TC and front end questions

[Dfish1247]

Have a couple questions about my sons kart. Carter bothers yard kart, live axle, predator 420 stock, still has governor, 40 series tc.

1st, the kart has the dreaded wanting to move while idling, does comet make a bushing for the belt to ride on like the 30 series has? Or, I have the 2600rpm springs and weights kit, I figured I’d install that if there is a bushing for the belt to install, kill two birds with one stone. The belt has plenty of slack and both pulleys fully open and close, so I don’t think it’s a belt issue. Btw, it’s a clone comet, not a real one.

2nd, the steering knuckles have had it, they are missing the bushings, and the kingpin holes are wallard out as well. Plus, the front wheels are dolly wheels, they’re shot as well. So, should I just get a 3/4“ diameter 6” long arm kit? I need the longer stud for the wheel because of tires hitting the frame when turning. As for wheels and tires, the backs are 13x5, front is 13x3, I’d like to keep the same front size tires. Would you folk suggest going with 3/4” hole wheels, or go with hubs? If hubs, what is the most common bolt pattern?

Thanks in advance.

 

[Budget GoKart]

can we get pictures of the setup teeth on the jack shaft and on the rear tire size for the back etc?

 

[madprofessor]

Idle movement: A parking brake is handy when parking on an incline, but IMHO its best use is when yanking the pullrope from outside the cart, brake preventing it running away before you can get in. Blap blap goes the dog. Make sure you've got the right config. belt, symmetrical V-belt or asymmetrical belt. If latter, be sure it's not on backwards.
Worn out knuckles: Excellent choice on 3/4" axles, don't go any smaller. You sure you need 6" axles? The further out the wheel is on the axle, the more strain there is that's trying to bend the axle and associated structure. If so, use (multiple) plain 3/4" washers on the outside to shim the wheels as far in as possible if there's any room to do so. Bonus fact is narrower wheelbase in front gets a tighter turn radius. All that said, no you don't need a 6" long "stud", if that means a weld-on axle. You need a whole new spindle assy., as bushings like I just received to replace some I crushed won't do it. You say the kingpin holes are wallowed out, so there you go. New assy.
Wheel size: Confused here. 13 x 3 ? Is that 3" diameter rims? With 3/4" bearings in them? Thinking you're not going to find 3" wheels or tires that size. "Dolly wheels" sounds like that setup with 3" rims is just that, dolly wheels. That means the bearings were never intended to go at gokart speeds, and that's dangerous along with unreliable. As for hubs or not, so far I've only used the largest 6" SPLIT RIMS available with 3/4" bearings (no hubs required) in them (from MFG S____y). Note that the offset of my rims made just for gokarts would be different than your "dolly wheels", point being that with something different than you have now, maybe a 4" axle would be all you need up front. That's what I've used, but notably WITHOUT brakes on them.

 

[Budget GoKart]

Idle movement: A parking brake is handy when parking on an incline, but IMHO its best use is when yanking the pullrope from outside the cart, brake preventing it running away before you can get in. Blap blap goes the dog. Make sure you've got the right config. belt, symmetrical V-belt or asymmetrical belt. If latter, be sure it's not on backwards.
Worn out knuckles: Excellent choice on 3/4" axles, don't go any smaller. You sure you need 6" axles? The further out the wheel is on the axle, the more strain there is that's trying to bend the axle and associated structure. If so, use (multiple) plain 3/4" washers on the outside to shim the wheels as far in as possible if there's any room to do so. Bonus fact is narrower wheelbase in front gets a tighter turn radius. All that said, no you don't need a 6" long "stud", if that means a weld-on axle. You need a whole new spindle assy., as bushings like I just received to replace some I crushed won't do it. You say the kingpin holes are wallowed out, so there you go. New assy.
Wheel size: Confused here. 13 x 3 ? Is that 3" diameter rims? With 3/4" bearings in them? Thinking you're not going to find 3" wheels or tires that size. "Dolly wheels" sounds like that setup with 3" rims is just that, dolly wheels. That means the bearings were never intended to go at gokart speeds, and that's dangerous along with unreliable. As for hubs or not, so far I've only used the largest 6" SPLIT RIMS available with 3/4" bearings (no hubs required) in them (from MFG S____y). Note that the offset of my rims made just for gokarts would be different than your "dolly wheels", point being that with something different than you have now, maybe a 4" axle would be all you need up front. That's what I've used, but notably WITHOUT brakes on them.

that reminds me what is up with the tiny wheels on the giant tall buggy???

 

[Snaker]

Are you taking any measurements with the belt, it so what are you going by?
Do you have a side gap between belt and sheave? How much?

 

[Dfish1247]

The tires are 13” tall, 3” wide. I was just wanting to keep the same tire size. The current spindles have a 4-5/8” axle, for the wheels not to hit, I’m left with 2 threads sticking out of the nut after tightening it down. Just wanting more thread to work with is why I wanted the longer axles.

I haven’t measured the belt, it’s the one that came with the converter. The belt is v shaped, does not have a flat side. I feel there’s enough slack as well, I can pinch the belt between my thumb and pointer finger and slide it back and forth easily, I’m not Hercules either. I haven’t stuck a feeler gauge between the belt and front pulley. Of course, the engine may just be idling too high and partially engaging the driver, I could try dropping the idle and see if that works. Oh, both driver and driven smoothly work, no binding or hanging up I can notice.

 

[madprofessor]

Remember that old "KISS", (Keep It Simple, Stupid). Turn out the idle screw until the motor tries to jerk, see if it sits still. If so, try some short raps on the gas to see if it tries to move with the momentary rev. Might be good enough to keep you happy without any hard work. If not, definitely change out clutch springs for higher stall ones.
TC may be a clone, but you can still look up the parts on a OEM Comet and see if you're missing any of that on your clone.

 

[Dfish1247]

Will do, it is a clone, I had asked about the red springs and medium weights a while back. I have them, just been lazy about installing them. I’ll put them in this week, won’t hurt to put graphite on everything inside anyway.

I did look up a comet parts diagram, they do not have a bronze bushing for the belt to ride on at idle. Only reason I asked about idle is the engine sounds too smooth and sounds too fast at idle if that makes sense, every small engine I’ve ever been around had at least some chop to the idle, this one has none. When it’s first started, it has some chop and doesn’t try and move, but it’s cold and hasn’t settled in.

Thank you guys.

 

[madprofessor]

Unfamiliar with the ratings on the different color springs, can only make sense of numbers, but anything for a higher stall is good. That smooth sounding engine does seem suspect for too high an idle rpm. Is it possible the choke is staying part way on , causing unnatural idle speed? Or that you're working the choke lever in reverse, towards the front for choke? I got confused and did that once due to the direction sticker being gone after mods.

 

[Snaker]

The photo looks like a reasonable side gap.
If the drive pulley's movable sheave isn't moving and you can see the belt side gap during idle, you can rule out rpm being the cause of that particular problem.

My computer went totally whack trying doing the pictures so,
These are for Polaris P-85 P-90 systems so the numbers may or may not work for you but its a good description of the functions.

 

[Dfish1247]

I finally put the 2600 kit in last night, not a bad job.

Now it seems the belt is pinched in the driver, I can run the belt back and forth but it takes a lot more effort than before. The side gap in the belt is gone or at least far less than before. I’m thinking I need to loosen the nut, back the thin retaining washer on the threads out two threads and retighten the nut. Then see what happens. Either that or put the kart against a wall and let the belt wear itself thinner, I’m not a fan of that idea.

I had the kart on stands and started it up, driver moves in and out freely so no binding of anything. Also, I tried stopping one of the wheels and the engine started bogging down while idling, so I know the belt is grabbing too much at idle.

 

[madprofessor]

While on the TC's, anybody have an opinion about the difference between Dfish's V-belt unit and the asymmetrical one-sided belts? (The only ones I know about.) Plan to (possibly) order a new TC in near future.
I like the idea of a belt like Dfish's grabbing for traction on both sides of itself as opposed to just one side. Know everything there is to know about belt drives on fixed equipment, but nothing about them on gokarts.

 

[madprofessor]

By the way, your sliding sheave half is definitely shimmed in further than before since it pinches now.
Not sure what you mean about retaining washer, but it definitely sounds like something changed besides the springs.

 

[Dfish1247]

On the knockoff tc’s, it’s the paper thin washer meant to hold the driver together while you tighten the big retaining nut down. Once the retaining nut is tightened down, fold one part of the washer over one flat of the nut to lock it in place. Comets have the nut welded on.

This washer slides in the threads, you have to turn it with a flat head screwdriver, the washer has two flat parts inside to slide it on the threads, then turn it to engage the threads.

More I think about it, this may be why the 40’s don’t have the belt idler bushing the 30’s have, because you can open up the gap on the driver this way. I’ll try backing the washer out two threads and see if that helps the issue, if it does, I’ll keep going until the driver doesn’t grab at idle any more.

 

[Snaker]

While on the TC's, anybody have an opinion about the difference between Dfish's V-belt unit and the asymmetrical one-sided belts? (The only ones I know about.) Plan to (possibly) order a new TC in near future.
I like the idea of a belt like Dfish's grabbing for traction on both sides of itself as opposed to just one side. Know everything there is to know about belt drives on fixed equipment, but nothing about them on gokarts.

The asymmetrical style is very much a compromise design and is more limited in power capabilities.

CVT's are designed to have the fixed sheaves on opposite sides of the belt, and visey versy the movable sheaves on the other opposite sides.
With some machines its not easy or some people don't want to set the CVT up that way.
The asymmetric provides another option.

 

[madprofessor]

Not sure I get that, Snaker. I do see that if one sheave shifted back and forth on say the left side of the belt, and the other sheave shifting on the right side, that it would have to be a V-belt.
But unless my spatial grasp is on vacation again, seems that would keep shifting the belt alignment right and left out of parallel with the kart's wheelbase. And causing extra belt side wear, albeit matching wear. At least with the asymmetrical the belt's always in perfect parallel with the wheelbase, ie; stays against the backplate side.
So trying another way, let's say it's a V-belt that for whatever reason is on sheaves with the fixed sheaves on the same side of the belt. Would it be reasonable to assume better belt traction than on asymmetrical setup?

 

[Snaker]

Example:

Drive pulley:
Fixed sheave is inboard.
Belt is down in the pulley.
At shiftout the belt climbs the fixed sheave.
Because the sheave is angled, the belt moves laterally towards inboard.

Driven pulley:
Fixed sheave is outboard
Belt is up at the edge of the pulley
At shiftout the belt drops down the fixed sheave
Because the sheave is angled, the belt moves laterally towards inboard

So on upshift the belt moves inboard on both ends and moves outboard on both ends on downshift

If you put both fixed sheaves on the same side, the belt goes inboard at one pulley while going outboard at the other pulley.

 

[madprofessor]

Good example, I can actually see it in the mental picture now, and understand it.
Can't remember where my spatial grasp was that got it running out of parallel, that's how fuzzy things have gotten for me. Think maybe the old mental picture didn't have the driven closed up.
Answers most of the basic question too, easy to see that a V-belt does indeed get more "rubber to meet the road" than asymmetrical, get snappier response and be less likely to slip under hard load or after some belt wear.
Final theoretical: Would that faster and more precise response to the shifting sheaves angle be a desirable action to have, or is a little forgiveness in tracking the sharp changes created by throttle alone more desirable?

 

[Snaker]

Well the CVT pulleys are essentially a automatic transmission.
The drive is rpm sensing, flyweights respond only to engine rpm, not throttle
The driven is torque sensing (TS), responding to load conditions
From there the pulleys procced to a tug of war for position

The pulleys are engineered for whatever the mfg's are looking for.
Sheave angles, TS angles, pulley diameters and ratio ranges
There can be slight changes with brands/models, but their all within a useable range.

Its always a challenge to wrap ones head around this stuff, especially on paper vs hands on
I've spent decades figuring out the TS and am still a bit shakey

 

[madprofessor]

Now there's some new news for me. Never considered that one sheave responded only to load and the other only to rpm.
Don't think I ever even thought about it, just left it brain-packaged as the whole unit responds to load and rpm together. That way the only necessary considerations for me to busy the brain with would be how far to push the pedal and how fast it's going.
In case I've never said it, I really appreciate the input from others on all of this building stuff, love soaking up any kind of knowledge more than a sponge loves water.