI]

Hi All,

Pictured is my go cart with a torque converter (12 tooth gear) connected to a jack shaft (20 tooth gear) whose other end has a 12 tooth gear that goes to the wheel (60 tooth sprocket).

Although the performance is great with the new torque converter, the low-end torque causes the chain to slip at the jack shaft (20 tooth gear); I can see the end which is not "pulling" loosen up and just slip.

The chain at rest is really tight; probably even too tight.

I'm guessing I need a tensioner, but the chain is so short, seems tough to get one in. Also, the standard ones don't have the right mounts. Looking for some ideas what to do (if even the tensioner is the right way to go).

One more problem: I buy the cheapy chain at bmi karts at $2/ft, and I notice that the chain links don't flex well after even a short amount of usage; even when I have it well oiled with WD40. I'm the primary rider, and I'm like 180 lbs, so I know I'm pushing everything, but I am wondering if the quality of that chain is just too poor.

Thanks for any assistance!

[x-bird]

short chain runs overheat and yes, a tensioner on a run like that is just about a no go because of space. You're running 8:1 ratio, what cc engine do you have? If you have the tools and ability, there are two options that might fix the issue by eliminating the short chain run. You could shift the engine back or upwards, move the axle sprocket inline with the driven pulley and chain direct that way. Or you could get rid of the driven pulley mount, raise the jackshaft and put the driven pulley on the jackshaft--this 2nd method is the type used by nearly all the 30 series go kart setups. Both will get rid of the short chain. Depending on the driven pulley shaft diameter, you'd have to drop down to an 8T drive sprocket to get a 7.5 ratio, a 10T would give you a 6:1. My other comment/question would be as to what size sprockets/chain are you using? If it's 50, you can get KMC HD non-oring chain for relatively inexpensive price. just make sure it has the HD on the part number, has thicker side plates on the links.

[BrianI]

Hi X-Bird, thank you for your comments.

I lack the vocabulary to fully understand your comments.

Your method 1: " You could shift the engine back or upwards, move the axle sprocket inline with the driven pulley and chain direct that way"

Do you mean eliminate the jack shaft completely and mount the engine next to the sprocket on the wheel? If that's the case, yes, I'd have to raise the engine up so the torque converter cleared the back wheel. I think I can manage that. I wouldn't have the same low-end torque because I would be eliminating the 20:12 ratio that the jackshaft offers, but maybe the torque converter itself doesn't need it (I had the jack shaft with a centrifugal clutch originally).

Your method 2: "could get rid of the driven pulley mount, raise the jackshaft and put the driven pulley on the jackshaft"

What is the driven pulley mount? Which is the driven pulley?

I totally get the disadvantage of a short chain. I'm using #35 chain, the cheapest I could find; from the pictures you see it is well oiled (because it splatters everywhere). BTW, both chains wear out fast. I will look into the HD chain.

I was thinking I could get this tensioner to fit:
https://www.ebay.com/i/251787455501?chn=ps&dispItem=1

I could mount it to that plate that the engine sits on, and then use a long spring to somehow pull it into the chain to the back of the go cart; always pushing it onto the sprocket from the bottom side of the chain.

The size of the engine is the Predator 6.5 HP.

Thanks again for your suggestions; any more would be appreciated.

[x-bird]

For some reason, yes you have an extra shaft and chain run in your setup than what is typically done with that size engine and kart type. The variable clutch (the driver) and pulley (the driven) is designed to give you a good low rpm pull and still make good speed at the top of the rpm range. the gear ratio you're running likely has cut your top speed by at least 5 mph.

I dug back into my old hard drive (literally hanging from cables off the side of my newish computer) to find a pic of a "typical" setup. Of course it's one area that i took very few pictures of. This is a top view, done to show pulley alignment from the engine to the jackshaft. This particular setup in stock form was a 9 tooth sprocket going to about a 60T if i recall correctly. this is a yerf 3203. the driven pulley and small sprocket going to the axle are on the same shaft, mounted on a plate that can be moved for alingment and tension, as can the engine. The driven pulley has one half of it removed for the picture/to fit the ruler.

[BrianI]

Hi X-Bird!

Thanks for digging through your old PC!

One difference between carts is that yours has a live axle, whereas mine has an axle riding within a tube. I can only access a sprocket bolted to the tire itself. So the jack shaft is also there to help me center the engine. I was also able to slide the engine back, giving me slightly more leg room.

I don't mind the loss of top speed; it was really too fast in my opinion; certainly for my two daughters. Because I ride it mostly on grass, and up hills (not steep ones), low-end torque was my priority.

I'd never buy anything without a live axle again, though.

So I think the picture you are showing describes your first possible solution.

I'm still not sure what you mean with the second one. I think you are suggesting I raise the jack shaft up so that it passes through the torque converter driven pulley (i.e., the one that has the sprocket on it). Then I would be left with only one chain, which is the longer chain. Do I have that right?

Thanks so much for your efforts to explain!

[x-bird]

gotcha on the way the axle sprocket is setup, so that pretty much has you limited in one manner.
for the second option, yes that would be the idea, get it down to one chain/one jackshaft.

[BrianI]

Good news! I found a way to add an $8 chain tensioner. I mounted it directly to the torque converter. Seems to be working, but I imagine I will need to buy a stronger spring.

Thanks again for your help!