Tav40 not working

BMPoland1993

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Hey forum,

I am new so I guess I should introduce myself. My name is Benedykt and I come from Poland, although I am also a British national.

My adventure with buggies/gokarts began roughly a year ago when I decided that I should put my skills to use and build something cool. I always wanted a buggy/gokart, but instead of buying one I began searching for plans on the internet and stumbled upon the Arachnid SpiderCart buggy/gokart, which for me at the time looked like a dream project. I thought that its completion would take me no more than 3 months. It's been a year and a bit now.

When I rolled out of the garage of the mechanic down the road (who was a really honest guy and was always helpful) I immediately noticed that my tav40 CVT (I have a 420cc lifan engine) started buckling, ratlling, making a whole cacophony of noises, and as I depressed the gas pedal even more the whole thing went from bad to worse. Upon inspection I noticed that the noise was coming from the driven unit. When I looked at it while pressing the gas pedal slightly, the driven was operating abnormally and I also noticed that the teeth were skipping over each other, producing a horrible metalic noise.

So.. I bought another one. Installed it on my engine (the drive pulley on my CVT is intended to be installed the other way round, as the instructions illustrate) and the problem occurred again. My thought was that it's impossible that both converters were broken, that perhaps I installed the whole unit wrong.. or maybe some other explanation was possible.

So I found a motorcycle repair shop down the road and showed them my gokart and presented the problem. I waited for 4 months for them to fix it (they had to strengthen some parts and make other adjustments as me and the other mechanic made mistakes which couldn't be left unattended.) Today it was ready for pickup, and the mechanic told me that he had eliminated the problem. Sadly, as I sat in the go kart and started moving, that same noise began again. However, and thankfully, as i started speeding up the noise dissipated and I was able to go full throttle back home and even drifted a little on the thawed ice and snow on my driveway and lawn.

But the problem emerges again and again during low speed and just as the vehicle starts moving.

If there I anyone out there who encountered similar issues with their TAV40 then I would be very grateful for any help you might be able to provide.

Thanks,

Benedykt.
 

itsid

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first.. there is no TAV40 ;)
the series 40 comet or clone can be mounted incorrectly quite easily.. especially if one's following a tav2 instruction. (series 30)

So..
make sure driver and driven are facing in different directions if you have a red spring in your driven cam!
(the big nut on the driver must NOT point in the same direction as the cam on the driven does!)
if at any point in time you tried to run it that way.. you might wore out the buttons.

post pics of your setup at least, a few good ones of the cam portion (so that we can see the state of the buttons and the spring)
a pic or two of how it's setup (so we can see belt alignment and both pulleys)

you get the idea... SHOW us what you're dealing with and then we can tell what might be wrong with it.

'sid
 

BMPoland1993

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first.. there is no TAV40 ;)
the series 40 comet or clone can be mounted incorrectly quite easily.. especially if one's following a tav2 instruction. (series 30)

So..
make sure driver and driven are facing in different directions if you have a red spring in your driven cam!
(the big nut on the driver must NOT point in the same direction as the cam on the driven does!)
if at any point in time you tried to run it that way.. you might wore out the buttons.

post pics of your setup at least, a few good ones of the cam portion (so that we can see the state of the buttons and the spring)
a pic or two of how it's setup (so we can see belt alignment and both pulleys)

you get the idea... SHOW us what you're dealing with and then we can tell what might be wrong with it.

'sid
@itsid thank you for your response. Maybe perhaps the buggy is too heavy and therefore the converter might be struggling for the first few metres at low speed and that's the issue? At higher speeds everything seems to be OK.

I will post some photos later.
 

BMPoland1993

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As promised, below are the photos of my setup. Please do not be alarmed by the ingenuity of how the converter is installed. Rides better than with standard configuration, so we can eliminate this as a reason for the converter to malfunction.

Also, perhaps the issue lies in the sprocket? I've been in touch with a guy here in Poland who actually knows what a torque converter is and has been using them, and he told me that my main axle sprocket could be the wrong size.
 

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karl

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It that a 3/4 belt? That looks skinny or burned down.

Both your moving sheaves are on the same side,
This is what sid was trying to tell you.
In this case the Driven clutch, the one on the jackshaft, needs flipped the other way, if you want the cvt to work like comet intended.
And keep the red spring.

That may only be part of the problem, but will not assist your efforts. What is your gear ratio, tire size, and approx vehicle weight?
 
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BMPoland1993

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It that a 3/4 belt? That looks skinny or burned down.

Both your moving sheaves are on the same side,
This is what sid was trying to tell you.
In this case the Driven clutch, the one on the jackshaft, needs flipped the other way, if you want the cvt to work like comet intended.

That may only be part of the problem, but will not assist your efforts. What is your gear ratio, tire size, and approx vehicle weight?
OK. The problem is that when I first bought my series 40 torque converter and installed it per the instructions (driven clutch inboard) drive pulley with spring facing outwards, the noises and abnormal running of the converter started. So I switched the pulleys around, the problem was still there. I drove my buggy down the road at like 5km/h because that's all it could do, and left it at the mechanic's. Picked it up a week ago and the problem seemed to be gone at higher speeds but at slow speeds the converter still starts producing weird noises. The belt has to be this size because a thicker one engages the clutch at idle, and moreover the belt was in the kit. I tried telling the seller that it seems to be the wrong size, but he told be that the belt comes with the converter from the factory.

I have no idea what the gear ration is. I'm using a 420 chain, i think 10 teeth on the small sprocket and 54 on the main one. Tire size is 20" at the back and 15" i think at the front. The kart is pretty heavy.

What I mean is that no matter what orientation the pulleys are the problem is still there.
 

karl

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What I mean is that no matter what orientation the pulleys are the problem is still there.
I would look into why you have to use a 30 series belt to make it work, and get a count on that front sprocket.

And is the belt symmetrical? Anyway when I troubleshoot something, I try to set everything right, reduce variables, and narrow down the problem.
 

BMPoland1993

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I would look into why you have to use a 30 series belt to make it work, and get a count on that front sprocket.

And is the belt symmetrical? Anyway when I troubleshoot something, I try to set everything right, reduce variables, and narrow down the problem.
The belt is symmetrical.
 

OPmini

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Try taking the driven off the jackshaft axel and inspect the keyway, make sure nothing is sheared. Also, try opening up your driven and see how much those little stamped roller guides have worn down. I think a video would be helpful if you could take one as well. Also, that belt looks worn down.
 

BMPoland1993

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Driven is brand new. I have inspected the keyway and everything is intact.

I will take a video tomorrow, will try to mount the camera above the engine so as to show you how the converter behaves.


Photo below of the kart so you can get an idea of how much it weighs.
 

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karl

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i think 10 teeth on the small sprocket
The details make a difference.
For your rig @3600rpm
10t=40mph
12t=48mph
14t=56mph, for sure to burn up belts , even when set up right.

But id start by getting the correct width belt for the clutch to fit correct and work,

you should not have to use a skinner belt, negates the point of having a beefier clutch.

Then get the clutch sheave issue straighted out,

get count on that sprocket, and we will be way ahead.

Or take it back to the shop and have them test ride it, if you don't want our advise.
 

BMPoland1993

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The vendor I got the converter from told me that the drive unit is built for a thinner belt. As you can see in the pictures below, my drive unit looks like it has a smaller gap than the one designed for thicker belts:

He has also told me that for my size tires the main sprocket should have more teeth. Also gave me FB of a guy here in Poland who apparently knows his way around torque converters and should be able to help
 

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Dingocat

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The only differnece I see in those pictures is the sheave is not all the way into the top of the pulley, therefore should be able to fit the belt. It could be an issue of it idling too high resulting in the belt engaging.
 

karl

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The vendor I got the converter from told me that the drive unit is built for a thinner belt. As you can see in the pictures below, my drive unit looks like it has a smaller gap than the one designed for thicker belts:
Ok, interesting design choice. Never seen a knockoff 40 series Comet with a thinner drive belt by choice.

In that case, the powered handling of the clutch is lowered, so, yes, gearing may be a big issue.

You may need to gear steeper to compensate for less meat on the belt.

I was trying to get a confirmation on your drive sprocket, to make sure it is really 10t,

so I know what your gear ratio is and can assist you better, but refused.

With your setup, and 10t on the drive sprocket, yes a bigger axle sprocket may be required.

And still , the sheaves are in mis-alignment due to the position of your clutch's , but that can be overlooked for now.
 

BMPoland1993

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Ok, interesting design choice. Never seen a knockoff 40 series Comet with a thinner drive belt by choice.

In that case, the powered handling of the clutch is lowered, so, yes, gearing may be a big issue.

You may need to gear steeper to compensate for less meat on the belt.

I was trying to get a confirmation on your drive sprocket, to make sure it is really 10t,

so I know what your gear ratio is and can assist you better, but refused.

With your setup, and 10t on the drive sprocket, yes a bigger axle sprocket may be required.

And still , the sheaves are in mis-alignment due to the position of your clutch's , but that can be overlooked for now.
will let you know tmoro how many teeth I have on the drive sprocket. On the other hand, would a 60 tooth sprocket be enough?
 

karl

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will let you know tmoro how many teeth I have on the drive sprocket. On the other hand, would a 60 tooth sprocket be enough?
Well, if the drive is really 10t, with a 54t rear sprocket , you have a 5.4 to 1 gear ratio

That , will give you, at a governed speed of 3600rpm, high ratio, 66KPH top speed.
Takeoff ratio , with clutch in low range , 13.122:1 . Starting speed of 12kph. Below that the belt has to slip to move the kart.

Given 1600rpm engagement , and 2.43:1 starting ratio from clutch *specs for an OEM comet 7/8 belt 40 series*

Add the 60 tooth, 6 to 1 ratio.

Same engine rpm , clutch high ratio , 60KPH
Takeoff ratio, with clutch in low range, 14.580:1 . Starting speed of 11kph. Not a huge difference.

But a small change in load can determine if the belt jumps or not.

Normally when the belt starts jumping, at low wheel speeds, it is under too much load, trying to transmit excessive torque.

You may need even more reduction, but lets see if you have this problem with a true 5.4:1 sprocket ratio first.

On my kart with a chunky v-twin and utv clutch, heavy frame, the only way I can get the belt to jump is to spin the tires on pavement , and do donuts until the tires warm up and start grabbing the road, bogging the engine down until there is too much torque for the belt to transfer.
All other riding and drag racing, the belt never jumps. Can donut on dirt or gravel all day.
 
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BMPoland1993

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Just checked 54 teeth. The tires are 20".

Found a place where they make custom sprockets on a CNC machine, and the question is how many teeth I should add for the converter to start working?
 

BMPoland1993

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Hey guys! Turns out the converter was rubbish in the end. I bought a new one with a wider belt and it works like magic. No more weird noises from the back!! It really is a joy riding my buggy/gokart.

While I'm here I might just ask if there is a way to make a DIY air filter adapter for a GX420? I did order one but the delivery date says middle of March which for me is a bit too long a waiting time.

If you have any advice, plans, schematics of a air filter adapter for a 420cc engine please let me know!

So long!
 

karl

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Good to hear! The new 7/8 belt unit should serve you much better.

I built this adapter from scratch, just a plate of metal and a piece of exhaust pipe.
 

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