Deep Six the TC (?)

[Iron John]

The TC in our Yerf-Dog 3200 (repowered with a HF Predator 212cc) is OK, but I must say that I am not thrilled with it.

Right up front, let me say that I have read the torque converter sticky and that the advice provided seems spot on.

I have a feeling that we might be a good candidate for deep-sixing the TC and replacing it with a centrifugal clutch.

All of our riding is on asphalt, with modest hills and a few sharp turns, including two U turns that are tight and must be negotiated slowly.

I feel that a properly-chosen centrifugal clutch would simplify things and provide adequate performance.

We are not after top speed with this cart as, IMHO, although we have taken steps to improve the handling and plan to make some more changes in that regard, this will never be a race kart. 30 mph is fine, anything more than that would be gravy but I see no need for it to top 40 under any circumstances.

I understand that I have to select the right clutch based on the wet weight of the kart, gear ratios, tire diameter and so on. I have not gotten to that yet.

My first question is if you pros agree that this might be a good thing to do, and also to enquire about cent clutches that kick in and lock up at specific (low) rpm. I have had good luck with these in the past on a smaller, lighter cart. Would they be a good choice for my Yerf? (My intention would be to minimize some of the seemingly inescapable low-speed slip.)

 

[Doc Sprocket]

As I cannot recognize manufactured karts by model number, I don't know what I am considering. Does it have large tires? How many seats?

While a clutch might indeed simplify things, I can't help but wonder if it is truly worth the cost and effort to convert. New clutch, chain, and quite possibly sprockets- as there's at least a fair chance you'll need to regear. What is your current ratio?

 

[Iron John]

Rear tires are 16" and it has a 60 tooth sprocket. Will an 11 up top be all right?

Single passenger, goofy tall CG.

Photos at post #18 in this thread:

http://www.diygokarts.com/vb/showthread.php?t=18272&highlight=yerf-dog+3200

BTW, a rear axle swap is in the cards. I will be installing a wider rear axle so I can mount dual 16" ATV tires. Gotta Tumbler it out! The TC replacement could be done at the same time, as everything in the rear will have to be opened up any way.

 

[OzFab]

I have to sat that, IMHO, now that you've had a taste of a CVT, I think you will be unsatisfied with a CC; it would be like trading a Corvette for a Pinto (ok, that's extreme but, you get what I mean)

 

[Doc Sprocket]

Hmmm. Knowing what I now know, I gotta say no. With the large tires and all that rotational mass, I really don't think a clutch is for you. Yes, you can get heavy-duty clutches that will tolerate higher ratios, but there's just no substitute for a variable ratio.

 

[Iron John]

For the COrvette vs Pinto comparison, are you talking about less acceleration with a CC as opposed to a TC?

I hate the thought of a wear item like a belt, as well as having the extra hardware (jackshaft, etc.).

So is the only down side less acceleration?

 

[Doc Sprocket]

It's not that simple (to me). It's a fixed ratio vs a variable one. It's comparing a single gear transmission to a multispeed transmission. A fixed ratio requires a compromise, whereas a multispeed transmission gives you a range to work with- no compromise required.

If you're worried about wear, forget it. It's not likely anywhere near the concern you think it is...

 

[Swabbster]

tc is the best way to go, you get a way better take off and just as good top end,

 

[Iron John]

tc is the best way to go, you get a way better take off and just as good top end,

Understood. I am having a problem getting past the crude friction belt and the wear characteristics.

The acceleration is not an issue for my kids and ther friends. Quite frankly, they seem to enjoy it better when the cart slowly goes faster and faster. It makes them feel like they are 'driving' it to go faster. I am happy without on-off switch acceleration. And I do like fewer parts, which usuallly translates into longer times between overhauls. The kids do not enjoy cart down time.

The pros have made a good case for keeping the TC. But I am just not sure.

 

[landuse]

With a axle sprocket of 60 and a clutch of 10, and 16" tyres, you can forget about using a CC. That ratio will be WAAY to high. You are going to need at least a 72T axle sprocket to give you any long term use out of a CC clutch.

IMHO, you will be dissatisfied with a CC over a TC.

There has to be some reason why your TC is not working effectively for you. I suggest that we go through the likely problems, get it working, and forget that you mentioned a CC.

 

[Doc Sprocket]

Well, if it helps-

I CAN tell you from personal experience that when a CVT is properly set up and in good working order, the result is a more than satisfactory experience. It shouldn't go "slowly faster and faster", it should be a fairly rapid acceleration. This is- amongst other factors- a function of the gear ratios being more or less correct.

 

[FatCat]

Understood. I am having a problem getting past the crude friction belt and the wear characteristics.

The acceleration is not an issue for my kids and ther friends. Quite frankly, they seem to enjoy it better when the cart slowly goes faster and faster. It makes them feel like they are 'driving' it to go faster. I am happy without on-off switch acceleration. And I do like fewer parts, which usuallly translates into longer times between overhauls. The kids do not enjoy cart down time.

The pros have made a good case for keeping the TC. But I am just not sure.

You really shoudnt be concerned with the moving pieces. Find a place to mount a spare belt and you'll be fine.(Murphy again, if you have it you'll never need it) If it is setup properly you will hardly ever have to touch it. You can put serious power through a CVT setup without any problems. I love the CVT's myself. Your always in the perfect gear. My buddy's on their quads try talking trash that it's inneficient because of belt slip. While they're letting off to grab another gear im still
pulling lengths. I'd recommend a Comet setup if you want ease of maintenance. They've
been around for years building great products. MADE IN THE USA!
Keep it lubed with Comet clutch lube and enjoy!

 

[Iron John]

With a axle sprocket of 60 and a clutch of 10, and 16" tyres, you can forget about using a CC. That ratio will be WAAY to high. You are going to need at least a 72T axle sprocket to give you any long term use out of a CC clutch.

IMHO, you will be dissatisfied with a CC over a TC.

There has to be some reason why your TC is not working effectively for you. I suggest that we go through the likely problems, get it working, and forget that you mentioned a CC.

The TC is actually working with the stock rear axle setup. I just happen to not like them for the reasons stated and a few more that relate to my own personal bias (I consider a slipping belt and variable pulleys a crude design). That's just me.

So, my thought was that when I swap out rear axles, I also can the TC. Doing so will reduce the parts count, save work, and give me more flexibility in component placement.

I don't mind going to a 72 tooth sprocket if that's what would work best. 20 to 25 mph is plenty for this cart. I can also add a jackshaft - but it might be a chain drive instead of a TC. More work but heck, I am really not feeling the love for the TC.

 

[OzFab]

Send it to me then...

 

[Iron John]

You really shoudnt be concerned with the moving pieces. Find a place to mount a spare belt and you'll be fine.(Murphy again, if you have it you'll never need it) If it is setup properly you will hardly ever have to touch it. You can put serious power through a CVT setup without any problems. I love the CVT's myself. Your always in the perfect gear. My buddy's on their quads try talking trash that it's inneficient because of belt slip. While they're letting off to grab another gear im still
pulling lengths. I'd recommend a Comet setup if you want ease of maintenance. They've
been around for years building great products. MADE IN THE USA!
Keep it lubed with Comet clutch lube and enjoy!

Hmm, you make a good point. I wonder what TC this thing has. The driver is stamped 'Comet' and it takes a 203591 asymmetrical belt, but I was under the impression that Comet clutches had some sort of backing plate. The Yerf setup does not.

Could I have some proprietary TC implementation? Yerf goofed up everything else about the design, I wonder if their TC setup had idiosyncracies as well?

Could someone post a picture of the type Comet setup you would recommend for my cart? I wonder if we are talking apples and oranges.

Here is a shot of what I have:

 

[FatCat]

The TC is actually working with the stock rear axle setup. I just happen to not like them for the reasons stated and a few more that relate to my own personal bias (I consider a slipping belt and variable pulleys a crude design). That's just me.

So, my thought was that when I swap out rear axles, I also can the TC. Doing so will reduce the parts count, save work, and give me more flexibility in component placement.

I don't mind going to a 72 tooth sprocket if that's what would work best. 20 to 25 mph is plenty for this cart. I can also add a jackshaft - but it might be a chain drive instead of a TC. More work but heck, I am really not feeling the love for the TC.

The chain setup would require much more maintenance. Some new cars use a CVT transmission. New Polaris utility quads and I'm sure others use it. Heck snowmobiles have used it for decades. I've had 35yo snowmobiles with the stock clutches still functioning. It's really a great design. Do as you wish but I bet you would be happier with this than CC

 

[Doc Sprocket]

Not only do some Comet CVT's not employ a back plate, I think I can safely say that most do not. I'm guessing you have a Comet 30. It is essentially the same as a Comet Torq-A-Verter (or "TAV") but without the self-contained convenience of a backplate.

With regards to the inefficiency of a slipping belt, I would submit that it's no more or less efficient than the slipping clutch. Just in case you're not aware of it, the belt only slips on a CVT when starting from a stop. This clutching action is required to get you moving no matter what sort of power transmission system you employ, including a standard centrifugal clutch. Should efficiency be an argument, I maintain that a CVT is inherently more efficient for no reason other than the variable ratios.

 

[Iron John]

Not only do some Comet CVT's not employ a back plate, I think I can safely say that most do not. I'm guessing you have a Comet 30. It is essentially the same as a Comet Torq-A-Verter (or "TAV") but without the self-contained convenience of a backplate.

With regards to the inefficiency of a slipping belt, I would submit that it's no more or less efficient than the slipping clutch. Just in case you're not aware of it, the belt only slips on a CVT when starting from a stop. This clutching action is required to get you moving no matter what sort of power transmission system you employ, including a standard centrifugal clutch. Should efficiency be an argument, I maintain that a CVT is inherently more efficient for no reason other than the variable ratios.

Thank you for clearing up the issue off the back plate.

I understand that the belt only slips until the clutch locks up, but there is also sliding friction as the belt walks up and down the diameter of the pulleys. There is always a tangential component between the belt and the slope of the pulley, so there is wear.

If I go with a CC, I can size the lock-up characteristics to match the characteristics of the engine and type of riding we do. Once the CC locks, there is no more wear.

In terms of overall ratio, I have a question. I expect that a TC belt cannot handle a radius as small as the least number of teeth that are possible on the pinion of a CC. My gut is that if I were to use an overall 6 to 1 (60 tooth sprocket and a ten tooth pinion) with a CC, that will be a somewhat steeper ratio that what I have now with the TC, because the belt cannot handle a diameter that small.

Is this correct? If so, i will have better pickup with the CC, with either a 60 or 72 tooth wheel. Again, good performance from 0 to 20 or 25 is more important than getting this thing up past 30 or more. The steeper ratio I can achieve with a CC will also help me get those heavy tires turning.

Also, I guess I should use a 9 or 11 tooth pinion so that the chain precesses around the sprocket. I don't know if a 9 is possible, but an 11 should be.

The crazy thing is that the very reasons being cited for keeping the TC seem to be driving me towards a CC. Please help me in case I am misunderstanding something.

 

[Doc Sprocket]

I don't think you're too far off base, but that said-

I'm not sure if you are fully aware of the gearing involved. Using a CVT requires a jackshaft of one sort or another, period. Now, whether that jackshaft is integral to the unit (as is with a backplate-equipped TAV) or entirely seperate (as is in many other cases), the jackshaft gearing is what you need to pay attention to. As such, the effective pulley diameter matters not one bit. Example- with a CC, you achieve a 6:1 final ratio with a 10T clutch and a 60T axle sprocket. To do the same thing with a CVT, you ignore pulley diameters (more on that later). You would use a 10T on the sprocket driven by the CVT's driven unit, and a 60T on the axle. Now- what you're left with, is a 6:1 final redux ratio assuming the CVT tops out at 1:1 internally. Some models are actually capable of a 0.9:1 overdrive which is a bonus. The effective pulley diameters combine to create a low speed (or "first-gear") ratio, that you may or may not want to factor into your calculations.

Belt wear in my experience, is not a huge concern. My kart is quite portly (320lbs not including myself) as equipped with the Honda GX340 and Comet40 CVT. Large (18") rear tires and an overall redux ratio of 4.8:1 put quite a strain on my CVT. That combined with my madman offroad driving style put quite a load on my CVT. Let's face it- I beat it like a bad puppy. In 4 years of driving the spit out of it through all conditions including rain, snow and mud, I only replaced the belt once. Frankly, an anomaly caused that belt breakage. My teenage niece ran my kart into a tree. Panicking, she pinned the throttle to the floor. With the rear wheels loaded up, they could not turn, and the incident resulted in a burnt spot on the belt. 6 months later, the belt broke at the burnt spot. The exact same circumstances would have horribly punished a centrifugal clutch, too- possibly rendering it junk, as the throttle stayed pinned for a good 60 seconds or so until I ran over and hit the kill switch.

 

[Iron John]

I don't think you're too far off base, but that said-

I'm not sure if you are fully aware of the gearing involved. Using a CVT requires a jackshaft of one sort or another, period. Now, whether that jackshaft is integral to the unit (as is with a backplate-equipped TAV) or entirely seperate (as is in many other cases), the jackshaft gearing is what you need to pay attention to. As such, the effective pulley diameter matters not one bit. Example- with a CC, you achieve a 6:1 final ratio with a 10T clutch and a 60T axle sprocket. To do the same thing with a CVT, you ignore pulley diameters (more on that later). You would use a 10T on the sprocket driven by the CVT's driven unit, and a 60T on the axle. Now- what you're left with, is a 6:1 final redux ratio assuming the CVT tops out at 1:1 internally. Some models are actually capable of a 0.9:1 overdrive which is a bonus. The effective pulley diameters combine to create a low speed (or "first-gear") ratio, that you may or may not want to factor into your calculations.

Belt wear in my experience, is not a huge concern. My kart is quite portly (320lbs not including myself) as equipped with the Honda GX340 and Comet40 CVT. Large (18") rear tires and an overall redux ratio of 4.8:1 put quite a strain on my CVT. That combined with my madman offroad driving style put quite a load on my CVT. Let's face it- I beat it like a bad puppy. In 4 years of driving the spit out of it through all conditions including rain, snow and mud, I only replaced the belt once. Frankly, an anomaly caused that belt breakage. My teenage niece ran my kart into a tree. Panicking, she pinned the throttle to the floor. With the rear wheels loaded up, they could not turn, and the incident resulted in a burnt spot on the belt. 6 months later, the belt broke at the burnt spot. The exact same circumstances would have horribly punished a centrifugal clutch, too- possibly rendering it junk, as the throttle stayed pinned for a good 60 seconds or so until I ran over and hit the kill switch.

Yes, you're right about the effect of the jackshaft gearing.

It sounds like you might have a heavier-duty clutch. Yours is a 40. I thought that I had a Comet 30, but there is a '20' on the outer driven sheave. ??